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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
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
BeachsandstoneNear Shelf
shaleFar Shelflimestone
Beach moves closerWater gets shallowerSediment gets coarser
Prograding Regression
Time Transgressive Rock Unit
Beach moves farther awayWater gets deeperSediment becomes finer
Transgression
BeachsandstoneNear Shelf
shaleFar Shelflimestone
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.
Transgressive Sequence
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.
Transgressive Sequence
http://www.bees.unsw.edu.au/future/geology.html
Transgressive Sequence
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
Meter Changes Over 18,000 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
Meter Changes Over 18,000 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
Sea Level Changes and CorrespondingTrangressions/Regressions are Fractal
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
Sea Level Changes and CorrespondingTrangressions/Regressions are Fractal
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
Facies are the many different sediments and resulting rocks that form at the same time, but in different depositional environments.
Facies are the many different sediments and resulting rocks that form at the same time, but in different depositional environments.
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/
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.
Subtler 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
BiostratigraphicZone Based
On Species 5
BiostratigraphicZone Based
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
Transgressive Sequence
Regressive Sequence
BeachsandstoneNear Shelf
shaleFar Shelflimestone
Beach moves closerWater gets shallowerSediment gets coarser
Time Transgressive Rock Unit
Beach moves farther awayWater gets deeperSediment becomes finer
BeachsandstoneNear Shelf
shaleFar Shelflimestone
Time Rock Unit
Time Rock Unit
Time Transgressive 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
Angular Unconformity
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
Angular Unconformity
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