fine scale 3d architecture of a deepwater channel complex, carbon county, south-central wyoming

UNIVERSITY OF OKLAHOMA

GRADUATE COLLEGE

FINE SCALE 3D ARCHITECTURE

OF A DEEPWATER CHANNEL COMPLEX,

CARBON COUNTY, SOUTH-CENTRAL WYOMING

A THESIS

SUBMITTED TO THE GRADUATE FACULTY

In partial fulfillment of the requirements for the

degree of

Master of Science

(Geology)

By

Staffan Kristian Van Dyke

Norman, Oklahoma

2003

FINE SCALE 3D ARCHITECTURE

OF A DEEPWATER CHANNEL COMPLEX,

CARBON COUNTY, SOUTH-CENTRAL WYOMING

A THESIS APPROVED FOR THE

SCHOOL OF GEOLOGY AND GEOPHYSICS

BY

Chair:

Dr. Roger Slatt

Member:

Dr. Douglas Elmore

Member:

Dr. Roger Young

ACKNOWLEDGEMENTS

I would like to extend an overwhelming appreciation and special thanks to my

advisor, Roger Slatt, for guiding me through this project as well as giving me

invaluable insight over the course of writing this thesis and during my 3 year stay at

the University of Oklahoma. Thanks for believing in me, Roger.

I would also like to extend appreciation to my committee members, Douglas

Elmore and Roger Young. They have not only provided valuable insight into the

project, but have also been very understanding with all the problems encountered at

the end of thesis writing. I thank Ozzie Ilaboya for all the help and advice regarding

GOCAD™, without whom, none of this would have been possible.

All teachers and fellow graduate students at the University of Oklahoma are

also thanked, and their memory will forever be burned into my conscious – thanks for

everything. A particular thanks goes to my field assistants, Andria Parker and Ash

Hall.

Lastly, I would like to thank my family, Gene, Astrid, and Tor Van Dyke.

This work is dedicated to them, in particular, to my mother for being the best mom in

the world and always being there for me when I needed somebody. I love you mom

and you will always be number one in my book.

TABLE OF CONTENTS

Acknowledgements…………………………………………………………….……..iv

Table of Contents…………………………………………………………………......v

List of Figures……………………………………...……………………………….....x

List of Appendices......................................................................................................xiii

Abstract…………………………………………………………………………...…xiv

CHAPTERS PAGE

1.

INTRODUCTION…………………………………………………………………….1

Research Objectives…………………………………………...………1

Significance……………………………………………………...…….1

Location of Study Area and Description of Outcrop………..……..….3

Geologic Overview……………………………………….….……..…6

Lithostratigraphy and Sequence Stratigraphy………………………..10

Lewis Shale Petroleum System……………………………….……...12

Previous Studies……………………………………………………...13

Data Collection………………………………………………………15

Data Analysis………………………………………………………...18

3-Dimensional GOCAD™ Model…………………………………...19

2. LITHOFACIES DESCRIPTION…………………………………………….…..20

Introduction…………………………………………………………..20

Lithofacies Types………………………………………………….....20

Lithofacies 1 (F1): Structureless to Cross-Bedded

Sandstone with Water-Escape Structures……………............22

Physical Description…………………………………….…...22

Hydrodynamic Interpretation…………………………….......23

Lithofacies 2 (F2): Structureless Sandstone

without Water-Escape Structures…………………….............24

Physical Description…………………………………………24

Hydrodynamic Interpretation………………………………...25

Lithofacies 3 (F3): Cross-Bedded Sandstones

without Water-Escape Structures ……………........................27



Lithofacies 4 (F4): Parallel to Subparallel Laminae……....................28



Lithofacies 5 (F5): Rippled or Climbing-Ripple Sandstone…............30

Physical Description…………………………………….…...30

Hydrodynamic Interpretation…………………………...……31

Lithofacies 6 (F6): Shale or Mudstone……………………................32



Lithofacies 7 (F7): Shale-Clast Conglomerates……………...............34



Lithofacies 8 (F8): Slump Beds……………………………...............37



3. ENVIRONMENT OF DEPOSITION AND FACIES RELATIONSHIPS..……..39

Introduction……………………………………………………………..........39

Interpretations………………………………………………………………..40

E1: Non-sinous (Straight) leveed-channel environment……………………..42

Interpretation…………………………………………………………42

Facies Relationship…………………………………………………..42

E2: Outer-side of sinuous channel bend………….……………….................43

Interpretation…………………………………………………............43

Facies Relationship………………………………………............…..44

E3: Inner-side of sinuous channel bend…………………………............…...45

Interpretation…….……………………………………............……...45

Facies Relationship……………………………………............……..46

E4: Proximal levee………………………………..……………….................47

Interpretation……………………………………………............……47

Facies Relationship………………………………………............…..50

E5: Distal levee…………………………………………………............……51

Interpretation…………………………………………............….…...51

Facies Relationship……………………………………............……..52

4. 3D MODEL DESCRIPTION AND INTERPRETATION…………………..…...53

Introduction…………………………………………………………………..53

Viewing the Data……………………………………………............……….55

Channel-Fill Sandstone 1……………………………………............….........58

Vertical and Lateral Geometry……………………............……..…...60

Lithologic Stacking Patterns and Locations………............……..…..61

Interpretation…………………………………………............…..…..65

Subsurface………………………………………............………..…..65

Channel-Fill Sandstone 2…………………………………............……….....71

Vertical and Lateral Geometry…………………………............….....72

Lithologic Stacking Patterns and Locations……………..............…..72

Interpretation……………………………………………..............…..74

Channel-Fill Sandstone 3……………………………………….....................74

Vertical and Lateral Geometry…………………………............….....75

Lithologic Stacking Patterns and Locations……………..............…..75

Interpretation…………………………………………............…..…..77

Channel-Fill Sandstone 4………………………………………............….....77

Vertical and Lateral Geometry…………………………….................79

Lithologic Stacking Patterns and Locations………………............…79

Interpretation…………………………………………............………81

Channel-Fill Sandstone 6………………………………………............….....83

Vertical and Lateral Geometry…………………………….................83

Lithologic Stacking Patterns and Locations…………............………85

Interpretation……………………………………………............……85

Channel-Fill Sandstone 7………………………............………………….....87

Vertical and Lateral Geometry…………………............………….....87

Lithologic Stacking Patterns and Locations………............…………88

Interpretation……………………………………............……………88

Channel-Fill Sandstone 8……………………………………............…….....90

Vertical and Lateral Geometry………………………............…….....90


Interpretation…………………………………………............………93

Channel-Fill Sandstone 9……………………………………............…….....94

Vertical and Lateral Geometry……………………............……….....95


Interpretation……………………………………………............……95

Channel-Fill Sandstone 10…………………………………............………...97

Vertical and Lateral Geometry………………............…………….....97

Lithologic Stacking Patterns and Locations………............…………98

Interpretation………………………………………............…………98

5. CONCLUSIONS……….…….……………………………………………….....100

6. REFERENCES CITED…………………………………………………………..105

APPENDICES………………………………………………………………………CD

FOLDER Detailed Measured Sections in Digital Format………………………DMS

Gamma-Logs of Eight Shallow Boreholes…………………………..BHGL

Copy of Thesis Text…………………………………………………THESIS

GOCAD™ Data Files……………………………………………….GOCAD

SUBFOLDER D1. Raw Data…………………………………………………RD

D2. Channel-Fill Sandstone 1……………………………….CFS01









D11. Channel-Fill Sandstone 10..…………………………….CFS10

D12. Digital Elevation Map……………………………………DEM

D13. Quickview………………………………………………….QV

LIST OF FIGURES

FIGURE PAGE

Fig. 1.01: Chronostratigraphic chart of Upper Cretaceous strata, southern

Wyoming……………………………………………………….…………… ..2

Fig. 1.02: Shaded relief map of Wyoming and Washakie

Basin………………………………….………...……………….…………….3

Fig. 1.03: Topographic map of Spine 1 and Spine 2…….……………………………5

Fig. 1.04: Spine 1 with 9 channel-fill sandstones with detailed measured

sections colored black; overlain on topographic contours (Generated in

GOCAD™ v.2.0.6, 003)……………….……………………………………...5

Fig. 1.05: Cretaceous Western Interior Seaway .……………………….……………..6

Fig. 1.06: Paleogeographic Map for Lower Maastrichtian time…..….……………….7

Fig. 1.07: Major geologic features surrounding field area..……………..…………….9

Fig. 1.08: Lewis Shale Stratigraphic Column.………………………...….………….11

Fig. 1.09: Initial work characterizing the Dad Sandstone Member..……….………..14

Fig. 1.10: Example of detailed measured section produced for thesis research ……16

Fig. 1.11: Channel-fill boundary nomenclature……..…………………………...…..17

Fig. 2.01: Classic Bouma Sequence deposits………..……………………………….21

Fig. 2.02: “Knobby” texture interpreted as weathered vertical/subvertical

dewatering pipes……………………………………………………………..22

Fig. 2.03: Dewatering pipes located at the top of Channel-fill Sandstone 1………...23

Fig. 2.04: Structureless Sandstone with geologically unrelated holes

pockmocking surface of Channel-fill Sandstone 3….……..………………...24

Fig. 2.05: Temporal and Spatial relations in flow environments.....…………………25

Fig. 2.06: Walker’s (1978) classification of deepwater deposits….…………………26

Fig. 2.07: Lowe (1982) classification of High Density Turbidity Current

(HDTC) and Low Density Turbidity Current (LDTC)………………………26

Fig. 2.08: Low-angle, high amplitude crossbedding from Channel 1……… …..…..27

Fig. 2.09: Planar laminae on outcrop exposure on Channel-fill Sandstone 6….…….29

Fig. 2.10: Planar laminae located in Channel-fill Sandstone 1……………… …...…29

Fig. 2.11: Climbing-Ripple Facies located in Channel-fill Sandstone 6………..…...31

Fig. 2.12: Climbing-ripple facies description……………………………………......32

Fig. 2.13: Shale/mudstone facies bounded by structureless sandstone facies……….33

Fig. 2.14: Stacked shale-clast conglomerates (A) interbedded with

turbidites (B) on Channel-fill Sandstone 1……..……………………………35

Fig. 2.15: Faint imbrication of shale clasts occur in Channel-fill Sandstone 1……...35

Fig. 2.16: Debris Flow Rheology……………..………………………..……….……36

Fig. 2.17: Slump beds bounded in yellow from Channel-fill Sandstone 1 “Prong.”...37

Fig. 3.01: Enviroments of Deposition (E) 1-5 contained within

a leveed-channel system ………......……………………..………………….39

Fig. 3.02: Situations leading to different flow behaviors…………..………….……..40

Fig. 3.03: Planform view of flow movement within a leveed-channel system……....41

Fig. 3.04: Flow movement within a sinuous channel-bend...…………..……………41

Fig. 3.05: 3D seismic horizon slice……………………..…………………………....44

Fig. 3.06: Sinuous submarine channel-fill deposit localities………………………...45

Fig. 3.07: Oblique depositional strike view of Channel-fill Sandstone 1…………....46

Fig. 3.08: Environments of deposition of Channel-fill Sandstone 4………………....48

Fig. 3.09: Proximal levee with convoluted bedding and climbing ripples

associated with Channel-fill Sandstone 4……………………..……………..49

Fig. 3.10: Proximal levee with nice set of climbing ripples associated

with Channel-fill Sandstone 4…………………………………….…………50

Fig. 3.11: Distal levee deposits from Channel-fill Sandstone 4…...…..…….………51

Fig. 4.01: 3D GOCAD™ model of Dad Sandstone Member,

Lewis Shale; “Prong” region of Channel-fill Sandstone 1

circled in red; brown represents “Outcrop Plane,” while other colors

represent “Outcrop Face” of the nine channel-fill sandstones..……..…….…55

Fig. 4.02: Planview basemap of nine stacked channel-fill sandstones...…….....……57

Fig. 4.03: Channel-fill Sandstone 1 location in Field Area...……………...…..…….58

Fig. 4.04: Locations of detailed measured sections on

Channel-fill Sandstone 1 (1.01 – 1.22) ……...……………………………...59

Fig. 4.05: Plan view map of surface outcrop dimensions of

Channel-fill Sandstone 1 …………………………………………………….60

Fig. 4.06: “Prong;” located in the eastern region of Channel-fill……………………62

Fig. 4.07: Shale-clast conglomerate facies found in northern-most

portions of Channel-fill Sandstone 1 model……..…………………………..63

Fig. 4.08: Western-most flank of Channel-fill Sandstone 1 ends at MS# 1.0.1.… …64

Fig. 4.09: Boreholes (1-8) with locations of dip (green; 5-3-6)

and strike (white; 1-2-3-4) cross-sections, located on eastern

flank of Channel-Fill Sandstone 1 ………………………...………………...66

Fig. 4.10: Example of gamma-ray log from Borehole 1…...……………….………..67

Fig. 4.11: Dip cross-section of Boreholes 5-3-6 of Channel-Fill Sandstone 1…....…68

Fig. 4.12: Strike cross-section of Boreholes 1-2-3-4 of Channel-Fill Sandstone 1.…69

Fig. 4.13: Electro-Magnetic Induction and GPR (3-B to 3-B’)

carried out on eastern flank of Channel-Fill Sandstone 1….……………...…70

Fig 4.14: Ground-Penetrating Radar facies located in the subsurface

of Channel-Fill Sandstone 1 …………………………………….…….…….71

Fig. 4.15: Location and number of detailed measured sections (black)

with outcrop dimensions (red) on Channel-fill Sandstone 2………..…….…71

Fig. 4.16: F7, shale-clast conglomerates and F3, crossbedded sandstone,

located on Channel-fill Sandstone 2…..……………………………..………73


with outcrop dimensions (red) on Channel-fill Sandstone 3…………..…….74

Fig. 4.18: Diagnostic facies of Channel-fill Sandstone 3...………………….....……76

Fig. 4.19: Location of Channel-fill Sandstone 4 on Spine 1……………..……....…77

Fig. 4.20: Location and number of detailed measured sections(black)

with outcrop dimensions (red) on Channel-fill Sandstone 4………….…..…78

Fig. 4.21: Diagnostic facies located on Channel-fill Sandstone 4.………………..…80

Fig. 4.22: Amalgamated channel-fills CFS 4a and CFS 4b,

comprising Channel-fill Sandstone 4………...................................................82


with outcrop dimensions (red) on Channel-fill Sandstone 6……………….83

Fig. 4.24: Diagnostic facies of Channel-fill Sandstone 6.……………………….…85

Fig. 4.25: Amalgamated channel-fills CFS 6a and CFS 6b,

comprising Channel-fill Sandstone 6…........................................................86


with outcrop dimensions (red) on Channel-fill Sandstone 7…………….…87

Fig. 4.27: Diagnostic facies of Channel-fill Sandstone 7…...……………………...89



Fig. 4.29: Diagnostic facies of Channel-fill Sandstone 8…...…………………...…92



Fig. 4.31: Diagnostic facies of Channel-fill Sandstone 9…………………………..96


with outcrop dimensions (red) on Channel-fill Sandstone 10….………..…97

Fig. 4.33: Diagnostic facies Channel-fill Sandstone 10...………………………….99

Fig. 5.01: First generation conceptual model representing channel-fill

sandstones in 3D space (no channel sinuosity recorded)………………….101

Fig. 5.02: Second-generation diagram representing channel-fill

sandstone sinuosity………………………………………………………..102

LIST OF APPENDICES

APPENDIX (LOCATED ON ATTACHED CD) FOLDER

A. Detailed Measured Sections in Digital Format………………………DMS

B. Gamma-Logs of Eight Shallow Boreholes………………………….BHGL

C. Copy of Thesis Text……………………………………….………THESIS

D. GOCAD™ Data Files…………………………………….……....GOCAD

SUBFOLDER

D1. Raw Data…………………………………………………RD










D11. Channel-Fill Sandstone 10..…………………………….CFS10

D12. Digital Elevation Map……………………………………DEM

D13. Quickview…………………………………………………QV

ABSTRACT

Nine channel-fill sandstones comprise a 255ft thick stratigraphic succession in

the deepwater Dad Sandstone Member, Lewis Shale, Wyoming. This succession has

been characterized by measuring 121 closely-spaced outcrop stratigraphic sections,

decimeter-scale GPS-tracing (Global Positioning System) of bed boundaries, drilling

and gamma-logging of 8 shallow boreholes, ground-penetrating radar (GPR), and

electro-magnetic induction (EMI) behind the outcrops. A 3D facies and architectural

model was built using GOCAD TM

.

Each channel-fill sandstone is separated by thin-bedded, very fine

sandstone/mudstone strata. Channel facies include structureless sandstone with fluid

escape structures, structureless sandstone without fluid escape structures, rippled to

climbing rippled sandstone, parallel to subparallel laminated sandstone, cross-bedded

sandstone, shale-clast conglomerate, thin-bedded sandstone/mudstone, and slumped

beds. In separate channel-fill sandstone, these facies can be complexly interbedded,

but there is a tendency for shale-clast conglomerates to comprise the base and one

side of a channel-fill, whereas cross-bedded sandstones comprise the opposite side.

Massive/fluid escape structured sandstones typically occupy the top of these

successions. Proximal to distal levee beds occur adjacent to some of the channel

sandstones.

This distribution of facies, coupled with GPR data, suggests the sandstones

filled sinuous channels. The shale-clast conglomerates are thought to be the product

of slumping of adjacent levee walls from the steeper channel margin, and the cross-

bedded sandstones are interpreted to be in-channel bar or dune forms. These channels

probably fed sand into the deeper basin contemporaneously with levee formation; the

channel-fill sandstones represent the product of later backfilling episodes. The

slumped and erosive nature of some channel margins support this interpretation.

This 3D outcrop characterization provides an excellent, scaled analog for

leveed channel reservoirs. The complex vertical stratigraphy indicates individual

channel sandstones can be mutually isolated reservoirs. The complex internal channel

sandstone distribution indicates internal reservoir fluid flow will also be complex. A

figure illustrating the relation of channel-fill sandstone sinuosity relative to one

another in outcrop has also been created.

Chapter 1

INTRODUCTION

Research Objectives

This thesis research has two main objectives. The first objective is to

document the 3-dimensional surface geometry of nine submarine slope channel

sandstones in outcrops of the Lewis Shale through detailed measured sections and

computer modeling via GOCAD™. The second objective is to correlate channel

facies in 3-D space in order to better document reservoir-scale features of leveed-

channel deposits and their lateral continuity and vertical connectivity. This research

study also attempts to better understand the reservoir aspect of the petroleum system,

i.e., the Dad Sandstone Member of the Upper Cretaceous Lewis Shale in southern

Wyoming (Fig. 1.01).

Significance

The study of submarine slope channel deposits is of great importance for

many different reasons: (1) documenting the facies scale character of channel-fill

sandstones, (2) reservoir characterization for better field development planning, (3)

understanding the progressive evolution of sinuous submarine channels, and (4)

determining the active mechanisms that force sinuosity. This thesis will not solve all

of these problems, but will offer insight into better understanding and documenting

these factors. It is also hoped that the resultant 3D model and its correlations will

help to shed light on expected lateral continuity and vertical connectivity of reservoir

scale facies in analog fields located within other deepwater sinuous channel systems,

such as those found in the deepwater Gulf of Mexico and offshore West Africa.

With the real-scale, outcrop-based 3-dimensional GOCAD™ model, fluid

flow simulation can also be performed and compartmentalization within channel

reservoirs can be modeled. The 3-D model will impact future work on reservoir

characterization within other submarine slope channel complexes around the world.

It is necessary to solve the unknowns in these types of problems by developing better

depositional models from outcrop work, which will have direct bearing on new field

development solutions in the future.

Fig. 1.01: Chronostratigraphic chart of Upper Cretaceous strata, southern Wyoming (Modified

after Schell, 1973).

Location of Study Area and Description of Outcrop

The study area outcrops along the Sierra Madre Uplift in the eastern portion of

the Washakie Basin, south-central Wyoming, Carbon County, within Sections 24 and

25 of T16N R92W (Fig. 1.02). From the town of Baggs, which is located 3 miles

north of the Wyoming-Colorado border, the outcrop can be easily accessed by

traveling 23.5 miles north on Hwy. 789 and approximately 4 miles east on a dirt road

(to the west of the dirt road is a metal quanset hut). The study area is a resistant ridge

referred to as Spine 1, which trends ENE-WSW. Spine 1 and another ridge to the

southeast, called Spine 2, are separated from one another by a 0.5 mile wide modern

floodplain (Fig, 1.03). Spine 2 trends E-W.

Fig. 1.02: Shaded relief map of Wyoming and Washakie Basin (Modified after Sterner,

1997).

This region nicely exposes all 3 successive components of a complete

Lowstand Systems Tract in one place (Witton, 2000); from the base of the outcrop,

there are two sheet sandstones (basin floor fans) overlain by nine leveed channel-fill

sandstones (the subject of this thesis) and then an interval of predominantly mudstone

(prograding complex).

Sinuous leveed-channel systems are formed in the deepwater regions of the

ocean basins. Those described in this text are found on the slope. They are

aggradational channels, i.e., the channel depression is a result of levee aggradation.

Upon sea level rise, these vacant channel depressions become backfilled with

sediment. The channel related sediments are referred to as channel-fill sandstones.

The processes involved with the deposition of channel-fill sandstones are

thought to resemble those of subaerial fluvial systems. Many of the geological

features recognized in subaerial fluvial systems are also recognized in submarine

leveed-channel systems. These features include: 1) inner-side, point-bar style

deposits, 2) outer-side cut-bank style erosion, 3) proximal levee regions, and 4) distal

levee regions.

Nine of these channel-fill sandstones have been identified as comprising Spine

1 and are the main focus of the research (Fig. 1.04). Originally, Witton (2000)

identified 10 separate channel-fill sandstones, but due to more in-depth work using

GPS and GOCAD™ v.2.0.6, sandstone boundaries mapped in 3D space indicate her

Channel-fill Sandstone #5 is actually the western part of Channel-fill Sandstones #2

and #4. As the nomenclature was already deeply entrenched in most of her work, I

have retained the original 1 – 10 designations. Channel-fill Sandstone #5 is no longer

present.

Fig. 1.03: Topographic map of Spine 1 and Spine 2 (from Slatt, 2003).

Fig. 1.04: Spine 1 with 9 channel-fill sandstones with detailed measured sections colored

black; overlain on topographic contours (Generated in GOCAD™ v.2.0.6, 2003)

Geologic Overview

This geologic overview has been modified from Pyles (2000) and Witton

(2000). During the Cretaceous, the Western Interior portion of the United States was

inundated with an elongate, relatively shallow epeiric seaway known as the Western

Interior Seaway (Fig. 1.05). The Western Interior Seaway was bounded on the west

by an active Cordilleran highland, through the modern day states of New Mexico,

Colorado, Wyoming, and Montana, and to the east by the Canadian Shield (Molenaar

and Rice, 1988). It stretched from the Gulf of Mexico to the Northern Boreal Sea

(Krystinik, 1995).

Fig. 1.05: Cretaceous Western Interior Seaway (Reproduced from Witton, 2000)

This Cordilleran Highland system was the main source of terrigenous material

to the Western Interior Cretaceous basin. Due to varying rates of sedimentation and

crustal loading throughout the basin at the time, varying rates of subsidence occurred.

The western portion of the Washakie Basin records thick sequences of marine and

non-marine clastic sediments interfingering with one another, thus representing

marine transgressions and regressions that occurred during late Cretaceous time.

Weimer (1960) indicated four major transgressions and regressions in the

early Upper Cretaceous. This was supported by his work of tracing the main

interfingerings of marine and non-marine clastic sediments, which represented the

paleo-shorelines. Kauffman (1977) suggested ten major transgressions and

regressions. Wiemer’s fourth transgressive-regressive cycle matched Kauffman’s

ninth transgressive-regressive cycle.

Fig. 1.06: Paleogeographic Map for Lower Maastrichtian time (After McGookey et al., 1972)

The final transgression and regression of the late Cretaceous was known as the

Bearpaw transgressive-regressive cycle. It was during this last phase that the Lewis

Shale was deposited in south-central Wyoming (Fig. 1.06). Deposition was largely

controlled by sediment supply, intrabasin tectonics, and eustacy. Active deltas from

the north-northeast and those projecting eastward from the Washakie basin (Hale,

1961) channeled sediments into deeper regions of the basin, particularly those similar

to regions as the study area location. At the time of sediment deposition in the

location of the study area, the water depth was calculated to be as deep as 1450 ft.

based on the decompacted relief of individual clinoforms from Pyles (2000) regional

cross section.

In the lower Maastrichtian, west of the study area, was the Sevier Orogenic

Belt, contained within the Cordilleran Highlands. This was a classic fold-thrust belt

resulting when the Farallone oceanic plate subducted under the continental plate. Just

east of the fold-thrust belt was the foreland basin, and most of Wyoming was

contained within this basin at the time.

During the Laramide Orogeny (Campanian to Paleocene) and its associated

uplifts, the foreland basin was segmented into many local sub-basins, including the

Washakie basin (McMillen and Winn, 1991). The Washakie basin is part of the

Greater Green River Basin, which itself is a product of horizontal compression and

fragmentation of the craton that occurred during the Laramide orogeny (Baars et al.,

1988). Figure 1.07, provided by Baars et al. (1988), shows that the basin is bounded

to the north by the Wamsutter Arch, to the east by the Sierra Madre Uplift, to the

south by the Cherokee Arch, and to the west by the Rock Springs Uplift.

Fig. 1.07: Major geologic features surrounding field area (Baars et al., 1988).

As relative sea-level began to rise, the Lewis Shale was deposited onto a

muddy slope; as sea-level deepened considerably in middle to late Lewis time,

sedimentation into the basin was mainly sourced from deltaic systems. During most

of the early Maastrichtian, basin subsidence rates outlasted rates of sedimentation;

this was due to either 1) subcrustal loading and subcrustal cooling caused by the low

angle subduction of the oceanic crust of the Farallone plate, 2) thermal decay and

crustal contraction, 3) supracrustal loading, or 4) stress-induced subsidence as a result

of tectonic loading (Cross and Pilger, 1978).

Lithostratigraphy and Sequence Stratigraphy

The Lewis Shale Formation can be broken into three informal members: the

Lower Shale Member, the Dad Sandstone Member, and the Upper Shale Member

(Fig. 1.08). The Lewis Shale was formally named by Cross and Spencer (1899) for

exposed thick marine sequences (Gill et al., 1970). The type locality is found east of

Mesa Verde National Park in Fort Lewis, southwestern Colorado. Originally the

name was meant to designate rocks deposited during a regression and transgression of

Campanian age in the San Juan Basin. Later, the name was mistakenly extended to

include rocks of younger regressive- transgressive cycles not even recorded in the San

Juan basin. This nomenclature is inherently wrong and is very confusing, but has

become entrenched in the literature.

Fig. 1.08: Lewis Shale Stratigraphic Column (from Slatt, 2003).

Both the underlying Almond Formation and the overlying Fox Hills

Sandstone interfinger with the Lewis Shale on a regional scale (Gill et al., 1970). The

Lower Shale Member comprises several hundred feet of black shale, while the Dad

Sandstone Member is composed of interbedded shale and sandstone, ranging in

thickness from 300 to 700 feet. The upper shale member is generally dark to olive

gray, silty to sandy, nonresistant, and locally contains fossiliferous limestone or

siltstone concretions (Gill et al., 1970).

McMillen and Winn (1991) studied well log and seismic reflection data. They

concluded that the Lower Shale Member was deposited as part of a 3rd

order

transgressive systems tract, while the Dad Sandstone Member and the Upper Shale

Member were deposited as part of the ensuing 3rd

order highstand systems tract.

Pyles’ (2000) work, the most comprehensive to date, detailed the region within a

fourth-order sequence stratigraphic framework. Pyles showed that although the

broader, more extensive third-order cycle existed, there in fact are many fourth-order

cycles of aggradation and progradation within the 3rd

order cycle. This work showed

the valuable use and wealth of knowledge gained from a high-order sequence

stratigraphic framework approach to an area.

Lewis Shale Petroleum System

Three major components to any petroleum system are: 1) source, 2) reservoir,

and 3) trap/seal. The source is defined as strata of high organic carbon (C) content; a

high total-organic-carbon (TOC) percentage is necessary for the generation of

kerogen, the precursor to hydrocarbons. If hydrocarbons are generated, there must be

a reservoir to house them. The reservoir can be any lithology with porosity and

permeability, e.g., limestone, sandstone, and siltstone. In order for these

hydrocarbons to be trapped, they must collect under some sort of trap or seal.

Stratigraphically this component is usually an impermeable lithology that seals the

hydrocarbons, or in structural traps, confines the hydrocarbons by a variety of means,

e.g. fault seals.

The Lewis Shale within south-central Wyoming is an unconventional gas

reservoir with an estimated 24 TCF of gas in place, with 10.7 TCF recoverable

(Doelger and Barlow, 1997). The Federal Energy Regulatory Commission designated

the formation as a tight gas sand (Winn et al., 1985). As of 1997, only 6% of the total

reserves had been produced, thus leaving much room for new unconventional

development concepts to exceed the production capabilities of reservoirs.

There is a third-order condensed section near the top of the Lower Lewis

Shale comprised of organic-rich shale known as the Asquith Marker; it ranges in

thickness from thirty to eighty feet. It is generally believed by most who work this

region, that the Asquith Marker is the most likely source-rock of the Lewis Shale

Petroleum System (Slatt, Lewis Consortium field notes, 2001).

The reservoir-prone lithology of the Lewis Shale petroleum system is the Dad

Sandstone Member. The hydrocarbon seals for this petroleum system consist of

bentonite clays and shales (Slatt, Lewis Consortium field notes, 2001).

Previous Studies

In 2000, work was completed in the field area by Elizabeth Witton (Witton,

2000). Her work characterized the field area by delineating the northernmost ridge,

Spine 1, into its constituent parts: the lowermost two sheet sandstone bodies, the

originally interpreted 10 separate channel sandstone bodies, and fourteen units within

the overlying prograding complex (Fig. 1.09). Her work, which included outcrop

interpretation and descriptions, was instrumental in setting up the basis for this

research. Witton classified four separate lithofacies: A) continuous thick-bedded

sandstones, B) discontinuous thick-bedded sandstones with rip-up clasts, C) thin-

bedded sandstones, and D) thin-bedded, laminated mudstones and shale.

Her work also involved the recognition of facies in a borehole image log from a

well drilled through the same stratigraphic interval about 8 miles away. This work

was accomplished by first describing detailed measured sections of the outcrop to

recognize and categorize the four different facies. The facies were then correlated to

sedimentary features identified on the image log. More recently, Slatt et al. (2002)

and Pyles and Slatt (2002) have provided evidence suggesting the channel sandstones

are leveed-channel deposits similar to those that produce hydrocarbons in many

deepwater settings (Abreau, 2002).

Fig. 1.09: Initial work characterizing the Dad Sandstone Member (Witton, 2000)

Data Collection

The succession of the nine stacked leveed channel-fill sandstones was

characterized by 121 closely-spaced, detailed, measured sections, dm-scale GPS-

tracing of bed boundaries, outcrop gamma-logging with a handheld scintillometer,

drilling/gamma-logging of 8 shallow boreholes, ground-penetrating radar (GPR)

behind outcrop, and Electro-Magnetic Induction (EMI). The GPR and EMI data were

not used in this thesis as they form parts of other thesis research at University of

Oklahoma. Lateral variations within each channel-fill sandstone were noted in the

field and at these points detailed measured sections were emplaced and described.

Enough detailed measured sections were completed so that all lateral variations

within each channel-fill sandstone outcrop were recorded.

The sections were measured using a Brunton Compass and a Jacob Staff. This

method was carried out for each channel-fill sandstone, with measured sections

ranging from as many as 26 for Channel-fill Sandstone 1 to as few as 6 for smaller

channel-fill sandstones, such as Channel-fill Sandstone 9 (Fig. 1.10). These

measured sections range in thickness from 2ft to 34ft. All 121 detailed measured

sections are cataloged on the CD in Appendix A.

Trimble ™ GPS units were used to delineate 3-D geometry of outcrops and to

accurately locate detailed measured sections in 3-D space. GPS “Line

Measurements” of bed boundaries were recorded in the field to best represent the 3-

dimensional nature of the outcrop (Fig. 1.11). Walking the three lines: 1) Base, 2)

Outside Top, and 3) Subsurface Top, provided two planes: 1) Outcrop Face and 2)

Outcrop Plane. “Outcrop Face” and “Outcrop Plane” were constructed in GOCAD™

allowing the raw data to portray the nine channel-fill sandstone bodies in their basic

morphological structure as seen on Spine 1 (Fig. 1.04). Along with all of the channel-

fill sandstone data, a topographic map was digitized and corrected for elevation. This

was than input into GOCAD™ as a pseudo-DEM (Digital Elevation Map).

Fig. 1.10: Example of detailed measured section produced for thesis research (located in CD as

Appendix A).

Fig. 1.11: Channel-fill boundary nomenclature

.

A handheld gamma-ray scintillometer was used to record the natural gamma

radiation of the channel-fill sandstones at all of the measured stratigraphic sections

(Slatt et al., 1995). A complete log profile of each measured section within every

channel sandstone was input into digital format for comparison with outcrop

measured sections (Appendix A). Eight shallow boreholes were also drilled and

gamma-logged for the lowermost Channel-fill Sandstone 1.

Data Analysis

Channel-fill sandstones 1 through 10 were mapped with the dm-scale Trimble

™ GPS units and detailed measured sections were completed on all nine channel-fill

sandstones. Enough of these detailed measured sections were obtained so that a very

accurate representation of all channel-fill sandstones on Spine 1 and all of their

internal facies characteristics were attained to build a 3D geologic model in

GOCAD™.

Each of the eight gamma-logged boreholes was input into digital format and

was interpreted for its internal lithology based on the merits of its gamma-log pattern

as well as cuttings from the borehole. The boreholes were then interpreted with both

strike and dip direction cross-sections, thus gaining valuable insight on the character

of subsurface facies within Channel 1 in a region where speculation was very high

and outcrop exposure very poor.

Additional work has been carried out by Dr. Roger Young and Ph.D. student

Julie Staggs who use GPR (Ground-Penetrating Radar) techniques to document the

shallow subsurface character of Channel Sandstone 1 (Young et al., in press), Dr.

Alan Witten and M.S. student Ryan Stepler used Electro-Magnetic Induction (EMI)

techniques to document the subsurface character of the sandstone and shale within the

eastern-most flank of the lowermost channel-fill sandstone. Most of Dr. Young’s and

Julie Stagg’s work on Spine 1 is focused primarily on Channel-fill Sandstone 1.

Some of their work will be incorporated within later chapters of the thesis since their

techniques have the means of tracking channel geometry in the subsurface.

3-Dimensional GOCAD ™ Model

A 3-Dimensional GOCAD ™ model has been designed to capture the

channel-fill sandstone outcrop geometry and internal fill architecture with 3-

Dimensional facies correlation through regions within the outcrop. The measured

sections were the basis for this correlation. Bed boundaries, recorded by the Trimble

™ GPS units, provide the skeletal structure for the model of the channel-fill

sandstones seen in outcrop. The detailed measured sections were input manually into

the model, whereby facies correlations were accomplished. As aforementioned,

Trimble™ GPS units were used to record X,Y,Z points in 3D space along outcrop

boundaries. After daily field work sessions, these data were retrieved and stored in

GPS Pathfinder™ on a laptop computer. Upon arrival back at the University of

Oklahoma, the files were then transferred as text (*.txt) files to GOCAD™ with

proper header format for computer recognition. The data was then capable of being

manipulated and viewed in GOCAD™. Each field day’s work was saved as a

separate file and each file contained its own cache of points in 3D space. These data

had to be meticulously sorted and classified in the GOCAD™ lab to fit points to their

proper channel boundary designations. After all points had been designated to their

proper locations and all channel boundaries had been defined, channel facies were

then input. The channel facies were then correlated to one another in 3D space.

Additional description of the model and its correlations are found in additional

chapters.

Chapter 2

LITHOFACIES DESCRIPTION

Introduction

Previous work performed by Witton (2000) and Slatt et al. (2000, 2001, and

2002) interpret Spine 1 to comprise a sinuous leveed-channel system. The steeper

side of each channel-fill sandstone was interpreted to have abundant debris flow

deposits (represented by facies F7, shale-clast conglomerate facies and the shallower

side was interpreted to contain cross-bedded sandstone) (Witton, 2000). The resultant

3D GOCAD™ model was built to test this interpretation and those offered in the text.

Lithofacies Types

Eight lithofacies were recognized in the field; they are: F1) sandstone with

water-escape structures (some cross-bedded), F2) structureless sandstone (without

water-escape structures), F3) cross-bedded sandstones (without water-escape

structures), F4) parallel to subparallel laminated sandstone, F5) rippled or climbing-

rippled sandstone, F6) shale or mudstone, F7) shale clast conglomerates, and F8)

slumped beds. With the exception of the shale-clast conglomerates (F7) and slump

beds (F8), the facies are fine-grained and well-sorted.

Fig. 2.01: Classic Bouma Sequence deposits (Modified from Jordan et al., 1993)

Three of the eight facies constitute classic Bouma Sequence deposits (Fig.

2.01); they are: F4, F5, and F6. F4, parallel to subparallel laminae is categorized as

Bouma division Tb. Rippled or climbing-rippled sandstone, F5, is interpreted as

Bouma division Tc and is the product of traction of grains along the sea bed during

lower flow regime conditions (Weimer and Slatt, in press). The final facies

categorized within the Bouma Sequence is F6, a shale or mudstone, denoted by Te.

Lithofacies 1 (F1): Structureless to Cross-Bedded Sandstone with Water-Escape

Structures

Physical Description

The structureless to cross-bedded sandstone with water-escape structures

consists of yellowish-tan, fine-grained, well-sorted sandstone. It is the second most

abundant facies. This facies exhibits primary low-angle cross-bedding in some

exposures, and in all of the exposures, secondary water-escape “knobs” (Fig. 2.02).

Water escape structures are common in the upper portions of the outcrop exposures,

particularly in Channel-fill Sandstone 1 (Fig. 2.02 and 2.03). This position within the

channel-fill facies sequence indicates that these sands may have been deposited as

liquefied/fluidized flows.

Fig. 2.02: “Knobby” texture interpreted as weathered vertical/subvertical dewatering pipes.

Fig. 2.03: Dewatering pipes located at the top of Channel Sandstone 1.

Hydrodynamic Interpretation

Sandstones with water-escape structures, such as vertical pipes, are formed by

hindered settling of sediments in a liquefied and/or fluidized flow (Weimer and Slatt,

in press). As the sediment in this facies is finally deposited, water migrates toward

the top of the flow, leaving a cavity in its pathway into which the surrounding

sediments collapse (Fig. 2.06). Because grain size varies within the deposit,

differential cementation occurs, giving rise to surficial differential weathering and the

development of the more resistant “knobs” (Slatt, personal communication, 2003).

Lithofacies 2 (F2): Structureless Sandstones without Water-Escape Structures


Structureless sandstone without water-escape structures are the most abundant

facies within the outcrops (Fig. 2.04). It is a yellowish-tan sandstone. This sandstone

does not exhibit any visible primary or secondary sedimentary structures. Thickness

of this facies can reach significant heights (up to 80% of the channel-fill stratigraphic

column, in some cases up to 24ft) and may represent many separate flow events.

Fig. 2.04: Structureless Sandstone with geologically unrelated holes pockmocking surface of

Channel-fill Sandstone 3.


Structureless sandstones are deposited in only one spatial and temporal flow

condition, steady depletive (Kneller, 1995; Fig. 2.05). Both Walker (Fig. 2.06; 1978)

and Lowe (Fig. 2.07; 1982) differentiated structureless sandstone from Bouma

division Ta. This was based on the interpretation that these sandstones tended to

exhibit: 1) water-escape structures, 2) fewer associated shale interbeds, 3) an increase

in erosionally-based and irregularly bedded sandstone, and 4) sandstone beds that are

thicker than associated beds (Weimer and Slatt, in press).

Fig. 2.05: Temporal and Spatial relations in flow environments (Modified from Kneller, 1995)

Fig. 2.06: Walker’s (1978) classification of deepwater deposits.

Fig. 2.07: Lowe (1982) classification of High Density Turbidity Current (HDTC) and Low

Density Turbidity Current (LDTC).

Lithofacies 3 (F3): Cross-Bedded Sandstones without Water-Escape Structures


This yellowish-tan sandstone is the third most abundant facies. These

deposits tend to manifest low-angle, high amplitude cross-bedding features (Fig

2.08). Many times it is difficult to reveal the low-angle cross-bedding in the field

because of the position of the sun.

Fig. 2.08: Low-angle, high amplitude crossbedding from Channel 1 (from Slatt, 2003).


Primary cross-bedding is formed by sediments that move along the seafloor as

tractive bedload. Traction can be defined as “a mode of sediment transport in which

the particles are swept along (on, near, or immediately above) and parallel to a bottom

surface by rolling, sliding, dragging, pushing, or saltation” (Jackson, 1997). Cross-

bedding is a lower flow regime feature. The low-angle nature of the cross-bedding

indicates that these features were most likely in-channel bar or dune forms (Slatt,

personal communication, 2003). The in-channel barforms are interpreted to lie on the

pointbar-equivalent side of the channel-fill system or upon the channel floor.

Lithofacies 4 (F4): Parallel to Subparallel Laminae


Parallel to subparallel laminae, L4, are found in yellowish-tan, fine-grained,

well-sorted sandstone (Fig. 2.09 and 2.10). The deposit was not found in abundance

in the field. This facies is characterized by parallel to subparallel bedding planes, or

laminations. It occurs within many of the stratigraphically higher channel-fill

sandstone bodies, i.e., Channels 6 – 10.

Fig. 2.09: Planar laminae on outcrop exposure on Channel-fill Sandstone 6.

Fig. 2.10: Planar laminae located in Channel-fill Sandstone 1.


Planar bedding occurs in both the lower and upper flow regime. It exhibits

parallel bedding. For lower flow regime deposits, the flow velocity is very low. This

is a very simple deposit, exhibiting only planar bedding in plan view and horizontal

laminae in side view.

Planar bedding, deposited in upper flow regime conditions, exhibits current

lineations due to the high flow velocity. Current lineations form as concentrations of

heavy minerals align themselves in the direction of flow. In plan view, the current

lineations are visisble, but only the laminae can be seen from the side view.

Figure 2.10 exhibits Bouma division Tb-Tc, categorizing Tb within the lower

flow regime; all F4 deposits in the field are interpreted to be lower flow regime planar

bedding.

Lithofacies 5 (F5): Rippled or Climbing-Ripple Sandstone


Facies F5, exhibits ripples or climbing-ripples in a yellowish-tan sandstone.

This deposit is not abundant within the outcrop exposures, however, nearly all nine

channel-fill sandstone bodies contain this facies. Channel-fill Sandstone 6 contains a

2’2” thick set of climbing-ripples (Fig. 2.11). The climbing-rippled sandstone

includes those with lee slope deposition, as well as those with lee and stoss slope

deposition (Fig. 2.12).

Fig. 2.11: Climbing-Ripple Facies located in Channel-fill Sandstone 6.


Rippled sandstone and climbing-rippled sandstone are categorized in the

uppermost division of lower flow regime deposits. Standard ripples are formed by

particles as they move by traction along the seafloor. Slowly they stack upon one

another until the angle of repose is met (28º - 30º), and at this point the sedimentary

particle is transported along the face of the lee slope, where either it remains or

continues to move. The climbing-rippled sandstone has a sedimentary input that

exceeds its sedimentary output, particularly those with lee and stoss slope deposition.

These deposits are diagnostic of a sediment-choked system and are interpreted to

occur at either the inner channel-levee margin of the channel-fill environment or in

proximal levee environments (Browne and Slatt, 2002).

Fig. 2.12: Climbing-ripple facies description.

Lithofacies 6 (F6): Shale or Mudstone


The shale and/or mudstone located within the channel-fill sandstones tend to

exhibit erosive tops (Fig. 2.13). This facies is colored light to dark gray and is

composed of clay-sized particles. F6 is mostly absent from many of the channel-fill

sandstone bodies, but is quite abundant within Channel-fill Sandstone 1.

Fig. 2.13: Shale/mudstone facies bounded by structureless sandstone facies.


Facies F6, shale and/or mudstone, is interpreted to be deposited from either

the tail-end of a turbidity current flow or as pelagic rain. The major process by which

this facies is deposited in the channel-fill environment is interpreted to be the tail-end

of a turbidity current flow. Channel-fill lithologies are comprised mainly of

sandstone facies. Since very few F6 facies are exhibited in the field, it is interpreted

that any shale and/or mudstone located in the channel-fill environment must be

deposited as the tail-end of a turbidity current as opposed to pelagic rain (not

quiescent enough in this environment for this type of deposition to occur).

Lithofacies 7 (F7): Shale-Clast Conglomerates


The shale-clast conglomerates of the channel-fill sandstones in Spine 1, F7

(Fig. 2.14 and 2.15), are light to dark gray in color. The shale clasts are light gray

and the matrix is dark gray or yellowish-tan. The internal architecture exhibited

within the shale clasts themselves show a thinly laminated facies. Additionally, the

shale clasts exhibit imbrication within this faices. L7 is quite abundant and is located

in almost all of the channel-fill sandstones. F7 tends to occur mainly as small, thin

deposits (usually 2-4in thick).

Fig. 2.14: Stacked shale-clast conglomerates (A) interbedded with turbidites (B) on Channel-fill

Sandstone 1.

Fig. 2.15: Faint imbrication of shale clasts occur in Channel-fill Sandstone 1.


The shale-clast conglomerates are interpreted to have originated as debris flow

deposits. These flows contain a high matrix strength and therefore move in a plastic,

laminar, cohesive state (Weimer and Slatt, in press). As the debris flow is

transported, the flow region is delineated into two components, the Shear Flow

Region and the Plug Flow Region (Fig. 2.16). The Shear Flow Region, located at the

basal part of the flow, generates shear stresses that overcome the matrix shear within

the flow (Weimer and Slatt, in press). It is possible that shale clasts found in the

lower regions of debris flows (i.e., in the Shear Flow Region) could have been

imbricated by these shear stresses (Fig 2.15). The Plug Flow Region contains the

major bulk-volume of sediments in transport. It tends to remain in the same position

during its entire transit, except at the flow/seawater contact where the sediments may

exhibit a decrease in velocity due to frictional forces (Weimer and Slatt, in press). In

Spine 1 deposits, shale clast conglomerates are interpreted to comprise the failed,

slumped margins of levees.

Fig. 2.16: Debris Flow Rheology (from Weimer and Slatt, in press)

Lithofacies 8 (F8): Slump Beds


Slump beds (Fig. 2.17) are found only in a few of the channel-fill sandstones,

but are a very diagnostic feature, helping to orient the channel-fill sandstone into its

environment within the channel system. They tend to range in thickness from 2ft to

7ft. F8 exhibits many different characteristics within their deposits, including the

parallel interbedding of sandstone and siltstone and a lower sand/shale ratio than

other lithofacies. They range in color from yellowish-tan to light and dark grey.

Fig. 2.17: Slump beds bounded in yellow from Channel-fill Sandstone 1 “Prong.”


Slump beds are interpreted to have formed as a coherent unit of the failed

inner-channel margin wall within a leveed-channel system. They represent the initial

flow event of any sedimentary gravity flow and exhibit high matrix strength. Due to

their high sediment concentration they move in a plastic flow state (Weimer and Slatt,

in press). This facies is closely related to the hydrodynamic interpretation of F7, but

it differs from it mainly by the fact that the deposit exhibits a coherent unit of

different beds while F7 is one bed. The interpreted slump beds contain what was

once the channel margin, comprised largely of proximal-levee facies deposits. All of

this evidence points to slump beds having been formed on the steep side of the

channel margin, or the cutbank-equivalent side of a channel-fill system.

Chapter 3

ENVIRONMENT OF DEPOSITION AND FACIES RELATIONSHIPS

Introduction

The purpose of this chapter is to categorize the facies into their environment

of deposition within a leveed-channel system. Descriptions of lithologic stacking

patterns found to occur in the field will also be included.

There are five major environments of deposition related to the leveed-channel

system (Fig. 3.01): E1) non-sinuous leveed-channel system, E2) outer-side of sinuous

channel bend, E3) inner-side of sinuous channel bend, E4) proximal levee, and E5)

distal levee.

Fig. 3.01: Enviroments of Deposition (E) 1-5 contained within a leveed-channel system.

Interpretations

Associated with each environment of deposition is a particular lithologic

stacking pattern which is diagnostic in determining its associated environment within

the channel-fill system. Kneller’s 1995 (Fig 2.05 and 3.02) diagrams were used to

develop the guidelines in interpreting these environments. Figure 3.03 and 3.04 were

also drawn to help support and guide the interpretations.

Fig. 3.02: Situations leading to different flow behaviors (Modified from Kneller, 1995).

Kneller’s (1995) (Fig. 2.05) diagrams relate the deposited facies to Bouma

divisions Ta-Te. Although these are noted in the chapter, Bouma division Ta is

classified as a separate deposit. This interpretation rests primarily on the fact that

both Walker (Fig. 2.06; 1978) and Lowe (Fig. 2.07; 1982) recognize the presence of

water-escape structures within their normally-graded to massive deposits (other than

the water-escape structures, most sandstones in F1 are structureless).

Witton (2000) interpreted the outer-side of a channel margin (E2) to contain

numerous debris flow deposits (F7). This concept was also very instrumental in

helping to guide the interpretations introduced in this chapter.

Fig. 3.03: Planform view of flow movement within a leveed-channel system.

Fig. 3.04: Flow movement within a sinuous channel-bend.

The following text in this chapter hypothesizes on the expected facies to be

found at these five environments of deposition (E1 – E5).

E1: Non-sinuous (Straight) leveed-channel environment

Interpretation:

E1 is interpreted as the straight, U-shaped portion of a sinuous channel

system. Figures 3.03 and 3.04 show that the flow out of a channel-bend, into the

straight portions of the system is interpreted to be spatially depletive (downcurrent

decrease in velocity; Fig. 3.02). Figure 2.05 shows there are three temporal

considerations to factor in with the spatial descriptions of the flows, they are: waxing

(increasing in velocity over time), waning (decreasing in velocity over time), and

steady (uniform velocity over time) (Kneller, 1995). Since the flow can do any three

of these when exiting the channel-bend, all deposits related to these three spatial-

temporal flows could be expected to be found in this non-sinuous environment.

Facies Relationship:

If the flow was to increase in velocity while exiting the channel-bend, the

expected spatial-temporal relation would be “waxing depletive.” A waxing depletive

deposit yields an inverted classic Bouma Sequence (Kneller, 1995). The expected

deposit contains Bouma divisions Te/Td, which underlie Tc, Tb, and Ta, respectively.

Relating these Bouma divisions to aforementioned facies would yield the expected

lithologic stacking pattern of (base to top): F6, F5, and F4. If there is a range in grain

size, this stacking pattern will exhibit reverse grading.

If the flow out of the channel-bend was to remain steady, the expected

lithologic stacking pattern would yield a continuous deposit of Bouma division Ta or

Tb (F4), and further downstream, Tc (F5). The last scenario is the least diagnostic of

all, waning depletive. In fact, all “waning” flows show more or less the same deposit:

a classic, normally graded Bouma Sequence (top to bottom): Ta, Tb (F4), Tc (F5),

Td, and Te (F6).

E2: Outer-side of sinuous channel bend

Interpretation:

E2 is the outer-side of a sinuous bend in a channel-fill system. Figures 3.03

and 3.04 show that the expected spatial flow in this environment is accumulative

(downcurrent increase in flow velocity), because the movement of the flow is similar

to that of water traveling down a waterslide. Since “waxing-accumulative” and

“steady-accumulative” both yield erosion within the system, the only setting that

deposition can occur is “waning-accumulative.”


In a “waning accumulative” flow, the classic Bouma Sequence is expected to

be deoposited. Thus the lithologic stacking pattern to be recognized in the field

contains the facies (from base to top): F4, F5, and F6. Ideally, this deposit would also

be normally graded, helping to define the boundary between flow events.

Frequently bounding the facies in the lithologic stacking pattern of E2, are

shale-clast conglomerates, or F7. The process by which this facies is deposited is the

slumping of adjacent levee walls into the channel-fill axis (Fig. 3.05 and 3.06). This

is the most diagnostic facies in the set.

Fig. 3.05: 3D seismic horizon slice (photo courtesy of H. Posamentier).

Fig. 3.06: Sinuous submarine channel-fill deposit localities (modified from Peakall et al., 2000).

E3: Inner-side of sinuous channel-bend

Interpretation:

This interpretation is based mainly on field observations and personal

communication with Slatt (2003). Witton (2000) initially interpreted the outer-side of

a sinuous channel-bend to contain debris-flow deposits (shale-clast conglomerates)

concentrated at one end (Fig. 2.14 and 2.15). Field observations show that directly

opposite these deposits are large sandstones exhibiting cross-bedding features (Fig.

3.07). These large structures of low-angle, high-amplitude, cross-bedding (Fig. 2.08)

are interpreted to occur as in-channel bar or dune forms (Slatt, 2003).

Fig. 3.07: Oblique depositional strike view of Channel-fill Sandstone 1 (from Pyles and Slatt,

2002).

Additionally, Abreau et al (2002) noted that these features dominate the fill of

many submarine channels and exhibit themselves as shingled seismic reflections that

dip toward the channel axis. These features are interpreted to form as a result of the

lateral and downdip migration of the channel, with deposition of lateral accretion

beds in the inner side of the channel and erosion at the outer side of the channel

(Abreau et al, 2002; Beaubouef, 2002).


The expected lithologic stacking pattern for E3 is simply a continuous deposit

of lateral accretion surfaces with contained cross-bedded sandstone (F3).

E4: Proximal levee

Interpretation:

E4, interpreted as the proximal levee region within the leveed-channel system,

is based on two extensive detailed measured sections taken on Channel-fill Sandstone

4 and 8 (Figs. 3. 08 - 3.10). Proximal levees are known to contain silt to very fine

grained sand because the sediments deposited in this environment originate from

overflows from the channel. These overflows tend to be finer grained than the rest of

the flow confined within the channel because larger grains are located near the base

of these flows. Significantly, dip magnitudes and orientations also vary because the

flows trend in different directions as they flow over the levee margin (Browne and

Slatt, 2002). Other facies exhibited in E4 are parallel/subparallel (F4) to

contorted/convoluted bedding planes, climbing ripples (F5, due to high sediment

input), reverse grading within associated splay deposits, and generally a higher

sand/shale ratio than distal levee facies.

Fig. 3.08: Environments of deposition of Channel-fill Sandstone 4 (from Slatt, 2003).

Fig. 3.09: Proximal levee with convoluted bedding and climbing ripples associated with Channel-

fill Sandstone 4

Fig. 3.10: Proximal levee with 2-inch set of climbing ripples associated with Channel-fill

Sandstone 4


All of the facies described above (convoluted bedding, climbing ripples, etc.)

are contained within the two detailed measured sections recorded. Along with

matching these facies, inversely-graded deposits also occur in the measured sections.

Another match is the sand/shale ratio, which is much higher here than in the

interpreted distal levee region.

E5: Distal levee

Interpretation:

Distal levee deposits contain a lower sand/shale ratio than proximal levee

deposits (Brown and Slatt, 2002). This is expected as the overbank flows typically

are depleted of energy as they reach the distal, lower gradient portions of the levee

region, depositing the finest material in the flow. The dominant facies within E5 is

continuous parallel bedding, making them more laterally extensive than the proximal

levee facies (Fig 3.11).

Fig. 3.11: Distal levee deposits from Channel-fill Sandstone 4.


E5 contains these two diagnostic facies, where they appear on a detailed

measured section of distal-levee deposits belonging to Channel-fill Sandstone 4

(Appendix A). Comparison of the above interpretation with this measured section

shows that the grain-size of the deposits are silt and clay sized particles, typically

interbedded. Immediately apparent is the low sand/shale ratio. Parallel bedding is

the dominant facies exhibited on the measured section (Appendix A).

Chapter 4

3D MODEL DESCRIPTION AND INTERPRETATION

Introduction

The 3D model that all outcrop measurements were based upon was built in

GOCAD™ v.2.0.6 (4th

Quarter, 2002). This is a robust package of software that

allowed the raw data collected from the Trimble™ GPS units to be viewed and

manipulated in 3D space. The software was instrumental in developing the resultant

3D model (see CD) and helped guide many new interpretations of the channel-fill

sandstone boundaries.

Data was first recorded in the field with Trimble™ GPS units which recorded

the position of the interpreter as he walked actual outcrop boundaries. These data

were then transferred to a PC-based laptop with Trimble™ Pathfinder GPS Software.

This software stored the data as *.ssf files which were then exported as *.dbf files

into Microsoft™ Excel. After the X,Y,Z points were isolated into their separate

columns, an appropriately designed header format was input so the file could be

recognized in GOCAD™ v.2.0.6. At this point, the files were viewed in 3D space

and appropriate lines that represented channel boundaries (Fig. 1.11) and detailed

measured section localities could be drawn.

After all channel-fill sandstone boundaries and detailed measured section

localities were drawn, facies boundaries were delineated from the measured sections

and emplaced on the measured section lines within GOCAD™. After this task had

been carried out for all nine channel-fill sandstone bodies, correlations then

commenced along the Outcrop Face (Fig. 1.11) of each. The resultant correlations

resemble fence diagrams that float in 3D space relative to one another. Another

benefit of GOCAD™ is the ability to measure the distance between two points and

also to find the precise X,Y,Z locality of any point, whether it be a channel boundary,

facies boundary, or any other point of interest. Additionally, the data may be rotated,

tilted, slid, or zoomed-in and out.

After the model was completed, the locations of particular lithologic stacking

patterns were recognized while examining the model. Some of these stacking

patterns are diagnostic in interpreting the environment within a leveed-channel

system as stated in Chapter 3. When these stacking patterns were recognized in the

model, the related environment (E1 – E5) was assigned to that locality of the

Channel-Fill Sandstone. These observations have led to a general interpretation of

each Channel-Fill Sandstone body and its classification within the environments of

deposition of a leveed-channel system. The above-ground vertical and lateral

geometry of each Channel-Fill Sandstone was also recorded.

Each facies within the model was represented by a unique color. The

classification is as follows: (F1) Sandstone with water-escape structures: blue, (F2)

Structureless sandstone: yellow, (F3) Cross-bedded sandstone: magenta, (F4) Parallel

to sub-parallel laminated sandstone: dark-gray, (F5) Rippled or climbing-rippled

sandstone: dark-green, (F6) Shale: blue-violet, (F7) Shale-clast conglomerate: red,

and (F8) Slumped bed: white.

Fig. 4.01: 3D GOCAD™ model of Dad Sandstone Member, Lewis Shale; “Prong” region of

Channel-fill Sandstone 1 circled in red; brown represents “Outcrop Plane,” while other colors

represent “Outcrop Face” of the nine channel-fill sandstones.

Viewing the Data

Representing 3D images in 2D space has proven to be a difficult task. The

following guidelines are recommended to the reader to help view the pictures offered

in this chapter.

Each picture has a figure in the lower left corner (Fig. 4.01) denoting three

axes: X (east), Y (north), and Z (altitude). Each axis has both magnitude and

direction, i.e. it not only points in these designated directions, but the inverse of the

length of the arrow also represents the amount of tilt in that direction. This figure is

essential to orient oneself in the 3D space, as viewed in the GOCAD™ model.

Referring back to Figure 1.11, two planes are defined here: 1) the Outcrop

Face and 2) the Outcrop Plane. The “Outcrop Plane” is colored brown in all figures

(Fig. 4.01). The “Outcrop Plane” does not designate any facies described, it is simply

the top plane of each individual channel-fill sandstone.

It is handy to keep a list of the color designations for the facies, as they appear

in every figure and are denoted by their classification (F1 – F8) and are seldom re-

described. Topographic contour intervals are also labeled on every figure where they

appear; these also help to orient the reader.

In some of the figures (Fig. 4.16 and 4.17) there is a black region seen; this

region is simply the extent of the Digital Elevation Map (DEM) where there is no

elevation data; i.e. a no-data zone.

Many of the figures are encapsulated within others to help orient the reader

when viewing certain pictures. Most pictures can be related back to the planview

basemap, pointing north, which contains all nine channel-fill sandstones (Fig. 4.02).

Note that the arrow is oriented differently in different figures due to the 3 dimensional

character of the outcrop faces.

Fig. 4.02: Planview basemap of nine stacked channel-fill sandstones. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2

(yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark

gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7:

(red) shale clast conglomerates, and F8: slumped beds.

Channel-Fill Sandstone 1

Fig. 4.03: Channel-fill Sandstone 1 location in Field Area. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):

structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray):

parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale

clast conglomerates, and F8: slumped beds.

Fig. 4.04: Locations of detailed measured sections on Channel-fill Sandstone 1 (1.01 – 1.22).

F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3

(magenta): cross-bedded sandstones (without water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark green):

rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red) shale clast conglomerates, and F8: slumped beds.

Vertical and Lateral Geometry:

The detailed measured sections of Channel-fill Sandstone 1 can be located on

Figure 4.03 and 4.04. The lateral geometry of Channel-fill Sandstone 1 can be

characterized by measuring the distance along the Outcrop Face in its two major

trends: N-S and E-W. All detailed measured sections located on Channel-fill

Sandstone 1 are located on Figure 4.03. A N-S trending face outcrops along the

narrow side of Spine 1, on its eastern side. This measurement is 62ft (Fig. 4.05).

Any E-W trending face outcrops along the wider edge of the spine in its northern

region. This associated measurement for Channel-fill Sandstone 1 is over 600ft. (Fig

4.05) for this trend. The thickness of this channel-fill ranges from 8ft to 34ft.

Fig. 4.05: Plan view map of surface outcrop dimensions of Channel-fill Sandstone 1. F1 (blue):

sandstone with water-escape structures (some cross-bedded), F2 (yellow): structureless

sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without

water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark

green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7: (red)

shale clast conglomerates, and F8: slumped beds.

Lithologic Stacking Patterns and Locations:

In the northern region of Channel-fill Sandstone 1 are numerous shale-clast

conglomerates dipping southward (Fig. 4.06 and 4.07). Also located in the northern

region, contained within the “prong” area is a large slumped bed (Fig. 4.06).

Channel-fill Sandstone 1 is capped primarily by F1 sandstone with water-escape

structures. The crossbedded sandstone facies (F3; magenta) is shown to occur in the

southern portions of the channel-fill region. Volumetrically, in most portions of the

channel, structureless sandstone (F2) dominates the channel-fill.

In the westernmost flank of the channel-fill, sandstones show tapering out to

the last measured section, 1.0.1 (Fig. 4.08). At this location, stacking patterns involve

significant amounts of shale and/or mudstone (F6).

Fig. 4.06: “Prong;” located in the eastern region of Channel-fill Sandstone 1. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2

(yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4 (dark

gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7:


Fig. 4.07: Shale-clast conglomerate facies found in northern-most portions of Channel-fill Sandstone 1 model. F1 (blue): sandstone with water-escape

structures (some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without

water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-

violet): shale or mudstone, F7: (red) shale clast conglomerates, and F8: slumped beds

Fig. 4.08: Western-most flank of Channel-fill Sandstone 1 ends at MS# 1.0.1. F1 (blue): sandstone with water-escape structures (some cross-bedded),

F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without water-escape structures), F4

(dark gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone,

F7: (red) shale clast conglomerates, and F8: slumped beds

Interpretation:

The large number of F7 (shale-clast conglomerate) beds in the northern region

of the channel-fill interbedded with slumped beds (F8) indicate deposition on the

outer side of a sinuous channel bend (E2; Fig. 3.06). The beds have slumped from

the channel margin/levee walls into the channel.

F3, lateral accretion surfaces (crossbedded sandstone), are located on the

southern portion of the channel-fill environment. This facies is once again very

diagnostic of its environment of deposition, in this case, it is interpreted to be located

on the inner-side of a sinuous channel bend, E3 (Fig. 3.08).

Coupled together, these two interpretations suggest the northern portion was

the steeper, cut-bank equivalent side to the channel-fill, while the southern portion

represented the tapering, feathered edge of the point-bar equivalent side of the

channel-fill.

Subsurface:

Channel-Fill Sandstone 1 was uniquely separated from the other eight

channel-fill sandstone bodies because it was the only one to include the drilling and

gamma-logging of eight shallow boreholes. The boreholes were drilled along the

eastern flank of the channel-fill sandstone (Figs. 4.09 – 4.12), Electro-magnetic

induction (EMI; Fig. 4.13) and ground-penetrating radar (GPR; Fig. 4.14) images of

the area are also shown.

The first major process carried out was the drilling of the eight shallow

boreholes (Borehole 1 – Borehole 8). While these shallow boreholes were being

drilled, the lithologic cuttings expelled from the borehole were recorded, measured,

and bagged for later analysis. After each borehole was drilled, a gamma-ray sonde

was lowered into the borehole and retrieved at a steady rate, recording the natural

gamma-radiation emitting from the lithologies in the subsurface. These

measurements were stored onto a PC-based field laptop computer. The data was then

manipulated in Microsoft™ Excel in order to create gamma-ray (cps) vs. depth (ft)

plots (Fig. 4.10).

.

Fig 4.09: Boreholes (1-8) with locations of dip (green; 5-3-6) and strike (white; 1-2-3-4) cross-

sections, located on eastern flank of Channel-Fill Sandstone 1.

Fig. 4.10: Example of gamma-ray log from Borehole 1

These plots were then positioned accordingly to their proper X, Y, Z location

and cross sections were drawn in both the dip (Fig 4.11) and strike (Fig. 4.12)

sections of the channel-fill sandstone body. Three main facies were recognized in the

subsurface, they are: 1) sandstone (interpreted as channel-fill sandstone), 2) shale-

clast conglomerates (debris-flow deposits), and 3) shale (interpreted to be deposited

outside of the channel-fill environment). The cross section interpretations were

guided by field notes and cutting samples from each borehole. The field notes were

instrumental in the interpretations because depth regions were recorded as “well” to

“poorly lithified.” These descriptions helped to guide the interpretation because the

sandstone in the subsurface showed it to be “poorly lithified,” while the shale was

found to be “well lithified” (shale-clast conglomerates fall between these two since

they comprise both lithologies).

Fig. 4.11: Dip cross-section of Boreholes 5-3-6 of Channel-Fill Sandstone 1.

Fig. 4.12: Strike cross-section of Boreholes 1-2-3-4 of Channel-Fill Sandstone 1.

Electro-Magnetic Induction techniques were carried out by Ryan Stepler and

Dr. Alan Witten (2003; Fig. 4.13). It involved a twenty-frequency (1 kHz to 20 kHz)

EMI dataset collected over a 54m by 70 m area grid and inverted for resistivity and

depth. Through Stepler’s geophysical work, EMI data correlates nicely with the

cross-section interpretations from the eight shallow boreholes (Fig 4.11 and Fig.

4.12).

Fig. 4.13: Electro-Magnetic Induction and GPR (3-B to 3-B’) carried out on eastern flank of

Channel-Fill Sandstone 1 (Blue arrow represents interpreted base of Channel-fill Sandstone

1;Stepler, 2003).

Ground-Penetrating Radar techniques were carried out by Dr. Roger Young

and Julie Staggs (2003). GPR involves high frequency radar waves penetrating the

subsurface. At bed boundaries these waves are reflected back upward where they are

recorded at a receiver on the surface. Their work identified different radar facies,

each denoting a portion of a radar profile characterizing a particular stratigraphic

facies and associated depositional features (Fig. 4.14; Young et al., 2003).

Fig 4.14: Ground-Penetrating Radar facies located in the subsurface of Channel-Fill Sandstone 1

(Young et al., in press).


Fig. 4.15: Location and number of detailed measured sections (black) with outcrop dimensions

(red) on Channel-fill Sandstone 2.


There are two major trends to the Outcrop Face of Channel-fill Sandstone 2,

N-S and E-W (Fig. 4.15). The N-S trend is recorded as 415ft. in length, while the E-

W trend is recorded as 360ft. in length. The detailed measured sections on Channel-

fill Sandstone 2 are found in Figure 4.15. The thickness of this channel-fill varies

from 2ft. to 10ft.


In the northern regions of the interpreted channel-fill environment are

numerous shale-clast conglomerates (F7; Fig. 4.16). To the base of these deposits lies

a shale/mudstone facies (F6). Capping these two units in the northern region and

continuing south to the crossbedded facies, F3, is F2, structureless sandstone. The

southern region is dominated by lateral accretion surfaces represented by low-angle

crossbeds (Fig. 4.16).

Fig. 4.16: F7, shale-clast conglomerates and F3, crossbedded sandstone, located on Channel-fill Sandstone 2. F1 (blue): sandstone with water-escape

structures (some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta): cross-bedded sandstones (without

water-escape structures), F4 (dark gray): parallel to subparallel laminated sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-

violet): shale or mudstone, F7: (red) shale clast conglomerates, and F8: slumped beds

Interpretation:

The northern region of the channel-fill environment is dominated by facies F7,

shale-clast conglomerates (Fig. 4.16). This is a diagnostic facies of the outer-side of a

sinuous channel bend.

The southernmost region within the model shows a laterally continuous

deposit of crossbedded sandstone. Once again, this is a diagnostic facies representing

the inner-side of a sinuous channel bend.

The two previous interpretations hold that the northern region of Channel-fill

Sandstone 2 is the cut-bank equivalent side of the channel-fill system, while the

southern region is interpreted as the point-bar equivalent side of the channel.





Channel-fill Sandstone 3 shows similar N-S and E-W trends as the previous

channels. The detailed measured sections on Channel-fill Sandstone 3 can be found

on Figure 4.17. The E-W trend, usually the longer of the two, is only 80ft. The N-S

trend has a length of 335ft (Fig. 4.17). Thicknesses of this channel-fill range from

4ft. to 8ft.


Within Channel-fill Sandstone 3, the following facies are present (Fig. 4.19):

F6 (shale/mudstone), F1 (sandstone with water-escape structures), F2 (structureless

sandstone), and F7 (shale clast conglomerate). F7 is located on the northeastern and

southeastern portions of the channel-fill. F6 (shale/mudstone) is located at the base of

the channel and is found in the northeastern region. The northern region of the

channel-fill environment is otherwise dominated by F2 (structureless sandstone

without water escape structures), while the medial and southern regions of the

channel are otherwise dominated by F1 (sandstone with water-escape structures).

Fig 4.18: Diagnostic facies of Channel-fill Sandstone 3. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):



clast conglomerates, and F8: slumped beds

Interpretation:

The presence of F7 in the northeastern and southeastern regions of the

channel-fill (Fig. 4.18) are interpreted to represent the outer-side of a sinuous channel

bend (E2), or the cut-bank equivalent side. Field observations and those made in

GOCAD™ lead to the additional interpretation that Channel-fill Sandstone 3 (CFS 3)

and the overlying channel-fill sandstone, CFS 4, are amalgamated.


Fig. 4.19: Location of Channel-fill Sandstone 4 on Spine 1

Fig. 4.20: Location and number of detailed measured sections (white) with outcrop dimensions (red) on Channel-fill Sandstone 4.


The detailed measured sections of Channel-fill Sandstone 4 can be found on

Figure 4.19 and 4.20. There are three major trends to the Outcrop Face of Channel-

fill Sandstone 4. This indicates that this channel-fill outcrop wraps around Spine 1

from its southern slope to its northern slope. The main trend, SE-NW is 430ft. in

length. The second main trend is located in a region known as the “Eagle’s Nest.”

This face is 88ft. in length and is located on the southern slope of Spine 1 (Fig. 4.20).

The northern-slope of Channel-fill Sandstone 4 is 70ft. in length. The thickness of

this channel-fill ranges from 4ft. to 16ft.


Channel-fill Sandstone 4 shows many interesting lithologic patterns located in

its southern-most flank (Fig. 4.21). Some of the facies included are F1 (sandstone

with water-escape structures), F2 (structureless sandstone), F3 (crossbedded

sandstone), F7 (shale-clast conglomerates), and F8 (slumped beds). While F1 and F2

dominate the rest of the channel-fill, they are represented equally with all other facies

at this portion of the channel-fill environment. The northernmost flank and the

eastern region of the channel-fill environment is dominated by facies F1 and F2 with

a rogue F7 facies lying near the base of the channel in the northeastern-most region

(Fig. 4.21).

Fig. 4.21: Diagnostic facies located on Channel-fill Sandstone 4. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):




Interpretation:

The southernmost flank, in the stratigraphically lower portions, shows the

dominant facies to be crossbedded sandstone (F3) and in the northern portion of the

channel-fill there resides a lone F7 facies near the base of the deposits. This

stratigraphically lower region of the channel-fill environment is interpreted to have

been a separate channel-fill system within the entire Channel-fill 4 “Complex” (Fig.

4.22). The overlying facies F8 and F7 are interpreted to be amalgamated onto the

channel-fill system of the lower region.

This interpretation holds that the stratigraphically lowest portion of the

channel-fill sandstone, denoted by CFS4a is overlain by CFS4b (Fig. 4.22). CFS4a

shows that the southern portion of the channel-fill environment was dominated by the

diagnostic facies, F3, crossbedded sandstone. This facies is interpreted to represent

the locality within the inner-side of a sinuous channel bend. The northernmost

portion of CFS4a shows F7 to be the only diagnostic facies. This facies is interpreted

to be the cut-bank equivalent side of the channel. Once again, two diagnostic facies

were used in conjunction to interpret the environments represented by the channel-

fill.

Fig 4.22: Amalgamated channel-fills CFS 4a and CFS 4b, comprising Channel-fill Sandstone 4.

CFS4b is dominated by F8 and F7 facies in the southern region of the

channel-fill. This interpretation holds that the southern region is the cut-bank

equivalent side of the channel and it eroded into the underlying crossbedded

sandstone of CFS4a to create amalgamated channel-fill deposits.


Fig. 4.23: Location and number of detailed measured sections (white) with outcrop dimensions



The detailed measured sections of Channel-fill Sandstone 6 can be located on

Figure 4.23. Channel-fill Sandstone 6 is another channel-fill body that extends across

both slopes of Spine 1 (Fig. 4.23). It also has three major trending faces (Fig. 4.23).

The major SE-NW trend is 355ft. The secondary southern-slope trend is 105ft. in

length, while the northern-slope trend is 95ft. in length. The thickness of this

channel-fill ranges from 2ft. to 8ft.


The northwestern regions of the channel-fill environment are dominated by

basal F7 units capped by F3 facies (Fig. 4.24). The western part of the medial portion

of the channel, trending NW-SE, is dominated by facies F1 and F2 with a small

portion of F5 (climbing rippled sandstone) cropping out near the top of the channel-

fill. The eastern segment of the medial portion of the channel-fill is underlain by

facies F3 and is capped by facies F1. In the southeastern-most region of the channel-

fill, F5 (rippled or climbing-rippled sandstone) is encapsulated within F1 deposits,

capped by facies F3.

Interpretation:

Two diagnostic facies occur in this channel-fill, F3 (crossbedded sandstone)

and F7 (shale-clast conglomerate). Once again, two diagnostic facies of different

channel environments are located in the same geographical region. This channel-fill

system is thus interpreted to contain two amalgamated channel-fills. The lower

region of CFS6 is interpreted as CFS6a, the lower fill, and CFS6b, the upper fill (Fig.

4.25).

Fig. 4.24: Diagnostic facies of Channel-fill Sandstone 6. F1 (blue): sandstone with water-escape structures (some cross-bedded), F2 (yellow):




Fig 4.25: Amalgamated channel-fills CFS 6a and CFS 6b, comprising Channel-fill Sandstone 6.

CFS6a is interpreted to have its steep side on the northwestern-most side of

the channel-fill system with a feathered, tapering edge on the southeast. CFS6b lacks

two diagnostic facies as CFS6a, but contain plentiful F3 deposits throughout the

entire stretch of its channel-fill. The resultant interpretation holds that CFS6b was

dominated in this region by the inner-side of a sinuous channel bend (E3).





The detailed measured section of Channel-fill Sandstone 7 can be located on

Figure 4.26. Channel-fill Sandstone 7 is primarily found on the northern slope of

Spine 1 and thus has only two major trends, NE-SW and E-W (Fig. 4.26). The major

E-W trending face is 430ft. in length, while the minor NE-SW trend is only 105ft.

The thickness of this channel-fill ranges from 2ft. to 10ft.


Dominated in the western portions of Channel-fill Sandstone 7 (CFS7) is

facies F2, structureless sandstone and F3, crossbedded sandstone (Fig. 4.27). In the

eastern region of CFS7 is facies F8, slumped beds (Fig. 4.27). Otherwise, CFS7 is

dominated by facies F2.

Interpretation:

Since the western portion of CFS7 includes the diagnostic facies F3, this

region of the channel-fill is interpreted to be the point-bar equivalent, inner-side of a

sinuous channel bend (E3). The eastern section of CFS7 shows a slight, but

prominent facies, F8. F8 is diagnostic of cut-bank equivalent, outer-side sinuous

channel bends, E2. This interpretation yields that the eastern portion of CFS7 is the

cut-bank equivalent side of the channel-fill, while the western portion is interpreted to

be the point-bar equivalent of the fill. Field observations and those made in

GOCAD™ lead to the additional interpretation that Channel-fill Sandstone 7 (CFS 7)

and the overlying channel-fill sandstone, CFS 8, are amalgamated (Fig. 4.01)..




clast conglomerates, and F8: slumped beds.





The detailed measured sections on Channel-fill Sandstone 8 can be found on

Figure 4.28. There are two major trends associated with the Outcrop Face of

Channel-fill Sandstone 8, they are N-S and E-W trends (Fig. 4.28). The major E-W

trend is 475ft. in length, while the N-S trend is 180ft. in length. The thickness of this

channel-fill ranges from 4ft. to 12ft.


Channel 8 shows some unique lithologic patterns. In the western portion of

the channel-fill system, the basal portion is dominated by facies F7, shale clast

conglomerates (Fig. 4.29). Capping these units and laterally extending to the east and

stratigraphically downward to the same plane as the F7 deposits are facies F3,

crossbedded sandstone.

In the eastern regions of the channel-fill this same type (mirror-image) of

lithologic stacking pattern exists, i.e., the shale-clast conglomerate (F7) facies resides

on the east and facies F3, crossbedded sandstone, resides on the west (Fig. 4.29).

Interpretation:

These unique stacking patterns reveal an interesting interpretation. The

eastern side of CFS8 is interpreted to have a steep, cut-bank side (E2) on its eastern

flank by the diagnostic F7 facies and a shallower, point-bar side (E3) on its western

flank by the diagnostic F3 facies.

The western side of CFS8 is interpreted as the mirror image of the above

interpretation. The western flank of the western portion of CFS8 is interpreted to be

the steep, cut-bank side (E2) of the channel-fill, while the eastern flank of the western

portion is interpreted to be the shallower, point-bar (E3) side of the channel-fill.


Fig. 4.30: Location and number of detailed measured sections (white) with outcrop dimensions (red) on Channel-fill Sandstone 9.


The detailed measured sections of Channel-fill Sandstone 9 are found on

Figure 4.30. This is the smallest channel-fill sandstone located on Spine 1 (Fig.

4.30). Although thicknesses range from 4ft. to 8ft., the surficial lateral extent is

simply not typical for channel-fills located in this area. The two trends, NE-SW and

NW-SE, are 50ft. and 25ft., respectively.


Channel-fill Sandstone 9 (CFS9) is dominated primarily by facies F2,

structureless sandstone (Fig. 4.31). In the northern region, there is a small cap of

facies F1, sandstone with water-escape structures, but there is a larger, more laterally

continuous deposit of F3, crossbedded sandstone, trending southward.

Interpretation:

The northern region of CFS9 contains the diagnostic facies, F3. Due to this

crossbedding, the northern region is interpreted to be the straight portion of the

channel (E1).


Fig. 4.32: Location and number of detailed measured sections (white) with outcrop dimensions



The detailed measured sections of Channel-fill Sandstone 10 can be found on

Figure 4.32. This is the stratigraphically highest channel-fill sandstone body. It

contains two major trends (Fig. 4.32). The first, NW-SE is 100ft. in length. The

second trend, NE-SW is 50ft. in length. The thickness of this channel-fill ranges

from 3ft. to 7.5ft.


This entire channel-fill sandstone body is dominated by facies F2,

structureless sandstone. In the northwestern-most region of the channel-fill is a

prominent, 50 ft. laterally continuous deposit of facies F3, crossbedded sandstone

(Fig. 4.33).

Interpretation:

The only diagnostic facies in the channel-fill is facies F3, located in its

northern flank. This northern flank was thus interpreted to be the inner-side, point-

bar equivalent side (E3) of the channel-fill system, while the southern flank is

interpreted as the straight portion of a channel-fill (E1).

Fig. 4.33: Diagnostic facies Channel-fill Sandstone 10. F1 (blue): sandstone with water-escape structures

(some cross-bedded), F2 (yellow): structureless sandstone (without water-escape structures), F3 (magenta):

cross-bedded sandstones (without water-escape structures), F4 (dark gray): parallel to subparallel laminated

sandstone, F5 (dark green): rippled or climbing-rippled sandstone, F6 (blue-violet): shale or mudstone, F7:


Chapter 5

CONCLUSIONS

This research has yielded many new insights into the depositional facies and patterns of

the Dad Sandstone Member of the Lewis Shale. Although Channel-fill Sandstone 1, the

lowermost channel-fill in the complex, has been and continues to be extensively studied, the

other eight channel-fill sandstones have now been classified into their interpreted environments

of deposition as classified in this thesis: E1) non-sinuous portion of a leveed-channel system, E2)

outer-side of sinuous channel bend, E3) inner-side of sinuous channel bend, E4) proximal levee,

and E5) distal levee. The 3D GOCAD™ model and its subsequent interpretations for the

environments of deposition within each channel-fill sandstone on Spine 1 help support the

interpretation that these outcrops belong to a leveed-channel complex. Witton (2000) created a

first-generation diagram showing the channel-fill sandstones in 3D space, but this diagram lacks

channel orientation for sinuosity (Fig. 5.01)

Eight separate diagnostic facies were recognized to be contained within the nine separate

channel-fill sandstones. They are: F1) sandstone with water-escape structures (some cross-

bedded), F2) structureless sandstone (without water-escape structures), F3) cross-bedded

sandstones (without water-escape structures), F4) parallel to subparallel laminated sandstone, F5)

rippled or climbing-rippled sandstone, F6) shale or mudstone, F7) shale clast conglomerates, and

F8) slumped beds. When asymmetry of these facies was exhibited in the model, the following

interpretation of the environment led to a sinuous leveed-channel interpretation with a steep “cut

bank” side and shallower “ point bar” side.. This asymmetry of facies was not encountered in all

nine channel-fill sandstones; some lacked the diagnostic facies required to make this

interpretation, such as Channel-fill Sandstone 10, which had only structureless sandstone without

water escape structures (F2) on one side of the channel-fill system (interpreted as E1: straight

portion of a leveed-channel environment).

Fig. 5.01: First generation conceptual model representing channel-fill sandstones in 3D space (no channel

sinuosity recorded; (Modified from Witton, 2000).

Precise GPS measurements of channel-fill sandstone boundaries and the 121detailed

measured sections located throughout the study area provided the basis for the architectural

facies model in true, 3D space. The facies recorded on these measured sections were observed in

the model and recorded to their geographical location and stratigraphic position within the

channel-fill sandstone body. Certain facies were then interpreted to diagnose a particular

environment (E1 – E5) located within a channel-fill system.

Fig. 5.02: Second-generation diagram representing channel-fill sandstone sinuosity.

Based on previous interpretations by Witton (2000) and Slatt et al. (2000, 2001, and

2002), two major facies were utilized to help guide interpretations of the environments of

deposition within each channel-fill sandstone body. These two facies are: 1) debris flow deposits

(F7, shale-clast conglomerate), and 2) lateral accretion deposits (F3, crossbedded sandstone).

Debris flow deposits are interpreted to form on the outer-side of a sinuous channel bend as

internal channel margin slumps, while the crossbedded sandstone is interpreted to form on the

inner-side of a sinuous channel bend as lateral accretion bar deposits.

The 3D GOCAD™ model was instrumental in modeling the lateral distribution of facies

for recording their geographical and stratigraphic position in 3D space. After these two positions

were delineated, the appropriate environment of depositon (E1 – E5) was then categorized to its

location (Fig. 5.02). This was carried out on all nine channel-fill sandstone bodies located on

Spine 1. After this was accomplished, a clear interpretation of the stacked channel-fill sandstone

bodies and their associated environments of deposition was recognized.

The first generation model, developed by Witton (2000; Fig. 5.01) only shows the

channel-fill sandstones relative to one another and the underlying sheet sandstones. There is no

indication of sinuosity in this diagram because it is conceptual. The second generation model,

developed in this thesis research (Fig. 5.02) not only shows the channel-fill sandstones relative to

one another and the underlying sheet sandstones, but also shows the interpreted orientation of

sinuosity within each channel-fill.

This diagram (Fig. 5.02) was based on observations seen in GOCAD™ v.2.0.6. The 3D

GOCAD™ model was a success because it clearly represents each channel-fill sandstone body

relative to one another (as seen in the field), as well as including the fine-scale, architectural

nature of each. The 3D model also allows for visual manipulation in a variety of ways (rotating,

tilting, zooming-in and out, and sliding). These features allowed for better interpretations of

actual channel-fill sandstone boundaries, e.g., leading to the reinterpretation and removal of

Channel-fill Sandstone 5. It should be noted that presenting 3D material in 2D space is a

challenging task and has led to some clever tricks to help view the data.

All facies correlations and interpretations are geologically sound. They match well with

many of the interpretations introduced by Witton (2000) and Slatt et al. (2000, 2001, and 2002).

While overall the project can be considered a success, more work must still be completed

in order to better define the depositional processes related to the deposits located in the channel-

fill sandstones of Spine 1. It is anticipated that the GPR (Ground Penetrating Radar) research by

J. Staggs will confirm the sinuosity interpreted in this thesis. Other work, including the

comparison of the model to seismic data sets, is currently being carried out by Dr. Roger Slatt

and his students. Building a 3D architectural facies model of the Lewis Shale submarine slope

channel complex not only helps to better understand Lewis Shale exploration, but will also help

shed light on other deepwater channel complexes located throughout the world.

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fine scale 3d architecture of a deepwater channel complex, carbon county, south-central wyoming

Technology

lithofacies description

lithofacies types

structureless sandstone

deepwater channel complex

sinuous channel bend

ripple sandstone

lithologic stacking

lateral geometry