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Ground Penetrating Radar Imaging of Ancient Clastic Deposits: A Tool for Three-Dimensional Outcrop
Studies
by
Oluwatosin Caleb Akinpelu
A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy
Geology Department University of Toronto
© Copyright by Oluwatosin Caleb Akinpelu 2010
ii
Ground Penetrating Radar Imaging of Ancient Clastic
Deposits: A Tool for Three-Dimensional Outcrop Studies
Oluwatosin Caleb Akinpelu
Doctor of Philosophy
Geology Department University of Toronto
2010
Abstract
The growing need for better definition of flow units and depositional heterogeneities in petroleum
reservoirs and aquifers has stimulated a renewed interest in outcrop studies as reservoir analogues
in the last two decades. Despite this surge in interest, outcrop studies remain largely two-
dimensional; a major limitation to direct application of outcrop knowledge to the three
dimensional heterogeneous world of subsurface reservoirs. Behind-outcrop Ground Penetrating
Radar (GPR) imaging provides high-resolution geophysical data, which when combined with two
dimensional architectural outcrop observation, becomes a powerful interpretation tool. Due to the
high resolution, non-destructive and non-invasive nature of the GPR signal, as well as its
reflection-amplitude sensitivity to shaly lithologies, three-dimensional outcrop studies combining
two dimensional architectural element data and behind-outcrop GPR imaging hold significant
promise with the potential to revolutionize outcrop studies the way seismic imaging changed
basin analysis.
Earlier attempts at GPR imaging on ancient clastic deposits were fraught with difficulties
resulting from inappropriate field techniques and subsequent poorly-informed data processing
steps. This project documents advances in GPR field methodology, recommends appropriate data
collection and processing procedures and validates the value of integrating outcrop-based
iii
architectural-element mapping with GPR imaging to obtain three dimensional architectural data
from outcrops.
Case studies from a variety of clastic deposits: Whirlpool Formation (Niagara Escarpment),
Navajo Sandstone (Moab, Utah), Dunvegan Formation (Pink Mountain, British Columbia),
Chinle Formation (Southern Utah) and St. Mary River Formation (Alberta) demonstrate the
usefulness of this approach for better interpretation of outcrop scale ancient depositional
processes and ultimately as a tool for refining existing facies models, as well as a predictive tool
for subsurface reservoir modelling. While this approach is quite promising for detailed three-
dimensional outcrop studies, it is not an all-purpose panacea; thick overburden, poor antenna-
ground coupling in rough terrains typical of outcrops, low penetration and rapid signal attenuation
in mudstone and diagenetic clay- rich deposits often limit the prospects of this novel technique.
iv
Acknowledgments
I sincerely appreciate the support and guidance of Dr. Andrew Miall throughout the
duration of my graduate studies and especially in seeing this research project to
completion; thank you for giving me an opportunity of a lifetime.
I am particularly grateful to Dr. Nick Eyles for releasing the Ground Penetrating Radar
equipment from his research group throughout the data collection phase of my research;
your guidance in the early years helped set me in the right direction. To Ms. Lynn
Slotkin, I appreciate your assistance from the inception of my graduate program; even
those blunt e-mails were motivational. The painstaking review of the thesis and
suggestions by Dr. Rebecca Ghent and Dr. Uli Wortmann are also well-appreciated.
GPR Field assistance by Thomas Meulendyk helped avoid several field seasons of futile
data collection efforts; I am thankful for helpful tips on GPR data collection and
processing. Field assistance and technical support from Tudorel Ciuculescu remains
matchless; I am highly indebted to you for those long summer days at the outcrops.
Gerald Bryant, I owe a few chapters of my thesis to your assistance, accommodation and
field guidance on all my Utah field trips; I am very thankful for your help.
I am also grateful for funding provided by Ontario Graduate Scholarship, Natural
Sciences and Engineering Research Council, American Society of Petroleum Geologists
(AAPG), International Association of Sedimentologists (IAS) and Society of Exploration
Geophysicists (SEG).
v
To Toyin and Elizabeth who bore the brunt of my dedicated effort to complete this
research project and for the countless hours of field assistance and proof-reading; I owe
the completion of this research project to you.
vi
Table of Contents
Abstract ii
Acknowledgement iv
Table of contents vi
List of Tables viii
List of Figures ix
List of Appendices xiii
Chapter 1: Research Problem, Objectives and Significance 1
Chapter 2: Research Methodology: 9
Pre-survey Assessment 13
GPR Survey Planning 18
GPR Data Acquisition and Recording 28
GPR Data Processing 29
GPR Interpretation Methodology and Radar Stratigraphy 47
Chapter 3: Case Studies:
Whirlpool Formation 65
Navajo sandstone 89
Dunvegan Formation, Pink Mountain (B.C) 114
vii
Shinarump Conglomerate, Hurricane Mesa (Utah) 137
St. Mary River Formation (Monarch, Alberta) 153
Chapter 4: Summary, conclusion and recommendation for future research 170
References 179
Appendix 1: Conductivity, relative permittivity and radar velocity data in sediment 219
Appendix 2: GPR instrumentation 220
Appendix 3: List of published GPR studies on sediments 227
Appendix 4: GPR Data Processing Software and Display 279
Appendix 5: GPR profiles from study locations 280
viii
List of Tables
Table 1 GPR data sheet 28
Table 2 Radar facies chart 61
Table 3 Whirlpool Sandstone lithofacies 75
Table 4 Whirlpool Sandstone Radar Facies 82
Table 5 Navajo Sandstone Radar Facies 105
Table 6 Dunvegan Formation Radar Facies 128
Table A1 Typical radar propagation data in sediment 219
Table A3 List of Published GPR studies on Sediments 227
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List of Figures
Figure 1: Relative resolution of different typical geophysical, geological and remote sensing measurement 2
Figure 2: Outcrop mapping combined with GPR profile 10
Figure 3: GPR measurement setup 11
Figure 4: GPR antennas size with decreasing antenna frequency 13
Figure 5: Various modes for antenna deployment 22
Figure 6: Single transmitter-receiver common offset survey mode 24
Figure 7: Single transmitter-receiver common midpoint survey mode 27 Figure 8: Artificial structure on downstream accretion element created
by elevation variation along the profile line 31
Figure 9: GPR profile before and after de-wow filtering 32
Figure 10: GPR profile before and after background removal 33
Figure 11: GPR profile before and after deconvolution 35
Figure 12: GPR profile before and after amplitude gain 37
Figure 13: GPR Profile before and after diffraction migration 38
Figure 14: Navajo sandstone outcrop and 100 MHz antenna GPR line 45
Figure 15: Bedding in sediments and associated porosity resulting from
changes in composition, size, shape, orientation and packing of sediment grains. 46
Figure 16: Implication of amplitude gain for GPR data interpretation 50
x
Figure 17: Analyses of published GPR studies on sediments 51
Figure 18: GPR Image of a fluvial channel from Dunvegan Formation outcrop 54
Figure 19: Radar facies from Fraser (B.C) and Niobrara River, Nebraska 55
Figure 20: Examples of inclined radar facies 57
Figure 21: Examples of reflection-free radar facies 58
Figure 22: Example of horizontal radar facies 59
Figure 23: Example of hyperbolic reflection 60 Figure 24: Radar facies chart of presumed characteristic reflection
patterns from various sedimentary environments 62 Figure 25: Generalized stratigraphic chart for the Silurian system in New York 69
Figure 26: Early Silurian paleogeographic map of the Niagara Region 70
Figure 27: Location of the Whirlpool sandstone outcrop at Artpark, New York 71
Figure 28: Outcrop photo of the Whirlpool sandstone at Artpark, New York 72
Figure 29: Raw, unprocessed GPR data from the Whirlpool Sandstone 73
Figure 30: Artpark vertical section summarizing the main outcrop observations 74
Figure 31: Location of GPR lines at Artpark State Park, New York 77
Figure 32: Annotated Whirlpool outcrop photo and GPR lines 79
Figure 33: GPR line orthogonal to the Whirlpool Sandstone outcrop at Artpark 81 Figure 34: Three-dimensional reconstruction of the Whirlpool Sandstone architecture at Artpark integrating outcrop and GPR data 84
Figure 35: Regional paleocurrent pattern for the lower Whirlpool Sandstone 85
Figure 36: Fence diagram display of GPR data from the Whirlpool Sandstone 86
xi
Figure 37: 3D GPR image of the ancient Navajo dune complex 90
Figure 38: Generalized stratigraphy of the Navajo Sandstone 94
Figure 39: Map of Navajo Sandstone location within Utah 96
Figure 40: Map showing field locations of radar profiles at Big Mesa, Utah 98
Figure 41: Outcrop photo of Navajo Sandstone central dune giant cross-bed compared with smaller cross-bed set at Big Mesa near Moab, Utah. 100 Figure 42: Outcrop photo showing damp eolian interdune deposits overlain
by flat-bedded fresh 101
Figure 43: Outcrop photo and GPR profile at Big Mesa, Utah 103
Figure 44: Radar profiles and perspective views of 3D GPR surveys at Big Mesa 107 Figure 45: Outcrop photo from Moab (Utah) revealing damp phase interdune
deposit from the Carmell Formation 110
Figure 46: Paleogeography during deposition of Dunvegan Formation 118 Figure 47: Lithostratigraphic relationships between the Dunvegan Formation
and the underlying Shaffesbury and overlying Kaskapau formations 119
Figure 48: Map location of Dunvegan Formation outcrop and GPR lines 121
Figure 49: Map showing location of GPR lines at Dunvegan outcrop 123
Figure 50: Dunvegan annotated outcrop photomosaic and GPR line 130
Figure 51: Dunvegan annotated outcrop photo and GPR line 131
Figure 52: Dunvegan annotated outcrop photomosaic and GPR line 133 Figure 53: GPR line and 3D schematic of Dunvegan depositional model, Pink Mountain 135
Figure 54: Permian and Triassic stratigraphy at Hurricane Mesa, Utah 138 Figure 55: Paleogeographic reconstruction of the Late Triassic within
the southwestern USA. 140
xii
Figure 56: Location of Shinarump Conglomerate outcrop at Hurricane Mesa 142 Figure 57: Location of Shinarump Conglomerate outcrop at Hurricane Mesa showing GPR line 144
Figure 58: Photomosaic of the Shinarump conglomerate outcrop 148
Figure 59: Uninterpreted and interpreted GPR line at Huricane Mesa 149
Figure 60: Combined Shinarump GPR profile and outcrop Photomosaic 151
Figure 61: St. Mary River Formation Upper Cretaceous Paleogeography 155
Figure 62: Alberta Cretaceous Stratigraphic chart showing St. Mary River 156
Figure 63: Location of St. Mary River formation outcrop 158
Figure 64: Location of GPR lines at St. Mary River formation outcrop 160 Figure 65: Outcrop photo showing St. Mary River Formation channel sandstone 161 Figure 66: Outcrop photo showing St. Mary River Formation crevasse
splay sandstone 162
Figure 67: Radar image of St.Mary River Formation ribbon channel sandstone 163
Figure 68: Radar profile showing ribbon channels and horizontal reflectors 164
Figure 69: Uninterpreted and interpreted St. Mary River Formation GPR profile 165 Figure 70: Block diagram depicting depositional model of St. Mary River Formation at the study site near Monarch, Alberta 168
Figure 71: Three-dimensional GPR data display from Navajo Sandstone
interdune deposit at Big Mesa, Utah 175
Figure A1: Mode of operation of Noggin system 221
Figure A2: Shielded PulseEKKO Pro system 222
Figure A3: Mala Geoscience unshielded bistatic antennas 223
xiii
Figure A4: Mala Geoscience Rough Terrain Antenna (RTA) 224
Figure A5: Mala Geoscience shielded antennas 225
Figure A6: GSSI monostatic and bistatic 100 MHz antennas 226
Figure A7: Analyses of 150 published GPR studies on sediments 278
Figure A8: GPR profiles from Artpark (New York, USA) 280
Figure A9: GPR profiles from Big Mesa, near Moab (Utah, USA) 281
xiv
List of Appendices
Appendix 1: Radar propagation data in sediment 219
Appendix 2: GPR Instrumentation 220
Appendix 3: List of published GPR studies on sediments 227
Appendix 4 GPR Data Processing Software and Display 279
Appendix 5: GPR profiles from study locations 280
1
Chapter 1 Research Problem, Object and Significance
1.1 Introduction The need for better prediction of reservoir architecture and distribution of lithological
heterogeneity in aquifer characterization, hydrocarbon primary field development and
enhanced recovery projects is driving a burgeoning interest in outcrop-based studies of
ancient clastic deposits both as analogues for subsurface reservoirs and as a tool for
refining existing facies models. This research is driven by the need to account for the
variability and architectural complexity in subsurface clastic reservoirs, especially for the
purpose of petroleum resource evaluation and development, where conventional seismic
resolution is too poor to unambiguously delineate sandbody geometry or map their
internal heterogeneity.
Subsurface interpretation of reservoir architecture currently relies on seismic, well logs
and core data which are rarely closely spaced enough to permit unequivocal
interpretation. Practical limitations of most sources of high-resolution data rarely permit
the close spacing required for unambiguous interpretation (Figure 1). Advances in
seismic data acquisition, data processing and three-dimension data visualization in the
last two decades have significantly improved the resolution of reservoir information
observable between wells at current well spacing. Also, development of procedures for
extracting useful information from attributes of the seismic signal like amplitude, phase
and frequency have in many cases facilitated delineation of stratigraphic traps and other
subtle geological features as well as improvement in determining porosity distribution
2
and fluid content in reservoirs. In spite of these advances, predicting sub-seismic scale
heterogeneities in reservoirs is still a daunting challenge for many primary field
development, enhanced oil recovery and aquifer characterization projects.
Figure 1: Chart showing trade-off between the relative resolution of the information obtained using different typical geophysical, geological and remote sensing measurement acquisition approaches and the relative scale of the investigations for which those acquisition geometries are typically used. (Image taken from Rubin and Hubbard, 2005).
The development of affordable digital imaging technologies as well as advances in
photogrammetry, aerial photography, LiDAR scanning, satellite imagery and positioning
have significantly improved outcrop studies. Increased spatial accuracy from satellite and
laser positioning systems provides access to geostatistical and geospatial analyses that
can inform hypothesis testing during fieldwork. High-resolution geomatic surveys allow
photorealistic outcrop images to be captured from several perspectives and interpreted
using novel visualization and analysis methods. Inaccessible outcrops can now be
3
‘captured and brought to the geological laboratory’ via LiDAR scanning for further
measurements and analysis; bedding orientations and dips can then be measured at the
laboratory, considerably saving time spent doing fieldwork.
Despite these developments, outcrop studies remain largely two-dimensional, as most of
these novel techniques are not penetrative; they only reveal outcrop-face sedimentary and
stratigraphic features that can only be inferred beyond the outcrop-face with much
difficulty. The need for a more reliable tool of reconstructing fluvial architecture from
outcrops led to Miall’s (1985) proposition of ‘architectural element analysis’ following
the pioneering work of Allen (1983). Architectural elements are associations of
genetically related facies, which have some environmental significance. In depositional
systems, they are packets of genetically related strata, which define depositional elements
larger than individual bedform and smaller than channels. In outcrops, they are defined
by grain size, bedform composition, internal sequence, and most importantly, their
external geometry. This mapping technique has not only been applied to ancient fluvial
deposits as proposed by Miall (1985); it has been successfully applied on outcrops of
diverse depositional origin (Kocurek, 1981; Nio and Yang, 1993; Clark and Pickering,
1996). While there have been many outcrop studies with geometry and lithofacies of
channel and channel-belt deposits determined in outcrops described as analogues for
subsurface strata (Tyler and Finley, 1991; Mjos and Walderhaug, 1993; Dreyer, 1993a,
1993b; Dreyer et al., 1993; Robinson and McCabe, 1997; Willis and Gabel; 2003), the
reliability of many of these studies has been questioned due to ambiguity in determining
sandbody geometry, dimensions, stacking pattern and heterogeneity in outcrop sections
(Bridge 2006)
4
The need to address the two dimensional limitation of outcrop studies motivated the
recent interest surge in Ground Penetrating Radar (GPR) imaging. However, due to the
operational difficulties of GPR imaging on outcrops and the susceptibility of GPR signals
to diffraction resulting in noise-laden images, very few outcrop-based GPR studies
(Appendix 3) have been successfully conducted (Corbeanu et al., 2001; Szerbiak et al.,
2001; Lee et al, 2009). Consequently, much of the current GPR effort has focused on
modern environment and Quaternary sediments (Beres and Haeni ,1991; Jol and Smith,
1991; Gawthorpe et al 1993; Huggenberger et al., 1994; Beres et al., 1995; Bridge et
al.,1995,1998; Van Overmeeren 1998; Bristow et al.,1999,2000b; Baker et al., 2001;
Corbeanu et al., 2001, 2002; Nobes et al.,2001; Hammon et al.,2002, Hornung and
Aigner 2002; Best et al, 2003; Cardenas and Zlotnik, 2003; Heinz and Aigner 2003;
Skelly et al., 2003, Woodward et al., 2003) as radar profiling is more convenient in
modern environments usually of less rugged terrain and modern sediments are less prone
to diagenetic alterations, which often make sedimentological interpretation of GPR data
from ancient clastic deposits a Herculean task. Although there has been an improvement
in our understanding of many ancient deposits via GPR studies of modern sediments, the
varied and unpredictable preservation potential of facies units in their modern setting
limits the usefulness of these studies. It is the preserved ancient record that is ultimately
what reservoir geologists are interested in. Miall (2006) sounded a caveat in this regard
and underscored the continued role of three-dimensional studies of ancient outcrop
analogues in providing a realistic database for predicting sub-surface alluvial
architecture. Outcrops are unarguably still the most important source for learning more
about the geometry, size, and distribution of sedimentary bodies because they permit
5
direct visual observation of rock types and their spatial arrangement, thereby providing
invaluable insight into reservoir complexities for subsurface modelling (Geehan, 1993).
Key components of significant relevance to reservoir characterization include facies
types, macro-scale lithological heterogeneity, channel dimensions, sandbody geometry
and their stacking pattern in relation to local and regional controls. These outcrop-scale
features control fluid-flow behavior in petroleum reservoirs, and aquifer and outcrop
analogs have been shown to provide valuable insight into reservoir architecture
(Grammer et al, 2004). While outcrop studies typically provide valuable data on vertical
dimensions of architectural elements within a depositional system, rarely do they yield a
three-dimensional picture of potential reservoir distribution especially from the
standpoint of aerial dimensions. Knowledge of the internal architecture is generally
limited because the exposures are either strike-oriented, dip-oriented, or at an orientation
oblique to these directions. These limitations have significantly weakened the usefulness
of outcrop studies as analogs for subsurface clastic reservoirs in the past; successful
application of GPR imaging on outcrop will provide an opportunity to validate current
clastic facies and architectural models that are mostly actualistic and conceptual
constructs.
The purpose of this research is four-fold:
to demonstrate that sedimentological and stratigraphic data can be obtained from
outcrop-based GPR profiles and dispel the widely held notion that GPR imaging
only works on Quaternary sediments,
6
to demonstrate the effectiveness of GPR imaging in addressing the limitations of
two dimensional outcrop studies of ancient non-marine sandstones in a manner
that has not been successfully explored before,
to develop a field methodology for outcrop-based GPR surveys, and
to provide a reliable framework for stratigraphic interpretation of GPR images as
a guide for future research.
By incorporating ground penetrating radar data with outcrop architectural element
analysis, data that are often difficult to unambiguously obtain, such as local paleoflow
variability, channel belt width, channel dimension, sinuosity, sandbody connectivity,
stacking patterns and lithological heterogeneity can now be readily obtained. Successful
application of GPR imaging on ancient clastic deposits will have far-reaching
significance; being able to obtain data such as true channel dimensions, channel
sinuosity, incised valley dimensions and their internal geometry will not only provide
hard data to validate or dispel many of the current clastic facies models based mostly on
studies of modern environment and Quaternary deposits; it will also test actualistically-
derived empirical equations (often used to predict channel belt width in the subsurface)
that relate maximum channel depth, channel width, and channel-belt width (Collinson,
1978; Lorenz et al., 1985, 1991; Fielding and Crane, 1987; Bridge and Mackey, 1993b).
Two features of GPR imaging make the technology exceptionally suitable for addressing
the limitations of outcrop study: its high resolution that makes imaging of sedimentary
structures, architectural elements and in some cases entire depositional system feasible,
as well as radar signal’s sensitivity to clay content, which makes it possible to map macro
scale lithological heterogeneities in outcrop.
7
Although GPR imaging has been used intermittently for outcrop studies for over 25
years, the technology was not widely embraced as GPR instrumentation and data
processing technology was in its infancy and many of the GPR profiles generated were
not thoroughly processed to remove extraneous reflections required to ensure
unequivocal sedimentological and stratigraphic interpretation (Pratt and Miall, 1993;
Stephens, 1994). In the last few years, there have however been significant advances in
GPR instrumentation, data processing and display. Recently developed GPR systems are
lightweight, portable, robust and digital. In addition, the fact that GPR data can be viewed
and test-processed in real time during surveys ensures that both quality and results can be
assessed in the field. These advances as well as the availability of GPR processing
applications with two and three-dimensional visualization and interpretation aids have
enhanced rapid acquisition of continuous, shallow subsurface profiles that are ideally
suited for the investigation of sediments, shallow stratigraphy and sedimentary
architecture from both a 2-D and 3-D perspective.
Outcrop studies will undoubtedly benefit more from full-resolution three-dimensional
GPR surveys which produce 3D volumes that can be sliced and rotated to reveal features
such as map views of channel geometry, dimensions, sinuosity, anabranching and
temporal changes in depositional patterns. However, most GPR surveys are still two-
dimensional due to operational difficulties of 3D GPR surveying on outcrops. The few
three-dimensional surveys conducted to date are limited to small areas because of the
need for decimeter scale elevation survey, high data volumes and relatively large time
requirements for data collection and processing. Despite this, the effectiveness of GPR
imaging for characterizing reservoir geometry and heterogeneity through studies of
8
outcrop analogs has been demonstrated with 2-D profiles from earlier studies (Meyers et
al., 1996; Lunt and Bridge, 2004) as well as with fence diagrams constructed from
staggered GPR profiles obtained in different directions behind outcrop face, ground-
truthed with outcrop sedimentological and architectural element mapping.
9
Chapter 2
Research Methodology
2.1 Introduction The reliability of GPR – outcrop based reservoir analogue studies depends on the quality
of outcrop data and GPR survey as well as subsequent processing of the GPR data. Many
of the earlier outcrop studies utilizing GPR (Pratt and Miall, 1993; Stephens, 1994; White
et al, 2004; Zeng et. al. 2004) were plagued with ‘noise’ making it difficult to correlate
outcrop observations to radar reflectors. This is attributed to susceptibility of
electromagnetic signals to diffractions resulting from fractures as well as diagenetic
cementation in rocks (Smith et al., 2006). Diffraction occurs at discontinuities of
reflectors (such as fractures) and objects whose dimensions are small compared to the
transmitted electromagnetic wavelength. Figures 2 A and B illustrate the prevalence of
diffraction noise in earlier outcrop GPR studies.
Advances in GPR instrumentation and data processing over the last decade have
significantly improved GPR data quality. The field methodology for this research
involves obtaining photomosaics of laterally extensive sandstone exposures
supplemented by GPR profiles behind the mapped outcrop face. The photomosaics serve
a dual purpose: they act as base maps for detailed mapping of bounding surfaces and
architectural elements in the outcrop face, as well as providing ‘ground truth’ control
required to ascertain the fidelity of the radar reflections.
10
Figure 2: (A) An example of outcrop face mapping of major bounding surface combined with GPR profile behind the cliff face. (Image taken from Zeng et al, 2004) (B) Ground-penetrating radar traverse measured about 100 m behind a dip-parallel outcrop of the upper Frewens sandstone body. (Image taken from White et al., 2004); note the difficulty in correlating GPR reflections with outcrop bounding surfaces.
Architectural-element analysis involves delineating major bounding surfaces as well as
recognition of suites of geometric elements characterized by distinctive facies
assemblages, internal geometry and external form. Over the years, this technique,
integrated with paleocurrent data, has proven to be a useful descriptive framework and a
valuable tool for comprehensive interpretation of ancient clastic deposits (especially
B
20 m
A
Diffraction noise
Diffraction noise
11
fluvial and eolian deposits) and unraveling their three-dimensional architecture (Miall,
1996)
Acquisition and processing of GPR data are the more laborious phases of the research
involving selection of the appropriate GPR system as well as efficient field survey and
data processing procedures. GPR is an electromagnetic method that, in many ways, is
similar to seismic reflection survey. A transmitting antenna radiates an electric pulse into
the ground that, under ideal conditions, behaves kinematically similar to an acoustic
wave. The pulse is transmitted, reflected, and sometimes diffracted by features that
correspond to changes in the dielectric properties of the earth. The waves that are
reflected and diffracted back toward the earth’s surface may be detected by a receiving
antenna, amplified, digitized, displayed, and stored for further analysis (Figure 3)
Figure 3: GPR measurement setup.
Reflections and diffractions in a GPR section are generated by changes in electrical
properties of the rock across lithofacies boundaries; visible sedimentary structures or
12
sometimes, sequence boundaries. The transmitter and receiver units are usually separate,
so the survey design is flexible. Data can be collected either in continuous or step mode.
In continuous mode, the antennas are dragged over the surface, whereas in step mode, the
antennas are placed on the ground in steps progressively along the profile. GPR surveys
usually proceed by recording a trace at each of a large number of survey points along a
line (or over a grid) with a fixed transmitter-receiver offset. As in reflection-seismic data,
GPR profiles may be plotted directly, or combined and plotted as a volume. The main
differences are that the scale of a GPR survey is about three orders of magnitude smaller
than that of a reflection seismic survey, and the resolution is correspondingly higher,
making the technology suitable for outcrop scale imaging.
The choice of antenna frequency is a tradeoff between the depth of target beds and the
intended resolution of the survey; the lower the frequency of the antenna, the poorer the
resolution but the greater the depth of penetration (Davis and Anan 1989; Jol, 1995).
Currently commercially available frequencies are between 12.5 and 1200 MHz, the time
sample increment is usually about 1 ns, the propagation velocities are one-quarter to one-
half that of light in a vacuum, and the average depth of penetration ranges from 5 to 40m,
depending primarily on the electrical conductivity and water content of the subsurface
materials. Generally, the lower the frequency, the bulkier the GPR equipment (Figure 4) ;
this implies that low frequency antenna (below 100 MHz) ideal for regional-scale
geological imaging may require more than one person to handle during surveys especially
when Common Midpoint (CMP) Surveys are being conducted.
13
Attenuation of GPR signals in rocks increases with water saturation and decreasing grain
size; wet and clayey rocks significantly attenuate radar signals thereby reducing depth of
penetration.
Figure 4: GPR antennas get bulkier with decreasing antenna frequency. (Image taken from http://www.sensoft.ca/products/pulseekko/pulseekkopro.htmll ; - accessed August 6, 2010).
2.2 Pre-survey Assessment
While GPR has proven to be an invaluable tool for high-resolution imaging in outcrop-
scale studies, it does not always work at every survey location especially on outcrops
with shaly lithology or in those that are highly conductive. Before planning GPR surveys,
it is important to investigate whether GPR would work at the location and on the target
outcrop. Prediction of whether GPR imaging is ideal for the problem at hand is not clear
14
cut; it is easier to rule out situations where georadar is totally unsuitable than to state with
certainty that ground radar imaging will be successful. The following criteria must be
thoroughly evaluated before embarking on a GPR survey program:
2.2.1 Depth of Formation of Interest
How deep is the formation of interest? is perhaps the most important question in planning
GPR surveys. Many geological formations that are potential targets for GPR imaging are
located beneath several metres of overburden (for instance, many outcrops of Whirlpool
Sandstone and St. Mary River Formation) or beneath formations that might significantly
attenuate transmitted radar signals. The lowest frequency antenna currently available for
GPR surveys is 12.5 MHz (Figure 4) and this is limited to less than 50 metres penetration
depth in most clastic rocks, even in dry, clay-free lithologies. In addition, the attenuation
characteristic of the overburden and target medium is critical to penetration depth of
radar signals. A conservative rule-of-thumb is that radar will be ineffective if the actual
target depth is greater than 50% of the maximum range. A rough guide to penetration
depth D is
where conductivity, σ is in mS/m. This equation is not universal but is applicable when
attenuation is moderate to high (attenuation > 0.1 dB/m or σ > 1 mS/m) which is typical
of most lithologies (Annan, 2004)
(2.1) (Annan, 2004)
15
In geological applications, the parameters which have the greatest influence on the
electrical properties, and hence on penetration depth, velocity and reflector characteristics
are: (i) water saturation, (ii) clay content and (iii) pore water salinity. Dry, clay-free
sediments generally have higher velocities of propagation and lower attenuation
coefficients than wet strata. Depth of penetration is therefore highest in dry, porous
sediments (e.g. limestone, where probing depths may theoretically be up to 100 m) and
lowest in water-saturated clay where depth of penetration may be less than 1 m (Cook
1975). In some cases, sand-rich formations can have diagenetic clays not obvious in
outcrop and could result in severe signal attenuation; hence, the need for pre-survey
assessment.
2.2.2 Contrast in electrical properties required to reflect or scatter a detectable amount of energy
GPR investigates the subsurface by making use of electromagnetic signals, which
propagate into the subsurface. Because reflections of radar signals are generated by
changes in electromagnetic impedance (contrast in electric and magnetic properties)
across the lithologies that the signals travel through in the same way seismic reflections
are generated across lithological contacts with acoustic impedance changes, detectable
reflections are expected in geological formations with contrasting lithologies. When an
electromagnetic wave propagates through the ground and encounters a surface where the
electric and/or magnetic properties of the ground change, part of its energy will be
reflected and part of it will be transmitted; this is controlled by the electrical and
magnetic properties of the rock layers. In most geological applications of GPR, electrical
properties tend to be the dominant factor controlling GPR responses; magnetic variations
16
are usually weak, although occasionally, magnetic properties can affect radar responses.
This is often the case when imaging diagenetically altered formations containing iron
oxides; hence, it is important to be cognizant of such magnetic effects as they can
significantly distort interpretation. Transmission of electromagnetic signals through rocks
is controlled by three parameters: dielectric permittivity, electrical conductivity and the
magnetic permeability. Dielectric permittivity is the ability of a material to store and
release electromagnetic energy in the form of electric charge or its ability to restrict the
flow of free charges or the degree of polarization exhibited by a material under the
influence of an applied electric field. Conductivity is the ability of a material to pass free
electric charges under the influence of an applied field; this in rocks typically occurs via
dielectric conduction (in resistive lithologies which require the atoms to slightly polarize
to produce displacement currents) and electrolytic conduction (dominant in moist or wet
lithologies). Magnetic permeability describes how intrinsic atomic and molecular
magnetic moments respond to a magnetic field. Magnetic permeability in most clastic
rocks is very low and its effect on electromagnetic signal transmission can be ignored.
Both dielectric permittivity and electrical conductivity are strongly dependent on water
content (which is largely dependent on lithology); hence radar reflections patterns are
closely linked with lithological variability in rocks. For outcrops with minimal
lithological heterogeneity, it is sometimes efficient to conduct a preliminary small scale
survey at the outcrop to determine optimal target depth, resolution and appropriateness of
GPR for the location before embarking on detailed survey.
17
2.2.3 Noise sources that could preclude the use of GPR
Recorded GPR signals during surveys can be masked by electromagnetic signals from
nearby sources such as a radio transmitter or an electric power line located near the
survey site; in such cases, external signals may saturate the sensitive receiver electronics.
Radio transmitters are potential sources of interference and powerful radio signals can
overwhelm receiver electronics. Mobile phones are increasingly becoming a ubiquitous
form of interference; proximity to metal objects can also be disastrous for GPR survey.
Reflections can come from objects away to the side (sideswipe) and may be very strong if
metallic reflectors are involved. Surface features can produce strong sideswipe resulting
from substantial radiation of energy along the ground/air interface if ground conductivity
is high. Shielded antennas are very useful in such situations and are available in the 100
MHz frequency range and above. The shields are about the same size as the antenna and
use absorbing material to damp out the undesired signals. At lower frequencies, antenna
size and portability makes shielding impractical (as antenna size increases with
frequency); these considerations probably explain why there are no commercially-
available shielded GPR systems for antenna frequencies below 100 MHz. Practical
limitation of portability also explains why most shielded GPR systems consisting of both
transmitter and receiver antenna elements are housed in a single housing; hence, bistatic
antennas useful for common midpoint surveys are rarely shielded.
2.2.4 Outcrop Accessibility
How feasible is hauling bulky GPR and survey equipment to outcrop top? While remote
outcrops can be reached by hiking for kilometers or climbing where necessary during
geological mapping or routine outcrop study, it is rarely possible carrying bulky GPR and
18
surveying equipment to the target outcrop. Difficulty in accessing outcrops is one of the
major factors explaining why there has been limited application of GPR imaging to
solving three dimensional outcrop problems. Although some can be reached by short
hikes, many outcrops ideal for GPR surveys can only be reached by ATVs (All Terrain
Vehicles) or helicopters; hence, accessibility to outcrops should be thoroughly evaluated
before embarking on GPR surveys.
2.3 GPR Survey Planning
Once the feasibility of GPR survey at an outcrop has been ascertained, proper design of
the survey as well as optimizing data acquisition to meet expectations and honor surface
constraints is the next challenge of outcrop-based GPR studies and requires thorough
planning.
In planning for GPR surveys on ancient sedimentary deposits, the following factors
critical to obtaining high-fidelity profiles must be considered:
Choosing the right GPR system – there is currently a wide range of
commercially available GPR systems to choose from (see Appendix 2); it is
therefore important to choose a GPR system suitable for the purpose of the study.
Stratigraphic studies requiring time-depth conversion via common mid-point
surveys (data collection by moving the antennas progressively apart at an equal
offset from a central survey point) which gives the flexibility of calibrating radar
profiles in metres cannot be conducted with most shielded systems as they are
mostly designed for common offset (taking data by moving both antennas in the
same direction with the same antenna separation along the survey line) method of
data collection. Choosing a system with the appropriate antenna frequency for the
19
project is also critical; this is a trade off between the depth of the geological
formations being studied and the resolution required in the study. Low frequency
antennas (below 100 MHz) are better-adapted for low resolution deeper target
(20-50 metres deep) surveys while high frequency antennas (above 100 MHz) are
better-suited for high resolution shallow (less than 20 metre deep targets). As a
rule of thumb, the vertical resolution is theoretically one-quarter of the
wavelength λ = v/f, where v is the velocity of the electromagnetic wave in the
rock (see Appendix 1 for typical velocities in different lithologies) and f is the
center frequency of the GPR antenna. It is also important to note that the
bulkiness of most GPR systems increase with decreasing antenna frequency
(Figure 4); this should be considered when planning GPR surveys as such low
frequency systems may require two or more people to handle.
Surface Elevation – Uneven topography is characteristic of most outcrop top.
GPR surveys require flat outcrop tops or centimeter-scale topographic survey over
the GPR transects or across the area covered by the 3D grid if three-dimensional
GPR survey is being planned. This is a major challenge in conducting GPR
surveys on outcrops. Collection of topographic data is an essential component of
GPR survey especially where the outcrop surface is not flat and this could gulp a
significant chunk of survey time. Improper incorporation of topographic data into
the GPR lines may result in inaccurate velocities for static correction, which often
results in introduction of artificial structures and false bedding into the radar
profiles (Figure 8). A variety of instruments can be employed to obtain elevation
data for GPR processing; these include optical levels, total station, laser levels,
20
and GPS. In areas with subdued topography (less than 5 m change in elevation),
laser levels provide a fast and accurate method for collecting topographic data. In
more complex terrains, a total station provides greater flexibility and higher
accuracy; optical levels are also ideal but increase survey time. Where GPS units
are being considered for GPR surveys, Differential GPS units with centimeter-
scale accuracy are required. GPS surveys significantly reduce GPR survey time
especially in three-dimensional surveys as GPS measurements obviate the need
for a survey grid. In addition, with GPS measurements, real world locations of
GPR profiles can be easily displayed in Google Earth or imported into digital
topographic maps. It is however important to note that GPS receivers have
difficulty working under thick vegetation and require post processing. Some high-
resolution GPS tools also have compatibility problems with GPR units; if possible
GPS unit should be connected to the GPR equipment and tested before setting out
on field surveys. Most of the GPR surveys for this research were conducted on
flat surfaces requiring minor or no elevation correction.
Mode of data collection and station spacing – while GPR data can either be
collected by dragging the antenna over the surface (continuous mode) or by
progressively moving the antenna along the survey line (step mode); the step
mode of data collection is less prone to data degradation and more suitable for
stratigraphic studies although it is more time-consuming. GPR antennas couple to
the ground by the concentration of electric field in the lower medium, and best
coupling is achieved by laying the antenna flat on the ground (Annan et al., 1975);
this is usually better accomplished in step mode. In step mode, data collection
21
distance between survey points must be small enough (usually between 0.25 to
0.5 metres) to be able to resolve steeply dipping and small features as well as to
minimize spatial aliasing of radar reflections. Due to less survey time required,
many GPR surveys are done in continuous mode. Most shielded GPR systems are
designed for continuous data collection mode; therefore, for surveys where
shielded antennas are being considered, care should be taken to ensure optimal
coupling with the ground for efficient transmission of radar signals.
Step size - Spatial resolution places a constraint on the survey design and
selection of antenna centre frequency. Step size (the distance between each data
collection point, also known as station spacing) is extremely important and should
be included in the survey design process. In order to ensure that the ground
response is not spatially aliased in sedimentary studies, a maximum step size of
one metre (less than 1m where antenna frequencies higher than 200MHz are being
employed) should be used to provide detailed horizontal resolution of sedimentary
structures, yet allow profiles to be completed in a timely manner. A typical survey
with 100MHz antenna theoretically should have a step size of 0.25m; however,
larger step sizes can be used where the subsurface stratigraphy is composed of
continuous horizontal layers. If the step size is too large, the data will not
adequately define steeply dipping reflectors or diffraction tails. For 3D GPR
surveys, using a GPR grid spacing larger than a quarter-wavelength in the
presence of diffractions not only decreases horizontal resolution, it also creates
aliased dipping events, which produce migration artifacts that blur the real
reflections. Imaging dipping beds and bounding surfaces is critical to many
22
geological studies; hence, very low step sizes are required for thorough definition
of dipping beds and surfaces. The decision to increase or decrease the step size
should be based on a variety of factors including: size of the sedimentary feature
being investigated, dip angle, and areal extent of the survey. From a practical
viewpoint, increasing the station interval reduces data volume and survey time,
yet from a data interpretation standpoint, adhering to the Nyquist close sampling
interval (which requires that measurements be spaced in all horizontal directions
near a quarter-wavelength of the highest signal and noise frequency content to
avoid spatial aliasing) is very important.
Antenna Orientation - Antennas used for most GPR surveys are dipolar and
radiate with a preferred polarity. The antennas are normally oriented so that the
electric field is polarized parallel to the long axis or strike direction of the target;
there is no optimal orientation for an equidimensional target.
Figure 5: Illustration of the various modes for antenna deployment - E field aligned along the antenna axis. (Image taken from Annan 2002).
23
Antenna orientation does affect the quality of collected data (Lutz et al., 2003) and it
should be taken into consideration when planning GPR surveys. The various
arrangements of GPR antenna deployment are illustrated in Figure 5; the most
common orientation that provides the widest angular coverage of a subsurface
reflector is the perpendicular broadside to direction of survey approach (PR-BD).
This orientation is also the easiest for surveying in sedimentary environments. In
some instances, it may be advisable to collect two data sets with orthogonal antenna
orientations in order to extract target information based on coupling angle. If the
antenna system is one which attempts to use a circularly- polarized signal, the antenna
orientation becomes irrelevant; however, as most commercial systems employ
linearly polarized antennas, orientation can be important. Maintaining a consistent
antenna configuration and electronic connections throughout a survey is important
because this will allow changes in polarity, due to increases or decreases in
permittivity (impedance) with depth, to be determined. Most shielded GPR units have
fixed antenna orientation, hence no need of deciding optimal antenna orientation.
GPR units with separate antennas however require determination of optimal antenna
orientation.
2.4 GPR Survey Design
Radar surveys for stratigraphic purpose are carried out either in common offset or
common midpoint mode; however, fixed offset, single-fold common offset reflection
profiling using a single transmitter and a single receiver is the most common. Multiple
source and receiver configurations are seldom used for specialized applications. Common
offset surveys usually deploy a single transmitter and receiver, with a fixed offset or
24
spacing between the units at each measurement location. The transmitting and receiving
antennas have a specific polarization character for the electromagnetic field generated
and detected. The antennas are placed in a fixed geometry and measurements made at
regular fixed station intervals, as depicted in Figure 6. Data on regular grids at fixed
spacing are normally needed if advanced data processing and visualization techniques are
to be applied. The parameters defining a common offset survey are GPR center
frequency, the recording time window, the time-sampling interval, the station spacing,
the antenna spacing, the line separation spacing, and the antenna orientation. During
surveying, antennas are either dragged along the ground and horizontal distances
recorded on a time-base, which can be converted to a distance-base through manual
marking or measuring wheel, or they are moved in a stepwise manner at fixed horizontal
intervals (‘step size’). Step-mode operation generates more coherent and higher
amplitude reflections, as antennas are stationary during data acquisition. This ensures
more consistent coupling between the antennas and the ground as well as better trace
stacking (Annan and Cosway, 1992).
Figure 6: Illustration of single transmitter-receiver common offset survey mode. (Image taken from Annan, 2009).
25
The MALÅ antenna used for this research (250 MHz MALÅ Geoscience shielded
antenna-Appendix 2) is adapted for single-fold reflection profiling; this GPR unit has
fixed antenna distance and orientation, which makes it impossible to conduct common
midpoint surveys.
Common midpoint (CMP) soundings are primarily used to estimate the radar signal
velocity versus depth in the ground, by varying the antenna spacing (commonly referred
to as offset) and measuring the change of the two-way travel time. At all distances
between source and receiver with a fixed midpoint, most of the energy that is reflected
by, not too steeply dipping, subsurface reflectors comes from the same points straight
below that given midpoint (Figure 7A). From the differences in arrival time versus offset
very accurate velocity estimates can be obtained from all layers. When a CMP
measurement is carried out, different events can be distinguished in the received signal,
when plotted on a travel time versus offset plot as depicted in Figure 7C. These are the
results of the air wave (1), the ground wave (2), the direct reflection from an interface (3),
and the critically refracted airwave (4). Since the velocity in air is always greater than the
largest velocity in the ground, a critical angle of incidence exists where the transmitted
wave travels in the air along the interface. These angles only exist when the wave travels
from a slower medium to a faster medium, such as a reflection from below the ground
that travels toward the earth surface. In a common-offset survey, the above mentioned
events interfere and cannot be identified separately. On the other hand, in a CMP
measurement they can be recognized. A theoretical result is depicted in Figure 7C. From
the ground wave, the velocity of the waves just beneath the surface (through the soil if
there is a thin soil layer) can be extracted by determining the slope of the event,
26
The rock velocity can be calculated from
where a and b denote two different offsets (Figure 7B) and t(a) and t(b) are the
corresponding two-way travel times.
While CMP surveys have the advantage of allowing velocities to be calculated from the
variations in reflection time with offset, they are very slow, and therefore rarely used in
geological GPR studies; they are however routine in seismic reflection, where geophones
can be laid out in large numbers.
Two major benefits of this survey mode are that CMP stacking can improve signal-to-
noise (Fisher et al, 1992a), and that a full velocity cross section required for time-depth
conversion of the GPR profiles can be derived (Greaves et al., 1996). Multifold GPR
surveys are seldom performed because they are time-consuming, more complex to
analyze, and not cost-effective (most of the cost benefit is obtained with well-designed
single-fold surveys).
(2.2) (Ver der Kruk et al, 2004)
(2.3) (Ver der Kruk et al, 2004)
27
Figure 7: (A) Diagram illustrating single transmitter (s) -receiver (r) common midpoint survey mode (B) CMP configuration for GPR (C) Simple GPR CMP traveltime diagram for estimating velocities. (Images taken from Ver der Kruk et al, 2004).
A
B
C
28
2.5 GPR Data Acquisition and Recording
GPR data have the advantage of being viewed directly as they are being recorded in the
field and many GPR equipment control units have basic editing and data processing
capability. Despite this advantage over seismic data acquisition, radar data acquisition
parameters such as antenna frequency, sampling frequency, number of stacks and time
window can not be changed during data processing. To ensure that data acquisition time
is effectively used, laptop computers with installed data processing applications should be
taken to the field and GPR data edited, checked and test-processed in the field before the
completion of field surveys as it is often difficult to fix problems in GPR data that are due
to poor acquisition parameters without having to return to the field.
Detailed record of GPR lines, outcrop photos and their locations should be accurately
documented in the field as the effectiveness of data processing and geological
interpretation hinge on proper documentation of GPR line locations and other outcrop
observations. GPR data sheet such as Table 1 should be completed as each GPR line is
being recorded.
Table 1: Example data sheet that can be used for collecting data from daily GPR surveys
29
2.6 GPR Data Processing
GPR signals are usually processed like seismic data although the two are slightly
different. GPR data are most often treated as scalar although as electromagnetic fields,
they are vector quantities. Hence, GPR signals may behave differently due to frequency-
dependent absorption and phase changes at reflections.
In the early days of GPR data processing, much of the data processing was done with
seismic data processing software. However, GPR-specific processing software is now
commercially available from packages offered by manufacturers of GPR or as add-ons
for seismic processing software. For this study, REFLEX and GPR Slice processing and
display software were used for data processing and perspective display.
Like seismic reflection data, GPR data require processing aimed at sharpening the signal
waveform by improving the signal to noise ratio of the radar profiles (Reynolds 1997).
The amount of processing depends on the quality of field data obtained, and this can
range from basic processing steps to the more complex application of data processing
algorithms. Data obtained with shielded antennas are often less cluttered with extraneous
signals and usually require less rigorous data processing. In most instances, basic
processing steps can be applied in real-time during data acquisition; however, these might
not be enough to remove extraneous noise from the acquired data. A detailed discussion
of GPR processing steps is important, as the final output of GPR surveys is dependent on
processing steps; radar facies must therefore be compared only between data processed
with similar processing steps and criteria.
Definition of radar facies is based on shape of reflections; dip of reflections; relationship
between reflections, reflection continuity and reflection amplitude (Neal 1994); these
30
criteria can be significantly influenced by the processing steps. Continuous reflection can
appear discontinuous by applying inappropriate gains during data processing and
reflection dips can result from inappropriate processing algorithms; hence, the
importance of proper signal processing steps and outcrop data as ground truth to verify
the fidelity of radar data. This also underscores the importance of documenting data
acquisition and processing steps in GPR publications to allow comparison between
studies.
Commonly applied processing steps on GPR data include:
2. 6.1 Topographic Correction
The collection of topographic data is an essential component of GPR survey as radar data
collected in the field does not take into account topographic variation along a survey line.
This can be corrected by moving traces up and down by an appropriate two-way-time
relative to a common datum, based on knowledge of the velocity, and, therefore, depth
profile of the uppermost part of the radar profile. In order to do this, survey line
topography must be adequately characterized. Topographic surveys are typically
performed using a variety of instruments including optical levels, total station, laser
levels, and differential GPS as these have the required vertical resolution and allow
relatively rapid data collection. Spatial sampling in such surveys should ensure that all
significant breaks in slope are accounted for. While lower frequency antenna can tolerate
minor elevation changes, high frequency antennas (above 200 MHz) are very sensitive to
topographic variation (elevation changes over 1 metre) along the survey line and often
create artificial structures in the radar profiles if not corrected (Figure 8). Survey
31
equipment was not available for this study; hence outcrops with flat surfaces were chosen
for this study to avoid the need for elevation correction of the recorded GPR profiles.
Figure 8: Artificial structure on downstream accretion element created by elevation variation along the profile line. (Profile recorded on Castlegate sandstone outcrop, Tusher Canyon, Utah).
2.6.2 Dewow
Wow noise is peculiar to ground penetrating radar and it is as a result of the close
proximity of receiver to transmitter. Dewow is one of GPR processing basic temporal
filtering steps aimed at removing very low frequency components from the data (Figure
9). Very low frequency components of GPR data are associated with either inductive
phenomena or possible instrumentation dynamic range limitations. This process has
historically been done using analog filters in hardware but with the advent of true digital
data acquisition, it has also become a data processing step (Gerlitz et al, 1993). Dewow
filter acts on each trace independently by calculating a mean value of each trace and the
running mean subtracted from the central point.
32
Figure 9 (A) Display of a single data trace (left) and data section (right) with the low frequency wow component masking the real data. (B) Display of a single data trace (left) and data section (right) where the Wow seen in (A) above has been removed with the dewow high pass filter. (Image taken from Annan, 2004).
2. 6.3 Backgound Removal
One of the most common operations specifically applied to GPR data is the use of
background removal. Background removal is a form of spatial filtering; most often, this
takes the form of a high pass filter or a filter that takes the mean of all traces in a section
and substracts it from each trace.
B
A
33
Figure 10: (A) GPR profile before background removal (B) GPR profile after background removal. (Image taken from http://www.malags.com/Downloads/Product-Brochures.aspx; accessed, August 6, 2010).
In situations where antenna ringing, transmitter reverberation and time synchronous
system artifacts appear, it is very effective in allowing subtle weaker signals, which are
lost to become visible in a processed section. Background filter can eliminate temporally
consistent noise from the whole profile and therefore possibly make real signals
previously covered by this noise visible and suppress horizontally coherent energy
A
B
34
(Figure 10 A and B). It is quite effective in relatively lossy materials (conductive
lithologies such as wet or shaly rocks).
2. 6.4 Deconvolution
Deconvolution is aimed at removing effects of a previous filtering operation (Yilmaz,
1987, 2001; Kearey and Brooks, 1991). In both seismics and radar signals, deconvolution
attempts to remove filtering effects resulting from propagation of a source wavelet
through a layered earth, and the recording system response. The intended effect of the
deconvolution process is to shorten pulse length and, therefore, improve vertical
resolution (Figure 11).
It is often tempting to apply seismic processing steps like deconvolution to GPR because
of their kinematic similarity; it is however important to note that deconvolution of GPR
data is not straightforward and rarely yields impressive results (Fowler and Still, 1977;
Payan and Kunt, 1982; LaFleche et al., 1991; Maijala, 1992; Todoeschuck et al., 1992;
Fisher et al., 1996; Arcone et al., 1998). The primary reason for this is that the radar pulse
is often as short and compressed as can be achieved for the given bandwidth and signal-
to-noise conditions. Another important factor is that some of the more standard
deconvolution procedures have underlying assumptions required for wavelet estimation
such as minimum phase and stationarity, which oftentimes are not appropriate for GPR
data (Annan, 1999). The rapid attenuation of GPR signal amplitude means that
deconvolution artifacts may mask weaker deeper events if time gain is not applied first
and the non-linear nature of time gain may substantially alter wavelet character if gain is
applied before deconvolution. Hence, deconvolution can be difficult to apply and might
yield marginal enhancement in resolution.
35
Figure 11: (A) GPR profile before deconvolution (B) GPR profile after deconvolution. (Image taken from http://www.malags.com/Downloads/Product-Brochures.aspx -accessed on August 6, 2010).
Few instances where deconvolution has proven beneficial occurred when extraneous
reverberation or system reverberation have been involved. In such instances,
deconvolution provides substantial pulse compression benefits (Turner, 1994; Xia et al.,
2003)
A
B
36
2. 6.5 Time Gain
Radar signals are prone to rapid signal attenuation as they propagate into the ground.
Signals from greater depths are often very weak, such that simultaneous display of this
information with signals from a shallower depth requires preconditioning for visual
analysis and display. When the amplitude of display is optimal for shallow depth signals,
events from greater depths may be invisible or indiscernible. Gains are required because
the amplitude of a reflected signal decreases with time and depth due to attenuation,
geometrical spreading, partial reflection and scattering (Davis and Annan 1989; Reynolds
1997). "Time gain" applied to radar data attempts to equalize amplitudes by applying
some sort of time-dependent gain function, which compensates for the rapid fall off in
radar signals from deeper reflectors. A variety of gain functions can be applied to radar
signals (e.g. constant, linear and exponential gains); it is however important to understand
that the choice of gain adopted might alter the amplitude fidelity of the signals in the
data.
Geological radar surveys are especially susceptible to signal attenuation in mud-rich
environments; hence, for stratigraphic horizon continuity, displaying all the information
irrespective of amplitude fidelity might be important. In this case, manual gain or a
continuously adaptive gain such as AGC (automatic gain control) is often used. With
AGC gain, each data trace is processed such that the average signal is computed over a
time window and then the data point at the centre of the window is amplified (or
attenuated) by the ratio of the desired output value to the average signal amplitude.
Systematic gains, such as Spherical and Exponential Compensation (SEC) gain, attempt
to emulate the variation of signal amplitude as it propagates in the ground. Whichever
37
gain function is chosen, it should be selected based on the specific goal of the survey and
data processing requirement; the objective should be to modify the data while retaining
fidelity without introducing artifacts.
Figure 12: (A) Un-gained Whirlpool Sandstone GPR Profile. (B) Manually-gained profile at the Whirlpool Sandstone outcrop at Artpark, USA.
It is important to document the type of gain function applied to radar data while
discussing radar facies as radar reflector character is dependent on the signal processing
steps applied to the data (relative amplitudes and/or phase relationships are changed); for
instance, reflectors described as discontinuous low amplitude facies may show up as
continuous reflectors where stronger gains are applied (Figure 12).
Queenston Shale
Whirlpool channel sand
A
B
38
2.6.6 Migration
Migration relocates reflections to their true spatial position based on the velocity
spectrum of radar signals through the rock layers to produce a real structure map of
subsurface features. Migration algorithms do this by removing diffractions, distortions,
dip displacements and out-of-line reflections resulting from the fact that radar antenna
radiate and receive electromagnetic energy in a complex 3- D cone.
The goal of migration is to make the reflection profile look like the geological structure
in the plane of the survey. It attempts to correctly position subsurface reflection events
(Hatton et al., 1986). However, due to various uncertainties, a significantly improved but
still imperfect image is usually achieved (Figure 13). Such improvements are quite
beneficial in sedimentological studies, where the nature and form of stratigraphic units
and primary sedimentary structure is of utmost importance.
Figure 13: (A) Unmigrated GPR Profile (B) GPR profile migrated by diffraction hyperbola collapse. (Image taken from Anan, 2004).
A
B
39
Migration is generally used for improving section resolution and developing more
spatially realistic images of the subsurface and is, perhaps, the most controversial of the
GPR processing techniques. Migration techniques, like deconvolution, were originally
developed for the seismic industry where they are considered as vital for even basic
interpretations. Unfortunately, migration tends to be less successful with GPR, and
although it can be used in relatively homogeneous environments, it is not so good with
complex, heterogeneous environments (lithologies) with variable radar velocity typical of
clastic many rocks. Despite this, migration is still a vital georadar processing step and
classical techniques have been applied successfully to a range of different applications.
Examples include reverse time migration (Sun and Young, 1995; Meats, 1996), F–K
migration (Fisher et al., 1994; Pettinelli et al., 1994; Pipan et al., 1996; Yu et al., 1996;
Hayakawa and Kawanaka, 1998) and Kirchhoff migration (in Moran et al., 1998).
Specific GPR-based methods have been developed to overcome some of the limitations
in the seismic data migration algorithms. Examples include matched filter migration
(Leuschen and Plumb, 2000); Kirchhoff migration modified for radiation patterns and
interface reflection polarisation (Moran et al., 1998; Van Gestel and Stoffa, 2000);
eccentricity migration for pipe hyperbola collapsing (Christian and Klaus-Peter, 1994),
3D-based vector and topographic migration (Lehman and Green, 2000; Heincke et al.,
2006; Streich et al., 2007) and frequency domain migration for lossy soils (Di and Wang,
2004; Sena et al., 2006; Oden et al., 2007). These new methods are yet to be incorporated
into mainstream GPR processing packages, although most do contain some form of
relatively sophisticated (if classical) migration algorithm. The most common are
diffraction stack migration, F–K migration (or Stolt migration), Kirchhoff migration and
40
wave equation or finite-difference modelling migration. These can be applied to 2D GPR
profiles or across 3D volumes of data. The specific theories and quantitative details of
how each method works are discussed in Yilmaz (2001). Success of GPR data migration
is dependent on accurate estimation of the velocity profile through the different layers of
the rocks which is often obtained by Common Mid-Point (CMP) surveys. Unfortunately,
increased surveying time/equipment cost required for CMP surveys often limit the
number of CMP surveys conducted, hence, sparse velocity information is usually
available. Other less reliable methods such as average radar velocity associated with the
lithologies at the outcrop as well as hyperbola matching are often used but these
determine only the average velocity to isolated horizons or spatially restricted zones.
While migration is a routine seismic processing step, GPR data obtained for stratigraphic
studies are rarely migrated; perhaps this is because migration requires a thorough
knowledge of the velocity structure in the imaged formation (which is often not available
in most GPR single fold common offset surveys) and susceptibility to errors in the
velocity structure which introduces artifacts into migrated GPR section. Data obtained
with shielded antennas are usually less prone to diffractions than data obtained with
unshielded antennas; shielded antennas might therefore be more advisable in locations or
outcrops susceptible to significant signal scattering; they are however not designed for
CMP surveys needed to obtain velocity profile required for data migration.
2.6.7 Advanced Data Processing
Advanced data processing techniques address the types of processing, which require data
processing expertise to be applied and which often results in data which could be
significantly different from the raw information fed into the processing unit. Application
41
of such processing techniques well-known in seismic processing operations such as trace
attribute analysis, FK filtering, selective muting, normal move out correction, dip
filtering, and velocity semblance analysis is still in its infancy in GPR data processing;
although there has been an increasing application of the more GPR-specific operations
such as multiple frequency antenna mixing and polarization mixing (Tillard and Dubois,
1992). With careful data collection and effective ground coupling of radar antennas,
however, most GPR profiles hardly require advanced post-processing to enable basic
interpretation of sedimentological features.
2. 6.8 Time - Depth Conversion
GPR data are usually displayed as distance-two way time (in nanoseconds) profiles;
conversion to distance-depth profiles is more easily done with data obtained in CMP
(Common-Midpoint) mode. Reliable subsurface-radar-wave velocity information is
important for converting two-way-travel time (TWT) to an accurate estimation of depth.
The standard approach to velocity estimation in many studies is the CMP survey as it is
entirely non-invasive and can be supplemented by subsequent ground truthing (Annan
and Davis, 1976; Beres and Haeni, 1991; Tillard and Dubois, 1995; Greaves et al., 1996;
Van Overmeeren et al., 1997). Because most shielded antennas are not designed for CMP
surveys and significant data acquisition time associated with CMP surveys, most GPR
profiles are obtained in common offset mode. In such cases, velocity can be roughly
estimated by measuring TWT to a bounding surface or bedding of known depth where
major bounding surfaces in outcrop can be directly correlated to radar reflectors. The
travel time for a pulse to travel from the transmitter to a reflector and up to the receiver,
the two-way travel time, t, as a function of the velocity at which the electromagnetic
42
pulse is propagated through the host medium, Vm, and the depth to the bounding surface
d, are related by the Equation
t= 2d/Vm
Velocity for depth conversion of the radar profiles recorded in this study was estimated
using this relationship. Although rarely, velocity required for time-depth conversion is
also estimated by direct laboratory measurements of dielectric permittivity on field
samples; measuring travel time between two wells using borehole radar; and
transillumination surveys between two parallel exposures (Annan and Davis, 1976; Topp
et al., 1980; Fisher et al., 1992a; Greaves et al., 1996; Reynolds, 1997; Binley et al.,
2001; Hammon et al., 2002; Tronicke et al., 2002a).
2. 7 Visualization and Display
Ground-penetrating radar has been used for geological imaging since the 1980s and has
since developed into a valuable tool for stratigraphic studies. Most studies utilize
common-offset, 2-D radar reflection profiles to display stratigraphic information obtained
in modern environments and outcrop. Where there is significant lateral variability in
internal structure, pseudo-3D or true 3D surveys may be desirable. Pseudo-3D surveys
involve collecting data on regular or irregular survey grids, usually in two mutually
perpendicular directions, and often displaying results as fence diagrams (for example,
Bristow, 1995; Aigner et al., 1996; Bristow et al., 1996, 1999, 2000b; Roberts et al.,
1996; Asprion and Aigner, 1997, 1999; Leclerc and Hickin, 1997;; Pedley et al., 2000;
Neal and Roberts, 2001; Russell et al., 2001; Holden et al., 2002; Skelly et al., 2003). In
the 1990s, time-slicing, a mechanism for producing horizontal plan maps routine at that
(2.4)
43
time in three dimensional seismic imaging revolutionized the way GPR results are
displayed and interpreted (Goodman et al., 1995), and recent GPR three-dimensional
imaging produced exciting results for visualization and enhanced interpretation (Conyers
et al., 1997; Jol et al, 2003; Leckebusch, 2003).
While full resolution 3D GPR surveys are generally more informative than single
profiles, it requires significantly increased data acquisition time. Hence, they are seldom
used in geological studies. Data processing for three dimensional GPR surveys is more
time consuming partly because of greater data volumes and complexity, but also due to
lack of efficient commercially available software for three dimensional GPR data
processing; these explain why there are few 3D GPR outcrop studies in the GPR
literature. Not all studies require 3D surveys; staggered GPR lines parallel and orthogonal
to the outcrop face displayed as a fence diagram often yield sufficient architectural details
for stratigraphic interpretation.
2. 8 Causes of GPR Reflections
Although GPR images appear similar to seismic reflections generated across surfaces due
to changes in acoustic impedance in the subsurface, GPR reflections are generated by
changes in electromagnetic impedance due to variation in the electrical and magnetic
properties of the lithologies that an electric pulse transmitted from the antenna into the
ground passes through as it makes its way through lithologies with different electrical and
magnetic properties. While the theoretical basis of radar signal propagation and reflection
have been exhaustively discussed by many authors (Daniels, 2004; Baker et al., 2007;
Rubin and Hubbard, 2005), the actual causes of GPR reflections in sediments and rocks
and their implications for interpretation of GPR data from modern and ancient sediments
44
have been loosely defined. Few studies that have investigated the causes of GPR
reflection in sediments (Van Dam and Schlager, 2000; Van Dam, 2001) discovered that
propagation of electromagnetic signals is primarily dependent on the electrical
conductivity and magnetic permeability of the medium that the signals pass through.
Electrical conductivity is the ability of the material to transmit electric charges under the
influence of an applied field. In rocks and sediment, this often depends on the dielectric
permittivity associated with variations in water content and ionic concentrations. Water
in sediment pore space normally contains ions, and the electrical conductivity associated
with ion mobility is the dominant factor in determining bulk-material electrical
conductivity. Since water is invariably present in the pore space of sediments and rocks,
it has a dominant effect on electrical properties. Magnetic permeability is the degree of
magnetization of a material that responds linearly to an applied magnetic field; this is
significant in rocks or sediments rich in ferromagnetic minerals. However, in most
sedimentary rocks, the amount of ferromagnetic minerals is minimal and hardly
contributes significantly to generation of radar reflections. Hence, in most GPR surveys
on sediments and rocks, the dominant control on radar transmission and reflection is
electrical conductivity governed by water content and the sediment static conductivity.
The variation in sediment water content often relates to both changes in sediment
porosity and permeability, which in turn is dependent on changes in grain size and fabric
often associated with lamination, cross-bedding and bounding surfaces. Rock property
research in the petroleum industry in the seventies and eighties geared at understanding
controls on permeability distribution in clastic reservoirs suggested that fluid flow in
cross-bedded sandstone is controlled by porosity and permeability contrasts of the cross-
45
bed laminae and the associated bottom-set layer (Pryor, 1973; Beard and Weyl, 1973,
Jordan and Pryor, 1987). Emmet et al (1971) observed that porosity and permeability
parallel to the cross-bed laminae are higher than perpendicular to the laminae. Such
porosity and permeability changes have direct control on water content, which determines
electrical conductivity changes that generate radar reflections (Figure 14).
Figure 14: (A) Navajo Sandstone outcrop at Zion National Park, Utah (B) Behind outcrop GPR profile using 100 MHz antenna across the Navajo Sandstone outcrop in (A). (Image taken from Jol. et al., 2003).
A
High porosity cross-bed
Low porosity bounding surface
B
5 m
46
Sedimentary bedding is a product of changes in sediment composition and changes in the
size, shape, orientation and packing of grains (Collinson and Thompson, 1989) which
results in corresponding changes in porosity (Figure 15).
Figure 15: Bedding in sediments and sedimentary rocks and associated porosity resulting from changes in composition, size, shape, orientation and packing of sediment grains. (Image modified from Neal, 1994).
Van Dam et al., (2002a) reported that goethite iron-oxide precipitates, occurring either in
bands or irregular layers, were responsible for significant reflections in the aeolian sands
they studied. This was due to the higher water retention capacity of goethite with respect
to the host quartz sand, which resulted in higher dielectric permittivity.
While most radar reflections are associated with electrical conductivity associated with
porosity changes across primary bedding, bounding surfaces and lithological breaks,
changes in magnetic permeability (although rarely) may generate radar reflections.
Higher porosity and permeability
Lower porosity and permeabilitty
47
Textural differences between laminae of differing origins may also control cementation
patterns and, hence, post depositional diagenesis, which may influence radar reflection
patterns in consolidated sediments.
2. 9 GPR Interpretation Methodology and Radar Stratigraphy
Because seismic reflection and GPR data are analogous in terms of wave propagation
kinematics (Ursin, 1983; Carcione and Cavallini, 1995) as well as reflection and
refraction responses to subsurface discontinuities (McCann et al., 1988; Fisher et al.,
1992a) many of the broad assumptions that underpin processing and interpretation of
seismic reflection data (Sangree and Widmier, 1979; Yilmaz, 1987, 2001) are often
routinely applied to GPR data. However, it must be borne in mind that radar images are
different from seismic images in the following respect:
1. Signal penetration and reflection amplitude are controlled by water saturation,
clay content and magnetic property of the sediment.
2. Radar signals are more prone to scattering making diffraction noise more
prominent in radar profiles.
3. The investigation depth is much less.
4. Resolution is in sub-metre scale.
5. Radar surveys require direct contact between the pulse-transmitting antenna and
the medium which the signals are transmitted through (rocks or water/moist
sediment for surveys conducted in modern fluvial environments); this limits the
size of most GPR surveys and often results in much smaller coverage than seismic
surveys.
48
From the interpretation standpoint, the basic assumption in both techniques is that, at the
resolution of the survey and after appropriate data processing, reflection profiles will
contain accurate information regarding the external geometry and internal structure of a
sediment body. This implies that the form and orientation of bedding and sedimentary
structures in the plane of the survey will be adequately represented by recorded
reflections, and non-geological reflections can be readily identified and removed by data
processing, or by simply discounting them from the interpretation. While this assumption
holds in many instances, accurate interpretation of GPR data is dependent on the nature
and appropriateness of data processing steps undertaken, the interpretation techniques
employed, and the overall understanding and experience of the interpreter with respect to
GPR; hence, care must be taken to ensure that GPR profiles are not treated as geological
cross sections but interpreted in the context of the local geology and ground-truthed with
outcrop data.
Based on the similarities between GPR and seismic reflection, the concept of seismic
stratigraphy was adapted for interpretation of GPR profiles soon after the realization that
GPR could provide useful data for stratigraphic and sedimentological studies (Baker,
1991; Beres and Haeni, 1991); Jol and Smith (1991) coined the term ‘radar stratigraphy’
for this new interpretation technique. Gawthorpe et al (1993) defined radar facies based
on the terminology used to describe seismic facies (Mitchum et al., 1977; Brown and
Fisher 1980) as three-dimensional packages that represent particular combinations of
physical properties such as lithology, stratification style and fluid content, and may be
used to interpret depositional processes and environments. They also defined radar
sequence boundaries as systematic reflector terminations indicating non-depositional and
49
erosional hiatuses despite acknowledging that “while seismic sequences can be mapped
on at least a basin scale and reflect units that form over hundreds of thousands to millions
of years, radar sequences may be limited to particular depositional environments (e.g. a
point bar in a fluvial channel belt) and may form over a much shorter time scale of tens to
thousands of years”. Although, this interpretation methodology has been widely
embraced over the years, it is important to underscore the fact that GPR resolution is an
order of magnitude higher than conventional seismic resolution and coverage of GPR
surveys rarely has the capability to image stratigraphic sequences and sequence
boundaries; it is more appropriate for imaging of meso-scale depositional features or
outcrop scale architectural elements. Although decimeter-scale resolution has been
reported in high resolution seismic surveys, the technology is rarely used for outcrop
studies; hence, ground penetrating radar remains the choice technology for high
resolution outcrop imaging.
To avoid interpretive connotations in describing radar reflections, it is recommended that
unambiguous descriptive criteria such as geometry; dip of reflections, relationship
between reflections be used to describe radar reflections rather than terms with
interpretive connotations like, sequence boundaries, systems tract, etc used in seismic
stratigraphy. Interpretations based solely on processing-dependent attributes such as
reflection continuity and amplitude should also be avoided as these are dependent on the
data processing algorithms or gain magnitude applied to the data and are hardly
comparable between different GPR studies. The potential for misinterpretation of radar
data based on reflection continuity is illustrated below (Figure 16 A and B)
50
Reflection packages a, b and c (Figure 16A) could be interpreted as different architectural
elements based on reflection continuity but the reflectors are seen as continuous in the
better gained data (Figure 16B).
Figure 16: (A) Poorly-gained radar profile giving the impression of facies with low continuity (B) Same data in (A) with gains applied to display all reflectors. GPR data acquired at Whirlpool Sandstone.
Also, while in most cases, radar reflections parallel bedding and bounding surfaces, care
must be taken to ensure that reflections generated by the water table and diagenetic
horizons, diffractions generated by isolated reflector points, out-of-line reflections,
reflections generated by faults and joints, surface reflections, and ambient and systematic
noise are not interpreted as primary sedimentary bedding or bounding surfaces.
a c b
A
B
0
6
0
6
Depth (m
) D
epth (m)
51
2.10 Radar Facies
Analysis of 150 published studies in the last thirty years on stratigraphic imaging with
ground penetrating radar reveals an obvious bias towards studies of modern and recent
deposits (Figure 17 and Table A3, Appendix 3). Much of the GPR effort on rocks has
been concentrated on carbonates as the low electrical conductivity of carbonate rocks
make them highly conducive to georadar imaging.
Figure 17: (A) Analyses of 150 published GPR studies on sediments showing bias for Quaternary sediments (B) Analysis of ancient deposit studies in (A) showing comparatively more GPR studies on carbonate rocks.
Nu
mb
er o
f p
ub
lish
ed G
PR
stu
die
s N
um
ber
of
pu
blis
hed
GP
R s
tud
ies
A
B
52
Observations from analyses of published studies also show that highest radar signal
penetration is observed in carbonate rocks due to their high resistivity. This study
however focuses on the application of GPR imaging technology to the studies of ancient
clastic depositional units.
There is currently no formal methodology for documenting radar profiles and radar
facies; this in addition to different processing and display formats adopted by various
authors make comparison of radar facies rather challenging; but an attempt is made
below to summarize observations and describe radar facies commonly observed in a
variety of depositional environments. Radar facies are defined by: external reflection,
geometry, dip of reflections and relationship between reflections. Due to the paucity of
GPR studies on ancient sediments, most of the radar facies discussed in this section are
from modern sedimentary environments and Quaternary deposits.
Since the inception of its use as a tool for stratigraphic and sedimentological
interpretation, much of the emphasis of GPR studies has been on characterization and
interpretation of radar facies, with radar surfaces and radar packages typically not being
defined. This overemphasis on radar facies analysis, rather than true radar stratigraphy,
led to the common misconception that any radar reflection pattern constituted radar
facies. As a result, use of radar facies to describe reflections not related to primary
sedimentary structure and stratigraphy became rife in the GPR literature. Terms such as
‘water-table radar facies’ and ‘hyperbolic’ or ‘diffraction radar facies’ can be found
throughout the GPR literature. In addition, radar surfaces have also been described as
radar facies. The term ‘palaeosol radar facies’ has been used on several occasions, despite
the fact that the ‘facies’ is defined by a single reflection (it is a radar surface at the
53
resolution of the radar profile). These examples are in violation of the correct use of the
term radar facies and, therefore, the true principles of radar stratigraphy. Further
confusion to the interpretation of radar profiles has also been caused by use of
interpretive facies names, such as ‘channel-fill facies’ and ‘overbank facies’. If the
context is not made clear, use of interpretive facies names has the danger of suggesting
that particular depositional environments or sub-environments are characterized only by
certain radar facies which is not true based on the findings from published studies and
GPR outcrop data obtained in this study. Radar facies should therefore be described
without interpretive connotations and an uninterpreted version of the radar facies
provided to provide readers an unprejudiced data and basis for interpretation.
The value of radar facies interpretation is demonstrated in all the case studies for this
research especially at the Shinarump Conglomerate (Figure 21 A), Navajo Sandstone
(Figure 21 B) and Whirlpool Sandstone (Figure 22A). Common radar reflection patterns
(facies) typically observed from a variety of sedimentary environments are discussed
below:
2.10.1 Concave upward/trough-shaped reflectors
Concave-upward ground radar reflectors are observed as valley fill (Ilya, 2006), cut and
fill (Heinz et al, 2003) channel (Figure 18), chute, scour, bar top hollows (Best et al,
2006) and trough cross-beds (Bristow et al, 1999). Documented concave upward GPR
reflectors range from sub-metre length to a few kilometers, although published kilometre-
scale GPR studies are very few (Møller and Anthony, 2003; Hickin et al., 2007). Sub-
metre scale concave-upward reflectors are usually trough cross beds or minor scours.
54
Channels are often several metres to hundreds of metres in width and may have simple to
complex fill.
Figure 18: GPR Image of fluvial channels from Dunvegan Formation outcrop (Pink Mountain, British Columbia). Valleys are typically hundreds of metres to kilometre-scale in width, they contain
channels and channel belts and are rarely defined in GPR profiles.
While the various concave-upward radar facies are sometimes geometrically-identical, it
might be difficult to correctly interpret them; they can however be discriminated by their
scale, internal geometry and facies associations. This underlines the importance of
documenting the horizontal and vertical scale of GPR profiles. The geometry of
reflectors often depends on the orientation of the GPR line in relation to the channel axis
(for bedload deposits). GPR profiles along the axis of a channel deposit usually reveal
different reflector geometry compared to profiles perpendicular to the channel axis; hence
it is important to document the orientation of GPR profile from which the radar facies are
obtained.
CH CH
55
Figure 19: (A) Radar facies from Fraser and Squamish River showing concave upward reflectors. (Image taken from Wooldridge and Hickins, 2005) (B) Concave upward radar facies from Niobrara River, Nebraska. (Image taken from Bristow, 1999) – Red arrow highlights major channel.
B
A
56
2.10.2 Inclined Reflectors
Inclined radar reflectors are observed in a variety of environments; they range from
planar cross-beds, lateral accretion and downstream accretion in fluvial deposit to
Inclined Heterolithic Stratification (IHS) in tidal bars. Inclined radar facies are also
observed in eolian deposits as giant cross-beds and also in deltaic clinoforms (Figure 20).
They are often vital paleocurrent indicators; hence the orientation of the GPR profiles
where they are observed as well as the orientation with respect to channel trend or
regional paleocurrent direction should be carefully documented. They can be
discriminated by the vertical and horizontal scale of the reflectors as well as the
association with contiguous facies, ground-truthed with outcrop observations or sediment
trenches. Examples from modern and ancient sediments are given below:
2.10.3 Reflection-free facies
Reflection-free configuration often indicates one of the following:
massive homogenous lithological units with no contrasting dielectric properties
the presence of highly conductive dissolved minerals in groundwater
magnetic sediment
or the presence of sediments containing high clay content that rapidly attenuates
transmitted electromagnetic signal.
57
Figure 20: (A) Inclined Radar facies from Fraser and Squamish River (Image taken from Wooldridge and Hickins, 2005) (B) Downstream accretion macroform from Castlegate sandstone, Utah (C) GPR profile at the aeolian Navajo Sandstone from Zion National Park, Utah revealing a set of cross stratification. (Image taken from Jol et al., 2003).
The susceptibility of radar signals to rapid attenuation in argillaceous sediments is vital
for interpreting lithology from radar profiles. Chanel cutbank, overbank and floodplain
B
C
A
58
deposits can be clearly interpreted in fluvial deposits and interdune deposit discriminated
from dry phase eolian dunes based on reflection geometry and amplitude (Figure 21)
Figure 21: (A) Example of reflection-free radar facies- Shinarump Sandstone (Hurricane Mesa, Utah) (B) Radar facies from Navajo Sandstone (Moab, Utah)
2.10.4 Horizontal Reflectors
These facies is characterized by continuous, sub-horizontal to horizontal reflectors.
They are observed from diverse depositional environments: fluvial overbank levees
(Figure 22 A), vertically aggraded channel deposit (Figure 22 B), sheetflood deposit,
Reflection-free facies
Reflection-free facies
B
Shinarump Conglomerate
Moenkopi Shale
Muddy interdune deposits
Amplitude Scale
Low
High
A
59
floodplain deposits and lacustrine sediments. They are often recognized by their
reflection amplitudes and facies association; for instance, muddy horizontal overbank
deposits are usually high to medium amplitude reflectors with low amplitude at the
base as observed at the Whirlpool Sandstone Figure 22A) while sand-rich intra channel
horizontal reflectors are usually characterized by high amplitude sometimes underlain
by a thin layer of low amplitude reflectors indicating shaly channel base breccia or mud
chips (Figure 22 A and B). Mud beds typically have low amplitude thin horizontal
reflectors with indistinguishable reflectors at the base.
Figure 22: (A) Horizontal radar facies – overbank deposit from Whirlpool Sandstone, Artpark, New York (B) Horizontal reflectors from Shinarump sheet conglomerate, Utah interpreted as upper plane bed flood deposits.
2.10.5 Hyberbolic Reflections
Hyperbolic radar reflections were once thought to be diagnostic of glacial push moraine
deposits (Van Overmeeren, 1998); observations from several published GPR studies
Queenston Shale
Overbank deposit
Channel margin
A
B
Sandy Bedform
60
(Arcone, 1998; Sénéchal et al., 2000; Ekes and Friele 2003; Van Dam, et al., 2003)
however reveal that these reflections are due to diffractions of radar signals and thus, are
not diagnostic of any depositional environment. Due to the acute susceptibility of radar
signals to scattering; they are common in un-migrated radar profiles especially those
obtained with unshielded antenna. Diffraction noise is easily recognized in GPR sections
as hyperbolas (Figure 23).
Unfortunately, migration requires a thorough knowledge of the velocity structure in the
rock or sediment being imaged which is not often easily determinable; hence, uninformed
signal processing steps aimed at removing diffraction hyperbolas might introduce
artefacts into the radar profile (section 2.6.6).
Figure 23: Example of hyperbolic reflection (HP) from an un-migrated GPR profile. (Image taken from Woodward et al., 2003). Red arrow points at hyperbolic reflections.
In the early days of GPR imaging on sediments, observation of distinct reflection patterns
from a variety of modern sedimentary environments led to the assumption that certain
reflection configurations are diagnostic of specific sedimentary environments (Table 2).
61
Table 2: Radar facies elements of different sedimentary depositional environments. (Table obtained from Van Overmeeren, 1998)
Based on this surmise, Van Overmeeren (1998) suggested a compilation of ‘radar facies
atlas’ from a variety of depositional environments as guide for facies interpretation and
identification of depositional environment from sediments (Figure 24). Although there
have since been many published studies involving GPR imaging of sediments, many of
the early ideologies still persist.
62
Figure 24: Radar facies chart of characteristic reflection patterns from various sedimentary environments. (Image taken from Van Overmeeren, 1998).
Analysis of radar facies observed in this study and from other published GPR studies
evaluated confirms that no reflection configuration is diagnostic of a specific
depositional environment. For instance, concave upward radar reflections could be
associated with confluence scours, main channel fill, small cross-bar channels adjacent
to unit bars, scours upstream of obstacles such as logs or ice blocks or bases of trough
63
cross strata. Hyperbolic reflectors are observed in most un-migrated or poorly-migrated
radar profiles irrespective of the sedimentary environment (modern or ancient) where the
radar profiles are obtained. Also, while the link between sedimentary architecture and
radar reflection patterns implies that different radar facies represent spatially varying
geologic settings in the subsurface, Jol and Bristow (2003) cautioned that many different
geologic scenarios can produce similar reflection patterns in a GPR image. Similarly, the
dependence of GPR resolution on frequency means that a single depositional
environment could produce many different textures depending on antenna frequency
used for the survey (Huggenberger and Pugin, 1994; Jol, 1995; Jol et al., 2003). While
certain reflection patterns are more common in certain environments (e.g large scale
high amplitude dipping reflectors characteristic of eolian dunes) similar reflection
patterns can be observed in different depositional environments.
Hence, without additional information or data to provide a geologic context for the field
site, the interpretation of geologic facies directly from a GPR image or radar facies
interpretation should be avoided; rather, interpretation of radar reflections should be
made in the context of their three dimensional geometry and an understanding of adjacent
strata ground-truthed by outcrop observations. The scale and vertical exaggeration of the
radar profile should also be considered when making sedimentological interpretation
from radar reflections (Bridge and Lunt, 2006).
In summary, many studies have interpreted sedimentary facies and facies associations
and have determined depositional environment and formative processes from radar
reflection profiles ground truthed with sedimentological data from trenches, cores or
outcrop (e.g. Jol and Smith, 1991; Smith and Jol, 1992; Gawthorpe et al., 1993;
64
Huggenberger, 1993; Bristow, 1995; Beres et al., 1999; Neal and Roberts, 2000, 2001;
Corbeanu et al., 2001; Heinz, 2001; Neal et al., 2001, Russell et al., 2001; Szerbiak et al.,
2001; Hornung and Aigner, 2002; O’Neal and McGeary, 2002; Heinz and Aigner, 2003;
Skelly et al., 2003). While these studies confirm the usefulness of GPR imaging as a
powerful technique for imaging clastic sedimentary rocks, the idea that radar facies
elements used in interpretation of radar reflection patterns are characteristic of certain
sedimentary depositional environments should be applied with caution while interpreting
outcrop data as many radar facies are not diagnostic of specific ancient depositional
environments. Unlike seismic attributes, extraction of radar reflection attributes (e.g
coherence, azimuth and dip) as proxy data for sedimentary architecture is still in its
infancy; such attributes can be easily distorted by the signal algorithms employed in data
processing as well as misinterpreted due to moisture content of the imaged lithologies
and should be applied with much care. For most stratigraphic studies, it seems preferable
to adopt processing steps that highlight bedding continuity and reveal all reflectors
irrespective of amplitude fidelity as this often provides a more reliable basis of
interpretation. Reflection amplitude can also yield vital clues about lithology and guide
architectural interpretation (Figure 22); in this case, amplitude distorting algorithms
should be avoided and amplitude comparison between data subjected to different
processing algorithms should be done with caution or avoided.
65
Chapter 3
Case Study 1 - Whirlpool Formation
3.1 Introduction
There have been significant advances in our understanding of flow dynamics and
associated fluvial deposits in the last decade and much of the result is credited to the use
of ground penetrating radar on sediments ground-truthed with sedimentological data from
cores and trenches. Most of these studies focused on modern fluvial deposits as earlier
attempts to apply GPR imaging technology to ancient fluvial deposits were largely
unsuccessful due to poor data acquisition practice, fractures and diagenetic signal
overprint (Bristow and Jol, 2003).
Despite several years of GPR imaging of modern rivers and Quaternary fluvial sediments
with impressive results, there have been very few applications of GPR imaging
technology to ancient fluvial deposits due to operational difficulty of conducting GPR
surveys on outcrops. This study however, shows that with careful survey planning and
efficient data collection and processing, GPR imaging technology can be successfully
applied to the study of ancient fluvial deposits in the quest for refining current fluvial
architectural models and as analog data for subsurface reservoirs.
The lower unit of the Whirlpool Sandstone at Artpark (New York, USA) provides an
opportunity for GPR imaging integrated with outcrop architectural element analysis in an
attempt to evaluate the effectiveness of GPR imaging on outcrops as well as to refine
existing interpretation via three-dimensional architectural study of the Whirlpool
Sandstone. The Whirlpool Sandstone outcrop at Artpark was chosen as a case study
66
because of its distinct architecture (apparently clean, trough-cross-bedded fine to
medium-grained texture), flat top, reasonably extensive exposure, absence of thick
overburden (which prevents radar signals from reaching the target formation) and
moderate stratigraphic thickness (this makes it feasible to image the entire formation).
Although lithological contrast is often suggested as a pre-requisite for successful GPR
survey, the Whirlpool Sandstone provides a test of the effectiveness of GPR imaging on
sandstone with considerable homogeneity and minimal obvious lithological contrast.
3.1.1 Study Objectives
The objectives of this study are:
to demonstrate that sedimentological and architectural interpretation can be made
from GPR profiles by correlating outcrop observation with GPR images.
to document radar facies from the Whirlpool Sandstone; currently there are few
documented radar facies from ancient fluvial deposits. Radar facies from the
Whirlpool Sandstone will provide an opportunity to compare radar reflection
patterns with lithofacies and architectural elements observed in similar outcrops.
to re-evaluate current interpretation of the Whirlpool Sandstone at the study
location in the light of integrated outcrop and GPR data
extend interpretation of the Whirlpool Sandstone outcrop at Artpark based on
two-dimensional architectural element analysis into three dimensions by
integrating outcrop with GPR data.
to test the reliability of three-dimensional GPR imaging over vertical profiles and
architectural element analysis (from earlier studies of the Whirlpool Sandstone at
Artpark) in unravelling depositional processes from outcrops
67
3.1. 2 Whirlpool Sandstone - Geological Overview
Overlying the Queenston Shale is the Whirlpool Sandstone (Figure 25); an Early Silurian
prograding siliciclastic wedge in the Appalachian Basin derived from tectonic source
areas to the southeast (Figure 26). It unconformably overlies the red Queenston Shale
with a sharp, near-planar contact in outcrop described by Dennison and Head (1975) as
the Cherokee unconformity. The Queenston Formation, which represents an extensive
deposit displaying environments ranging from coastal plains to supratidal and shallow
marine settings, is dominated by mud and in some places calcareous silt and sand,
bioclastic-rich terrigenous units and silty bioclastic limestones. The upper continental
muddy part of the Queenston Formation in Ontario and New York as well as the
overlying Whirlpool Sandstone (Martini and Salas, 1983; Middleton et al., 1983) has
been attributed to the westernmost filling phase of the Appalachian Basin during the
relaxation stage of the Taconic orogeny (Quinlan and Beaumont 1984; Beaumont et al.,
1988; Ettensohn 1991). Eustatic drop in sea level, associated with Upper Ordovician
Saharan glaciations, was also postulated to have enhanced a continental setting and led to
the development of the unconformity at the top of the Queenston Formation (Dennison
1976; Ziegler et al., 1977; Brenchley and Newall 1984) and subsequent deposition of the
Whirlpool Sandstone. More recent studies in the light of foreland basin models however
pointed out (Middleton 1983; Cheel and Middleton 1993) that the development of the
unconformity at the top of the Ordovician rocks and subsequent spreading of a braided
plain across southwestern Ontario, which led to the deposition of the lower part of the
Whirlpool quartzose sandstone, are best explained tectonically. Whirlpool Sandstone
deposition was attributed to lithospheric flexure resulting from tectonic loading of
68
adjacent Taconic highlands (Figure 26). A period of tectonic quiescence in the westward
thrusting of the Appalachians would have allowed for isostatic uplift and erosion
accompanied by rapid spreading of a clastic unit over the foreland basin. Easing off of
thrusting just prior to this would explain reduced subsidence and rarer marine incursions
into the basin in the early stage of Whirlpool deposition. The thin Whirlpool Sandstone
extends very far out into the foreland basin because accommodation space was exceeded
by sediment supply derived from the Taconic orogen. Thickness of the lower part of the
Whirlpool Sandstone is variable because of irregular topography on the unconformity,
which may have been related locally to differential incision and, more broadly, to highs
and lows caused by tectonic activity.
The Whirlpool Sandstone has been extensively studied resulting in a gamut of
interpretation of its architecture as well as its depositional environment (Gilbert 1899;
Fairchild, 1901; Wilson 1903; Grabau, 1913; Williams, 1919; Johnson, 1934; Alling,
1936; Holstein, 1936; Lockwood, 1942; Bolton, 1949; 1953, 1957; Geitz, 1952; Fisher,
1954; Koepke, 1960; Martini, 1966; Sanford 1969; Pitrowski 1981; Seyler, 1981,
Metzeger, 1982; Calow, 1983; Martini and Salas, 1983; Laughrey, 1984; Martini and
Kwong, 1985; Pees, 1986; Coogan, 1990). Brett et al., (1990) interpreted the lower, non-
marine part of the Whirlpool as a major eustatic lowstand deposit, while Ryder et al.,
(1996) attributed Whirlpool deposition to fluvial backfilling of incised valleys during sea-
level rise. Cores from the Whirlpool show evidence for transgressive reworking of the
upper part of the sandstone, and it is likely that the lower part was deposited in shallow
incised valleys either during late lowstand or during early transgression. These two parts
69
of the Whirlpool are separated by a distinct, regionally correlative boundary, which may
represent a transgressive surface (Castle, 1998).
Figure 25: Generalized stratigraphic chart for the Silurian system in New York. (Modified from Telford 1978).
A near-shore marine environment has also been proposed for the Whirlpool Sandstone,
but studies in the last decade tilt evidence in favour of a near-shore, wave-influenced
marine upper unit and a lower unit formed in a braided fluvial depositional environment
(Rutka et al., 1991) probably deposited in incised valleys developed on the Cherokee
unconformity (Castle and Byrnes, 1998).
10 m
Vertical Scale
Whirlpool Sandstone
70
Figure 26: Early Silurian paleogeographic map of the Niagara Region. (Image taken from Tesmer, 1981); study area highlighted in red circle.
This study focuses on the lower unit of the Whirlpool Sandstone exposed at Artpark,
New York and applies the concepts of architectural element analysis aided with GPR
imaging in the interpretation of the anatomy as well as the fluvial style responsible for its
deposition.
3.1. 3 Study Location and Direction
The Artpark exposure of the Whirlpool Sandstone is located on the U.S side of the
Niagara River near Lewiston (New York, USA) by the Niagara River (Figure 27).
71
Figure 27: (A) Location of the Whirlpool Sandstone outcrop in New York (B) Detailed outcrop location - outcrop highlighted in red.
From Robert Moses Parkway, turn west to Centre Street and south on 4th Street. Earl
Brydges Park is at the south end of 4th Street (Figure 27B). The outcrop is at the
southwest end of the park by the Niagara River. Location coordinates of the outcrop are
N A
B
80 Km
500 m
72
43° 9'44.01"N, 79° 2'41.18"W. The entire outcrop is about 200 metres wide and it is
reasonably well exposed (Figure 28). Accessbility is limited and outcrop photos had to be
taken from the Canadian side of the Niagara River.
Figure 28: (A) Outcrop photo of Whirlpool Sandstone at Artpark (B) AB section of the outcrop in (A).
3.1. 4 Study Methodology
Outcrop interpretation is based on identification of architectural elements defined by
grain size, bedform composition, internal sequence, and external geometry (Miall, 1985)
in addition to geophysical data from Ground Penetrating Radar profiles obtained behind
the outcrop face both parallel and orthogonal to outcrop orientation. GPR surveys were
conducted with MALÅ Geoscience Ramac 250 MHz shielded antenna designed for sub-
metre scale resolution and moderate penetration depth. This antenna is ideal for surveys
in urban areas where surface electromagnetic signals (from power lines and radio towers)
A B
NE SW
20 mQueenston Shale
A
B5 m
5 m
A
B
73
interfere with reflected radar signals. The antenna resolution is also ideal for resolving
channel-scale features and intra-channel architectural elements.
Four GPR profiles were recorded in common offset mode; two parallel to the outcrop and
the other two orthogonal to the outcrop. Each line was re-recorded in reverse direction to
detect and remove transient noise that does not repeat at the same location in the
radargram.
Data acquisition parameters used are:
Antenna separation: 0.36 m
Sampling Frequency: 2415 MHz
Trace Interval: 0.099 m
Velocity: 0.12 m/ns (calculated from depth to Whirlpool - Queenston contact horizon on
the radar profile).
Figure 29: Raw, unprocessed GPR data from the Whirlpool Sandstone, Artpark (USA)
In raw unprocessed GPR data, beddings and bounding surfaces are hardly visible (Figure
29); acquired radar profiles were processed with REFLEX GPR processing software and
displayed in three dimensions with GPR-Slice display and interpretation software.
Shielded antennas used for data acquisition minimized the occurrence of spurious
74
reflections in the radar profile; hence, few data processing steps like de-wow, signal gain,
and diffraction stack migration were applied.
3.1. 5 Outcrop Description
The Whirlpool Sandstone is thin, sheet-like in character and rarely exceeds 9 metres in
thickness. It has been studied in many locations along the Niagara Escarpment but the
fairly continuous exposure of about one hundred and fifty metres at Artpark, provides a
suitable dimension required for architectural element analysis. The Whirlpool Sandstone
was interpreted as a two-unit division consisting of lower unit (generally 1-7 m thick)
deposited in a braided fluvial depositional environment overlain by a marine unit
(generally 1-2 m thick) formed in nearshore wave-influenced environment.
Figure 30: Artpark vertical section summarizing the main outcrop observations (Image taken from Rutka, 1986).
75
The upper unit of the sandstone outcrop studied at Artpark has however been lost to post
depositional erosion leaving predominantly the lower unit of braided fluvial origin.
Rutka (1986) earlier studied the Whirlpool Sandstone at Artpark and compiled her
observations at various outcrop exposures along the Niagara Escarpment at Artpark into a
vertical profile. The vertical section reveals three upward fining successions dominated
by trough cross-beds. Planar cross-beds and ripple cross-laminations occur only as minor
lithofacies at the top of each trough cross-bedded unit reflecting waning flow (Figure 30).
Table 3: Lithofacies in the Whirlpool Sandstone at Artpark (New York)
Facies Code Facies Sedimentary Structures Interpretation
St Medium to Solitary or grouped Sinuous crested and
fine sand trough cross beds. linguoid (3-D) dunes
Sr Medium to Ripple cross Ripples
fine sand lamination (lower flow regime)
Sp Medium to solitary or grouped Transverse and
fine sand planar cross beds. linguoid bedforms
Sh fine sand Horizontal Lamination Plane bed flow
Parting lineation
76
This study extends previous interpretations at the outcrop to three dimensions via
architectural element analysis and GPR imaging. Architectural elements are defined and
annotated on an outcrop photomosaic of the Whirlpool Sandstone at Artpark. Lithofacies
types in the Whirlpool Sandstone exposure at Artpark are listed in Table 3. They are
based on Miall (1978c) lithofacies codes for fluvial environments.
The Artpark exposure of the Whirlpool Sandstone is about 150 metres long oriented
northwest-southeast and has a thickness of 4 -7 metres. The sandstone is thicker (about 7
metres) towards the southeast end while much of the upper part of the sandstone beds in
the northwestern end of the profile have been eroded (Figure 28 A).
Interpretation of the rank and bounding surfaces is based on their shape, lateral extent and
associated lithofacies. Three main bounding surfaces numbered 1, 2 and 3 subdivide the
sandstone exposure into three major units (Figure 32A) described as lower, middle and
upper sand sheets.
Bounding surface 1 is the channel base separating the Lower Silurian Whirlpool
Sandstone from the underlying Ordovician Queenston Shale; it is the lower bounding
surface of the basal sand sheet with a slight upward curvature and shaly fill of rip up
clasts from the underlying Queenston Shale. This surface is a well-known marker
observed at many other locations where the Whirlpool Sandstone is exposed. It is
interpreted as a 6th order unconformity surface separating the Ordovician Queenston
Shale from the Silurian Whirlpool Sandstone. This surface is observable on outcrop
photomosaic and GPR profile (Figure 32A and B)
Surface 2 is the lower bounding surface of the middle sand sheet. This unit comprises
about 2 metres of thick trough-cross-bedded sands of mostly sandy bedforms. The upper
77
3 metres of the sandstone succession rests on Surface 3 and reveals scour (oriented east-
west and filled with shaly trough cross-bedded sandstone) into the underlying sandsheet,
3.1.6 GPR Profiles
Unlike most Whirlpool Sandstone outcrops along the Niagara escarpment, the absence of
thick overburden overlying the Whirlpool Sandstone and a flat surface (Elevation
changes across recorded profiles are less than 1 metre) make GPR survey feasible at the
Artpark outcrop.
Figure 31: Location of GPR lines at Artpark State Park.
Niagara River
Earl Brydges
Robert Moses
Outcrop exposure (see photo in Figure 32 A)
N
200 m
104
A
B
G C D
E F
HGPR Lines
78
Radar facies observed are sedimentary structures and architectural element-scale features
described and interpreted based on shape of reflectors, reflection dip, relationship
between reflectors, reflection continuity and amplitude.
Line AB (Figures 28A and 31) is the transect where a GPR profile parallel to outcrop
face was acquired; it was recorded one metre behind the outcrop. The GPR profile
reveals major bounding surfaces labeled 1, 2 and 3 also observed on the outcrop photo
(Figure 32A and B). Northwest dipping inclined reflectors at the east end of the GPR
profile are visible in outcrop; they are interpreted as sandy planar cross-beds (facies Sp in
Figures 32A and B). Metre scale curved reflectors seen on the radargram and outcrop are
interpreted as trough cross-beds (facies St). The larger scale concave upward reflectors
with low amplitude fill (indicative of high mud content) observed towards the north end
of the GPR profile and annotated outcrop photo is labeled SC on Figures 32A and B. It is
interpreted as late stage scour incised into the middle sand sheet (Figures 32A and B).
Ground Penetrating Radar profiles orthogonal to the outcrop clearly reveal that the
Whirlpool Sandstone-Queenston Shale contact is erosional – Figure 33 (interpreted from
reflection attenuation pattern and horizontal to sub-horizontal low reflection amplitude
away from the channel margin).
79
Figure 32: (A) Annotated Whirlpool Sandstone photo at Artpark (B) Annotated GPR line AB (SB – Sandy Bedform; SC – Scour; St – troughcross-bedded sandstone, Sp - planar cross-bedded sandstone).
SC
Sp
Sp
1
2
3
St
Amplitude Scale
St
Low
High
B A B
6
0
1
2
3
SB
SB
5 m Sp
Sp
St
St St St
A
B
Sp
Sp
SC
3 m
A
SB
SB
Depth (m
)
Queenstone Shale
Queenstone Shale
Sp 1
80
The main channel dimension, not obvious in outcrop, is evident in radar section recorded
orthogonal to the outcrop (Figure 33); the channel is about 6 m deep and between 60 and 100 m
wide (assuming the width of the channel is at least twice the width of the portion of the channel
imaged.
3.1.7 Radar Facies
Radar facies observed are lithofacies and architectural element-scale features described and
interpreted in the context of the depositional environment of the Whirlpool Sandstone. Individual
sedimentary structures are not described as radar facies or correlated to the outcrop photomosaic
as the resolution of the photo and GPR image do not permit unequivocal correlation of most
sedimentary structures to the radargram; where they can be clearly resolved, they are however,
highlighted on the radar profiles. Orientation of the GPR lines is documented to reflect the fact
that reflection patterns and geometry observed in radar profile depends on the orientation of the
profile in relation to the imaged channel fill.
Four major radar facies (architectural element scale features) were recognized and correlated to
their lithological expression in outcrop in addition to the major bounding surfaces. These facies
are described below and summarized in table 4.
Concave-upward reflector with low amplitude fill
This is highlighted in Figure 32B as SC; this facies is characterized by low amplitude concave-
upward basal reflector with a low amplitude fill. It is interpreted as intra-channel scour about 15
metres wide and 2 metres deep filled with muddy sand (interpreted from low reflection
amplitude)
81
Concave-upward reflector with high amplitude fill
This is highlighted in Figure 33 as CH; this facies is characterized by high amplitude fill
adjoining low amplitude planar to sub-horizontal reflectors at the margin (OF). This is
interpreted as the main Whirlpool Sandstone channel.
High amplitude planar reflectors
This is highlighted below in Figure 33 as OF (Channel overbank deposit); this facies is
characterized by high amplitude horizontal reflectors underlain by low amplitude planar to sub-
horizontal reflectors. This is interpreted as channel margin overbank deposit.
Figure 33: GPR line EF orthogonal to the Whirlpool Sandstone outcrop at Artpark (CH – Channel; OF – Overbank deposit).
Low amplitude horizontal reflectors
This facies is characterized by ‘thinly-bedded’ low amplitude horizontal reflectors with a basal
indistinguishable reflection (reflection-free) zone indicating attenuation of radar signals typical
of clay-rich sediment. This radar facies is interpreted as the basal the Queenston Shale.
OF
CH
E F
Queenston Shale
Depth (m
)
82
Radar Facies
Outcrop Photo
Architectural Elements
Geometry and Radarfacies description
Profile perpendicular to outcrop – photo not available. Main Channel. Concave upward base and channel margin
outline resting on the Queenston Shale.
Channel fill is characterized by high
amplitude reflectors with low amplitude
basal section suggesting significant shale
content.
Profile perpendicular to outcrop – photo not available. Overbank sand sheets
underlain by muddy
overbank fines.
Horizontal reflectors with lower amplitude
near contact with underlying Queenston
Shale.
Intra-channel Scour
(2-3 m deep) at the
top of the Whirlpool
Sandstone. Scour
outline suggests an
East-West trend.
Profile parallel to the channel axis
Concave upward reflectors within the main
channel with lower amplitude near the base.
Profile perpendicular to outcrop – photo not available. Queenston Shale. Low amplitude horizontal reflection
underlain by weak indistinguishable
reflection.
CH
OF
SC
Table 4: Radar facies identified in the Whirlpool Sandstone GPR profile at Artpark. (Radar facies are annotated on profiles - Figures 32 and 33).
SC
OF
5 m
Queenston Shale
2 m
83
3.1.8 Outcrop-GPR Integration
While outcrop observation at Artpark reveal a sheet geometry and apparently homogeneous
lithology, integration of outcrop mapping at Artpark with GPR data suggests that the entire
outcrop lies in a northwest-southeast trending channel geometry (Figures 34 and 36) with a
sandy mostly trough-cross-beded fill. Depth and width obtained from radar profiles show the
small scale of the Whirlpool River and reflection amplitude suggests a shaly fill. Variability in
reflection amplitude (Figure 32B) shows that even in braided fluvial deposits, there could be
significant lithological heterogeneity (lower amplitude towards the north end of the outcrop) not
obvious in outrop section. The implication of this study is that architectural data that are often
difficult to obtain from outcrops such as reliable channel dimension, local paleoflow data,
sandbody stacking patterns and lithological heterogeneity can be obtained via GPR imaging.
3.1.9 Discussion
Definition of the various types and scales of bounding surfaces, the constituent lithofacies
assemblage, lack of fossils or ichnofossils, predominantly sheet-like geometry, lack of lateral
accretion macroform as well as radar reflection patterns suggest deposition in a distal low
sinuosity sheetflood sand-bed river characteristic of distal braidplain. Preservation of transitional
to upper flow-regime beds, presence of plane-laminated sand, trough cross-beds, low angle
cross-bedded sand, erosional facies relationships as well as vertical aggradation within the
shallow channels and radar facies validate this interpretation. Paleocurrent measurements by
Rutka (1986) at the Whirlpool Sandstone outcrops along the Niagara escarpment shows variable
local paleoflow possibly due to intra-channel braiding and scours (Figure 35)
84
Figure 34: Three-dimensional reconstruction of the Whirlpool Sandstone architecture at Artpark integrating outcrop and GPR data.
N
Braid bar
Braid bar
Overbank deposit
Crossbar channel
5 m
Depth (m
)
6
0
85
Outcrop data and radar profile parallel to the outcrop face suggests predominance of
element SB (Sandy Bedforms) with late stage muddy cross channel deposit. GPR profiles
perpendicular to the axis of the main channel show channel margin and overbank areas
with elements OF (Overbank deposit) predominant; they were probably deposited as a
product of waning overbank flow.
Figure 35: Regional paleocurrent pattern for the lower Whirlpool Sandstone based on trough cross-bed measurements. (Image taken from Rutka, 1986) – red circle highlights outcrop location at Artpark.
86
While the lack of vegetation and abundant sediment supply from the Taconic orogen
might have influenced the fluvial style, the cohesive Queenston Shale possibly exerted an
opposing bank stabilizing control on the Whirlpool channels resulting in the formation of
channelized deposition observed in the GPR profiles.
Figure 36: Fence diagram display of GPR data from the Whirlpool Sandstone, Artpark (New York, USA) – See location of GPR lines in Figure 31.
The origin of the Whirlpool Sandstone has been explained by both lithospheric flexure
associated with the Taconic Orogeny (Rutka et al, 1991) and eustatic drop in sea level
resulting in the development of incised valleys into the Queenston Shale (Castle et al,
1998). Brett et al., (1990) interpreted the lower, nonmarine part of the Whirlpool as a
major eustatic lowstand deposit, while Ryder et al., (1996) attributed Whirlpool
O v e r ba nk De p os i t
Depth (m
)
87
deposition to fluvial backfilling of incised valleys during sea level rise. Similar braided
fluvial deposits such as Lower McMurray Formation and Dina Formation (Riediger
1999; Crerar and Arnott, 2007) overlain by transgressive deposits have been observed as
the basal fill of incised valleys cut into the sub-Cretaceous unconformity in Alberta and
Saskatchewan respectively. Regional study of the Whirlpool Sandstone integrating
outcrop and GPR data will be vital for validating either model.
The Queenston-Whirlpool contact has often been described as distinctively flat because
most of the Whirlpool Sandstone exposures are near parallel to Whirlpool channel axes,
giving an apparent impression of a planar contact. In outcrops, the apparent planar
contact with the underlying Queenston Shale suggests a non-erosional contact described
by Rutka et al (1991) as a disconformity and the Whirlpool Sandstone as the product of
weakly and possibly unconfined fluvial channels. This implies lack of deep channels cut
into the Queenston Shale, interpreted as an indication that most of the Whirlpool streams’
energy was used primarily for bedload transportation rather than for erosion of channels
into the underlying shale. Radar profiles perpendicular to the outcrop, however, reveal
about 7 metres of incision into the Queenston Shale by the lower Whirlpool channels
(Figure 33 and 34), suggesting that the Whirlpool Sandstone was not deposited in
unconfined channels.
Lack of vegetation is sometimes invoked as an important control on pre-Devonian fluvial
architecture (Schumn 1968; Long 1978; Cotter; 1978; Davies and Gibling, 2010) as
vegetation affects channel morphology and shifting behavior through increased bank
stability. Experimental study by Gran and Paola (2001) demonstrates that vegetation
plays a critical role in bank stability, constrains channel migration resulting in the
88
formation of deep and narrow channels. Pre-Devonian fluvial systems such as those that
deposited the Whirlpool Sandstone might have had reduced bank stability which
promotes braided sheetlike deposition. While the lack of vegetation in the Lower Silurian
has been invoked as a possible explanation of predominance of weakly-channelized
bedload streams with the resultant fluvial architecture and composition similar to low
energy distal braidplain sand sheets (Rutka et al., 1991), evidence of cross channel scour,
main channel margin and upper plane bed channel margin deposit suggest a channelized
higher energy sandy braided fluvial system.
3.1.10 Conclusion
GPR imaging at Artpark shows that even in a geological formation with minimal
lithological contrast, GPR imaging can be quite revealing. This study also shows that
reflection configuration, geometry, and radar reflection amplitude can be vital
interpretive tools in the study of ancient fluvial environments, since amplitude is
controlled largely by lithology. While full three-dimensional GPR survey was not
conducted at the outcrop, it is obvious from this study that a few staggered GPR lines
acquired properly with the ideal equipment can yield vital architectural information.
This study illustrates the value of three dimensional outcrop studies integrating GPR with
outcrop data as it reveals a more complex architecture than portrayed by earlier outcrop
study at the site (Figure 30). This confirms the usefulness of GPR as an invaluable tool
for three dimensional outcrop studies, as it reveals architectural details not otherwise
visible in outcrop and helps refine previous interpretations based on two-dimensional
outcrop data.
89
Case Study 2 – Navajo Sandstone
3.2.1 Introduction
Aeolian deposits were long thought of as relatively simple and homogeneous reservoirs,
yet production histories from well-known eolian reservoirs such as the Permian
Rotliegendes Formation in the North Sea (Glennie, 1990) and Jurassic eolian deposits in
the Western USA (Lindquist, 1988) prove that this is far from reality. Research findings
in the last two decades suggest that eolian reservoirs are highly heterogeneous and are
often characterized by highly layered architecture with strong directional permeability.
Detailed and basin studies of modern and ancient eolian deposits over the last few
decades reveal that despite their internal architectural complexities, anisotropy in eolian
reservoirs is quite predictable, as this is often controlled by the initial depositional history
(Glennie, 1990 ; Kocureck and Havholm, 1993)
There has been considerable research effort in the last few decades geared at unraveling
controls on eolian depositional architecture, but much of the effort has been focused on
modern and recent eolian deposits (Leatherman, 1987; Bristow et al., 1996, 2000a, b;
Harari 1996; Jol et al., 1996a; Van Heteren et al., 1996, 1998; Smith et al., 1999; Neal
and Roberts 2000; Møller and Anthony, 2003). Because many ancient eolian deposits do
not have applicable modern analogs (Fryberger, 1990a), unraveling architectural
complexities in eolian reservoirs hinges on detailed studies of ancient eolian deposits via
subsurface three dimensional seismic imaging and three-dimensional outcrop studies.
Jol and Bristow (2003) assessed the viability of three dimensional eolian outcrop studies
utilizing Ground Penetrating Radar imaging at a Navajo Sandstone outcrop in Utah. They
90
evaluated the effectiveness of various GPR antenna frequencies in delineating the internal
stratification of the Navajo Sandstone and conducted a test three dimensional GPR survey
(Figure 37) at Zion National Park, Utah.
Figure 37: 3D GPR image of the ancient Navajo dune complex obtained with 200-MHz antenna .The image shows three sets of dipping reflections interpreted as cross-stratification with two horizontal reflections that are interpreted as erosional truncation surfaces. (Image taken from Jol et al., 2003).
They concluded that the technique holds immense potential as a source of input data for
computerized simulations of sedimentary successions and realistic geostatistical
modelling of eolian deposits with better constraint on paleocurrent trends, distribution of
nonrandom heterogeneities and scale of architectural units. Penetration depth of greater
than 40 m was obtained with the 50-MHz antenna and 16 m penetration depth with the
200-MHz antenna.
91
Unlike the test study at Zion National Park, considered to be within the centre of the
Navajo erg, this study was conducted on the interdune deposits at a Navajo outcrop near
Moab, Utah (Figure 39A) ; the study location is strategically chosen, because
stratigraphic relationships and facies associated with interdune processes, and their
internal architecture often yield vital clues about allogenic controls (especially climate
and relative sea level) and autogenic controls (groundwater levels and vegetation) on
sedimentation and subsequent preservation. This study also shows the value of GPR
imaging in revealing architectural details that are not visible in outcrop due to limited
exposure. In addition, it demonstrates the capability of GPR imaging on ancient interdune
deposits as a tool for high-resolution three dimensional outcrop studies in the quest for
deciphering autogenic and allogenic controls on architecture of ancient eolian deposits.
The sophistication of current eolian facies models reflects the tortuous journey from 1D
facies model to 4D facies models that combine the spatial geometrical and architectural
complexity of dune and interdune deposits on a variety of scales with the temporal
dimension. Despite these advances, there are still many unsolved puzzles in eolian
sedimentary research, especially those relating preserved sedimentary architecture to the
processes responsible for its generation. Demonstrating an unequivocal link between
allogenic forcing mechanisms such as climate change and the generation of stratal bodies,
differentiating between the products of intrinsic (autogenic) process such as bedform
migration and external (allogenic) processes such as climate change and tectonic basin
evolution, and demonstrating the extent to which these two sets of processes are
independent of each other remain a challenge. While much effort is currently being
expended in the study of modern ergs (Bristow et al., 1996, 2000 a, b, c; Harari 1996; Jol
92
et al., 1998; Bailey et al., 2001; Clemmensen et al., 2001, Botha et al., 2003; Havholm et
al., 2003; Hugenholtz et al, 2007), the answer to most of these unanswered questions lie
hidden in ancient eolian deposits, and GPR imaging technology holds significant promise
in unraveling these mysteries.
3.2.2 Study Objectives
The objectives of this study are:
to demonstrate that sedimentological and architectural interpretation can be made
from GPR reflection amplitude, reflection configuration and stratal pattern.
to document interdune radar facies from the Navajo Sandstone as a guide for
future research on eolian interdune deposits; currently there are few documented
radar facies from ancient eolian deposits, mostly from dry phase dune strata.
Radar facies from the Navajo Sandstone will provide an opportunity to compare
interdune radar reflection patterns with lithofacies and architectural elements
observed in other eolian outcrops.
to evaluate the architecture of interdune deposit at the study site and the
relationship to local and external stratigraphic controls.
to evaluate the value of three-dimensional versus two-dimensional GPR imaging
for outcrop studies.
3.2.3 Navajo Sandstone - Geological Overview
The Jurassic Navajo Sandstone is the largest preserved eolian accumulation on earth. The
volume of sand deposited by the Navajo Sand Sea is estimated at between 40000 and
60000 km3 (Marzolf, 1988) covering about 265,000 km2 in the US Western interior
93
(Blakey et al 1988) and exposed extensively on the Colorado Plateau (USA). The Navajo
Sandstone has been extensively studied (Freeman and Visher, 1975; Middleton and
Blakey, 1983; Kocureck and Hunter, 1986; Herries, 1993) as an excellent analogue for
subsurface eolian reservoirs, yet it continues to pose puzzles for eolian researchers.
The Navajo Formation is the uppermost part of the Glen Canyon Group and overlies the
Triassic Kayenta Formation; it is overlain by the Middle Jurassic Temple Cap and
Carmel Formations (Figure 38). The Navajo Sandstone consists of fine grained, well-
sorted frosted quartz sands. Crossbeds are typically long, sweeping sigmoidal shaped
structures, over 15 metres in length, with longer asymptotic bottom sets. Within the
dunes, cross-bed sets can reach over 30 metres in thickness with foresets dipping 20 0-
350. Body fossils and ichnofossils are rare in the Navajo Sandstone; terrestrial biota such
as ostracods, freshwater crustaceans, dinosaur tracks and skeletal remains of mammal-
like reptiles have, however, been reported from interdune areas (Blaird, 1980; Lockley
and Conrad, 1989).
While the Navajo Sandstone is best known for the occurrence of gigantic, sweeping sets
of cross-bedding and their internal lamination, significant lithological heterogeneity
occurring as lacustrine limestones, cherts, fluvial deposits, conglomerate lenses and
deformed cross-bedding are present as non-aeolian facies, mostly in the eastern fringe of
the ancient erg. Most of these non-eolian facies are associated with interdune processes,
lacustrine and fluvial incursions into the ancient eolian deposit; their internal architecture
and stratigraphic relationships often unravel regional controls on eolian sedimentation
and preserved architecture. Interdune areas are troughs between dunes ranging from
interdune flats to interdune depressions. They are typically classified as dry, damp and
94
wet eolian systems with the greatest variety of interdune structure occurring in wet and
damp eolian systems commonly expressed as wind ripples, adhesion laminae, adhesion
ripples and contorted bedding.
,
Figure 38: Generalized stratigraphy at the study site showing the Navajo Sandstone. (Chart from Blakey, 2008).
Chart Legend
95
They consist of thin sandstone laminae capped by a calcareous unit possibly formed in
ephemeral ponds. Although, it has long been recognized that interdune deposits pose
problems in petroleum reservoirs as permeability barriers to fluid flow, the wealth of
information within the relatively small proportion of facies within interdune regions has
rarely been given adequate consideration, although this facies often holds vital clues to
paleoenvironmental interpretation and provides predictive insight into depositional
controls (Ahlbrandt and Fryberger, 1980; Hummel and Kocurek, 1984). This study
evaluates the usefulness and limitations of GPR imaging in discriminating centimeter-
scale interdune facies as observed in the radar profiles as well as the potential for a basin-
wide three-dimensional study of eolian interdune deposits using this technology.
Compared to cross-bedded sand dunes, interdune deposits have received little attention.
Where reported in the Navajo Sandstone, interdune deposits occur as beds 2-6 metres in
thickness sandwiched between the eolian cross-bedded dune sandstone.
3.2.4 Study Location and Direction
This study was conducted at Big Mesa, a Navajo Sandstone exposure about 21 km
Northwest of Moab (Figure 39A and B), Utah (USA). The outcrop is located off
Highway 163 via Highway 313 through Mineral Bottom Road, about 900 m from the
intersection of Highway 313 and Mineral Bottom Road (Figure 40). GPS location of the
outcrop is 38°38'6.84"N, 109°48'20.68"W.
96
Figure 39: (A) Map showing study location within Utah (B) Map showing outcrop location relative to Moab, Utah.
N
A
B
3 Km
N
313
313163
163
279
97
3.2.5 Methodology
GPR surveys were conducted with MALÅ Geoscience Ramac 250 MHz shielded antenna
designed for centimetre scale resolution and moderate (5-15 m) penetration depth. This
antenna is ideal for surveys in areas where extraneous surface electromagnetic signals
(from power lines and radio towers) interfere with reflected radar signals. The antenna
frequency provides the required resolution for sub-metre scale sedimentary features and
interdune architectural elements observed at the study site.
Acquisition parameters used are:
Antenna separation: 0.36 m
Sampling Frequency: 2760 MHz
No of stacks: 16
Trace Interval: 0.099 m
3D survey line spacing: 45 x 45 lines at 1 m spacing
Velocity: 0.118 m/ns (calculated from diffraction hyperbolae)
Acquired radar profiles were processed with REFLEX GPR processing software and
displayed in three dimensions with GPR-Slice display and interpretation software.
Data processing steps include de-wow, signal gain, background filtering and diffraction
stack migration. Penetration depth was significantly lower than observed at Zion National
Park (maximum penetration of 6 metres), Utah where earlier GPR surveys on the Navajo
dune have been conducted (Jol. et. al, 2003) suggesting higher clay content.
98
3.2.6 GPR Lines
Ninety-five GPR profiles were recorded in common offset mode: single lines 136 - 140
and ninety lines (forty five each in othorgonal directions) laid out in order to obtain a 3D
GPR volume of the outcrop at the survey site. Topographic survey was not conducted at
this site, hence GPR lines were recorded along transects with reasonably flat topography
(elevation variation of 1 metre or less). The GPR profiles were recorded about 20 – 50
metres behind the outcrop; location and scale of the GPR lines are documented in Figure
40.
Figure 40: Map showing field locations of radar profiles and 3D survey.
3D
136
138
139 140
Mineral Bottom Road
N
313 137
150 m
Outcrop (see Figure 41B and 43A for outcrop photo)
99
Radar reflection and signal attenuation patterns reveal three radar facies corresponding to
outcrop observation. They are annotated on the radar profiles, described below and
summarized in Table 5.
3.2.7 Outcrop Data
Outcrop exposure at the study location reveals a wetting upward interdune succession
from a basal dry eolian cross-bed phase through damp stage typified by adhesion ripple
and contorted beds to a fully wet phase preserved as an interdune pond carbonate (Figure
42).
Three facies associations were identified at the outcrop, each indicative of the dune
phases preserved at Big Mesa. They are described below:
Facies Association 1
This unit comprises well-developed foreset laminae which dip downwind at angle of 15–
25°. Near the base of the slip face, the foreset laminae often flatten out, giving rise to a
concave-upwards profile.
Individual foreset laminae, which are usually 5–10cm thick, are grouped together into
cross-bed sets which are separated by sub-horizontal bounding surfaces. Crossbed sets
are much smaller (mostly 3 – 5 metres high) than their gigantic central dune counterparts,
which commonly reach heights of over 20 metres (compare Figure 41A and B).
100
Figure 41: (A) Outcrop photo showing central dune giant cross-bed sets of the Navajo Sandstone, Utah (USA) – note geologist highlighted in white oval for scale (B) Photo showing smaller cross-bed set of Facies Association 1 at Big Mesa near Moab,Utah (photo taken on Mineral Bottom Road looking north east - see outcrop location in Figure 40).
Facies Association 2
This unit comprises a reddish-brown, diagenetically altered, fine-grained sandstone unit
with contorted bedding (Figure 42) indicating an episode of increased moisture within the
interdune environment. Contorted beds typically occupy the stoss slope, slip face and
apron of the underlying undeformed cross-bed set.
Crossbed Set
Crossbed Set
B
A
5 m
Interdune carbonate
1.5 m
101
Figure 42: Outcrop photo showing damp eolian interdune deposits of Facies Association 2 overlain by flat-bedded fresh water carbonates of Facies Association 3 – photo taken at Mineral Bottom Road looking north east. Image location is from the south end of the outcrop outline shown in Figure 40. Scale rod is 1.5m in length.
Facies Association 3
This unit, about 1.5 m thick, comprises 10 – 20 cm of bedded cherty limestone with
horizontal to warty bedding planes (Figure 42). This facies is indicative of fully wet
interdune conditions in which limestone was precipitated in fresh-water interdune ponds.
Contorted damp interdune deposit
Interdune freshwater carbonate
2 m
102
3.2.8 GPR Facies
Radar facies at Big Mesa are defined based on reflection configuration and amplitude.
They are interpreted in the context of outcrop observations and knowledge of local
geology. Four radar facies were observed, they are described below:
High-amplitude horizontal reflectors
This facies is characterized by high amplitude horizontal reflectors each about 20 cm
thick comprising a unit of about 1 metre in thickness (Figure 43B). It is the topmost set of
reflectors capping the underlying dipping reflectors. This facies is interpreted as
interdune cherty limestone observed in outcrop section recording the wet interdune phase
of the Navajo Sandstone at the study location
Low-amplitude reflectors
Low amplitude reflectors are observed underlying the high amplitude planar reflectors.
They are found on the flanks of the underlying mound shaped reflector (Figure 43B) with
internal dipping surfaces. They are interpreted as clay-rich damp phase interdune deposits
High amplitude mound-shaped reflectors High amplitude mound-shaped reflectors are observed underlying the high amplitude
planar reflectors (Figure 43B); they are interpreted as dry-phase eolian dunes. Their scale
as observed in outcrop suggests comparatively small cross-bed sets typical of dry-phase
interdune deposition (Figure 43 B)
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Figure 43: (A) Outcrop photo annotated with major architectural elements (B) First outcrop-parallel radar line of the 3D survey annotated with major radar facies (C) Radar line 139 showing wavy interdune beds (D) Radar line 140 showing wavy interdune beds – see location of GPR lines in Figure 40.
Interdune carbonate
Dry phase interdune cross-beds
North
Damp phase interdune deposit
South
Wet phase interdune carbonate
Dry phase dune Damp phase interdune deposit
A
B
C
D
Depth (m
) D
epth (m)
Depth (m
)
Wavy interdune beds
Wavy interdune beds
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High amplitude wavy reflectors 20-30 cm high amplitude wavy reflectors with about 5 metres wavelength (figures 43C
and D). This facies was not observed in outcrop probably due to limited exposure.
105
Radar Facies Radar Facies Configuration Facies Interpretation
Planar reflectors each between 20 to 30 cm thick
Wet phase thinly-laminated cherty freshwater limestone pond
deposits
High amplitude wavy reflectors.
Damp phase interdune wavy beds
High amplitude mound-shaped reflectors with
internal dipping reflectors.
Mound-shaped dry phase eolian dune with internal cross-beds
Low amplitude reflections with
indistinguishable bedding pattern
Wet phase clay-rich interdune deposit occupying flanks of the
mound shaped dry phase deposit
Table 5: Radar facies at Big Mesa Navajo outcrop, Utah. (Red oval highlights major radar facies)
106
3.2.9 3D Survey
The test 3-D GPR survey at Big Mesa, Utah evaluated the usefulness of 3-D surveys over
staggered 2D lines; three dimensional GPR imaging shows the benefit of GPR imaging
especially via time slicing and and incorporation of a plan-view image with vertical
reflection profiles (Beres at al, 1995). Three dimensional surveys have been particularly
informative in seismic imaging where changes in channel planform and large scale intra-
channel features have been observed in GPR time slices (Posamentier et al, 2007); this
has however not been widely embraced in GPR imaging due to the seb-metre spacing
required between GPR lines for three dimensional surveys. The advantage of three-
dimensional GPR survey lies in the possibility of viewing depositional patterns via fence
diagrams of closely spaced profiles and map-view amplitude mapping. Analysis of
amplitude variation in time slices is one of the most important uses of time slices
obtained from 3D surveys as reflection amplitude is closely linked with lithology. 3D
GPR survey at study site reveals the northwest orientation of higher amplitude dry phase
interdune deposits flanked by clay-rich low amplitude interdune sands (Figure 44B). This
is of predictive value for subsurface modelling of interdune reservoir sands as
understanding the spatial trends of reservoir type facies relative to the clay-rich damp and
wet phase facies is a critical prerequisite for interpreting facies distribution. Similar
mound-shaped dunes can be expected on either side of the clay-rich interdune deposits
with identical orientation to the imaged dune, as this is typical of eolian dunes recording
the prevailing wind direction at deposition.
107
Figure 44: (A) Perspective view of GPR cross sections. (B) 3-D GPR survey showing map view of major facies; profile locations shown in Figure 40.
Dry phase interdune deposit
Depth (m)
0
10
Damp phase interdune deposit Wet phase limestone beds
Damp phase interdune deposit Dry phase interdune deposit
A
B
0
10
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3.2.10 Discussion
Interdune units commonly form flat-lying regions between eolian dunes and exhibit a
range of geometries varying from hollows and corridors to extensive sheets. Strata of
interdune origin reflect the depositional surface at the time of accumulation and can be
classified into three broad facies associations: dry, damp and wet interdune deposits.
Dry interdune deposits are characterized by well-sorted and mature sediments forming
sets of cross-bedded sandstones a few metres thick, indicative of interdune sedimentation
on a reasonably dry surface. Damp interdune deposits include adhesion structures
characterized by wavy laminated sets formed by the adhesion of wind blown sand grains
to a damp surface, creating a bedding surface covered in low relief warts. A surface is
maintained in damp condition by capillary rise from a water table in the shallow sub-
surface. These sands commonly contain relatively high amounts of clay and anhydrite
cement. They are characterized by low amplitude radar reflections indicating a clay-rich
lithology rapidly attenuating radar signals. The adhesion of grains in motion to a damp
surface results in the generation of a range of structures including adhesion plane beds,
adhesion ripples (Kocurek and Fielder, 1982), and adhesion warts (Olsen et al., 1989),
which are characterized by low-relief ridges and mound that grow by adhesion to their
upwind edge and thereby undergo upwind migration. Adhesion structures are preserved
both on bedding surfaces and in section where strata form crinkly and wavy laminae. The
generation of adhesion strata requires the accumulation surface to be damp, and such
strata often occur in low-lying damp interdune and dune-flank settings (Hummel and
Kocurek, 1984).
109
Damp interdune deposits display a range of structures that imply the periodic presence of
standing water: wavy laminae, contorted bedding whereas wet interdune facies such as
interdune pond carbonates suggest subaqueous deposition.
Outcrop observations and radar facies from Big Mesa (Moab, Utah) reveal dry phase
eolian cross-beds overlain by clay-rich damp interdune deposits capped by flat-bedded
fresh water carbonates. These imply an upward evolution from a dry depositional phase
evidenced by the well-formed eolian cross-beds (Figure 43A) through a damp phase
recorded as interdune adhesion wavy beds typical of wind ripples in damp interdune
environments (Reading 1996) to wet conditions where fresh water pond carbonates
accumulate as a result of continued rise of the water table.
At the early stage of damp interdune deposition, clay-rich deposits are preferentially
preserved in troughs flanking the dry phase dunes (Figure 43A and B). Damp and wet
interdune deposits usually contain high clay content; in the North Sea Rotliegende
Sandstone, wet interdune deposits are distinguished from dry interdune deposits by their
higher gamma-ray response, reflecting higher clay content (Glennie, 1983; Lahann et al.,
1993). Damp and wet interdune deposits are known to pose permeability challenges in
subsurface eolian reservoirs (Lahann et al., 1993) and ability to predict their spatial
distribution is critical to characterization of eolian reservoirs. As these deposits are
typically caused by wet episodes, thorough observations and documentation of evidence
of wet conditions within eolian deposits may yield vital clues to paleoclimatic changes
during erg deposition. GPR amplitude maps play a vital role in this respect as they reveal
the orientation of dry phase dunes and the clay-rich interdune facies occupying the dune
110
flanks (Figure 44B). The uppermost unit of horizontal reflectors (Figure 43 A and B),
about 1.5 m thick capping the underlying mound-shaped reflector shows that conditions
were increasingly wetter through the deposition of the Navajo interdune deposits
preserved at Big Mesa (Moab, USA); the interdune area was eventually completely
flooded and interdune ponds developed where the limestone beds were precipitated.
Absence of large-scale eolian cross-beds (compare Figure 41A with Figure 41B),and
presence of adhesion wavy beds as well as horizontally-laminated limestone beds suggest
a clear contrast in depositional processes within the Navajo Sandstone at the study site.
Observations at Big Mesa (Moab, Utah) are indicative of eolian dune migration that
occurs synchronously with accumulation in damp, water-table-controlled interdunes
(Kocurek 1993).
Figure 45: Outcrop photo from Moab (Utah) revealing damp phase interdune deposit from the Carmell Formation (Image taken from Chan et al., 2007).
25 m
111
Similar damp phase structures have been observed at other locations within the western
U.S Jurassic erg deposits and have been described as Harmonic crenulations by Chan et
al., (2007). These structures are seen in outcrops on a bed to multi-bed scale and are
commonly bounded above and below by undeformed units (Figure 45).They typically
display an undulating morphology, occur on tens of centimeter to metre scale and tend to
be laterally extensive.
3.2.11 Implications for Reservoir Development
Eolian sandstones typically form prolific oil and gas reservoirs due to their excellent
sorting; Leman Sandstone of the Permian Rotliegend Group is a very prolific example
(Weber, 1987; Ellis, 1993). Sedimentary structures and associated textural variations
exert an important influence on the porosity and permeability characteristics of eolian
hydrocarbon reservoirs and aquifers (Lupe et al, 1979; Ahlbrandt and Fryberger 1981;
Weber 1987) and much of the heterogeneity in the reservoirs is attributed to damp or wet
interdune depositional processes. Discriminating dry phase interdune deposits from damp
and wet phase interdune facies is very critical to well placement within the dry phase
facies in developing reservoirs formed in interdune environments. Directional and
horizontal wells drilled through the long axes of the cross-bedded dune selectively
targeting dry phase interdune facies constitute perhaps the most efficient means of
developing such reservoirs.
112
3.2.12 Conclusion
This study underscores the potential of GPR imaging as a tool for three-dimensional
stratigraphic studies of ancient eolian deposits. While Jol et al (2003) earlier proved the
viability of GPR imaging technology for detailed stratigraphic studies of large-scale
eolian dunes; this study shows that interdune deposits can be imaged at decimeter scale
resolution although at comparatively shallower penetration depth than on the dry erg
dunes.
Interdune deposits are of interest to eolian sedimentary research for two main reasons.
First, their internal structures have been extensively used although with varying degrees
of success, to distinguish between eolian and subaqueous depositional processes and to
identify the bedform types represented by ancient eolian deposits (e.g. Glennie 1972;
Kocurek and Dott Jr 1981; Rubin and Hunter 1983, 1985; Steele 1983). Second, internal
structures in fossil interdune deposit provide clues about paleoclimatic conditions at the
time of deposition of the dunes.
While radar signals could only target depth of less than 7 metres at the study site, higher
penetration depth could be achieved with lower frequency antennas although with a
consequent loss in resolution. A shielded 100 MHz antenna might provide a practical
compromise to achieving deeper penetration in such a situation without significant loss in
resolution. Within the damp interdune beds occupying the flanks and troughs of the dry
phase dune, sedimentary structures and beddings are hardly visible in outcrop. This study,
however, shows that in such highly altered outcrops with significant obliteration of
primary sedimentary structures such as those studied here; GPR imaging could reveal
113
features that would be otherwise invisible. The revealing findings of Jol et al (2003) and
the interdune architectural details imaged in this test study shows that three-dimensional
GPR imaging of ancient dune and interdune deposit, hold significant promise in
answering many questions about controls on eolian dune and interdune architecture still
unanswered in eolian research.
114
Case Study 3 – Dunvegan Formation, Pink Mountain (B.C)
3.3.1 Introduction
Predicting the internal architecture of subsurface clastic deposits, especially deep water
turbidites (Stow and Johansson, 2000, Pyrcz et al, 2005; Deptuck et al, 2008), incised
valley fills (Lericolais, 2001; Chaumillon et al, 2008) and those of fluvial origin (Larue
and Hovadik, 2006; Nichols and Fisher, 2007) has been an area of active research over
the last two decades. Because it is not possible to observe the processes of development
of fluvial architecture over the large spatial and temporal scale involved in fluvial
evolution and preservation of associated sediment, studies of alluvial architecture have
largely been model-based. While qualitative and quantitative models of fluvial
architecture have been insightful in predicting subsurface alluvial architecture (Fielding
and Crane, 1987; Shanley and McCabe 1993; Bridge and Mackey, 1993b; Deutsch and
Tran, 2002), the validity of many of these models is yet to be thoroughly tested on three
dimensional seismic and outcrop data. Three dimensional seismic data has contributed
immensely to our understanding of macro scale architecture of clastic deposits (Brown,
2003; Cartwright and Huuse, 2005) but inability to unambiguously resolve architectural
elements and meso-scale depositional features has been the major limitation of three
dimensional seismic imaging. This limitation of 3D seismics makes outcrop studies the
most applicable methodology of understanding architectural complexities in clastic
reservoirs. Unfortunately, outcrop studies are still largely two-dimensional and this
115
makes it difficult to apply outcrop observations as analogue data for subsurface three-
dimensional reservoir modelling.
This study evaluates the use of Ground Penetrating Radar imaging on outcrop as a tool
for extending outcrop studies into three dimensions. GPR profiles behind roadside
outcrops near Pink Mountain, British Columbia were recorded and integrated with
outcrop interpretation.
3.3.2 Study Objectives
Most of the earlier Dunvegan studies focused on basin-scale mapping of Dunvegan
deltaic allomembers (Plint, 1996, 1997; Plint and Nummedal, 2000; Plint, 2002); very
few studies examined the valleys incised into the top of the allomembers with an
emphasis on the sedimentology and internal architecture of the valley fills due to
limitations of sparse cores and well spacing (Plint and Wadsworth, 2003 ; Lumsdon-West
et al., 2005); this study however examines the architectural details of the outcrop exposed
near Pink Mountain, British Columbia and evaluates the use of ground penetrating radar
as a tool for future three-dimensional Dunvegan studies.
Specific objectives of this study are:
to demonstrate the importance of decimetre-scale elevation survey for GPR
surveys.
to evaluate the added value of GPR imaging as an aid for future three dimensional
outcrop studies.
116
to document radar facies from the Pink Mountain outcrop as a guide for future
studies; the nature of radar reflections is best evaluated via actual recorded data.
Documented radar facies from ancient fluvio-estuarine deposits are very scanty;
radar facies from the Pink Mountain outcrops will provide an opportunity to
compare radar reflection patterns with lithofacies and architectural elements
observed in similar ancient deposits.
to extend interpretation of the Dunvegan Formation outcrop at the study site based
on an earlier two-dimensional architectural element analysis into 3 dimensions by
integrating outcrop with GPR data.
3.3.3 Dunvegan Formation – Introduction
The middle Cenomanian (lowermost Upper Cretaceous) Dunvegan Formation has been
studied extensively in outcrops and subsurface in Northwestern Alberta and Northeastern
British Columbia (Bhattacharya and Walker, 1991b; Bhattacharya, 1994; Gingras et al,
1998; McCarthy et al., 1999; Batten, 2000; Lumsdon-West, 2000; McCarthy 2002). The
Dunvegan Formation is a deltaic complex about 300 m thick which prograded 400 km
parallel to the Cordillera, over a period of about 2 million years. It ranges from 90 - 270
m in thickness and crops out extensively on thrust sheets in the Alberta and British
Columbia Foothills, as well as in the Peace River Valley, where undeformed strata are
exposed in the vicinity of Fort St. John, (British Columbia). Hydrocarbon-bearing
intervals within the Dunvegan Formation are confined to Alberta.
117
3.3.4 Geological Setting
Regional tectonic and eustatic forces played significant roles in Dunvegan deposition.
The Dunvegan Formation was deposited on the western margin of the Cretaceous
Western Interior Seaway of North America which was at the time a retro-arc foreland
basin that experienced over 3 kilometres of subsidence during the Late Jurassic and
Cretaceous (Beaumont, 1981). North America was progressively flooded from the south
by warm saline waters of the ancestral Gulf of Mexico-Tethys and from the north by
cooler, less saline water of the Boreal Ocean during the Cretaceous. These marine
embayments merged just before the Albian–Cenomanian boundary (96 Ma) to form the
Western Interior Seaway (Figure 46), which continued to widen until mid-Turonian time
(Williams and Stelck, 1975; Hay et al., 1993; Kauffman and Caldwell, 1993).
The seaway was bounded to the west, by the rising Cordillera, which yielded large
volumes of clastic detritus. To the east, the low-lying cratonic interior of North America
yielded little sediment. The bulk of the sediment forming the Dunvegan Formation was
sourced from northeastem British Columbia and southern Yukon, and was transported to
the southeast by rivers flowing parallel to the active margin of the basin (Stott, 1982).
Additional sediment was introduced by rivers flowing to the east and northeast,
perpendicular to the adjacent Cordillera (Kaulbach, 1995; Plint, 1996). The source of
sediment was related to tectonism in the ancestral Rocky Mountains (Stott, 1982). The
Interior Seaway was not only influenced by regional tectonic processes, eustatic sea level
rise, broadly ascribed to accelerated plate-spreading rates (Kauffman and Caldwell,
1993), is also considered to have been a factor, with Turonian sea level estimated to have
118
peaked at 180 m (Sahagian and Jones, 1993) to 300 m (McDonough and Cross, 1991)
above the present level. A relative sea-level rise at the Albian–Cenomanian boundary led
to widespread deposition of marine shales, marking the onset of the Greenhorn Cycle
(Kauffman and Caldwell, 1993).
Figure 46: Paleogeography of the Western Interior Seaway during the middle Cenomanian including the distribution of the Dunvegan delta complex in Alberta and British Columbia. (Image modified from Williams and Steck, 1975).
119
3.3.5 Stratigraphy
The Dunvegan Formation is a river-dominated deltaic complex comprising a succession
of alluvial and shallow marine sandstones, siltstones and shales that separate underlying
marine shales of the Shaftesbury Formation from overlying marine shales and minor
sandstones of the Kaskapau Formation (Figure 47). The formation was divided into ten
allomembers (denoted by letters A to J, A being the youngest), broadly comparable to
transgressive-regressive sequences, bounded updip by erosional valleys and interfluve
surfaces and downdip by regionally traceable marine ravinement and flooding surfaces
(Plint, 2000).
Figure 47: Summary of the lithostratigraphic relationships between the Dunvegan Formation and the underlying Shaftesbury and overlying Kaskapau Formations (Image taken from Plint and Wadsworth, 2003). Outcrop section in the stratigraphy highlighted with red circle.
120
This study focuses on the fluvio-estuarine deposit presumed to have formed in an incised
valley cut into Dunvegan Allomember E (Batten, 2000) although direct evidence of an
incised valley was not observed at the study site.
Dunvegan valleys are 0.5–2 km wide and between 20 to 30 m deep; they are traceable for
up to 20 km in outcrop, and for over 320 km in the subsurface (Plint, 2002). Plint and
Wadsworth (2003) mapped Allomembers J to E using a dense database of subsurface
logs; allomembers D to A were however lumped together as they could not be mapped
individually with available logs and outcrop data.
The valleys are typically filled with stacked fluvial channel deposits separated by fifth-
order channel-base erosion surfaces. Individual channel sandstones filling the valleys are
less than 8 m thick, a few tens to about 100 m wide and rarely mappable in the subsurface
due to wide well spacing (McCarthy et al., 1999; Lumsdon-West, 2000; Lumsdon-West
and Plint, 2004).
Dunvegan valleys tend to be channel sandstone-dominated and are usually between 3 and
10 m thick. Some exposures of the sandstone units show horizontal stratification, whereas
others reveal fourth order (based on architectural elements definition in Miall, 1985)
accretion surfaces with dips of up to 15 degrees. Accretion surfaces are sometimes
marked by erosion surfaces that separate cross-bedded sandstone layers and sometimes
are defined by alternating decimeter to metre-scale sandstone and mudstone layers,
defining inclined heterolithic stratification (IHS; Thomas et al., 1987).
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Dawson Creek
Grand Prairie
Chetwynd
Mackenzie
Fort Nelson
5 Km
N
97 97
97
Figure 48: Map location of Dunvegan Formation outcrop (outcrop location denoted by red circle).
122
Muddy layers often grade down the accretion surface into more massive sandstone;
where IHS is present, it is usually confined to the uppermost storey of the valley fills
(Aitken and Flint, 1996).
3.3.6 Study Location
Roadside exposures of the Dunvegan Formation 26 km southwest of Pink Mountain,
British Columbia (Figure 48) provide an ideal setting for combining outcrop architectural
element study with behind-outcrop georadar imaging. The outcrop is easily accessible,
without overburden and has sufficient lithological contrast considered critical to
generating radar reflections. The outcrop is about 350 m long and about 8 metres high.
Location coordinate of the outcrop location is N56 59 27.0, W12210.2.
3.3.7 Methodology
GPR surveys were conducted with MALÅ Geoscience Ramac 250 MHz shielded antenna
designed for moderate (5-10 m) penetration depth and sub-metre scale resolution ideal for
resolving intra channel architectural elements and lithofacies. The shielded antenna is
particularly ideal at this Dunvegan exposure as nearby radio towers could have caused
significant signal interference if unshielded antennas were used.
Three GPR profiles were recorded in common offset mode; two lines recorded parallel to
the outcrop and one line in orthogonal direction to the outcrop face (Figure 49). Each line
was re-recorded in reverse direction to detect occurrence of spurious signals not
generated by geological boundaries.
123
Figure 49: Map showing location of GPR lines at Dunvegan outcrop.
Acquisition parameters used are:
Antenna separation: 0.36 m
Sampling Frequency: 2760 MHz
No of stacks: 16
Trace Interval: 0.099 m
Velocity: 0.17 m/ns (calculated from depth to outcrop bounding surface observable on the
radar profile). Acquired radar profiles were processed with REFLEX GPR processing
software. With a shielded antenna, few data processing steps were required; data
processing steps are dewow, signal gain and diffraction stack migration.
97
Campground
Townsend Creek N
A B
C
D
E
200 m
124
Three radar lines AB, BC and DE were recorded behind the outcrop; lines AB and BC
parallel to the outcrop face were recorded 2 metres behind the outcrop. Line DE is
perpendicular to the outcrop face with D, 35 metres behind the outcrop (Figure 49).
Surface elevation along lines BC and DE is reasonably flat (less than one metre relief);
relief along line AB is significant (more than 5 metres) and the effects on radar reflection
patterns are documented to highlight the importance of elevation surveys to GPR outcrop
studies.
Radar facies are defined based on reflection configuration and amplitude; identified radar
facies and their outcrop equivalents are described below and summarized in Table 6.
High Amplitude Inclined Reflectors
This facies is characterized by high amplitude dipping reflectors each about 20 - 30 cm
thick comprising a unit of about 1 metre in thickness. These reflectors downlap into a
layer of low amplitude horizontal reflectors representing horizontally bedded sandstone
(Figure 50C). This facies is interpreted as lateral-accretion macroforms in the topmost
sand-rich and inclined heterolithic stratification in the more tidally dominated intervals
typical of the middle sandstone unit at the study site.
Low Amplitude Horizontal Reflectors
This facies underlies the high amplitude curved reflectors with high amplitude fill at the
top of the succession interpreted as channel fill sandstone. They are interpreted as mud
beds (facies sh) charactized by low amplitude horizontal reflectors each 10 – 20 cm thick
(Figure 50C) with indistinguishable reflectors at the base. This reflection pattern was also
125
observed at the Whirlpool Sandstone (Figure 33) and St. Mary River Formation (Figure
67) outcrops and it is indicative of mud beds.
Concave-Upward Reflector with Medium to High Amplitude Fill
This facies is observed mostly incised into the underlying moderate to high amplitude
horizontal reflectors; it is observed in radar lines recorded parallel and perpendicular to
the outcrop (Figure 50C and Figure 53A). It is characterized by a basal concave upward
reflector with internal reflectors interpreted as channels fills; the latter occur at various
scales, the small (less than 10 metres wide) interpreted as chute channel and the wider
ones as main (possibly meandering) channels.
3.3.8 Outcrop Description
Major architectural elements observed in outcrop and radar profiles (Figures 50 and 51)
are described below and annotated on outcrop photomosaic.
Lateral Accretion (LA)
This facies is observed within the topmost unit containing clean channel sandstone. It is
characterized by 20 – 30 cm thick dipping sandstone beds (dips of 10 – 22 degrees)
bounded by second order (coset-bounding) surfaces with gradational top and erosive
base; the lower terminations of these surfaces downlap onto the channel floor and often
terminate downdip into massive channel sandstone (Figure 50A). Although the lateral
accretion macroform are inclined bedsets like the inclined heterolithic stratification, they
are predominantly sandstone without the muddy interbeds.
126
Lateral accretion macroforms are typically indicative of meandering channels and their
recognition can be an important first step in paleohydraulic analysis. The height or
thickness of the element has been used as approximate bankfull depth of the channel and
the width is often used as input data for reconstructing channel width (Allen, 1965).
Inclined Heterolithic Stratification (IHS)
This architectural element is a variant of the lateral accretion macroform and is defined
by alternating decimetre- to metre-scale sandstone and mudstone layers with dips of
between 10 and 20 degrees described as inclined heterolithic stratification (Thomas et al.,
1987). They constitute erosive-base, channel-filling units 2 to 3 m thick and few hundred
metres wide that are laterally and vertically interstratified with the cross-bedded
sandstone facies. Muddy layers commonly grade down the accretion surface into more
massive sandstone; this element constitutes a major proportion of the middle unit
observed at the study site.
The predominance of inclined heterolithic stratification in the middle unit (labeled 2 in
Figure 50B) suggests deposition on tidally dominated point bars. A similar style of
stratification has been observed in some ancient point-bar deposits interpreted to have
been tidally influenced (e.g. Thomas et al., 1987; Ainsworth et al., 1994). The relatively
large thickness (decimetres–metres) of the layers comprising the IHS observed in the
Dunvegan valley fills seems to be incompatible with semi-diurnal tidal rhythms and,
instead, is more likely to record a complex response to up and down channel migration of
a turbidity maximum zone in response to episodic (possibly seasonal) changes in the
balance between fluvial discharge and tidal current strength (Allen, 1991).
127
Mud Plug (MP)
This facies is observed only within the heterolithic unit at the studied outcrop; it is
annotated on the outcrop photomosaic as MP (Figure 50B). The only occurrence of this
facies is about 15 m wide and 4 m in thickness; it occurs on the down-dip end of the
adjoining inclined heterolithic stratification unit. Such mud plugs often record the cut-off
of the active meander and an establishment of an oxbow lake.
Channel (CH)
This is observed at the upper unit of the Dunvegan outcrop; the channels range in
dimension from the typical Allomember E channel sandstone (about 50-100 metres wide
and 5 metres thick) to small chute channel deposit (3 metres wide and 2 metres thick).
The channel sandstones are predominantly clean with minimal mud content.
128
Radar Facies
Radar Facies
Outcrop Photo
Lithofacies
Architectural Element
Facies Description
High amplitude inclined reflectors dipping between 10 and 20 degrees downlapping to flat-bedded reflectors
Fm, Sp, Sh Inclined Heterolithic Stratification (IHS)
Rhythmically-bedded sandstone and mudstone beds (each between 0.3-0.5 m thick) ; beds are moderately dipping (10-20 degrees)
Moderately dipping (200-300) reflectors concave upward towards the base
Sp, Sh, Sl Lateral accretion (LA)
Sandstone beds dipping towards the channel floor with inclinations from 20 – 30 degrees; beds do not have the mud interbeds of IHS.
High amplitude Concave upward reflector cut into the underlying horizontal reflectors
No photo ; profile line orthogonal to the outcrop
St, Sp, Sl Channel cut into underlying flat-bedded sandstone, most have width: depth ratio of about 30 (CH)
Sandstone channels; filled with lateral accretion and sandy bedforms
Low amplitude indistinguishable reflectors bounded by adjoining IHS unit
Ss, Sp Mud Plug (MP)
Remnant of abandoned channel filled with mud
2 m
8 m
5 m
Table 6: Radar facies and architectural elements from Dunvegan outcrop (Pink Mountain, BC); radar facies and their outcrop equivalents are highlighted with red arrows.
129
3.3.9 Integration of GPR and Outcrop
Descriptions of major architectural elements observed in outcrop and radar facies are
summarized in Table 6. Although the major architecturral elements were imaged with
reasonable clarity depsite the surface relief at the outcrop, the relative positions of some
of the architectural elements are distorted.
Radar Profiles AB and BC reveal low-amplitude basal horizontal reflectors overlain by
inclined reflectors with low amplitude toesets (Figure 50C). Incising into this unit at the
midsection of the outcrop is high amplitude concave upward reflector with inclined
reflectors at the margin underlain by the basal low amplitude horizontal reflectors (Figure
50C). Outcrop observations also reveal a three stage depositional history (labeled 1, 2 and
3 in Figure 50B): unit 1, the basal unit dominated by horizontally-bedded sandstone of
low sinuosity possibly fluvial braidplain origin overlain by unit 2, a tidally influenced
meandering IHS-dominated (Inclined Heterolithic Stratification) unit and mudstone. This
fine-grained meandering fluvial style is characteristic of low energy estuarine
environments with significant tidal influence preserved as sand-mud couplets within the
point bars (Thomas et al., 1987); such IHS-dominated fluvial style is common in the
McMurray Formation, host of the gigantic oil sands resource in Alberta also interpreted
as estuarine point bar deposit.
Overlying this unit are unit 3 sand-dominated high sinuosity channel sandstones with
well-developed lateral accretion macroforms. Radar line DE recorded orthogonal to the
outcrop reveals evidence of channel migration (Figure 53A) and preserved lateral
accretion deposits typical of meandering fluvial environments.
130
IHS IHS
LA
CA
MP
No reflection – signals attenuated
LA
B
FF
No reflection – signals attenuated
A
C
B
C A B
IHS IHS MPCH LA
1
3 2 LA
CH
CH
20 m
Figure 50: (A) Uninterpreted outcrop photomosaic (B) Annotated outcrop photomosaic (C) GPR lines recorded parallel to the outcrop (see GPR profile locations in Figure 49).
FF
IHS – Inclined Heterolithic Stratification CH – Channel LA – Lateral Accretion MP – Mud Plug FF - Floodplain Deposit
IHS
5 m
CH
CH
Ground surface
3rd Order bouding surface
5th Order bounding surface
IHS
131
Figure 51: (A) Outcrop photo – AB section of Figure 50 (B) Annotated GPR profile (Note the apparent postion of elements CH and IHS at the same depth due to surface relief not corrected for in radar profile).
IHS
CH
IHS CH CH SB
A B
SB
A
CH
A
B
10 m
B
FF
FF2 m
IHS – Inclined Heterolithic Stratification CH – Channel LA – Lateral Accretion SB – Sandy Bedform FF - Floodplain Deposit
132
Low mud content in the topmost unit is indicative of an active fluvial system and minimal
or no tidal influence as observed in the underlying IHS-dominated unit.
Regional stratigraphy of the Dunvegan Formation suggests that the study area lies in a
proximal delta plain environment and was influenced by accommodation changes
controlled by regional tectonic events (Batten 2000). Observation at the Pink Mountain
outcrop demonstrates an evolution in fluvial style from low sinuosity sheet sandstone
through mud-rich tidally-influenced meandering to migrating sand-bed meandering
fluvial system. This may represent a fluvial response to tectonically driven
accommodation change (possibly modified by eustatic sea level changes).
Change in regional paleoslope is commonly accommodated by river systems by changes
in channel patterns (Schumm, 1993). Wescott (1993) noted that valley slope and channel
sinuosity are directly related such that an increase in regional slope due to tectonic
activity, as was the case during Dunvegan deposition, is typically compensated for by an
increase in river sinuosity. Vertical juxtaposition of fluvial styles at the studied Dunvegan
outcrop could therefore be explained by allogenic tectonic subsidence controlling
accommodation, sediment dispersal and deposition patterns during Dunvegan Formation
deposition. During the deposition of Dunvegan Allomember A, rates of tectonic
subsidence were accelerating, tilting the basin towards the west (Batten 2000); this
increasing subsidence and tilting might have resulted in the observed change in fluvial
style from sand sheets through mud-rich meandering to migrating sand bed meandering
fluvial style.
133
LA
Figure 52: (A) Enlarged outcrop photomosaic of the sand-bed channels (BC section of Figure 50): third stage of fluvial evolution (labeled 3 in Figure 50B) (B) GPR line behind the outcrop showing major radar facies.
A
Radar signals attenuated
LA LA
FF
IHS LA SB CH
C B
LA
CH SB CLA
IHS
B
LA
FF
B
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3.3.10 Implications for Petroleum Field Development
Paleovalleys may have complex architecture reflecting the depositional controls through
the successive stages of the valley infill. Architectural changes from unchannelized
fluvial depositional style through a heterogeneous tidally dominated unit to channelized
meandering fluvial style could indicate regional tectonic or eustatic control or a
combination of both. Based on outcrop observations and GPR reflection configuration
and attenuation pattern (indicative of mud content), the best reservoir sands are the
stacked high sinuosity sandy meandering channel deposits at the top of the succession
(Figure 50A). Well log correlation typically used for building reservoir models at
conventional well spacing cannot reliably delineate reservoirs of this complexity. Also,
the scale of the channels (width of 50 – 70 metres; depth of 3-5 metres) imply that their
resolution via seismic imaging requires ultra-high quality three dimensional seismic data
which is usually unavailable. Closely spaced dipmeter logs, in addition to conventional
log suites, could help in mapping the internal architecture of such paleovalleys; the
cleaner sandstone is better targeted with horizontal wells drilled through the long axis of
the meander belt of the sinuous channels guided by analogue data from Dunvegan
outcrop studies.
135
LA SB
D E
No reflection – signals attenuated Radar signals attenuated
Topsoil
CH
N
IHS
FF
IHS
FF
A
Figure 53: (A) Annotated GPR profile of line DE (B) Schematic showimg depositional model at Pink Mountain (SB – Sandy Bedform ; IHS – Inclined Heterolithic Stratification ; CH – Channel ; FF – Floodplain Deposit).
B
20 m
FF
CH LA
CH
CH
136
3.3.10 Conclusion
This study shows that combining GPR imaging with outcrop mapping is a potent tool in
the study of ancient paleovalley deposits. While surface constraints and unavailability of
survey equipment required for topographic correction did not allow for three-dimensional
survey and resulted in depth errors in profile AB recorded along line AB with significant
relief (Figure 51), this study confirms that a few GPR lines properly oriented relative to
the outcrop can provide architectural details not observable in outcrop and significantly
improve interpretation of outcrop observations. Evidence of migrating high sinuosity
channels as well as channel dimensions are observable on the GPR line recorded
orthogonal to the outcrop.
Although signal penetration depth is an obvious limitation of GPR imaging at most
outcrops, especially those with prevalence of muddy units, antenna frequency in the 100 -
200 MHz might provide a practical compromise between resolution and penetration
depth. This study also shows the promise of GPR imaging for the field of
paleohydraulics; geometrical data of ancient clastic sandbodies rarely obtainable from
two dimensional outcrop data could become available via three dimensional GPR images
of ancient clastic deposits. Having been successfully applied at the Pink Mountain
outcrop (although with significant limitation due to lack of topographic data required for
elevation correction), GPR imaging can by applied at other Dunvegan outcrops for more
detailed architectural studies.
137
Case Study 4 – Shinarump Conglomerate (Utah)
3.4.1 Introduction
This study integrates GPR and outcrop data from an outcrop exposure of the Shinarump
member of the Chinle Formation and evaluates the usefulness of architectural element
analysis combined with Ground Penetrating Radar imaging as an aid for three dimensional
outcrop interpretation. An outcrop of the Shinarump conglomerate was studied, supported by
a GPR line recorded orthogonal to the outcrop.
The Shinarump Conglomerate lies at the base of the Chinle Formation, a fluvio-lacustrine
unit of Late Triassic age (Figure 54) widely exposed in the Colorado Plateau of the
southwestern USA (Lucas, 1993). Deposited in paleovalleys carved in the underlying
Moenkopi Formation, the Shinarump directly overlies the reddish brown soft mudstone
deposits of the Middle Triassic Moenkopi Formation (Figure 58) across a regional
unconformity representing about 17 m.y. (Stewart et al., 1972; Doelling, 1985).
The Shinarump conglomerate has been a long-standing puzzle (Blakey and Gubitosa, 1983;
Dubiel, 1987, 1989, Dubiel et al., 1991); its enigmatic widespread deposition covering over
250,000 km2 across the Colorado Plateau has attracted various explanations. The earliest
attempt to explain the areally extensive deposition of the Shinarump Conglomerates was by
Stokes (1950); he suggested erosion at the top of the Moenkopi unconformity and a
contemporaneous fill of the incised channels with the overlying comglomeratic sandstone
formed via the process of pedimentation.
138
Lithospheric tilting of the U.S Cordillera was also suggested as a possible explanation of
Shinarump Conglomerate’s widespread deposition (Heller et al., 2003). This study however
focuses on the architectural details of the Shinarump conglomerate at the Hurricane Mesa
outcrop and relates the outcrop observations to the various sedimentary controls postulated
for Shinarump deposition.
Figure 54: Triassic stratigraphy at Hurricane Mesa, Utah (chart taken from Blakey, 2008).
139
3.4.2 Regional Setting and Stratigraphy
The Upper Triassic Shinarump member of the Chinle Formation on the Colorado Plateau
was deposited in a continental back-arc basin located about 5-15° north of the
paleoequator near the west coast of Pangaea (Dickinson, 1981; Pindell and Dewey, 1982;
Ziegler et al.,1983; Parrish and Peterson, 1988; Molina-Garza et al 1991; Bazard and
Butler,1991). A magmatic-volcanic arc on part of the western edge of the Triassic
continent probably provided volcanic ash and clastic sediment to the Chinle depositional
basin (Stewart et al., 1972; Blakey and Gubitosa, 1983; Busby-Spera, 1988), although a
clearly defined source area remains a puzzle (Stewart et al., 1986). Paleogeographic
reconstructions of the Late Triassic Western Interior suggest that the Ancestral Rocky
Mountains in Colorado, the Mogollon Highlands to the south, and a more distant
volcanic-arc complex (Cordilleran Arc) to the west (Figure 55) served as the sediment
source areas for these northwest-trending fluvial systems. Kraus and Middleton (1987)
suggest that the dominant control on Chinle deposition is tectonism. Climate might also
have influenced Chinle deposition, but the relationship between climatic changes and the
chronology of Chinle depositional style is still not very clear. Climatic changes that
occurred during Chinle deposition show a general shift from a sub-humid, seasonal
climate during Shinarump deposition to a more arid climate towards the late stage of
Chinle deposition (Stewart et al., 1972; Blakey and Gubitosa 1983, 1984; Dubiel 1987,
1989; Blodgett 1988; Dubiel et al., 1991; Therrien and Fastovsky 2000; Tanner 2003b;
Prochnow et al., 2006b). The widespread, cross-stratified sandstone and conglomeratic
units of the Shinarump Formation represent the deposit of a complex braided fluvial
system deposited under conditions of rising base level in the lowest parts of the
140
paleovalleys cut into the Moenkopi Formation (Blakey and Gubitosa, 1984; Dubiel, 1983,
1987).
Figure 55: Paleogeographic reconstruction of the Late Triassic within the southwestern U.S.) The study location is denoted by red circle. (Image taken from Cleveland et al., 2007). Blakey and Gubitosa (1984) described several Chinle sandstone bodies in detail in an
effort to understand the basin dynamics controlling the architecture of coarse-grained
deposits in Upper Triassic strata. They described two types of Shinarump deposits:
paleovalley fills and sheet sandstones. Paleovalley fills are thick, multistory sandstone
units filling erosional valleys that developed at the base of Chinle succession. These units
represent aggradational deposition by braided streams in a region with a high gradient
(Blakey and Gubitosa, 1984). Sheet sandstones are relatively thin, commonly only a few
141
meters thick, and are regionally extensive. Blakey and Gubitosa (1984) interpreted these
sandstone bodies to represent braided stream complexes within a broad plain.
(Dubiel, 1987, 1989; Dubiel et. al., 1991) revisited the Shinarump Member in northern
New Mexico and southern Utah and examined its sedimentology in detail. He interpreted
the coarse-grained conglomeratic sandstones at the base of the Shinarump as bedload
deposition in braided streams, and the fine- to coarse-grained sandstones in the upper
Shinarump as suspended and mixed-load deposition in a more sinuous fluvial system.
This study focuses on the basal sheet sandstone of the Shinarump Conglomerate and
integrates outcrop observation with behind-ouctrop GPR imaging.
3.4.3 Study Objectives
The objectives of this study are:
to document radar facies from conglomeratic Shinarump member of the Chinle
Formation; currently there are very few documented radar facies from ancient
conglomeratic braided fluvial deposits. Radar facies from the Shinarump
Sandstone will provide an opportunity to compare radar reflection patterns with
lithofacies and architectural elements observed in other conglomeratic fluvial
sandstone.
to extend interpretation of the Shinarump Sandstone outcrop at Hurricane Mesa
based on two dimensional architectural element analysis into the third dimension
by integrating outcrop with GPR data
142
3.4.4 Study Location
The Shinarump Conglomerate outcrop examined for this study is located at Hurricane
Mesa, southwest Utah. The outcrop is located 10 Km NE of Hurricane, Utah (Figure 56).
St. George
Hurricane
Kanab
Utah
N
18
15
59
9
59
9
89
89
Mesa Road
Figure 56: Location of Shinarump Conglomerate outcrop at Hurricane Mesa, Utah. (Outcrop location denoted by red circle).
5 Km
143
Mesa road is precipitous towards the outcrop and requires extreme driving care. GPS
coordinate of the Shinarump outcrop studied is 37°14'20.45"N; 113°12'24.90"W.
3.4.5 Methodology
This study is based on architectural element analysis of the Shinarump outcrop exposed at
Hurricane Mesa (Utah, USA) and a GPR line (broken line EF; E is 10 metres behind the
outcrop) recorded behind outcrop (Figure 57). GPR survey was conducted with MALÅ
Geoscience Ramac 250 MHz shielded antenna designed for moderate (5-10 m)
penetration depth and sub-metre scale resolution ideal for resolving intra channel and
channel-scale architectural elements. The major limitation of this study is inaccessibility
to outcrops on nearby private land and inability to acquire GPR data along lines of
varying elevations due to unavailability of differential GPS or survey equipment; hence,
only one GPR profile was recorded in common offset mode (in orthogonal direction to
the outcrop face) along a flat surface behind the outcrop.
Acquisition parameters are:
Antenna separation: 0.36 m
Sampling Frequency: 2760 MHz
No of stacks: 16
Trace Interval: 0.05 m
Velocity: 0. 10 m/ns (calculated from depth to known reflector)
Acquired radar profile was processed with REFLEX GPR processing software. Data
processing steps include de-wow, signal gain and diffraction stack migration.
144
Figure 57: Location of Shinarump Conglomerate outcrop (red circle) at Hurricane Mesa, Utah (USA) showing EF – GPR line.
Outcrop Description
Outcrop observation at the Hurricane Mesa Shinarump conglomerate reveals two distinct
architectural features: a lower succession of horizontally bedded sandstone and minor
planar cross-bedded units with thin mudstone interbeds and an upper channelized unit
consisting of pebbly to coarse-grained planar cross-bedded sandstone. Individual outcrop
units (Figure 58) are described below:
100 m
Hurricane Mesa Testing Facility
Mesa Road
Mesa Road
N
E
F
145
Unit 1
Medium-grained planar bedded sandstone with coarse-to-pebble size sands at the base
and medium scale planar cross-beds towards the top of the unit. Dominant lithofacies is
plane bed horizontal stratification with planar tabular cross stratification toward the top of
the unit. Some petrified logs are present. This unit rests on the basal Chinle
Unconformity.
Unit 2
This unit is dominated by fine-grained planar cross-bedded sandstone with ripple-
laminated sands towards the top. A few pebbly sandstones are also found in this unit.
Unit 3
This unit comprises rippled silty and fine grained sand interbeds about 1 to 3 metres
thick. Individual beds have sharp, planar upper and lower contact. The beds are laterally
extensive with sharp planar basal contact and a concave upward erosive top. This unit is
truncated at the top by overlying channels.
Unit 4
This unit comprises coarse to pebble-size channel sandstone with medium scale planar
cross-beds. Each bed is about 1 to 3 metres thick. Lenses of coarse-grained sands are
interspersed in this unit as well as preserved petrified wood.
Unit 5
This unit consists of medium-grained trough cross-bedded channel sandstone with planar
beds at the top of the unit. Lenses of pebbly sandstone are also found in this unit.
146
Unit 6
This unit consists of medium to coarse-grained trough cross-bedded channel sandstone
overlying pebble size sandstone unit. This unit is predominantly coarse sand with
minimal mud content.
Three architectural elements based on Miall (1985) fluvial architectural element
classification scheme were identified at the Shinarump sandstone outcrop; recognition of
architectural elements is based on facies associations, tracing of bounding surfaces and
bedform interpretation in the context of local paleoflow. Identified architectural elements
are described below:
Element LS (Laminated Sand Sheets)
Element LS comprises sheets of laminated sand with rippled and planar cross-bedded
sandstone. This element is found in many ancient fluvial successions and is interpreted as
product of flash floods deposited under upper flow regime plane bed conditions. The
sandstone beds are fine to medium grained and about 1-3 m thick; mudstone beds are
thinner and light grayish in color. Element LS is dominated by rippled sandstone towards
the top indicating waning flow after flood event.
Element CH (Channel)
Element CH is the preserved Shinarump Conglomerate sandstone deposited in channels
incised into the underlying element LS. The channel sandstone observed in outcrop
(Element CH in Figure 58) is 4-6 metres thick comprising mostly sandy bedforms and
147
thin pulses of gravelly sandstone. Channel width obtained from GPR profiles suggest
narrow width (40 -50 metres).
Element SB (Sandy Bedforms)
This lithofacies assemblage dominates the middle to upper part of the Shinarump
conglomerate; it comprises planar-tabular cross-stratified sandstone units each 1-3 metres
thick. Architectural element is predominantly Sandy Bedforms with a varying assemblage
of planar and trough cross-beds. This element represents intra-channel bedforms that
accumulated by predominantly vertical aggradation.
148
62
Figure 36: Section of GPR line EF from Hurricane Mesa, Utah highlighting major radar facies
A B
20 m
LS
SB
A B
CH
Unit 5
20 m Unit 2
St
Unit 1
Unit 6
LS
Sp
Figure 58: Photomosaic of the Shinarump conglomerate outcrop at Hurricane Mesa (Utah, USA) – photo taken looking northeast.
Unit 3
Unit 4
Moenkopi Shale
6th order surface 5th order surface 3rd order surface
Mean Paleoflow direction - 2480
SB
SB
SB
Shinarump-Moenkopi Unconformity
2 m
149
Remnants of petrified wood are also preserved within the sand sheets observed at the mid
section of the outcrop.
Radar Facies
The radar line reveals four radar facies (Figure 59): concave upward reflectors (Element
CH) with a fill of high amplitude horizontal reflectors (Element SB) underlain by low
amplitude planar reflectors (Element LS), beneath which radar signals are rapidly
attenuated (Moenkopi Shale). Horizontal intra-channel reflectors are interpreted as
horizontally-bedded coarse-grained Shinarump sheet sandstone.
Shinarump-Moenkopi
Sandy Bedform
Channel Base
Basal sandstone-mudstone interbeds
A
B
Figure 59: (A) Uninterpreted black and white GPR section of GPR line EF from Hurricane Utah (B) Color section of GPR line in (A) annotated with main depositional features.
150
The concave upward surfaces are Shinarump channel bases incised into interbedded
horizontal laminated sandstone-mudstone interbeds blanketing the Shinarump-Moenkopi
unconformity (Figure 58).
3.4.6 Discussion
Outcrop observation and GPR data at the Shinarump Conglomerate outcrop suggest
deposition in a sandy braided fluvial environment. The Shinarump channels were incised
into laminated sheet sandstones interpreted as flood stage deposits.
The lithofacies assemblages and architectural-element characteristics including lack of
lateral accretion, lack of preserved muddy facies, presence of coarse to pebble-grained
sand sheets, deposition by vertical aggradation, observed in this study (both in outcrop
and radar profile) suggests that the Shinarump Conglomerate was deposited in low
sinuosity proximal conglomeratic sand bed river. At the outcrop, element SB
predominates, with lithofacies Sp (sandy planar cross-beds) and St (sandy trough cross-
beds) present in varying assemblage and comprising planar sand sheets separated by
minor internal erosional scour surfaces. Observed channel fill is about 3-4 metres thick
with small width (about 60 m wide); channel margins are hardly identifiable in outcrop;
they are seen in the GPR profile recorded orthogonal to the outcrop. The Shinarump
outcrops reveal stacked multistory sandsheets with little preserved overbank fines typical
of the Platte fluvial style.
The exact climatic conditions under which the Shinarump was deposited have been the
subject of much discussion, and no conclusion appears to be generally accepted. Regional
climate during the deposition of the Chinle Formation is interpreted to have been
subtropical monsoonal (Dubiel, 1987; Dubiel et al., 1991), although paleosol data at other
151
Figure 60: (A) Combined GPR profile and outcrop Photomosaic at the Shinarump conglomerate outcrop (Hurricane Mesa, Utah); paleocurrent data from Hurlbert, 1995 (B) Depositional model built from (A)
B E
F A
B
A B
A
3 m
152
Chinle Formation outcrops imply semiarid conditions during some intervals (Prochnow et
al., 2006). An arid or semi-arid climate however seems improbable at the study site;
abundance of petrified wood found preserved in the lower and mid section of the outcrop
suggests a climate suitable for the growth of large trees.
3.4.7 Conclusion
This study underscores the value of GPR imaging in outcrop studies. Outcrop observation
and GPR data at the Shinarump Conglomerate outcrop suggest a braided fluvial system
with small channels filled with vertically aggraded sheet sandstone. Shinarump channel
dimensions (about 50 metres wide; 3 metres deep) and architecture are clearly defined by
integrating outcrop observations with GPR imaging. Although only one GPR line was
recorded at Hurricane Mesa outcrop due to inavailability of survey equipment for
topographic correction of GPR data and restricted access, GPR data obtained shows that
future GPR imaging at the study site holds immense potential in unraveling detailed
architecture of the Shinarump Conglomerate.
153
Case Study 5 – St. Mary River Formation (Alberta)
3.5.1 Introduction
This study evaluates the usefulness of Ground Penetrating Radar as an aid for three
dimensional outcrop study on the outcrop exposures of St. Mary River Formation at
Oldman River, 7 km west of Monarch (southern Alberta). St Mary River Formation is
one of the few ancient clastic deposits interpreted as an anastomosing fluvial deposit
(Nadon, 1994). Current facies model for anastomosing rivers are based mostly on
actualistic studies of modern rivers propagated by Smith (1983, 1986), Smith and Smith
(1980) and augmented by Törnqvist et al., (1993) and Weerts and Bierkins (1993). These
workers and recently North et al., (2007) have distilled the variability in their
observations of modern anastomosing rivers and constructed facies models to provide a
means of interpreting anastomosed fluvial deposits in the stratigraphic record.
Anastomosing rivers have been less studied than their meandering and braided
counterparts in modern environment and more so in ancient deposits; this explains the
gap in our understanding of the architecture of ancient anastomosing fluvial deposits.
North et al (2007) warn that since current geomorphological knowledge of anabranching
systems is incomplete, it logically follows that knowledge of the sedimentological record
created by anastomosing rivers is even more incomplete. Hence, sedimentological
interpretation of ancient anastomosing rivers is much less certain and considerably more
varied than implied by published facies models and caution should therefore be exercised
in applying those models.
154
To this end, outcrop studies of ancient deposits of interpreted anastomosing origin aided
by ground penetrating radar imaging holds significant promise in expanding our
understanding of depositional processes in ancient anastomosing rivers and their
preserved products.
This study documents outcrop observations of facies associations as well as stacking
patterns of architectural elements and evaluates the potential for detailed three
dimensional outcrop studies using ground penetrating radar imaging technology at St.
Mary River Formation outcrops in southern Alberta and similar ancient anastomosing
fluvial deposits. Although St. Mary River Formation is exposed extensively in southern
Alberta, many of the outcrops are covered by thick relict Pleistocene glacial deposit
making it difficult to run GPR profiles on the outcrops.
3.5.2 Regional Stratigraphy
The sediment of the St. Mary River Formation was deposited as an eastward-thinning
clastic wedge that recorded the progradation of continental conditions linked to the Late
Cretaceous southeast retreat of the Bearpaw Sea within the Alberta foreland basin.
Sediment source was principally from the west and depositional environments of the
aggrading section were predominantly fluvial (Figure 61). The St. Mary River Formation
is a non-marine unit about 230 m thick observable as extensive exposures in the river
valleys of the Plains and in the thrusted strata of the Foothills of the Rocky Mountains in
southwestern Alberta (Nadon, 1994). Palynomorph data indicate that the St. Mary River
Formation is uppermost Campanian to upper Maastrichtian in age (Nadon, 1994). The St.
Mary River Formation overlies marine shoreface sandstones and brackish water shales of
the Blood Reserve Formation (Figure 62) and underlies the fluvial redbeds of the Willow
155
Creek Formation (Nadon, 1991). The formation consists of medium-grained lenticular
channel sandstone surrounded by thin sheets of sandstone, siltstone and mudstone.
Figure 61: St. Mary River Formation Upper Cretaceous Paleogeography (Image taken from Dawson et al, 1994).
Alberta Saskatchewan Manitoba
Mountains
Uplands
Lacustrine (schematic)
Coal swamp (schematic)
Fluvial coastal plain
Barrier islands
Seaway
Sediment transport direction
Transgression-regression direction
200 Km
British Columbia
N
156
Petrographic evidence suggests that the main sediment sources for the St. Mary River
Formation were Upper Paleozoic sediments and older Mesozoic rocks of the then rising
Ancestral Rocky Mountains to the west (Rahmani and Schmidt, 1982).
Figure 62: Alberta Cretaceous Stratigraphic chart showing St. Mary River Formation. (Chart taken from Alberta Energy Resource Conservation Board Table of Formations, 2009).
Clastics Shale Carbonates
Lithology Code
157
3.5.3 Study Objectives
The objectives of this study are:
to document radar facies from sandy ribbon-shaped channels of St. Mary River
Formation; currently there is no documented radar facies from ancient
anastomosing fluvial deposits. Radar facies from the St. Mary River Formation
will provide an opportunity to compare radar reflection patterns with lithofacies
and architectural elements observed in other ribbon fluvial sandstone.
to create a depositional model of the St. Mary River formation at the study site by
integrating outcrop and GPR data
evaluation of added value of GPR imaging as an aid for three dimensional outcrop
studies.
Study Location
The location for this study is by the Canadian Pacific railway, about 7 Km northwest of
Monarch in Southern Alberta (Figure 63A). The location can be reached via Range Road
244 off Highway 519 (Figure 63B). GPS location of the study site is N49 49 08.1 W113
12 09.1.
3.5.4 Methodology
GPR survey was conducted with MALÅ Geoscience Ramac 250 MHz shielded antenna
designed for moderate (5-15 m) penetration depth and decimetre-metre scale resolution
ideal for resolving intra channel and channel-scale architectural elements. Two GPR
profiles were recorded (Figure 64) in common offset mode (1 parallel and 1 in orthogonal
direction to the outcrop). Acquisition parameters are:
158
Edmonton
Calgary
Alberta
2
3
Barons
23
520
519
Granum
Claresholm
Monarch
N
3A
5 Km
200 Km
519
Township Road 104
500 m
N
A
B
Figure 63: (A) Location of study outcrop in Alberta (B) Detailed outcrop location. (Outcrop location highlighted in red).
Canadian pacific rail
Ran
ge R
oad
244
Ran
ge R
oad
243
159
Antenna separation: 0.36 m
Sampling Frequency: 2760 MHz
No of stacks: 16
Trace Interval: 0.05 m
Velocity: 0. 16 m/ns (calculated from depth to outcrop bounding surface observable on
the radar profile)
Line AB has significant relief (about 3 metres); relief along line CD is minimal (less than
1 metre). Elevation correction was not performed on the acquired data due to lack of
survey equipment.
Acquired radar profiles were processed with REFLEX GPR processing software. Data
processing steps include de-wow, signal gain, background filtering and diffraction stack
migration.
Facies Description
Facies Assemblage 1: Channel Sandstone
Facies assemblage 1 consists of northeast-southwest trending ribbon-shaped channel
sandstones. These channels are either simple or have at the most two stories; individual
channel sandstones are about 3-5 m thick and 60-90 m wide. The basal contacts vary
from erosional to sharp and flat or slightly undulatory at the margins. Above the erosional
base is a lag, a few decimeters to half a metre thick, composed of shale/ siltstone
intraclasts. The overlying sandstone varies from fine- to medium-grained and is mostly
trough cross-bedded sandstone at or near the base (Figure 65) and in some cases planar-
tabular cross-beds toward the top. Multistory channels are commonly separated by half
160
500 m
N
Canadian pacific rail
Ran
ge R
oad
244
Ran
ge R
oad
243
519
Ran
ge R
oad
244
Ran
ge R
oad
243
Canadian pacific rail B
A
100 m D
C
Figure 64: Location of study outcrop and GPR lines. ( Outcrop exposure)
O
ldman River
161
metre to a metre layer of mudstone. The channel lenses are capped by rippled siltstone to
very fine sandstone.
Figure 65: Outcrop photo showing St. Mary River Formation trough-cross-bedded channel sandstone. (Photo taken looking north).
Facies Assemblage 2 - Small Sandstone Lenses
Sandstone lenses of Facies Assemlage 2 are observed between the northeast-southwest
oriented main channels. These smaller lenses are composed of fine to medium sandstone
with sharp, planar bases with no basal lag (Figure 66). Where paleocurrent indicators are
observable, they are generally perpendicular to the main channel (facies assemblage 1)
trend. Facies Assemblage 2 lenses are interpreted as crevasse splays. The small scale of
these sandstone bodies and their general orientation perpendicular to the thicker channel
162
sandstone lenses implies that these channels were conduits delivering sediment from the
main channels onto the floodplain.
Figure 66: Outcrop photo showing St. Mary River Formation crevasse splay sandstone (photo taken looking north).
Facies Assemblage 3 – Overbank Fines
Facies Association 3 is a mud-dominated recessive unit typically found underlying the
channels of facies assemblage 1. The mudstone is in some cases interbedded with thin
sandstone beds interpreted as overbank levees. Paleosols are also preserved in this unit
with thickness varying from less than 20 cm to about a metre. Internal structures are
seldom visible because of the combination of grain-size uniformity, rooting, and
bioturbation. This facies assemblage represents environments on the floodplain of the St.
Mary river system.
2 m
163
Radar Facies
Radar reflections from GPR line along and orthogonal to one of the channels reveal a few
radar facies described below:
Concave upward reflector with high amplitude fill
This facies consists of concave upward reflectors about 55 metres wide and 3 metres
thick with high amplitude dipping and horizontal internal reflectors. The dipping
reflectors are interpreted as lateral accretion macroforms (LA) based on their scale and
dip into the channel (Figure 67).This radar facies is interpreted as the ribbon-shaped
channels of St. Mary River Formation with evidence of lateral accretion and vertical
aggradation.
Figure 67: Radar image of St.Mary River Formation ribbon channel sandstone (Line CD); see location of GPR line in Figure 64.
Horizontal Reflectors
High amplitude continuous horizontal reflectors between the concave upward reflectors
(channels) are interpreted as crevasse splays; they are characterized by high amplitude
upper reflectors and low amplitude basal reflectors (figure 68) indicative of crevasse
sands deposited on underlying muddy floodplain lithology.
LA SB
FF
164
Figure 68 (A) Radar profile CD showing ribbon channels and adjoining horizontal reflectors (B) Radar profile CD showing horizontal reflectors interpreted as crevasse splay deposits
These deposits are expressed geomorphologically as flat surfaces adjoining mound-
shaped surface topography characteristic of the St. Mary River Formation channels.
Radar profile AB recorded along the channel axis contains a few slightly dipping
reflectors underlain by horizontal low reflectors interpreted as floodplain mudstone.
CH
A
165
Figure 69: (A) Interpreted Radar profile AB (B) Uninterpreted profile AB in greyscale (C) Profile CD annotated with major interpreted architectural elements (D) Uninterpreted profile CD ingreyscale. (LA – Lateral accretion, CH – Channel, SB – Sandy Bedforms, FF – Floodplain mudstone)
SB
B A
C D
D
C D
A
B
C
B A
LA FF
SB CH
FF
166
3.5.5 Discussion
The overall facies distribution of the St. Mary River Formation at the study site near
Monarch Southern Alberta) shows that the unit is dominated by northeast-southwest
trending channels separated by either recessive inter-channel island mudstone (Figure 70)
or by horizontally-bedded crevasse splay deposits. The channels have ribbon geometry
with width: depth ratio of less than 25. Textural trends in the crevasse-splay sediments
are consistent with those described from Holocene anastomosed deposits (Weerts and
Bierkens, 1993). The geometry and internal structures of the main channel observed in
outcrop photos and radar profile show that they are products of vertical aggradation with
minor evidence of lateral accretion and possible downstream accretion.
Splay channels suggest dominance of vertical aggradation noted also in both modern and
Holocene studies (Smith and Smith 1983, 1986; Törnqvist et al., 1993). Absence of coals
within the St. Mary River Formation is probably due to repeated inundation of the
floodplain with clastic detritus. Presence of lateral accretion indicates sinuosity in St.
Mary River channels as also observed from modern rivers (Bridge 2006). Overall
observations from St. Mary River Formation suggest an anastomosed fluvial system
characterized by ribbon sandstones encased in finer floodplain sediments (figure 70).
North et al (2007) however, cautioned that single thread, non anabranching rivers could
create a similar sedimentary record in a setting where accommodation is large
(subsidence rate is high), avulsion frequent, or the sediment supply to the river system is
mud-rich; as might occur on a large-scale fluvial fan entering a foreland basin envisaged
as the context for the St. Mary River Formation.
167
While low width-depth ratio (less than 20) is typical of the St. Mary River Formation
channels observed in this study, a regional study of the dimensions of the St. Mary River
Formation channels utilizing GPR imaging might reveal an interesting trend in channel
dimension with possible correlation with syn-depositional regional tectonic processes.
Regional studies of other ancient fluvial deposits similar to St. Mary River Formation
aided by ground penetrating radar could help reconcile observations from modern
environments with those from ancient deposits.
168
3.5.6 Conclusion
Although thick bed of glacial drift on many St. Mary Formation outcrops in Southern
Alberta as well as outcrop accessibility posed significant difficulty to finding ideal sites
for GPR surveys, where the overburden is thin, GPR imaging is a promising technology
for three dimensional outcrop studies.
Figure 70: Block diagram depicting depositional model of St. Mary River Formation at the study site.
Ribbon channels
Crevasse splay
Muddy Inter-channel Island
N
169
At the study outcrop, two GPR lines, one parallel and orthogonal to the St. Mary River
lenticular channels reveal architectural elements and reflection patterns typical of
anastomosing rivers. Lithological contrasts between channel fills, mud-rich crevasse
splays and inter-channel floodplain typical of anastomosing deposits indicate that other
ancient anastomosing fluvial deposit could be possible targets for GPR imaging. With
sub-metre accuracy survey equipment, other St. Mary Formation outcrop sites with
uneven surface topography could be imaged and a more regional study of the sandstone
conducted to understand regional depositional trends and how this correlates with
allogenic controls.
Low penetration depth is the major limitation of Ground Penetrating Radar at the study
site; lower frequency antennas (100 and 200 MHz) might improve signal penetration
without significant loss in resolution.
170
Chapter 4
Summary, conclusion and recommendation for future research
This study represents the first extensive test of the application of the GPR technique to
ancient clastic units under a wide range of field and sedimentological conditions. Based
on the high resolution data observed in GPR profiles from various outcrops studied in the
course of this research, there is no doubt that contrary to a widely held notion, GPR
imaging technology works on outcrop and it will play a pivotal role in three dimensional
outcrop studies as analogues for subsurface reservoirs. The clarity with which channel
and intra-channel scale features are revealed at the studied outcrops suggests that lack of
success with previous studies is a result of inappropriate choice of GPR instrumentation,
inefficient data acquisition and poorly informed data processing steps. This research
confirms the usefulness of outcrop-based GPR imaging as a tool for refining outcrop-
based interpretation of processes from ancient depositional environments and as an
imaging technology with the potential to revolutionize outcrop studies in the way
reflection seismology changed basin analysis.
This study as well as analysis of previous studies involving application of GPR imaging
technology on sediments and rocks shows that data obtained with shielded antennas are
less prone to extraneous noise and require less rigorous data processing than those
obtained with unshielded antennas. While most GPR surveys are prone to diffraction,
often seen as hyperbolas in radar profiles, these must be carefully removed by appropriate
migration algorithm. Diffraction migration algorithm worked quite well on data acquired
for this study but this requires a fairly accurate knowledge of the velocity profile through
171
the rocks being imaged; common-mid-point surveys or actual measurement of the
dielectric properties of the lithologies at the outcrop might be required to correctly
estimate velocity.
Topographic survey of the surface where the GPR mapping is conducted is a compulsory
prerequisite for all outcrop-based GPR studies; it helps prevent artificial structures
created in the profile by uneven surface elevation. Other than shallower depth of
penetration at shale-rich outcrops, GPR imaging works on all formations surveyed
including those with minimal lithological heterogeneity (intra-channel reflectors at the
Whirlpool Formation and Shinarump Conglomerate outcrops) widely considered as
necessary for providing electromagnetic impedance. With the 250 MHz antenna used for
this study, individual bedding units and sedimentary structures were clearly imaged;
higher resolution and deeper penetration can be achieved by using a range of antenna
frequency for future studies.
Seismic imaging technology has been one of the most potent tools that advanced our
understanding of regional and reservoir scale architecture of clastic deposits and the
results of its evolution into three dimensional imaging and visualization realm in the last
decade have been magical. Developments in three-dimensional seismic acquisition,
processing and data visualization as well as advances in seismic attribute analysis have
significantly reduced exploration risks and dry holes over the years (Brown, 2003) but the
resolution of conventional seismic data limits its applicability in detailed reservoir
characterization which is increasingly required in many primary field development
projects and enhanced oil recovery schemes. This resolution gap especially in predicting
inter-well permeability beyond seismic resolution will continue to drive three-
172
dimensional outcrop research as analogue data for the subsurface as well as serving as a
predictive tool for reservoir characterization.
Amongst the myriads of technology available to date, Ground Penetrating Radar imaging
technology holds the greatest promise for detailed three-dimensional studies. GPR
imaging, in combination with detailed outcrop sedimentology and architectural element
analysis constitute a powerful set of tools.GPR is currently the only high resolution, sub-
metre non-destructive, non-invasive and relatively inexpensive penetrative imaging
technology available for outcrop studies and it has the potential to transform outcrop
studies, refine existing facies models and provide more realistic input for quantitative
modelling of reservoir architecture and heterogeneities. Although the current cost of GPR
equipment is still beyond the reach of an average outcrop researcher, the costs are
significantly cheaper than seismic data acquisition.
The high resolution nature of GPR data makes it susceptible to image degradation due to
subtle changes in topography; this makes detailed elevation survey a critical requirement
for GPR surveys. Equipment for sub-metre scale topographic surveys (differential GPS,
Total Station) are quite expensive and will likely keep GPR research only within the
reach of research institutions and companies. Because GPR data interpretation depends
significantly on the data processing steps employed; more involvement of geophysicists
in projects involving three-dimensional GPR studies is required, especially as GPR data
processing, GPR attribute analysis and visualization get increasingly advanced.
GPR imaging will significantly improve studies on sand body architecture. Attempts to
create statistical distribution of sediment-body geometry based on outcrop observations
(Fielding and Crane 1987; Dreyer, 1990; Gibling, 2006) have been criticized for inability
173
to provide unambiguous determinations of the 3-D geometry and orientation of channels,
channel belts and other sand bodies in most outcrops due to limited and often two
dimensional exposures (Bridge, 2006). More accurate sand body dimensions can now be
obtained in outcrops via GPR imaging as demonstrated clearly in this study.
Advances in GPR data acquisition, data processing and visualization still trail similar
developments in seismic imaging due to less interest in GPR technology by the petroleum
industry that has funded much of the advances in seismic data acquisition, processing and
three dimensional visualization; however, the current growing interest in GPR imaging
technology is stimulating rapid advances in GPR processing as well as data display and
the trend will likely continue.
The recent development and application of Seismic Geomorphology to exploration and
field development was triggered by the advent of high-quality and increasingly more
affordable and widespread 3D seismic data currently available. 3D seismic data affords
plan-view images of depositional elements and in some instances entire depositional
systems. Attribute analyses of such images have significantly enhanced predictions of the
spatial and temporal distribution of subsurface lithology (reservoir, source, and seal),
compartmentalization, and stratigraphic trapping capabilities, as well as enhanced
understanding of process sedimentology and sequence stratigraphy (Posamentier and
Kolla, 2003). Combining vertical and plan view images via integrated seismic sections
and stratal slices have aided extraction of geological insights and geomorphologic
analyses of depositional systems from three-dimensional seismic data. This approach has
also aided quantitative assessment of paleogeomorphic features observable in subsurface
reservoirs; such attributes as channel sinuosity, slope, width-thickness ratios, as well as
174
measures of channel bifurcation, internal architecture and distribution of architectural
elements in various clastic deposits are now readily measured.
In contrast to advances in three-dimensional seismic imaging, three dimensional full
resolution Ground Penetrating Radar surveys on outcrops are rare; this is mostly due to
very close line spacing required for unaliased recording of reflections and diffractions
coupled with 3D migration processing. Applying the Nyquist criterion requires 3D GPR
measurements to be spaced in all horizontal directions near a quarter-wavelength of the
highest signal and noise frequency content, because diffractions are hyperboloids.
The well-known half-wavelength spatial sampling formula (e.g., Sheriff and Geldart,
1995), valid for a seismic spread with one source and multiple receivers, often leads to
spatially aliased 3D data sets when applied to fixed-offset, single source-and-receiver
GPR surveys. Theoretical line spacing for 250 MHz antenna used in this study is about
10 cm; such close line spacing will significantly increase data acquisition time and
greatly increase the field cost for large-scale three-dimensional surveys; this explains
why full resolution three-dimensional GPR surveys are rarely conducted. Lower
frequency antennas require wider line spacing but even the lowest GPR antenna (12.5
MHz) will need less than 5 metre spacing, which still requires huge data acquisition time
for channel-belt-scale surveys. Due to the practical limitations of adhering to the
theoretical line spacing for GPR surveys, most surveys use coarser line spacing aided
with the knowledge of the outcrop stratigraphy and sedimentology.
Despite the limitations that line spacing imposes on outcrop GPR imaging; full resolution
three-dimensional GPR surveys hold significant promise for high-resolution outcrop
studies (Beres et al, 1995; Jol, 2003; Heinz and Aigner, 2003) and with refinement in
175
GPR data processing and visualization could herald the field of radar geomorphology and
provide outcrop-based data for paleohydraulics and paleoclimatic studies. Results of the
three-dimensional GPR survey at the Navajo Sandstone outcrop show that depositional
trends and facies distribution are better evaluated with time slices, as GPR amplitude
maps are often indicative of lithological trends (Figure 71).
Figure 71: Three-dimensional GPR data display from Navajo Sandstone interdune deposit at Big Mesa, Utah (USA) showing low amplitude damp interdune facies preserved in the dry phase dune flanks.
Damp phase interdune facies
Dry phase interdune facies
0
10
176
Where three-dimensional GPR data acquisition is not feasible, this study shows that two-
dimensional GPR lines integrated with outcrop data could provide architectural details at
the resolution required for reliable three-dimensional interpretation.
As observed from the outcrop locations studied in this research; significant signal
attenuation and low penetration depth are the primary limitations of GPR imaging
technology to outcrop studies. There is virtually nothing that can be done to reduce signal
attenuation due to shale content and the presence of diagenetic clay in the formation
being studied or overlying formations. Deeper signal penetration can be achieved by
using lower frequency antenna (12.5 MHz to 100 MHz) for GPR surveys, although lower
frequency antennas are usually bulkier which implies longer data acquisition time and in
some cases, additional survey crew. Resolution will also be sacrificed with lower
frequency antennas but the lower end (100MHz and 200MHz) of the high frequency
antennas is still ideal for resolving architectural elements and macroforms.
The ultimate goal of outcrop-based GPR studies is to obtain analog data on architecture
and distribution of lithological heterogeneities from ancient clastic deposits as analogue
data for subsurface aquifers and reservoirs. Future outcrop studies could utilize hand-held
gamma ray scintillometers (used for detecting natural radioactivity as proxy for clay
content) for a quantitative correlation of GPR reflection amplitudes with lithology. Probe
permeameters could also be used to correlate reflection amplitude with variation in
permeability.
In conclusion, four major findings from this research that are of immense significance to
outcrop studies are summarized below:
177
1. All the case studies show that clastic deposits especially of eolian, fluvial and
estuarine origing are significantly heterogeneous even at outcrop scale. This
implies that petroleum reservoir modeling using wells spaced several kilometers
apart can rarely yield a reliable prediction of reservoir properties in such
heterogeneous clastic deposits.
2. Observations from all the case studies suggest that sedimentological and
stratigraphic data (especially of decimeter-scale outcrop features) can be obtained
from outcrop-based GPR profiles; architectural elements and lithofacies observed
in outcrop were unequivocally correlated to their radar equivalent. This suggests
that the failure of outcrop GPR imaging in earlier studies is not due to diagenetic
overprints but inappropriate choice of GPR equipment, ill-informed data acquition
and processing steps. Appropriate choice of GPR instrumentation (with proper
attention paid to the choice of antenna frequency and antenna shielding) is
therefore critical to the success of GPR surveys, subsequent data processing and
geological interpretation. It is important to understand the mode of operations of
the various GPR products and their appropriateness for specific problems
addressed by the intended outcrop research.
3. Amplitude variation and reflection configuration of GPR images are closely
linked with lithology as well as depositional environment and they are vital
interpretive features critical to outcrop-based research. They are quite
instrumental for identifying architectural elements as well as revealing sandbody
geometry and internal architecture. Interpretation of radar images should however
be ground-truthed by outcrop observations.
178
4. GPR data degrading due to poorly collected data can rarely be fixed during data
processing; hence, adhering to best practices of GPR data collection spelt out in
this thesis is critical to the success of GPR surveys. In addition, topographic
survey data must accompany GPR surveys as these are required for static
correction during the data processing phase.
5. Properly acquired GPR data require less vigorous data processing; few processing
steps such as dewow, signal gain, elevation correction and migration are sufficient
in most cases. Whereever possible, shielded antenna should be used for surveys as
data collected with unshielded antenna are more prone to extraneous noise.
179
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219
Appendix 1
Table A1: Typical conductivity, relative permittivity and radar velocity data in sediment (Annan, 2004)
220
Appendix 2
GPR Instrumentation
Considering the surging interest in GPR imaging of modern and ancient sedimentary
deposit, a brief discussion of GPR instrumentation is pertinent to understanding the
capabilities and limitations of the various GPR systems available in order to achieve
efficiently- planned GPR surveys. The three major manufacturers of GPR equipment are
Sensors and Software, MALÅ Geoscience, and Geophysical survey Systems Inc. (GSSI).
Sensors and Software and MALÅ Geoscience equipment are used more for GPR surveys
in Canada as these companies have offices/distributing agents in Canada. Each of these
companies manufactures array of GPR equipment designed for specific survey type.
Sensors and Softwares Inc., a Mississuaga (Canada) based GPR company manufactures
Noggin, PulseEKKO Pro, Conquest and SnowScan. Conquest is used mostly for concrete
imaging while Snowscan is used to evaluate snow thickness. Noggin and PulseEKKO
Pro are often used for geological applications. Noggin Smart Systems are integrated
ground penetrating radar (GPR) data acquisition platforms designed for shallow target,
high resolution imaging; they range in frequency from 250 MHz to 1000 MHz. The
Noggin systems are available in three different configurations: the SmartCart system, the
SmartHandle system and the Rock Noggin. Data acquisition is done simply by pushing
(or pulling) the Smart System along the survey line. This is usually done with an
odometer used as the triggering device, however, it is possible to change the triggering
method and run the Smart System in continuous operation or using the trigger button
(step mode). Noggin systems, because they are either pulled or dragged save survey time;
they are however only adapted for continuous mode data collection and Common Offset
221
surveys, not Common Midpoint (CMP) surveys usually required for time-depth
conversion of GPR profiles.
Figure A1: Mode of operation of Noggin system (Image taken from http://www.sensoft.ca/products/noggin/noggin.html - Accessed August 7, 2010)
PulseEKKO Pro antennas are low frequency, unshielded, bistatic antennas designed for
lower resolution, deeper target surveys. The antennas come in pairs; one transmitting
antenna and one receiving antenna. The shortest antennas, the 200 MHz, are 0.5 metres
long while the longest; the 12.5 MHz are 8 metres long. The 12.5 MHz antenna is the
lowest frequency currently available for GPR imaging and offers the deepest target
capability possible for any GPR survey. The length of the antennas (8 metres each)
however, makes surveys with these antennas cumbersome and time consuming (Figure
4). The pulseEKKO PRO can also be used with high frequency (100MHz, 250MHz, 500
MHz), shielded, bistatic antennas designed for high resolution shallow target imaging.
Each antenna box is really a “transducer” because it consists of both an antenna and the
electronics (Figure A2). The transmitting transducer is indicated with a “T” on the label,
e.g. T500, while the receiving transducer is indicated with an “R” on the label, e.g. R500.
222
Figure A2: High frequency, shielded, bistatic antennas available for the pulseEKKO PRO. The antennas come in pairs, one transmitting transducer and one receiving transducer. These are indicated by a “T” and an “R” on the labels. The 1000 MHz transducers are 14.5 cm (6 in) across, the 500 MHz transducers are 22.5 cm (9 in) across and the 250 MHz transducers are 38 cm (15 in) across. (Image taken from http://www.sensoft.ca/products/pulseekko/pulseekkopro.html - Accessed August 7, 2010)
MALÅ Geoscience manufactures unshielded antenna in the 25MHz to 200 MHz and
shielded antenna in the 100MHz to 1 GHz range. MALÅ’s unshielded antennas consist of
separate transmitter and receiver elements and electronics, allowing them to be operated
in several modes for different survey techniques, such as reflection profiling, velocity
profiling (common mid-point (CMP), or wide angle reflection and refraction (WARR)),
and cross-scanning (tomography). MALÅ’s unshielded antennas are designed for use in
applications that require maximum depth penetration. However, due to the fact that these
antennas are unshielded, they are more suitable for use in areas with little or no
background noise. Wooden handles are provided for use with the 50, 100 and 200 MHz
antennas; these are used to carry the antennas and to also keep them separated and
stabilized during measurements (Figure A3)
223
Figure A3: MALÅ Geoscience unshielded Bistatic antennas (Image taken from http://www.malags.com/Downloads/Product-Brochures.aspx - Accessed August 7, 2010)
Due to the size of the 25 MHz unshielded antenna elements, wooden handles are not
practical, so strapping is provided to aid in separation and carrying. MALÅ also
manufactures low frequency (25 MHz , 50 MHz and 100 MHz) Rough Terrain Antennas.
The Rough Terrain Antenna (RTA) series from MALÅ affords flexibility required in
low-frequency Ground Penetrating Radar (GPR) surveying in rough terrains typical of
outcrops. The antenna design provides improved performance for deeper penetration and
the flexible “snake” like design allows the antenna to be maneuvered easily and
efficiently through dense vegetation or most uneven of terrain without affecting ground
contact, providing optimum results in the most difficult of environments; the most
important benefit being that the operator doesn’t have to clear an access path or route
224
prior to the profile or survey. MALÅ Geoscience claims reductions in survey time and
manpower requirements to a third of those experienced when using traditional unshielded
antennas. However, as the RTA is an antenna of unshielded type, unwanted noise most
often in form of air reflections can also occur in the data due to the fact that the antenna
emits electromagnetic waves in any direction and also receive them from any direction.
Figure A4: Mode of operation of MALÅ Geoscience Rough Terrain Antenna (Image taken from http://www.malags.com/Downloads/Product-Brochures.aspx - Accessed August 7, 2010)
MALÅ shielded antennas are designed for use in urban areas or sites with a background
noise. A shielded antenna consists of both transmitter and receiver antenna elements in a
single housing. The design ensures that the transmitted radar energy is only emitted from
the bottom of the antenna housing where it is in contact with the ground and protects the
receiver element from externals signals (noise) from directions other than the bottom of
the housing where it is located (Figure A5)
225
Figure A5: MALÅ Geoscience shielded antennas; note increase in antenna size with frequency (Image taken from http://www.malags.com/Downloads/Product-Brochures.aspx - Accessed August 7, 2010)
GSSI manufactures adjustable multiple low-frequency (15-80 MHz) antennas designed
for deep penetration depth. The antenna design consists of interchangeable elements; by
changing the length of the antenna, the transmission frequency is changed. This antenna
can be deployed in discrete measurements (step mode) or continuous profile data
collection modes; this affords the user some flexibility in resolution/target depth during
GPR surveys. GSSI also manufactures 100 MHz, 200 MHz and 270 MHz antennas in
addition to the high resolution antenna (>500 MHz) useful for low target high resolution
outcrop studies. The 100 MHz antenna is used for deep (10-20 m depending on the
dielectric properties of the transmitting medium) subsurface applications. The 100 MHz
antennas are produced in monostatic and bistatic format. The 100 MHz monostatic (left)
combines the transmitter and receiver electronics in a single antenna housing. The 100
MHz bistatic (right) is a versatile antenna pair that can operate in different configurations
(common offset and common mid-point) to optimize performance.
800 MHz
100 MHz
500 MHz
250 MHz
226
Figure A6: GSSI 100 MHz antennas available in monostatic and bistatic mode (Image taken from http://www.geophysical.com/antennas.htm - Accessed August 7, 2010)
surface
227
Appendix 3
Table A3- List of Published GPR studies on Sediments from 1980 - 2010
Deposit /
Environment
Age /
Formation
Equipment
Type
Lowest
Successful
Antenna
Frequenc
y (MHz)
Survey
Mode
(Common
Offset /
CMP/Both)
Max Depth
of
Investigation
(m)
Survey
Type
(2D
/3D /
Both)
Survey
Area
(m2)
Study Title Publication
Year
Authors
Carbonate Cretaceous PulseEKKO 100 Common
Offset
10 2D GPR and marine
seismic imaging of
carbonate mound
structures in
Denmark and
southwest Sweden: A
case study of imaging
structures at different
scales
2003 Lars Nielsen,
Lars Ole
Boldreel, and
Jette Vindum
Table A3 continued
228
Carbonate Cretaceous Unknown 400 Common
Offset
10 2D Geoelectrical
constraints on radar
probing of shallow
water-saturated zones
within karstified
carbonates in semi-
arid environments
2010 Damayanti
Mukherjee,
Essam Heggy,
Shuhab D. Khan
Carbonate Jurassic Ramac
Shielded
250 Common
Offset
4 3D Photographing layer
thicknesses and
discontinuities in a
marble quarry with
3D GPR visualisation
2008 Selma Kadioglu
Carbonate Jurassic GSSI SIR-2 100 Common
Offset
40 2D Ground penetrating
radar application in a
shallow marine
Oxfordian limestone
sequence located on
the eastern flank of
the Paris Basin, NE
France
2000 Guy Dagallier,
Ari I. Laitinen,
Fabrice Malartre,
Ignace P. A. M.
Van
Campenhout,
Paul C. H.
Veeken
Table A3 continued
229
Carbonate Mississippia
n /
Livingstone
Formation
Ramac
Unshielded
50 Common
Offset
40 2D Mapping fractures
with GPR; a case
study from Turtle
Mountain
2006 Ulrich Theune,
Dean Rokosh,
Mauricio D.
Sacchi, and
Douglas R.
Schmitt
Carbonate Ordovician PulseEKKO 50 Common
Offset
14 2D Characterization of a
coalesced, collapsed
paleocave reservoir
analog using GPR
and well-core data
2002 George A.
McMechan,
Robert G.
Loucks, Paul
Mescher, and
Xiaoxian Zeng
Carbonate Ordovician /
Ellenburger
dolomite
Unknown 50 Common
Offset
10 2D Ground penetrating
radar imaging of a
collapsed paleocave
system in the
Ellenburger dolomite,
central Texas
1998 George A.
McMechan,
Robert G.
Loucks,
Xiaoxian Zeng,
Paul Mescher
Carbonate Triassic Unknown 100 Common
Offset
20 3D 1000 Full-resolution 3D
GPR imaging
2005 Mark
Grasmueck, Ralf
Weger, and
Heinrich
Horstmeyer
Table A3 continued
230
Carbonate Upper Farley
(Pennsylvani
an)
Unknown 400 Both 12 2D Improving resolution
and understanding
controls on GPR
response in carbonate
strata: Implications
for attribute analysis
2007 Evan K.
Franseen, Alan
P. Byrnes,
Jianghai Xia, and
Richard D.
Miller
Carbonate Triassic GSSI SIR
10B
200 Common
Offset
5 2D Visualization and
characterization of
active normal faults
and associated
sediments by high-
resolution GPR
2003 Stefan Reiss,
Klaus R.
Reicherter, and
Claus-Dieter
Reuther
Carbonate Paleocene PulseEKKO 100 Common
Offset
11 Both 3150 Application of GPR
for 3-D visualization
of geological and
structural variation in
a limestone formation
1998 Thrainn
Sigurdsson,
Torben
Overgaard
Table A3 continued
231
Turbidite Carbonifero-
us
PulseEKKO 50 Both 20 Both 30000 3D high-resolution
digital models of
outcrop analogue
study sites to
constrain reservoir
model uncertainty: an
example from Alport
Castles, Derbyshire,
UK
2004 J. K. Pringle, A.
R. Westerman, J.
D. Clark, N. J.
Drinkwater, and
A. R. Gardiner
Deltaic Cretaceous /
Ferron
Sandstone
PulseEKKO 100 Both 12 3D 660 3-D characterization
of a clastic reservoir
analog; from 3-D
GPR data to a 3-D
fluid permeability
model
2001 Robert B.
Szerbiak, George
A. McMechan,
Rucsandra
Corbeanu, Craig
B. Forster, and
Stephen H.
Snelgrove
Table A3 continued
232
Fluvial Jurassic /
Kayenta
PulseEKKO 50 Both 15 2D Architectural element
analysis within the
Kayenta Formation
(Lower Jurassic)
using ground-probing
radar and
sedimentological
profiling,
southwestern
Colorado
1994 Mark Stephens
Marine Dad
Sandstone
Ramac
Unshielded
100 Common
Offset
20 3D 3780 Three-dimensional
imaging of a deep
marine channel-
levee/overbank
sandstone behind
outcrop with EMI
and GPR
2004 Ryan P. Stepler,
Alan J. Witten,
and Roger M.
Slatt
Table A3 continued
233
Turbidite Carboniferou
s
PulseEKKO 225 Common
Offset
8 30000 The use of GPR to
image three-
dimensional (3-D)
turbidite channel
architecture in the
Carboniferous Ross
Formation, County
Clare, western
Ireland
2003 J. K. Pringle, J.
D. Clark, A. R.
Westerman, and
A. R. Gardiner
Marine Lewis Shale PulseEKKO 100 Common
Offset
2D A hybrid laser-
tracking/GPS
location method
allowing GPR
acquisition in rugged
terrain
2002 Roger A. Young
and Neal Lord
Turbidite Cretaceous /
Lewis Shale
PulseEKKO 100 Both 10 2D Application of
ground penetrating
radar imaging to
deepwater (turbidite)
outcrops
2003 R. A. Young, R.
M. Slatt, J. G.
Staggs
Table A3 continued
234
Carbonate Ordovician /
Ellenburger
dolomite
GSSI
SIR10A
300 Common
Offset
15 Both 288 GPR data processing
for 3D fracture
mapping in a marble
quarry (Thassos,
Greece)
1996 G. Grandjean, J.
C. Gourry
Deltaic Cretaceous /
Ferron
Sandstone
PulseEKKO 50 Common
Offset
20 3D 230 Integration of GPR
with stratigraphic and
lidar data to
investigate behind-
the-outcrop 3D
geometry of a tidal
channel reservoir
analog, upper Ferron
Sandstone, Utah
2007 Keumsuk Lee,
Mark Tomasso,
William A.
Ambrose, and
Renaud
Bouroullec
Deltaic Cretaceous /
Ferron
Sandstone
PulseEKKO 100 Both 16 2D Estimation of the
spatial distribution of
fluid permeability
from surface and
tomographic GPR
data and core, with a
2-D example from
the Ferron Sandstone,
Utah
2002 William S.
Hammon,
Xiaoxian Zeng,
Rucsandra M.
Corbeanu, and
George A.
McMechan
Table A3 continued
235
Deltaic Cretaceous /
Ferron
Sandstone
PulseEKKO 100 Both 15 3D 660 Prediction of 3-D
fluid permeability
and mudstone
distributions from
ground-penetrating
radar (GPR)
attributes; example
from the Cretaceous
Ferron Sandstone
Member, east-central
Utah
2002 Rucsandra M.
Corbeanu,
George A.
McMechan, and
Robert B.
Szerbiak
Barrier spit
and Beach
plain
Holocene PulseEKKO 100 Both 15 2D Ground water surface
trends from ground-
penetrating radar
(GPR) profiles taken
across late Holocene
barriers and beach
plains of the
Columbia River
littoral system,
Pacific Northwest
coast, USA
2007 Curt D. Peterson,
Harry M. Jol,
David Percy, and
Eric L. Nielsen
Table A3 continued
236
Coastal
Barrier
Holocene Unknown 200 Both 6 2D Annual Layers
Revealed By GPR in
the Subsurface of a
Prograding Coastal
Barrier,Southwest
Washington, U.S.A.
2004 L.J. Moore,
H.M. Jol, S.
Kruse, S.
Vanderburgh,
and G.M.
Kaminsky
Coastal Holocene Unknown 100 Both 10 2D Applications of
ground-penetrating
radar (GPR) to
sedimentological,
geomorphological
and
geoarchaeological
studies in coastal
environments
2000 Adrian Neal and
Clive L. Roberts
Lake Holocene Ramac
Unshielded
50 Both 40 2D Rapid lake infill
following major
rockfall (bergsturz)
events revealed by
ground-penetrating
radar (GPR)
measurements,
Reintal, German Alps
2007 O. Sass, M.
Krautblatter, and
D. Morche
237
Glacio-fluvial Holocene PulseEKKO 50 Both 30 2D Gpr-derived
Sedimentary
Architecture and
Stratigraphy of
Outburst Flood
Sedimentation Within
a Bedrock Valley
System, Hraundalur,
Iceland
2007 Jonathan L.
Carrivick, Jamie
K. Pringle,
Andrew J.
Russell, and
Nigel J. Cassidy
Coastal
Barrier
Holocene GSSI SIR-3 120 Common
Offset
8 2D High-Resolution
Subsurface (GPR)
Imaging and
Sedimentology of
Coastal Ponds,
Maine, U.S.A.:
Implications for
Holocene Back-
Barrier Evolution
2003 Ilya V.
Buynevich and
Duncan M.
Fitzgerald
Table A3 continued
238
Coastal
Barrier
Holocene PulseEKKO 100 Common
Offset
10 2D A GPR study of
sedimentary
structures within a
transgressive coastal
barrier along the
Danish North Sea
coast
2003 Ingelise Moller
and Dennis
Anthony
Eolian Holocene Common
Offset
2D GPR survey of a
Holocene
aeolian/fluvial/lacustr
ine succession,
Lauder Sandhills,
Manitoba, Canada
2003 K. G. Havholm,
N. D. Bergstrom,
Harry M. Jol,
and G. L.
Running
Eolian Holocene PulseEKK-
O
100 Common
Offset
15 2D Evidence for dune
reactivation from
GPR profiles on the
Maputaland coastal
plain, South Africa
2003 Greg A. Botha,
Charlie S.
Bristow, Naomi
Porat, Geoff
Duller, Simon J.
Armitage, Helen
M. Roberts,
Brendan M.
Clarke, Mxolisi
Kota, and Philo
Schoeman
Table A3 continued
239
Pyroclastic
deposits
Holocene PulseEKKO 200 Both 8 3D GPR studies of
pyroclastic deposits:
Subsurface
information where
there are no outcrops
2001 B. Cagnoli and
T. Ulrych
Glacial Holocene PulseEKKO 50 VRP 43 2D Downhole GPR for
high-resolution
analysis of material
properties near
Fairbanks, Alaska
2003 Lewis E. Hunter,
Allan J. Delaney,
Daniel E.
Lawson, and Les
Davis
Pyroclastic
deposits
Holocene PulseEKKO 100 Both 6 2D Joint time-frequency
analysis of GPR data
over layered
sequences
2008 S. Guha, S.
Kruse, and P.
Wang
Mud Volcano Holocene GSSI SIR-II 200 Both 5 Both 1000 GPR reflection
characteristics and
depositional models
of mud volcanic
sediments;
Wushanting mud
volcano field,
southwestern Taiwan
2006 Joseph Jinder
Chow, Su-Kai
Chang, and Ho-
Shing Yu
Table A3 continued
240
Carbonate Holocene PulseEKKO 50 Both 10 2D The recognition of
barrage and paludal
tufa systems by GPR;
case studies in the
geometry and
correlation of
Quaternary
freshwater carbonates
2003 Martyn Pedley
and Ian Hill
Lake Holocene Common
Offset
2D Amplitude analysis
of repetitive GPR
reflections on a Lake
Bonneville Delta,
Utah
2003 Sarah E. Kruse
and Harry M. Jol
Coastal
Barrier
Holocene Ramac
Unshielded
500 Both 5 2D Cyclical Evolution of
a Modern
Transgressive Sand
Barrier in
Northwestern Spain
Elucidated by GPR
and Aerial Photos
2006 S. Costas, I.
Alejo, F. Rial, H.
Lorenzo, and
M.A. Nombela
Table A3 continued
241
Deltaic Holocene PulseEKKO 100 Both 12 2D A comparison of the
correlation structure
in GPR images of
deltaic and barrier-
spit depositional
environments
2000 Paulette Tercier,
Rosemary
Knight, and
Harry Jol
Coastl beach Holocene PulseEKKO 100 Both 6 2D Quantifying rates of
coastal progradation
from sediment
volume using GPR
and OSL; the
Holocene fill of
Guichen Bay, south-
east South Australia
2006 C. S. Bristow
and K. Pucillo
Coastal
Barrier
Holocene Ramac
Unshielded
100 Common
Offset
8 2D Internal structure of a
barrier beach as
revealed by ground
penetrating radar
(GPR); Chesil Beach,
UK
2009 Matthew R.
Bennett, Nigel J.
Cassidy, and
Jeremy Pile
Table A3 continued
242
Coastal
Barrier
Holocene PulseEKKO 200 Both 7 2D Digital ground
penetrating radar
(GPR); a new
geophysical tool for
coastal barrier
research (examples
from the Atlantic,
Gulf and Pacific
coasts, U.S.A.)
1996 Harry M. Jol,
Derald G. Smith,
and Richard A.
Meyers
Eolian Holocene GSSI SIR-8 100 Common
Offset
30 2D Ground-penetrating
radar (GPR) for
imaging stratigraphic
features and
groundwater in sand
dunes
1996 Zaki Harari
Eolian Holocene GSSI SIR
2000
35 Common
Offset
20 2D GPR stratigraphy of a
large active dune on
Parengarenga
Sandspit, New
Zealand
2003 Remke L. Van
Dam, Scott L.
Nichol, Paul C.
Augustinus,
Kevin E. Parnell,
Peter L.
Hosking, and
Roger F.
McLean
Table A3 continued
243
Eolian Holocene GSSI SIR
3000
400 Common
Offset
6 3D Mapping the internal
structure of sand
dunes with GPR: A
case history from the
Jafurah sand sea of
eastern Saudi Arabia
2008 Ademola Q.
Adetunji,
Abdullatif Al-
Shuhail, and
Gabor Korvin
Fluvial Holocene 225 Common
Offset
3D 400 Architecture and
sedimentology of an
active braid bar in the
Wisconsin River
based on 3-D ground-
penetrating radar
2003 Andrew J.
Mumpy, Harry
M. Jol, William
F. Kean, and
John L. Isbell
Coastal Holocene Unknown 100 Both 12 2D Imaging fluvial
architecture within a
paleovalley fill using
ground-penetrating
radar, Maple Creek,
Guyana (in
Stratigraphic analyses
using GPR)
2008 Adrian S.
Hickin, Peter T.
Bobrowsky,
Roger C. Paulen,
and Mel Best
Table A3 continued
244
Eolian Holocene PulseEKKO 100 Both 15 2D Combining ground
penetrating radar
surveys and optical
dating to determine
dune migration in
Namibia
2005 C.S. Bristow, N.
Lancaster, and
G.A.T. Duller
Glacio-fluvial Holocene PulseEKKO 100 Common
Offset
8 2D The Architecture of
Prograding Sandy-
Gravel Beach Ridges
Formed During the
Last Holocene
Highstand:
Southwestern British
Columbia, Canada
2005 Simone Engels
and Michael C.
Roberts
Coastal
Barrier
Holocene PulseEKKO 100 Common
Offset
8 2D Minimum Runup
Heights of
Paleotsunami from
Evidence of Sand
Ridge Overtopping at
Cannon Beach,
Oregon, Central
Cascadia Margin,
U.S.A.
2008 Curt D. Peterson,
Kenneth M.
Cruikshank,
Harry M. Jol,
and Robert B.
Schlichting
Table A3 continued
245
Carbonate Holocene Unknown 50 Common
Offset
30 2D Ground-penetrating
radar; a near-face
experience from
Washington County,
Arkansas
1995 Christopher L.
Liner and Jeffrey
L. Liner
Coastal
Barrier
Holocene GSSI SIR-
2000
200 Common
Offset
10 2D Coastal
Environmental
Changes Revealed in
Geophysical Images
of Nantucket Island,
Massachusetts,
U.S.A.
2006 Ilya V.
Buynevich
Coastal Holocene PulseEKKO 100 Common
Offset
15 2D The structure and
development of
foredunes on a
locally prograding
coast: insights from
ground-penetrating
radar surveys,
Norfolk, UK
2000 Charlie S.
Bristow, P. Neil
Chroston, Simon
D. Bailey
Table A3 continued
246
Coastal Holocene GSSI SIR-3 120 Common
Offset
15 2D Radar facies of
paraglacial barrier
systems: coastal New
England, USA
1988 Sytze Van
Heteren, Duncan
M. Fitzgerald,
Paul A.
Mckinlay, Ilya
V. Buynevich
Coastal
Barrier
Holocene Ramac
Unshielded
100 Common
Offset
8 2D Internal structure of a
barrier beach as
revealed by ground
penetrating radar
(GPR): Chesil beach,
UK
2009 Matthew R.
Bennett, Nigel J.
Cassidy, Jeremy
Pile
Eolian Holocene GSSI SIR-
8
100 Common
Offset
35 2D Ground-penetrating
radar (GPR) for
imaging stratigraphic
features and
groundwater in sand
dunes
1996 Zaki Harari
Eolian Holocene Ramac
Unshielded
200 Common
Offset
7 Both 300 Parabolic dune
reactivation and
migration at
Napeague, NY, USA:
Insights from aerial
and GPR imagery
2010 James D.
Girardi, Dan M.
Davis
Table A3 continued
247
Fluvial Holocene PulseEKKO 50 Both 10 2D Ground penetrating
radar images of
selected fluvial
deposits in the
Netherlands
1999 J. Vandenberghe,
R. A. van
Overmeeren
Eolian Holocene PulseEKKO 50 Both 22 2D Unveiling past
aeolian landscapes: A
ground-penetrating
radar survey of a
Holocene coastal
dunefield system,
Thy, Denmark
2005 Karsten
Pedersen, Lars
B. Clemmensen
Alluvial Fan Holocene PulseEKKO 50 Common
Offset
40 2D Ground penetrating
radar facies of the
paraglacial Cheekye
Fan, southwestern
British Columbia,
Canada
2001 Csaba Ékes,
Edward J. Hickin
Table A3 continued
248
Coastal
Barrier
Holocene PulseEKKO 100 Both 15 2D Integrating ground-
penetrating radar and
borehole data from a
Wadden Sea barrier
island
2009 L. Nielsen, I.
Møller, L.H.
Nielsen, P.N.
Johannessen, M.
Pejrup, T.J.
Andersen, J.S.
Korshøj
Fluvial Holocene PulseEKKO 100 Both 14 2D The internal structure
of scrolled floodplain
deposits based on
ground-penetrating
radar, North
Thompson River,
British Columbia
1997 Rene F. Leclerc,
Edward J. Hickin
Fluvial,
Eolian,
lacustrine
Holocene PulseEKKO 50 Both 30 2D Radar facies of
unconsolidated
sediments in The
Netherlands: A radar
stratigraphy
interpretation method
for hydrogeology
1998 R. A. van
Overmeeren
Table A3 continued
249
Deltaic Holocene PulseEKKO 25 Both 35 2D Radar structure of a
Gilbert-type delta,
Peyto Lake, Banff
National Park,
Canada
1997 Derald G. Smith,
Harry M. Jol
Eolian Holocene GSSI
SIR3000
200 Common
Offset
8 2D The internal structure
of modern barchan
dunes of the Ebro
River Delta (Spain)
from ground
penetrating radar
2009 D. Gómez-Ortiz,
T. Martín-
Crespo, I.
Rodríguez, M.J.
Sánchez, I.
Montoya
Coastal
Barrier
Holocene PulseEKKO 25 Both 10 2D Ground penetrating
radar: 2-D and 3-D
subsurface imaging
of a coastal barrier
spit, Long Beach,
WA, USA
2003 Harry M. Jol,
Don C. Lawton,
Derald G. Smith
Table A3 continued
250
Beach Holocene PulseEKKO 100 Both 10 2D Ground-penetrating
radar profiles of
Holocene raised-
beach deposits in the
Kujukuri strand plain,
Pacific coast of
eastern Japan
2008 Toru Tamura,
Fumitoshi
Murakami,
Futoshi
Nanayama,
Kazuaki
Watanabe,
Yoshiki Saito
Beach Holocene PulseEKKO 100 Common
Offset
10 2D Internal architecture
of a raised beach
ridge system (Anholt,
Denmark) resolved
by ground-
penetrating radar
investigations
2010 Lars B.
Clemmensen,
Lars Nielsen
Alluvial Fan Holocene PulseEKKO 50 Common
Offset
16 2D Long-term bed load
transport rate based
on aerial-photo and
ground penetrating
radar surveys of fan-
delta growth, Coast
Mountains, British
Columbia
2004 Channa P.
Pelpola, Edward
J. Hickin
Table A3 continued
251
Coastal
Barrier
Holocene PulseEKKO 100 Both 3 2D Investigation of
large-scale washover
of a small barrier
system on the
southeast Australian
coast using ground
penetrating radar
2006 Adam D.
Switzer, Charles
S. Bristow, Brian
G. Jones
Eolian Holocene PulseEKKO 100 Common
Offset
20 2D Investigation of the
age and migration of
reversing dunes in
Antarctica using GPR
and OSL, with
implications for GPR
on Mars
2010 C.S. Bristow,
P.C. Augustinus,
I.C. Wallis, H.M.
Jol, E.J. Rhodes
Eolian Holocene PulseEKKO 450 Both 6 2D Slipfaceless
‘whaleback’ dunes in
a polar desert,
Victoria Valley,
Antarctica: Insights
from ground
penetrating radar
2010 C.S. Bristow,
H.M. Jol, P.
Augustinus, I.
Wallis
Table A3 continued
252
Eolian Holocene GSSI SIR-
2000
400 Common
Offset
10 2D Dune advance into a
coastal forest,
equatorial Brazil: A
subsurface
perspective
2009 Ilya V.
Buynevich,
Pedro Walfir M.
Souza Filho, Nils
E. Asp
Coastal Holocene GSSI SIR 3 120 Common
Offset
15 2D Sedimentary records
of intense storms in
Holocene barrier
sequences, Maine,
USA
2004 Ilya V.
Buynevich,
Duncan M.
FitzGerald, Sytze
van Heteren
Glacio-fluvial Holocene PulseEKKO 100 Both 12 Both Using two- and three-
dimensional georadar
methods to
characterize
glaciofluvial
architecture
1999 Milan Beres,
Peter
Huggenberger,
Alan G. Green,
Heinrich
Horstmeyer
Fluvial Holocene Unknown 400 Common
Offset
7 2D Combining
sedimentological and
geophysical data for
high-resolution 3-D
mapping of fluvial
architectural elements
in the Quaternary Po
plain (Italy)
2007 R. Bersezio, M.
Giudici, M. Mele
Table A3 continued
253
Eolian Holocene GSSI SIR
3000
200 Common
Offset
6 2D Internal structure of
the aeolian sand
dunes of El Fangar
spit, Ebro Delta
(Tarragona, Spain)
2009 Inmaculada
Rodríguez
Santalla, María
José Sánchez
García, Isabel
Montoya
Montes, David
Gómez Ortiz,
Tomas Martín
Crespo, Jordi
Serra Raventos
Fluvial Holocene PulseEKKO 12.5 Both 36 2D Characterizing large
river history with
shallow geophysics:
Middle Yukon River,
Yukon Territory and
Alaska
2005 Duane G. Froese,
Derald G. Smith,
David T.
Clement
Table A3 continued
254
Beach Holocene PulseEKKO 50 Common
Offset
15 2D Dating Of Late
Holocene Beach
Shoreline Positions
By Regional
Correlation of
Coseismic Retreat
Events In The
Columbia River
Littoral Cell, USA
2010 Curt D. Peterson,
Harry M. Jol,
Sandy
Vanderburgh,
James B. Phipps,
David Percy,
Guy Gelfenbaum
Coastal
Barrier
Holocene GSSI SIR
3000
200 Common
Offset
9 2D The sedimentary
architecture of a
Holocene barrier spit
(Sylt, German Bight):
Swash-bar accretion
and storm erosion
2008 Sebastian
Lindhorst,
Christian
Betzler, H.
Christian Hass
Fluvial Holocene PulseEKKO 200 Both 5 2D Bar-top hollows: A
new element in the
architecture of sandy
braided rivers
2006 Jim Best, John
Woodward, Phil
Ashworth, Greg
Sambrook Smith,
Chris Simpson
Table A3 continued
Table A3 continued
255
Fluvial Holocene PulseEKKO 100 Both 5 2D Architecture of
channel-belt deposits
in an aggrading
shallow sandbed
braided river: the
lower Niobrara River,
northeast Nebraska
2003 Raymond L.
Skelly, Charlie
S. Bristow,
Frank G.
Ethridge
Eolian Holocene Unknown Unknown Common
Offset
25 2D A Holocene history
of dune-mediated
landscape change
along the
southeastern shore of
Lake Superior
2004 Walter L. Loope,
Timothy G.
Fisher, Harry M.
Jol, Ronald J.
Goble, John B.
Anderton,
William L.
Blewett
Table A3 continued
256
Glacio-fluvial Holocene PulseEKKO 100 Both 12 2D Sedimentary and
tectonic architecture
of a large push
moraine: a case study
from Hagafellsjökull-
Eystri, Iceland
2004 Matthew R.
Bennett, David
Huddart, Richard
I. Waller, Nigel
Cassidy,
Alexandre
Tomio, Paul
Zukowskyj,
Nicholas G.
Midgley, Simon
J. Cook, Silvia
Gonzalez, Neil
F. Glasser
Glacio-fluvial Holocene PulseEKKO 100 Both 15 2D Architecture and
sedimentation of
outwash fans in front
of the Mýrdalsjökull
ice cap, Iceland
2004 Kurt H. Kjær,
Lina Sultan,
Johannes Krüger,
Anders
Schomacker
Beach Holocene PulseEKKO 200 Both 5 2D Geomorphic evidence
for mid–late
Holocene higher sea
level from
southeastern
Australia
2009 Adam D.
Switzer, Craig R.
Sloss, Brian G.
Jones, Charles S.
Bristow
Table A3 continued
257
Lake Holocene PulseEKKO 200 Common
Offset
10 2D The influence of
seasonal precipitation
and temperature
regimes on lake
levels in the
northeastern United
States during the
Holocene
2006 Bryan Shuman,
Jeffrey P.
Donnelly
Glacio-fluvial Holocene PulseEKKO 100 Both 20 2D The formation of
sawtooth moraine
ridges in Bødalen,
western Norway
2009 Valentin Burki,
Eiliv Larsen, Ola
Fredin, Aninna
Margreth
Coastal
Barrier
Holocene Radar
Systems Inc
- Zond 12c
300 Common
Offset
6 2D Solar-forced 2600 BP
and Little Ice Age
highstands of the
Caspian Sea
2007 S.B.
Kroonenberg,
G.M.
Abdurakhmanov,
E.N. Badyukova,
K. van der Borg,
A. Kalashnikov,
N.S. Kasimov,
G.I. Rychagov,
A.A. Svitoch,
H.B. Vonhof,
F.P. Wesselingh
Table A3 continued
258
Beach Holocene GSSI 120 Common
Offset
10 2D Sand budgets at
geological, historical
and contemporary
time scales for a
developed beach
system, Saco Bay,
Maine, USA
2005 Joseph T. Kelley,
Donald C.
Barber, Daniel F.
Belknap, Duncan
M. FitzGerald,
Sytze van
Heteren, Stephen
M. Dickson
Eolian Holocene PulseEKKO 100 Common
Offset
12 2D Formation of aeolian
dunes on Anholt,
Denmark since AD
1560: A record of
deforestation and
increased storminess
2007 Lars B.
Clemmensen,
Mette Bjørnsen,
Andrew Murray,
Karsten Pedersen
Coastal
Barrier
Holocene Ramac
Unshielded
100 Both 12 2D Lithological
heterogeneity in a
back-barrier sand
island: Implications
for modelling
hydrogeological
frameworks
2008 Jonathan
Hodgkinson,
Malcolm E. Cox,
Stephen
McLoughlin,
Gary J. Huftile
Table A3 continued
259
Fluvial Holocene PulseEKKO 50 Both 12 2D Integrated
geophysical and
geological
investigation of a
heterogeneous fluvial
aquifer in Columbus
Mississippi
2007 Jerry C.
Bowling, Dennis
L. Harry,
Antonio B.
Rodriguez,
Chunmiao Zheng
Coastal Holocene Unknown 200 Common
Offset
3 2D Evidence for late
Holocene highstands
in Central Guilan–
East Mazanderan,
South Caspian coast,
Iran
2009 Hamid Alizadeh
Ketek Lahijani,
Hossain
Rahimpour-
Bonab, Vahid
Tavakoli, Muna
Hosseindoost
Eolian Holocene PulseEKKO 100 Both 10 2D Origin of a complex
and spatially diverse
dune-field pattern,
Algodones,
southeastern
California
2008 Dana Derickson,
Gary Kocurek,
Ryan C. Ewing,
Charlie Bristow
Table A3 continued
260
Eolian Holocene GSSI
Shielded
270 Common
Offset
15 2D An extended field of
crater-shaped
structures in the Gilf
Kebir region, Egypt:
Observations and
hypotheses about
their origin
2006 Philippe Paillou,
Bruno Reynard,
Jean-Marie
Malézieux, Jean
Dejax, Essam
Heggy, Pierre
Rochette, Wolf
Uwe Reimold,
Patrick Michel,
David Baratoux,
Philippe Razin,
Jean-Paul Colin
Beach Holocene PulseEKKO 50 Both 20 2D Composition, age,
and depositional rates
of shoreface deposits
under barriers and
beach plains of the
Columbia River
littoral cell, USA
2010 Curt D. Peterson,
Sandy
Vanderburgh,
Michael C.
Roberts, Harry
M. Jol, Jim
Phipps, David C.
Twichell
Table A3 continued
261
Lake Holocene GSSI SIR
2000
200 Common
Offset
15 2D Evidence of
centennial-scale
drought from
southeastern
Massachusetts during
the
Pleistocene/Holocene
transition
2009 Paige E. Newby,
Jeffrey P.
Donnelly, Bryan
N. Shuman,
Dana
MacDonald
Glacio-fluvial Holocene Unknown 80 Common
Offset
15 2D Early Holocene
regressive spit-
platform and
nearshore
sedimentation on a
glaciofluvial complex
during the Yoldia Sea
and the Ancylus Lake
phases of the Baltic
Basin, SW Finland
2003 Joni Mäkinen,
Matti Räsänen
Table A3 continued
262
Coastal Holocene Unknown 100 Common
Offset
8 2D Lagoa da Apúlia: A
residual lagoon from
the Late Holocene
(NW coastal zone of
Portugal)
2009 H. Granja, F.
Rocha, M.
Matias, R.
Moura, F.
Caldas, J.
Marques, H.
Tareco
Coastal Holocene GSSI SIR-3 120 Common
Offset
25 2D Influence of relative
sea-level change and
tidal-inlet
development on
barrier-spit
stratigraphy, Sandy
Neck, Massachusetts
1997 Van Heteren and
VandePlassche
(1997)
Table A3 continued
263
Glacio-fluvial Holocene PulseEKKO 200 Common
Offset
4 3D Estimating 3D
variation in active-
layer thickness
beneath arctic
streams using
ground-penetrating
radar
2009 Troy R. Brosten;
John H.
Bradford; James
P. McNamara;
Michael N.
Gooseff; Jay P.
Zarnetske;
William B.
Bowden;
Morgan E.
Johnston
Fluvial Holocene PulseEKKO 200 Both 5 2D The use and
application of GPR in
sandy fluvial
environments;
methodological
considerations
2003 John Woodward,
Philip J.
Ashworth, James
L. Best, Gregory
H. Sambrook
Smith, and
Christopher J.
Simpson
Table A3 continued
264
Glacio-fluvial Holocene GPR derived
architecture of
November 1996
jokulhlaup deposits,
Skeidararsandur,
Iceland
2003 N. J. Cassidy, A.
J. Russell, P. M.
Marren, H. Fay,
O. Knudsen, E.
L. Rushmer, and
T. A. G. P. van
Dijk
Flood deposit Pleistocene PulseEKKO 100 Common
Offset
8 Both
3,600
GPR imaging of
clastic dikes at the
Hanford Site,
Hanford, Washington
2007 William P.
Clement and
Christopher J.
Murray
Eolian Pleistocene PulseEKKO 100 Common
Offset
6 2D GPR surveys of
vegetated linear dune
stratigraphy in central
Australia; evidence
for linear dune
extension with
vertical and lateral
accretion
2007 C. S. Bristow, B.
G. Jones, G. C.
Nanson, C.
Hollands, M.
Coleman, and D.
M. Price
Eolian Pleistocene Nogging
Plus
250 Common
Offset
4 2D Ground-penetrating
radar (GPR) imaging
of the internal
structure of an active
parabolic sand dune
2007 C. H.
Hugenholtz, B. J.
Moorman, and S.
A. Wolfe
Table A3 continued
265
Glacio-fluvial Pleistocene GSSI SIR-
10A
300 Both 10 3D Three-dimensional
GPR analysis of
various Quaternary
gravel-bed braided
river deposits
(southwestern
Germany)
2003 J. Heinz and T.
Aigner
Estuarine Pleistocene Nogging 250 Common
Offset
8 2D GPR investigation of
multiple stage-5 sea-
level fluctuations on
a siliciclastic
estuarine shoreline,
Delaware Bay,
southern New Jersey,
USA
2003 Michael L.
O'Neal and
Richard K. Dunn
Coastal Pleistocene PulseEKKO 100 Both 18 3D 400 A GPR analysis of a
Quaternary
stratigraphy at the
coast of Rio de
Janeiro
2007 Maria C. Pessoa
and Jandyr M.
Travassos
Table A3 continued
266
Glacial Pleistocene Ramac
Unshielded
100 Both 5 2D GPR images of
periglacial slope
deposits beneath peat
bogs in the Central
European Highlands,
Germany
Matthias
Leopold and
Joerg Voelkel
Coastal Pleistocene PulseEKKO 50 Both 25 2D GPR stratigraphy
used to infer
transgressive
deposition of spits
and a barrier, Lake
Bonneville, Stockton,
Utah, USA
2003 Derald G. Smith,
Christopher J.
Simpson, Harry
M. Jol, Richard
A. Meyers, and
Donald R.
Currey
Glacial Pleistocene GSSI SIR-2 100 Common
Offset
5 2D GPR-based detection
of Pleistocene
periglacial slope
deposits at a shallow-
depth test site
2007 Rolf Gerber,
Christina Salat,
Andreas Junge,
and Peter Felix-
Henningsen
Glacial Pleistocene Common
Offset
2D Structure of a
Pleistocene push
moraine revealed by
GPR; the eastern
Veluwe Ridge, the
Netherlands
2003 Marcel A. J.
Bakker and Jaap
J. M. van der
Meer
Table A3 continued
267
Glacial Pleistocene PulseEKKO 50 Both 15 2D Morphology and
GPR stratigraphy of a
frontal part of an end
moraine of the
Laurentide ice sheet;
Paris Moraine near
Guelph, ON, Canada
2006 S. Sadura, I. P.
Martini, A. L.
Endres, and K.
Wolf
Carbonate Pleistocene Unknown 100 Both 6 3D 1104 3D GPR reveals
complex internal
structure of
Pleistocene oolitic
sandbar
2002 Mark Grasmueck
and Ralp Weger
Carbonate Pleistocene Unknown 250 5 3D 350 Karst and Early
Fracture Networks in
Carbonates, Turks
and Caicos Islands,
British West Indies
2007 Sean A. Guidry,
Mark
Grasmueck,
Daniel G.
Carpenter,
Andrew M.
Gombos, Jr.,
Steven L.
Bachtel, and
David A.
Viggiano
Table A3 continued
268
Coastal Pleistocene Ramac
Unshielded
200 Both 8 2D Significance of
shallow seismic
reflection (SSR) and
ground penetrating
radar (GPR) profiling
on the Modern Coast
line History of the
Bedre Area, Eğirdir
Lake, Isparta, Turkey
2010 Z. Kanbur, M.
Gormus, S.
Kanbur, Z.
Durhan
Carbonate Pleistocene GSSI
SIR10A
100 Both 8 2D Application of
ground-penetrating
radar, digital optical
borehole images, and
cores for
characterization of
porosity hydraulic
conductivity and
paleokarst in the
Biscayne aquifer,
southeastern Florida,
USA
2004 Kevin J.
Cunningham
Table A3 continued
269
Fluvial Pleistocene GSSI SIR-
20
200 Common
Offset
8 2D Fluvial
geomorphology and
neotectonic activity
based on field and
GPR data, Katrol hill
range, Kachchh,
Western India
2007 A.K. Patidar,
D.M. Maurya,
M.G. Thakkar,
L.S. Chamyal
Volcaniclastic Pleistocene GPR Zond
12c
300 Common
Offset
5 2D Correlation of near-
surface stratigraphy
and physical
properties of clayey
sediments from
Chalco Basin,
Mexico, using
Ground Penetrating
Radar
2003 Dora Carreón-
Freyre, Mariano
Cerca, Martín
Hernández-
Marín
Table A3 continued
270
Coastal Pleistocene PulseEKKO 50 Both 20 2D Late Quaternary
stratigraphy and sea-
level history of the
northern Delaware
Bay margin, southern
New Jersey, USA:: a
ground penetrating
radar analysis of
composite
Quaternary coastal
terraces
2002 Michael L.
O’Neal, Susan
McGeary
Coastal Pleistocene PulseEKKO 900 Both 3 2D Sedimentology of
coarse-clastic beach-
ridge deposits, Essex,
southeast England
2003 Adrian Neal,
Julie Richards,
Ken Pye
Deltaic Pleistocene PulseEKKO 25 Both 57 2D Ground penetrating
radar: antenna
frequencies and
maximum probable
depths of penetration
in Quaternary
sediments
1995 Derald G. Smith,
Harry M. Jol
Table A3 continued
271
Glacio-fluvial Pleistocene Oyo
Georadar 1
250 Both 15 2D Ground-probing radar
as a tool for
heterogeneity
estimation in gravel
deposits: advances in
data-processing and
facies analysis
1994 Peter
Huggenberger,
Edi Meier,
André Pugin
Glacio-fluvial Pleistocene GSSI SIR
10A
100 Common
Offset
10 2D Contribution of
geophysics to the
study of alluvial
deposits: a case study
in the Val d'Avaray
area of the River
Loire, France
2003 Jean-Christophe
Gourry,
Francoise
Vermeersch,
Manuel Garcin,
Denis Giot
Glacio-fluvial Pleistocene GSSI SIR
10A
300 Common
Offset
8 Both 308 Towards realistic
aquifer models:
three-dimensional
georadar surveys of
Quaternary gravel
deltas (Singen Basin,
SW Germany)
1999 U. Asprion, T.
Aigner
Table A3 continued
272
Glacio-fluvial Pleistocene Ramac
Unshielded
100 Common
Offset
20 2D Sequence
stratigraphy in a
marine moraine at the
head of
Hardangerfjorden,
western Norway:
evidence for a high-
frequency relative
sea-level cycle
2004 Stein Kjetil Helle
Glacio-fluvial Pleistocene GSSI SIR
10
300 Common
Offset
10 2D Sedimentology and
ground-penetrating
radar characteristics
of a Pleistocene
sandur deposit
1995 Henrik Olsen,
Frank Andreasen
Coastal
Barrier
Pleistocene GSSI SIR 3 120 Common
Offset
12 2D Evidence for storm-
dominated early
progradation of
Castle Neck barrier,
Massachusetts, USA
2004 Amy J.
Dougherty,
Duncan M.
FitzGerald, Ilya
V. Buynevich
Table A3 continued
273
Alluvial Fan Pleistocene GSSI SIR
2000 &
GSSI SIR
3000
100 Both 10 2D 3-D architecture,
depositional patterns
and climate triggered
sediment fluxes of an
alpine alluvial fan
(Samedan,
Switzerland)
2010 J. Hornung, D.
Pflanz, A.
Hechler, A.
Beer, M.
Hinderer, M.
Maisch, U. Bieg
Glacio-fluvial Pleistocene Unknown 200 Both 12 2D Controls on the
sedimentary
architecture of a
single event englacial
esker:
Skeiðarárjökull,
Iceland
2008 Matthew J.
Burke, John
Woodward,
Andrew J.
Russell, P. Jay
Fleisher, Palmer
K. Bailey
Deltaic Pleistocene GSSI SIR
2000
100 Both 9 2D 3-D sedimentary
architecture of a
Quaternary gravel
delta (SW-Germany):
Implications for
hydrostratigraphy
2005 Boris Kostic,
Andreas Becht,
Thomas Aigner
Table A3 continued
274
Glacio-fluvial Pleistocene 200 Both 10 2D Aquifer
characterisation using
Surface NMR jointly
with other
geophysical
techniques at the
Nauen/Berlin test site
2002 Ugur Yaramanci,
Gerhard Lange,
Marian Hertrich
Glacio-fluvial Pleistocene Oyo
Georadar 1
250 Both 10 2D Ground-probing radar
as a tool for
heterogeneity
estimation in gravel
deposits: advances in
data-processing and
facies analysis
1994 Peter
Huggenberger,
Edi Meier,
André Pugin
Deltaic Pleistocene Ramac
Unshielded
100 Common
Offset
8 2D An integrated
geophysical
investigation of the
hydrogeology of an
anisotropic
unconfined aquifer
2002 S. K. Sandberg,
L. D. Slater, R.
Versteeg
Table A3 continued
275
Glacio-fluvial Pleistocene GSSI SIR-
10A
300 Both 8 3D 975 Morphology and
sedimentology of a
giant supraglacial,
ice-walled,
jökulhlaup channel,
Skeiðarárjökull,
Iceland: implications
for esker genesis
2001 A. J. Russell, Ó.
Knudsen, H.
Fay, P. M.
Marren, J. Heinz,
J. Tronicke
Alluvial Fan Pleistocene PulseEKKO 100 Common
Offset
5 2D Relationship between
extensional tectonic
style and the
paleoclimatic
elements at Laguna
El Fresnal,
Chihuahua Desert,
Mexico
1999 J. O. Campos-
Enriquez, J.
Ortega-Ramírez,
D. Alatriste-
Vilchis, R. Cruz-
Gática, E.
Cabral-Cano
Carbonate Unknown Ramac
Unshielded
400 Both 4 2D Application of
deterministic
deconvolution of
ground-penetrating
radar data in a study
of carbonate strata
2004 Jianghai Xia,
Evan K.
Franseen,
Richard D.
Miller, Thomas
V. Weis
Table A3 continued
276
Gypsum Unknown GSSI
SIR10A
500 Common
Offset
7 2D GPR and seismic
imaging in a gypsum
quarry
2000 Xavier Dérobert,
Odile Abraham
Alluvial Fan Unknown Unknown 25 Both 40 2D Assessing fault
displacement and off-
fault deformation in
an extensional
tectonic setting using
3-D ground-
penetrating radar
imaging
2009 M. Christie, G.P.
Tsoflias, D.F.
Stockli, R. Black
Carbonate Unknown PulseEKKO 50 Common
Offset
5 2D Ground penetrating
radar imaging of cap
rock, caliche and
carbonate strata
2000 S. E. Kruse, J. C.
Schneider, D. J.
Campagna, J. A.
Inman, T. D.
Hickey
Fluvial Unknown Unknown 200 Common
Offset
5 3D 1670 Results of 3-D
georadar surveying
and trenching the San
Andreas fault near its
northern landward
limit
2003 Alan Green, Ralf
Gross, Klaus
Holliger,
Heinrich
Horstmeyer,
John Baldwin
Table A3 continued
277
Carbonate Unknown 200 Both 8 3D 110 GPR imaging of
dual-porosity rocks:
Insights to fluid flow
2008 Georgios P.
Tsoflias
Architecture and
evolution of a fjord-
head delta, western
Vancouver Island,
British Columbia
2004 Jeffrey E.
Gutsell, John J.
Clague, Melvyn
E. Best, Peter T.
Bobrowsky, Ian
Hutchinson
Fluvial PulseEKKO 100 Both 8 2D Radar signatures and
structure of an
avulsed channel:
Rhône River, Aoste,
France
1997 Michael C.
Roberts, Jean-
Paul Bravard,
Harry M. Jol
Table A3 continued
278
Nu
mb
er o
f p
ub
lish
ed G
PR
stu
die
s
Nu
mb
er o
f p
ub
lish
ed G
PR
stu
die
s
A
B
Figure A7: (A) Analyses of 150 published GPR studies on sediments showing bias for Quaternary sediments (B) Analysis of studies in (A) showing comparatively more GPR studies on carbonate rocks than clastics
279
Appendix 4
GPR Data Processing Software and Display
Various GPR processing are now commercially available; although many GPR users still use
seismic data processing software (such as VISTA, ProMax 3-D) for GPR data processing after
conversion of GPR data to SEGY (seismic software compatible) format.
The major GPR product manufacturers (Sensors and Software, GSSI, Mala Geoscience) have
developed software for processing data obtained with their products although many of these
applications do not accept data format generated by GPR equipment from other manufacturers
(except GPR data converted to SEGY format). Data acquired with Sensors and Software systems
are usually processed with the PulsEkko or Noggin processing system including data view, data
processing and 3D visualization modules. GSSI GPR equipment are typicallly processed with
RADAN software while GPR equipment from Mala Geoscience are processed with
RadExplorer. Few other commercially available software like Reflex W from Sandmeier
Scientific Software and GPR-Slice software can be used to process data from most GPR
equipment manufacturers without the need for data conversion. Many GPR users do export
processed GPR data into 3D data visualization software such as Gocad, petrel, Slicer Dicer, Easy
3D, Stratimagic 3-D due to their advanced visualization capability.
For this study, ReflexW was used for GPR processing as it has robust data processing features
and GPR-Slice software used for 3D data visualization and interpretation.
280
Appendix 5
GPR profiles from study locations
Figure A8: (A) GPR line AB in grayscale (B) Bounding surfaces and architectural elements in radar line AB (SC – Scour; SB – Sandy Bedform ;St – Trough cross—bedded sandstone ; Sp – Planar coss-bedded sandstone)
6th Order surface 5th order surface 3rd order surfcas
Sp
St
St Sp
Sp
Amplitude Scale
Low
High
A
B
SC
SB
SB
6
Queenston Shale
5 m
0
3
2
1
Depth (m
)
3 m
281
Figure A8: (A) GPR line 136, 137 and 138 from Big Mesa (Utah) showing major radar facies – see GPR line location in Figure 40
Interdune wavy beds
Interdune freshwater carbonates
Dune flank damp phase deposit
Dry phase dune
Wet interdune carbonate
Line 136
Line 137
Line 138
Duine flank damp phase deposit
Wet interdune carbonate