stratigraphic facies and geologic time amantz gressley, 1834, and the jurassic rocks of the jura...

Stratigraphic Facies and Geologic Time

Amantz Gressley, 1834, and the Jurassic Rocks of the Jura Mountains between France and Switzerland

The Interpretation of Geologic HistoryRequires Knowledge of the Following

1. Sedimentary Rocks

2. Igneous Rocks

3. Metamorphic Rocks4. Origin and History of Life5. Tectonics, including:

• Structural geology• Plate tectonic theory• Etc.The core concept is tectonics

since nothing in geology makes sense except in the light of

tectonics

1. Rock Classification

The Interpretation of Sedimentary Rocks

Requires Knowledge of the Following:

2. Depositional Environments

3. Sedimentary Structures

4. Sedimentary Tectonics

5. Sedimentary Facies and Time

Abraham Gottlob Werner’s Geologic Time Scale

Primitive

Primitive – crystalline rocks, both igneous and metamorphic. Thought to represent first chemical precipitates from a worldwide ocean.

The Neptunist World View

Sea Level after deposition of the Primitive rocks

Transition

Transition – stony, indurated stratified rocks such as graywacke, limestones, sills.

Stratified

Stratified – obviously stratified fossiliferous rocks, thought to represent the first deposits after receding of the worldwide oceans, formed by erosion of emergent mountains.

Sea Level after deposition of the Transition rocks

Transported

Transported – Poorly consolidated clays, sands and gravels. Thought to have been deposited after final withdrawal of a worldwide ocean.

Sea Level after deposition of the Stratified rocks

Volcanic – Younger lava flows associated with volcanic vents (added to the classification later as an afterthought, lavas were thought to be local phenomena resulting from the burning of coal beds.

Layer Cake Stratigraphy

Werner’s theory made a firm prediction, that the same kinds of rocks should have been laid down in the same sequence all over the world.

The study of rock strata, especially the distribution, deposition, and age of

sedimentary rocks

P 126

It is not certain who first noticed that rocks were not layer cake. Levoisier in 1789 is the earliest mention we have, but Amantz Gressley coined most of the important concepts while working in the Jura Mountains.

The Facies Concept

While describing the rocks he observed lateral changes in the composition and described them with clarity calling these changes facies. But, then later in his paper he spoke of facies changes “in the vertical direction” meaning that the rocks were different vertically as well as horizontally. This has led to ongoing confusion.

Perhaps a dozen different concepts and definitions about the facies have been proposed. But, they all go back to the two original ways Gressley used the term – his formal definition, and his offhanded use of the term.

Two Facies DefinitionsDefinition

OneThe facies is the sum total of all the physical, biological and chemical characteristics imparted to a sedimentary rock at the time of deposition.

Definition TwoFacies are the many different sediments and

resulting rocks that form at the same time, but in different depositional environments.

Sedgewick, 1835

Cambrian

Murchinson, 1835

Silurian

The Transition from Wernerian "Transition Rocks"To the Lower Paleozoic PeriodsBy Sedgewich and Murchinson

Sedgewick, 1835 Murchinson, 1835Charles Lapworth

1879OrdovicianCambrian Silurian

overlapOpps !

Gressley 1795 Jurassic

D’Halloy 1822 Cretaceous

Carbonif.

Alberti 1834 Triassic

UnstudiedUntil

1830’s

“Old Red ss”

Sedgewick 1835 Cambrian

Murchinson 1835 SilurianLapworth 1879 Ordovician

Sedgewich & Murchinson 1839 Devonian

Murchinson 1841 Permian

Williams 1891 Pennsylvan.

Williams 1891 Mississippian

Lyell 1833

PleistocenePlioceneMioceneEocene

The Transition from Wernerian "Transition Rocks"To the Lower Paleozoic PeriodsBy Sedgewich and Murchinson

Adapted from Dott and Batten: Evolution of the Earth

http://www.picturescape.co.uk/gallery%20pages/gallery%20one/caldey%20sandstone.htm

http://www.picturescape.co.uk/gallery%20pages/gallery%20one/caldey%20sandstone.htm

Early Devonian fishes from the Old Red Sandstone of Spitzbergen (Wood Ray Formation)

Old Red Sandstone

http://virtual.yosemite.cc.ca.us/ghayes/Siccar%20Point.htm

The Old Red Sandstone exhibited many changes over short distances, with thinly layered areas alternating with conglomerates and outstanding crossbedded sandstones.

Old Red Sandstone

http://www.ukfossils.co.uk/sec084c.htm

The cliffs at Fremington are Devonian with Glacial beds on top of this, below the Devonian beds follows the carboniferous beds. Both Upper and Lower Carboniferous rocks have been found at Fremington, however it is suspected that some of these rocks have drifted from up or down stream, this could explain why occasionally blocks of Carboniferious limestone can be found.

Devonian Marine Rocks of Devon, England

http://www.earthfoot.org/places/uk005.htm

Devonian Marine Rocks of Devon, England

http://www.camelotintl.com/heritage/counties/england/devon.html

http://www.devonshireheartland.co.uk/

After their work on the Cambrian and Ordovician – but before they had their falling out over the overlap of their systems – Sedgewick and Murchinson decided to tackle the problem of the Old Red Sandstone and the marine bearing rocks of Devonshire exposed on opposite sides of Bristol Bay.

Devonshire

Bristol Bay

Wales

http://www.picturesofengland.com/Devon/pictures-1.htm

Scenes of Devonshire, England

The Problem

There are different rocks sandwiched between the Silurian and Carboniferous rocks as found in

Wales and Devonshire.

Onlap (Transgressive) SequencesShifting Facies through Time

Beach moves farther away

Water gets deeper

Sediment becomes finer

Time Rock Unit

Time Rock Unit

Time Rock Unit

Time Rock Unit

Time Rock Unit

Time Rock Unit

Transgression

Time Transgressive Unit

BeachsandstoneNear Shelf

shaleFar Shelflimestone

FUS – Fining Upward Sequence= Transgressive Sequence

Offlap (Regressive) SequencesShifting Facies through Time

Beachsandstone

Near Shelfshale

Far Shelflimestone

Beach moves closer

Water gets shallower

Sediment gets coarser

Prograding Regression

Time Transgressive Rock Unit

Time Rock Unit

Time Rock Unit

Time Rock Unit

Time Rock UnitTime Rock Unit

CUS – Coarsening Upward Sequence= Regressive Sequence

Transgressive Sequence

Regressive Sequence



Beach moves closerWater gets shallowerSediment gets coarser

Prograding Regression


Beach moves farther awayWater gets deeperSediment becomes finer

Transgression



Facies One

Facies Two

A couple of hundred miles

There are Facies, and then there are Facies

The facies is the sum total of all the physical, biological and chemical characteristics imparted to a sedimentary rock at the time of deposition.

Facies are the many different sediments and resulting rocks that form at the same time, but in different depositional environments.

The Problem

There are different rocks sandwiched between the Silurian and Carboniferous rocks as found in

Wales and Devonshire.

CUS

FUS

CUS

FUS

CUS

FUS

http://instruct.uwo.ca/earth-sci/300b-001/

Transgressive Sequence in theGrand Canyon of Arizona

http://www.canyondave.com/TontoPg.html

TONTO GROUPCambrian Period, 500-520 Million Years Old, 1025 Feet Thick

Yellowish ledges on top, the Tonto Platform between, and brown cliff below

FINING

UPWARD

SEQUENCE

Transgressive Sequence in theGrand Canyon of Arizona

http://www.uga.edu/~strata/sequence/transgressivesurface.html

Shown above is an example of a prominent transgressive surface, combined with a sequence boundary. This surface separates underlying shallow subtidal carbonate from overlying deep subtidal carbonate and mudstone. Note the pyritization, visible as a rusty stain, at this surface. Photograph taken at the contact between the Upper Ordovician Carters Limestone (below) and Hermitage Formation at the Nashville International Airport. This outcrop has subsequently been removed and is no longer visible.


The next example of a transgressive surface separates underlying shallow subtidal carbonate from overlying offshore mudstone. Photograph taken at the basal contact of the Nolichucky Formation in southwestern Virginia.


http://www.bees.unsw.edu.au/future/geology.html


Table mountain near Mitzpe Ramon, central Negev, Israel

http://www.geomorph.org/gal/mslattery/world.html

Regressive Sequence

cus

http://www.geneseo.edu/~gsci/pages/department/information/brochure/brochure_department.html

Regressive Sequence

cus

Transgressive-Regressive Sequences

http://www.geology.utoronto.ca/basinanalysis/photos.htm

The Fractal Nature of

Transgression and Regression

Properties of Complex Evolutionary Systems

Fractal Organization – Sea Level Changes+20

Rel

ativ

e S

ea L

evel

in M

eter

s

Time in YearsPresent50,000100,000

present sea level

glaciation-120

-100

-80

-60

-40

-20

0

Meter Changes Over 125,000 Years

enlarge to

-120

-100

-80

-60

-40

-20

0

Rel

ativ

e S

ea L

evel

in M

eter

s

24681012141618

Time in Thousands of Years


enlarge to

Sea

Lev

el in

Cen

timet

ers

Date

Centimeter Changes Over 100 Years8.0

4.0

0

-4.0

-8.0

-12.01900 1920 1940 1960 1980

5 year running mean

annual mean

-120

-100

-80

-60

-40

-20

0

Rel

ativ

e S

ea L

evel

in M

eter

s

24681012141618

Time in Thousands of Years


Universality 53

Sea

Lev

el in

Cen

timet

ers

Date

Centimeter Changes Over 100 Years8.0

4.0

0

-4.0

-8.0

-12.01900 1920 1940 1960 1980

5 year running meanannual mean

15

Me

an

Se

a L

eve

l in

Mill

ime

ters

10

5

0

-5

-10

-15

Millimeter Changes Over 2 Years

1993 1993.5 1994 1994.5 1995

Average Rate = 3.9 0.8mm/year+_

Periodic changein mean sea level

Date

Properties of Complex Evolutionary Systems

Fractal Organization – Sea Level Changes

Universality

patterns, within patterns, within patterns

53

Hierarchy of Sequences(All sequence orders may not be present in one section; depend on localtectonics, depositional rates, etc.)

Order Duration Range Probably Cause1 2

First Order

Second Order

Third Order

Fourth Order

Fifth Order

200 my

9-10 my

1-2 my

0.1-0.2 my

.01-0.2 my

750 feet

366 feet

200 feet

40 feet

20 feet

Tectonic

Glacio-Eustatic

Glacio-Eustatic

Milkanovitch cycle3

Milkanovitch cycle

Graph to left takes upOnly this much time on the

Above graph

Relative Sea Level Curves

Relative Sea Level Curves and Constructive and Destructive

Interference

Both curves go down; exaggerated sea level fall

3rd order up, 4th order down; muted sea level rise

3rd order up, 4th order down; muted sea level rise

3rd order down, 4th order up; muted sea level fall

Third Order Transgression . . . followed by . . . A Third Order Regression

Sea Level Changes and CorrespondingTrangressions/Regressions are Fractal

Third Order Transgression . . . followed by . . . A Third Order Regression


4th Order Regression . . . followed by . . . 4th Transgression. . . followed by . . .4th Regression . . .

followed by . . .4th Transgression

followed by . . .4th Regression

Patterns within patterns within patterns: i.e. fractal

http://pubs.usgs.gov/dds/dds-033/USGS_3D/ssx_txt/depomod.htm

Figure 8 shows upward and seaward increase in depositional energy (yellow dotted and green areas), which is tied to increases in porosity and permeability. The basal disconformity (wavy line) is the horizontal datum for the 3-D porosity and permeability models. The wedge shape of the Sussex "B" interval results from reworking by currents of seaward margins of sand ridges, and landward redeposition of sediment. The blue-lined areas are basal and landward low-depositional-energy facies; these exhibit low porosity, permeability, and petroleum production. The disconformity at the top of the Sussex "B" sandstone is generally marked by a thin chert-pebble sandstone (figure 9A). Shading variation of the quartz (figure 9B) results from fracturing of the grain in this cross-nicols photomicrograph view (light is transmitted differently due to rotation of the crystal axes). Quartz grains that were incorporated from underlying sand-ridge sediments commonly exhibit early stages of diagenesis within marine environments, primarily chamosite overgrowths under the quartz overgrowths. Grain-to-grain contacts within this facies are mainly point with lesser long-straight contacts.

CUS

FUS

CUSFUS


CorrelationDemonstrating the

Equivalency ofStratigraphic Units

Equivalency may mean:Lithologic: Same rock unit

Paleontologic:

Contain same fossils

Time: Deposited at same time

Biostratigraphic Facies # 2

Facies # 1



1. Ways of Correlating - Lithologic“Walking Out”

Physically tracing a bed from one place to another to insure it is in fact the same rock unit; literally “walking it out.”

Or, tracing an outcrop down the highway. Can be done in many places in the west where good exposure, and flat lying beds are easy to trace.

http://www.raphaelk.co.uk/main/worldwonders.htm

http://www.mongabay.com/external/grand_canyon_trouble.htm

Grand Canyonof Arizona

http://www.ggl.ulaval.ca/personnel/bourque/s4/cambrien.pangee.html

http://www.jgk.org/maps/grand-canyon-large.html

The problem is, . . . Rocks are not always flat laying, and traceable at the surface.

A cross section through the Harrisonburg and Bridgewater, Virginia area, showing a duplex “herd of horses.” The floor thrust is at the bottom of the drawing just above the basement rocks. The North Mountain fault is the roof thrust. In between are a series of splay faults that isolate a series of horses. Note the overturned anticline on the far left (west) side where the last ramp formed. From Gathright and Frischmann, 1986, Geology of the Harrisonburg and Bridgewater Quadrangles, Virginia.

2. Ways of Correlating - Lithologic“Key Beds”

Correlating by recognizing and identifying beds that are so distinctive you always know them when you see them.

1. Distinctive lithology

2. Distinctive mineral assemblage.

3. Particular sedimentary structures.

http://www.uta.edu/paleomap/homepage/Schieberweb/summer_2000_field_work.htm

“Key Beds”

The Chattanooga Shale

http://c3po.barnesos.net/homepage/lpl/fieldtrips/K-T/day3/day3.htmlhttp://www.bbc.co.uk/beasts/whatkilled/evidence/analyse1.shtml

An analysis of the chemical composition of this clay layer shows that it contains a relatively high concentration of an element called iridium. Iridium is rare in the Earth’s crust, but more common towards the Earth's centre, and in space. It continually filters down to earth from outer space, and so a high concentration of iridium is usually an indication that the sediment was deposited very slowly, absorbing lots of iridium over time.

“Key Beds”The iridium layer at the K-T boundary

http://www.uhaul.com/supergraphics/crater/what-is-it2.html

http://www.athro.com/geo/trp/ktm/ktmain.html

The hill in the background of this photograph is known as Iridium Hill. The bands on the side of the hill are layers of rock of different ages that span the time of the extinction of the dinosaurs.

http://www.student.oulu.fi/~jkorteni/space/boundary/

http://www.mines.utah.edu/geo/about_ES/Geology/ZionGIFS/XbedSS.html

“Key Beds”The Navajo Sandstone

http://www.olympic.ctc.edu/class/dassail/CapReef.html

http://www.creationsafaris.com/crev07.htm

3. Ways of Correlating - Lithologic“Position in Sequence”

Identifying a relatively nondescript formation, which could be confused with other similar looking beds, by its relationship to other more distinctive units.

Non-Descript Shale Non-Descript Shale

Quartz Arenite Arkose

Limestone Cross Bedded Sandstone

4. Ways of Correlating - Lithologic“Wire Line Well Logging”

Measuring geophysical properties of a rock as recorded by instruments lowered down a well hole.

http://www.bakerhughes.com/bakeratlas/about/log4.htm

In logging the well four main types of equipment are used: the downhole instrument (which measures the data), the computerized surface data acquisition system (to store and analyze the data), the cable or wireline (which serves as both mechanical and data communication link with the downhole instruments), and the hoisting equipment to raise and lower the instruments.

Resistivity LogsGamma Ray LogsAcoustic Logs

http://www.trianaenergy.com/ucwell/photos/march_26/march_26.htm

“Wire Line Well Logging”

Geophysical logging involves lowering a series of probes into drilled boreholes (or existing fractures or wells) as deep as several thousands of feet into the ground. One type of multiparameter probe that has been used in Maryland and Delaware measures several characteristics of subsurface properties, including natural gamma radiation, or a material’s resistance to electric current, which is useful for finding a good water-bearing sand aquifer for water-supply purposes. Another type is an acoustic velocity probe, which works by transmitting acoustic signals and recording the traveltime of the acoustic wave from one or more transmitters to receivers in the probe. The recorded information can be used to measure porosity and calculate the material’s density. This technique was used to determine the extent of jumbled geologic strata caused by a crater impact at the mouth of the Chesapeake Bay 30 million years ago. Another type of probe, called an Acoustic Televiewer, transmits acoustic signals to subsurface rock layers and uses state-of-the-art computer software to convert the recorded data into an actual image of the borehole. This image can be used to determine the amount of water that could be extracted from individual fractures in the rock formation.

Even though most of the parameters measured by these probes can only be determined in a newly drilled “open” borehole, certain probes emit signals that can penetrate well casings, making it possible to measure subsurface materials after a well is constructed. Gamma rays can travel through almost any type of well casing, while an “induction” probe can measure conductivity electromagnetically through polyvinyl chloride (PVC) casing. Other parameters, such as the borehole’s fluid temperature and conductivity, can also be measured, making it possible to evaluate water quality. The flow direction of ground water can also be determined with several types of probes. All of this equipment enables scientists to characterize the properties of subsurface materials, improving our knowledge of what lies beneath the Earth’s surface.

http://md.water.usgs.gov/publications/fs-126-03/html/

http://www.ldeo.columbia.edu/BRG/TOOLS_TECH/TOOLS/televiewer.html

http://www.ldeo.columbia.edu/BRG/TOOLS_TECH/TOOLS/televiewer.html

A typical well logging arrangement and the resultant logs from two types of tools, the GR and Resistivity Logs

http://www.brookes.ac.uk/geology/8345/8345welc.html#Wireline

http://www.kgs.ukans.edu/Dakota/vol3/fy89/app_b.htm

Gamma Ray Logs

One of the advantages of gamma ray logs is that the gamma ray intensity closely corresponds with texture of the rocks.

Typically, gamma ray radiation is higher with shales (because they have radioactive K40 in them which undergoes K to Ar decay.) Sandstones tend to have a lower gamma radiation.

Thus, we can use the gamma ray log as a proxy for texture of the sediment, and this allows us to read them like a strip log, obtaining information about the energy of deposition.

Gamma Ray Logs and Strip LogsHigh

RadioactivityLow

RadioactivitySANDSTONE SHALE

Gamma RayTrace from

Well log

CoarseningUpwardSequence

Very rapidFUS

Converted into a

Stratigraphic

Strip log

Observe that gamma ray strip logs are the mirror image of a regular strip

log where texture increases to the right.

Rapid FUS is a rapid rise in sea level. They are parasequence boundaries used for correlation.

Gamma Ray Strip LogsVary with Depositional

EnvironmentShoreface Tidal Shoreline

Rapid CUS is a parasequence boundary used for correlation.

Rapid CUS is a parasequence boundary used for correlation.

Rapid FUS is a parasequence boundary used for correlation.

Subtler FUS is a parasequence boundary used for correlation.



OverallCUS

Gamma Ray CorrelationFollowed by Facies Correlation

Shoreface

Coastal Plain

Offshore Shelf

Sea level rises affect large parts of the depositional basin, and their effects are therefore widespread making them ideal for correlations.

5. Ways of Correlating - Lithologic“Reflection Seismicity”

http://www.bakerhughes.com/bakeratlas/about/log2.htm

Seismic surveys use low frequency acoustical energy generated by explosives or mechanical means. These waves travel downward, and as they cross the boundaries between rock layers, energy is reflected back to the surface and detected by sensors called geophones. The resulting data, combined with assumptions about the velocity of the waves through the rocks and the density of the rocks, are interpreted to generate maps of the formations. Seismic surveys are usually performed using multiple geophones set at known distances from the energy source. Early seismic surveys used mechanical plotters to record the received signals, and were restricted to a few geophones. These surveys placed the source and geophones in a straight line, with the interpretation of the resulting data producing a 2-D cross section of the formation under that line. The interpretations were subject to error, which increased the difficulty, and cost, of accurately locating hydrocarbon-bearing formations. Today, the development of digital recording systems allow the recording of data from more that 10,000 geophones simultaneously, greatly speeding data collection. Sophisticated computer programs develop highly accurate 3-D models of rock structures. These models are more accurate than past 2-D maps, and increase the likelihood of accurately identifying hydrocarbon-bearing formations.

http://www.geocities.com/jtvanpopta/seismic_reflection.html

Dark lines are seismic reflection surfaces. Detailed study shows they are essentaily time lines corresponding also with lithologic contacts.

http://www.bgr.de/b322/index.html?/b322/text/d_sunda.htm

http://www.mala.bc.ca/~earles/hydrated-mantle-sep03.htm

Seismic profile across the Cocos and North American Plates adjacent to Costa Rica. Single and double-headed arrows delineate structural fabric in the crust and mantle

http://www.gfz-potsdam.de/pb4/pg3/projects/3-D_structural_modelling_CEBS/content_en.html

http://www.niwa.cri.nz/pubs/wa/11-3/images/news4_large.jpg/view

Ways of Correlating – Biostratigraphic

Biostratigraphic Correlation is based on the work of William Smith and George Cuviere who established the two principles by which geologic maps are drawn.

1. Principle of Faunal Succession

2. Principle of Faunal Correlation

The same strata are always found in the same order of superposition, and they

always contain the same peculiar fossils.

It had been towards the end of the seventeenth century that the first very few and very bold observers raised (albeit timidly) the ultimate heretical thought: the possibility that perhaps, just perhaps, these objects actually were what collectors and scientists and countrymen had long been loath to consider admitting - the organic remains of the very creatures that they looked like.

The Subversive Fossil

Basis of Biostratigrapic Correlation

Zone: A body of rock characterized, recognized and identified by one or more of the fossils it contains.

Range Zone: based on the entire vertical range of a single species.

Assemblage Zone: based on the entire vertical range of a community of species.

Teil Zone: “part zone” defined locally by only part of the known total range of a particular species.

Peak Zone: based on the greatest abundance (the abundance peak) of a species.

Fossil 6 first appears

Fossil 6 disappears

Sp

ecie

s 6

Sp

ecie

s 1

BiostratigraphicZone Based

On Species 6

Sp

ecie

s 2 Sp

ecie

s 3

Sp

ecie

s 4

Sp

ecie

s 5

Sp

ecie

s 7

Sp

ecie

s 8 S

pec

ies

9

Sp

ecie

s 13

Defining Biostratigraphic Zones

Sp

ecie

s 10

Sp

ecie

s 11

Sp

ecie

s 12

Assemblage ZoneWith Fossil 6


On Species 5


On Species 13

The Index FossilNot all fossils are equally useful for correlation.

Lingula, the inarticular brachiopod, for example appears in the record about 540 million years ago, and is still living today. The best knowledge we get from Lingula is that the rock was deposited between 450 million years ago and today. Not very useful.

On the other hand, Lingula prefers to live in tidal systems and so does provide us with paleoenvironmental information.

The Index FossilThe fossils that are most useful for correlation possess the following characteristics:

1. Abundant – no one wants to spend hours looking for the index fossil. They should be easy to find.

2. Rapidly Evolving – want species that evolve and diversify rapidly so that small stratigraphic intervals can be distinguished.3. Widely dispursed – the best index fossils are swimmers or floaters since their remains tend to show up in many different environments. Facies fossils, those living on the bottom in restricted habitats, are not as useful.

There are abundant practical problems associated with biostratigrapic correlation. Requires the work of specialists who have done the technical, nit-picking, careful, highly detailed work that is necessary.

LocalSection

#1

LocalSection

#2Tim

e

Hundreds of Miles

Fossil Zone

Sandstone Form

ation

Directio

n of Transgression

Biostratigraphic Correlation between local sections

Lirthologic Correlation between local sections

The Relationship Between Lithologic and Biostratigraphic Correlation

Time Rock Unit

Time Transg

ress

ive Unit


Regressive Sequence



Beach moves closerWater gets shallowerSediment gets coarser


Beach moves farther awayWater gets deeperSediment becomes finer



Time Rock Unit

Time Rock Unit


http://www-odp.tamu.edu/publications/198_IR/chap_05/c5_f6.htm

http://www-odp.tamu.edu/publications/183_SR/002/images/02_f02.gif

Diastems and UnconformitiesGaps in the Record

Premise 1 – We want a complete history of the Earth.

Premise 2 – The Record is preserved only in the rocks.Premise 3 – The Rock Record is incomplete, being destroyed by weathering and erosion, or lack of deposition.Therefore – A complete history of the Earth is not possible.

Consequenctly, in order to understand the Earth’s history we must understand the gaps in the record, what is missing, why it is missing, and how we know.

AngularNonconformity Disconformity

http://3dparks.wr.usgs.gov/nyc/parks/loc26.htm

The Taconic Unconformity, an angular unconformity between the vertical beds of the Ordovician Austin Glen Formation and the overlying, but steeply dipping, Late Silurian Rondout Formation.

Angular Unconformity

http://www.gly.uga.edu/railsback/FieldImages.html


http://www.gly.uga.edu/railsback/FieldImages.html

Angular Unconformity at Siccar PointJames Hutton’s Famous Unconformity

http://geology.asu.edu/~sreynolds/glg103/relative_age_principles.htm


http://www.geowords.com/lostlinks/c19/nonconformity.htm

Nonconformity

http://www.pittstate.edu/services/scied/Teachers/Field/Camp/Us67-1/us67-1.htm

Along U.S. Highway 67 south of Farmington, Missouri we came to a road cut which featured a very weathered section of granite (probably the Knob Lick granite) which is overlain by a sandstone layer (presumably the Lamotte). Shown in the image on the left, the granite layer is the white weathered debris on the bottom and the sandstone unit is the layered rock on top.

Nonconformity

View from Hout Bay towards Chapmans Peak, showing the nonconformity between the Cape Granite and strata of the Cape Supergroup. Cutting the granite and unconformity is a dolerite dyke

Nonconformity

http://web.uct.ac.za/depts/geolsci/dlr/peninsula%20geology.html

Closer view of contact point between Lykins formation (reds) and Canyon Spring sandstone (whites). The greenish layer in between is where iron has leached out of the uppermost Lykins formation. A disconformity exists here because approx. 70 million years of deposition is missing here between the early Triassic Lykins formation and the mid-to-late Juarssic Canyon Spring sandstone.

http://www.paleocurrents.com/cert_classes/2003_03_15_5/HTML/img_8159.htm

Disconformity

Disconformity

http://www.gc.maricopa.edu/appliedscience/gjc-nsf/reldat/reldat26.html

http://rockhounds.com/grand_hikes/hikes/cape_solitude/index.shtml

Diastems - 1 Invisible Gaps in the Record

1 - Erosion and Deposition on a Relative Sea Level

CurveIn this model a sea level rise leads to deposition, and a sea level fall to erosion and/or no deposition – resulting in a gap in the record.

The model assumes a simple relationship: only sea level rises not countered by a drop result in a permanent record. A sea level rise with a corresponding drop at any time in the future results in no permanent record.

Diastem – 2Next Page

Shore

NearShelf

FarShelf

Sea Level/Base LevelShoreline moves inland

Old Near Shelfnow becomes deep, distal far shelf

Rapid Rise in Sea Level

PROGRADING REGRESSION: With sea level not changing much sediment fills in the accommodation resulting in a regression and a CUS

Distal basin receives little sediment resulting in a condensed section

Para

sequence

= C

US

CondensedSection

Diastems - 2 Nearly Invisible Gaps

in the Record

Layer of black shale only a few mm or cm thick. Hard to see or find in ourcrop.

Prograding Regression = CUS

Diastems - 3 Invisible Gaps in the Record

3 - Episodic Depositional Events

When we look at an outcrop of rock is it easy to think that it represents continuous deposition. After all, we don’t see any gaps or holes in the outcrop. Yet, there are lots of holes (gaps) and not all deposits represent equivalent time.

HighRadioactivity

LowRadioactivitySANDSTONE SHALE

A few hours of time todeposit this.

But, this shale may representyears or decades of time.

Most of the beds we see in an outcrop represent geologically instantaneous events. They took at most a few hours or a few days to be deposited. The shale beds in between represent slow deposition over years of time.

The outcrop is a kaleidoscope of different lengths of time – and they are fractal. Most of the record is in fact gap.

We see the rocks, but we do not see the gaps.

http://www.sju.edu/research/bear_gulch/beargulch.shtml

http://jan.ucc.nau.edu/~rcb7/Oceanography.html

http://geology.sdsmt.edu/Stratsed.htm

Gaps in the record are fractal: imperceptible gaps, within

tiny gaps within small gaps, within larger gaps, within much larger gaps, etc.

Gaps resulting from third order sea level cycles

Within these rock units are 4th and 5th order gaps

Gaps in the Geologic Time Record are Fractal

stratigraphic facies and geologic time amantz gressley, 1834, and the jurassic rocks of the jura...

Documents

transition rocks

igneous rocks

metamorphic rocks

jurassic rocks

kinds of rocks

sedimentary facies

stratified fossiliferous

time slide