Transcript Facies and Time
Stratigraphic Facies and Geologic Time
Amantz Gressley, 1834, and the Jurassic Rocks of the Jura Mountains between France and Switzerland
The Interpretation of Geologic History Requires Knowledge of the Following
1. Sedimentary Rocks 2. Igneous Rocks 3. Metamorphic Rocks 4. Origin and History of Life 5. 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
The Interpretation of Sedimentary Rocks Requires Knowledge of the Following:
1. Rock Classification 2. Depositional Environments 3. Sedimentary Structures 4. Sedimentary Tectonics 5. Sedimentary Facies and Time
Abraham Gottlob Werner’s Geologic Time Scale The Neptunist World View Sea Level after deposition of the Primitive rocks Sea Level after deposition of the Transition rocks
Stratified
Sea Level after deposition of the Stratified rocks
Transported Transition Primitive Primitive
– crystalline rocks, both igneous and metamorphic. Thought to represent first chemical precipitates from a worldwide ocean.
Transition
– stony, indurated stratified rocks such as graywacke, limestones, sills.
Stratified
– obviously stratified fossiliferous rocks, thought to represent the first deposits after receding of the worldwide oceans, formed by erosion of emergent mountains.
Transported
– Poorly consolidated clays, sands and gravels. Thought to have been deposited after final withdrawal of a worldwide ocean.
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
The study of rock strata, especially the distribution, deposition, and age of sedimentary rocks
P 126
Werner’s theory made sequence all over the world.
a firm prediction, that the same kinds of rocks should have been laid down in the same
The Facies Concept
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.
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 Definitions
Definition One
The facies is the sum total of all the physical, biological and chemical characteristics imparted to a sedimentary rock at the time of deposition.
Definition Two
Facies are the many different sediments and resulting rocks that form at the same time, but in different depositional environments.
The Transition from Wernerian "Transition Rocks" To the Lower Paleozoic Periods By Sedgewich and Murchinson
Sedgewick, 1835 Charles Lapworth 1879 Cambrian Sedgewick, 1835 Ordovician Cambrian
overlap Opps !
Murchinson, 1835 Silurian Silurian Murchinson, 1835
Lyell 1833 D’Halloy 1822 Gressley 1795 Alberti 1834 Murchinson 1841 Williams 1891 Permian Pennsylvan.
Williams 1891 Sedgewich & Murchinson 1839 Mississippian Devonian Murchinson 1835 Lapworth 1879 Sedgewick 1835 Silurian Ordovician Cambrian Pleistocene Pliocene Miocene Eocene Cretaceous Jurassic Triassic Carbonif.
“Old Red ss” Unstudied Until 1830’s
The Transition from Wernerian "Transition Rocks" To the Lower Paleozoic Periods By Sedgewich and Murchinson
Adapted from Dott and Batten: Evolution of the Earth
http://www.picturescape.co.uk/gallery%20page s/gallery%20one/caldey%20sandstone.htm
Old Red Sandstone Early Devonian fishes from the Old Red Sandstone of Spitzbergen (Wood Ray Formation) http://www.picturescape.co.uk/gallery%20pages/gallery%20one/caldey%20sandstone.htm
Old Red Sandstone The Old Red Sandstone exhibited many changes over short distances, with thinly layered areas alternating with conglomerates and outstanding crossbedded sandstones. http://virtual.yosemite.cc.ca.us/ghayes/Siccar%20Point.htm
Devonian Marine Rocks of Devon, England 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.
http://www.ukfossils.co.uk/sec084c.htm
Devonian Marine Rocks of Devon, England http://www.earthfoot.org/places/uk005.htm
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.
Wales Bristol Bay Devonshire
http://www.camelotintl.com/heritage/counties/england/devon.html
http://www.devonshireheartland.co.uk/
Scenes of Devonshire, England http://www.picturesofengland.com/Devon/pictures-1.htm
Scenes of Devonshire, England http://www.picturesofengland.com/Devon/pictures-1.htm
The Problem There are different rocks sandwiched between the Silurian and Carboniferous rocks as found in Wales and Devonshire.
Onlap (Transgressive) Sequences Shifting Facies through Time
Far Shelf limestone
Time Rock Unit Time Rock Unit Time Rock Unit Time Rock Unit Time Rock Unit Time Rock Unit
Near Shelf shale Beach sandstone
Beach moves farther away Water gets deeper Sediment becomes finer FUS – Fining Upward Sequence = Transgressive Sequence
Offlap (Regressive) Sequences Shifting Facies through Time
Prograding Regression Time Transgressive Rock Unit
Near Shelf shale Beach sandstone Far Shelf limestone
Beach moves closer Water gets shallower Sediment gets coarser CUS – Coarsening Upward Sequence = Regressive Sequence
Transgressive Sequence
Far Shelf limestone Near Shelf shale Beach sandstone
Beach moves farther away Water gets deeper Sediment becomes finer Regressive Sequence Prograding Regression
Far Shelf limestone shale
Beach moves closer Water gets shallower Sediment gets coarser
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.
Facies One
A couple of hundred miles
The Problem There are different rocks sandwiched between the Silurian and Carboniferous rocks as found in Wales and Devonshire.
FUS CUS FUS CUS FUS CUS
Transgressive Sequence in the Grand Canyon of Arizona
http://instruct.uwo.ca/earth-sci/300b-001/
Transgressive Sequence in the Grand Canyon of Arizona
TONTO GROUP Cambrian Period, 500-520 Million Years Old, 1025 Feet Thick Yellowish ledges on top, the Tonto Platform between, and brown cliff below
FINING UPWARD SEQUENCE http://www.canyondave.com/TontoPg.html
Transgressive Sequence
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.
http://www.uga.edu/~strata/sequence/transgressivesurface.html
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
Regressive Sequence
cus Table mountain near Mitzpe Ramon, central Negev, Israel http://www.geomorph.org/gal/mslattery/world.html
cus
Regressive Sequence
http://www.geneseo.edu/~gsci/pages/department/information/brochure/brochure_department.html
Transgressive-Regressive Sequences http://www.geology.utoronto.ca/basinanalysis/photos.htm
The Fractal Nature of Transgression and Regression
Universality Properties of Complex Evolutionary Systems
Fractal Organization – Sea Level Changes
Meter Changes Over 18,000 Years Meter Changes Over 125,000 Years
0 +20 -20
pr esen t sea l ev el
0 -40 -20 -60 -40 -80 -60 -100 -80 -120 18 -100 16 14 12 10 8 6 4 Time in Thousands of Years 2 -120
g l a cia t i on
100,000 50,000 Time in Years Present
enla r g e t o
Centimeter Changes Over 100 Years
8.0
0 -20 -40 -60 -80 -100 -120 18 16
en la r g e t o
Meter Changes Over 18,000 Years
14 12 10 8 6 4 Time in Thousands of Years 2 4.0
0 -4.0
-8.0
-12.0
1900 annual mean 5 year running mean 1920 1940 Date 1960 1980 53
Universality Properties of Complex Evolutionary Systems
Fractal Organization – Sea Level Changes
Centimeter Changes Over 100 Years
8.0
4.0
0 -4.0
-8.0
annual mean 5 year running mean -12.0
1900 1920 1940 Date 1960 1980 patterns, within patterns, within patterns
Millimeter Changes Over 2 Years
15 10 5 Periodic change in mean sea level 0 -5 -10 -15 1993 1993.5
1994 Date 1994.5
1995 53
Hierarchy of Sequences (All sequence orders may not be present in one section; depend on local tectonics, depositional rates, etc.)
Order First Order Duration 200 my Range 750 feet Probably Cause 1 2 Tectonic Second Order 9-10 my 366 feet Glacio-Eustatic Third Order Fourth Order Fifth Order 1-2 my 0.1-0.2 my .01-0.2 my 200 feet 40 feet 20 feet Glacio-Eustatic Milkanovitch cycle 3 Milkanovitch cycle
Graph to left takes up Only this much time on the Above graph
Relative Sea Level Curves
Relative Sea Level Curves and Constructive and Destructive Interference
3 rd order down, 4 th muted sea level fall order up; 3 rd order up, 4 th order down; muted sea level rise 3 rd order up, 4 th order down; muted sea level rise Both curves go down; exaggerated sea level fall
Sea Level Changes and Corresponding Trangressions/Regressions are Fractal
Third Order Transgression . . . followed by . . . A Third Order Regression
Sea Level Changes and Corresponding Trangressions/Regressions are Fractal
Third Order Transgression . . . followed by . . . A Third Order Regression 4 th Order Regression . . . followed by . . . 4 th Transgression. . . followed by . . .
4 th Regression . . .
followed by . . .
4 th Transgression followed by . . .
4 th Regression
Patterns within patterns within patterns: i.e. fractal
Sea Level Changes and Corresponding Trangressions/Regressions are Fractal
FUS CUS FUS CUS
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. http://pubs.usgs.gov/dds/dds-033/USGS_3D/ssx_txt/depomod.htm
Correlation
Demonstrating the Equivalency of Stratigraphic Units
Equivalency may mean: Lithologic:
Same rock unit
Paleontologic:
Contain same fossils
Time:
Deposited at same time
Biostratigraphic
Facies # 2
Facies are the many different sediments and resulting rocks that form at the same time, but in different depositional environments.
Facies # 1
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.
Grand Canyon of Arizona
http://www.mongabay.com/external/grand_canyon_trouble.htm
http://www.ggl.ulaval.ca/personnel/bourque/s4/cambrien.pangee.html
http://www.raphaelk.co.uk/main/worldwonders.htm
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.
“Key Beds”
The Chattanooga Shale
http://www.uta.edu/paleomap/homepage/Schieberweb/summer_2000_field_work.htm
“Key Beds”
The iridium layer at the K T boundary
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.
http://www.bbc.co.uk/beasts/whatkilled/evidence/analyse1.shtml
http://c3po.barnesos.net/homepage/lpl/fieldtrips/K-T/day3/day3.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.uhaul.com/supergraphics/crater/what-is-it2.html
http://www.student.oulu.fi/~jkorteni/space/boundary/
“Key Beds”
The Navajo Sandstone
http://www.mines.utah.edu/geo/about_ES/Geology/ZionGIFS/XbedSS.html
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.
Limestone Cross Bedded Sandstone Non-Descript Shale Quartz Arenite Non-Descript Shale Arkose
4. Ways of Correlating - Lithologic
“Wire Line Well Logging”
Measuring geophysical properties of a rock as recorded by instruments lowered down a well hole.
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 instruments. to raise and lower the Resistivity Logs Gamma Ray Logs Acoustic Logs
http://www.bakerhughes.com/bakeratlas/about/log4.htm
“Wire Line Well Logging”
http://www.trianaenergy.com/ucwell/photos/march_26/march_26.htm
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.
drilled Even though most of the parameters measured by these probes can only be determined in a newly “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
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 K 40 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.
http://www.kgs.ukans.edu/Dakota/vol3/fy89/app_b.htm
Gamma Ray Logs and Strip Logs
Low Radioactivity SANDSTONE Very rapid FUS High Radioactivity SHALE
Rapid FUS is a rapid rise in sea level. They are parasequence boundaries used for correlation.
Observe that gamma ray strip logs are the mirror image of a regular strip log where texture increases to the right.
Gamma Ray Trace from Well log Converted into a Stratigraphic Strip log Coarsening Upward Sequence
Gamma Ray Strip Logs Vary with Depositional Environment
Shoreface
Rapid FUS is a parasequence boundary used for correlation.
Tidal Shoreline
Subtler FUS is a parasequence boundary used for correlation.
Rapid CUS 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.
Rapid CUS is a parasequence boundary used for correlation.
Gamma Ray Correlation Followed by Facies Correlation
Overall CUS
Coastal Plain Shoreface 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”
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.bakerhughes.com/bakeratlas/about/log2.htm
Dark lines are seismic reflection surfaces. Detailed study shows they are essentaily time lines corresponding also with lithologic contacts.
http://www.geocities.com/jtvanpopta/seismic_reflection.html
http://www.bgr.de/b322/index.html?/b322/text/d_sunda.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.mala.bc.ca/~earles/hydrated-mantle-sep03.htm
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 Subversive Fossil
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 same strata are always found in the same order of superposition, and they always contain the same peculiar fossils.
Basis of Biostratigrapic Correlation Zone:
A body of rock characterized, recognized and identified by one or more of the fossils it contains.
Range Zone: species.
based on the entire vertical range of a single 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 disappears Fossil 6 first appears Defining Biostratigraphic Zones
Biostratigraphic Zone Based On Species 13
Assemblage Zone With Fossil 6
The Index Fossil
Not 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 Fossil
The 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.
The Relationship Between Lithologic and Biostratigraphic Correlation
Local Section #1 Local Section #2 Biostratigraphic Correlation between local sections Lirthologic Correlation between local sections
Hundreds of Miles
Transgressive Sequence
Time Rock Unit
Far Shelf limestone Near Shelf shale Beach sandstone
Beach moves farther away Water gets deeper Sediment becomes finer Regressive Sequence Time Transgressive Rock Unit
Beach Far Shelf limestone shale
Beach moves closer Water gets shallower Sediment gets coarser
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 Unconformities Gaps 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.
Nonconformity Angular Disconformity
Angular Unconformity 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.
http://3dparks.wr.usgs.gov/nyc/parks/loc26.htm
Angular Unconformity http://www.gly.uga.edu/railsback/FieldImages.html
Angular Unconformity at Siccar Point James Hutton’s Famous Unconformity http://www.gly.uga.edu/railsback/FieldImages.html
Angular Unconformity http://geology.asu.edu/~sreynolds/glg103/relative_age_principles.htm
Nonconformity http://www.geowords.com/lostlinks/c19/nonconformity.htm
Nonconformity 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. http://www.pittstate.edu/services/scied/Teachers/Field/Camp/Us67-1/us67-1.htm
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 http://web.uct.ac.za/depts/geolsci/dlr/peninsula%20geology.html
Disconformity 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 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 Curve In 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 – 2 Next Page
Diastems - 2
Nearly Invisible Gaps in the Record
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
Condensed Section
Layer of black shale only a few mm or cm thick. Hard to see or find in ourcrop.
Shoreline moves inland
Shore
Sea Level/Base Level Distal basin receives little sediment resulting in a condensed section = CUS
Near Shelf Far Shelf
now becomes deep, distal far shelf
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.
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.
Low Radioactivity SANDSTONE High Radioactivity SHALE
But, this shale may represent years or decades of time.
A few hours of time to deposit this.
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 Geologic Time Record are Fractal
Gaps resulting from third order sea level cycles Within these rock units are 4 th and 5 th order gaps Gaps in the record are fractal: imperceptible gaps, within tiny gaps within small gaps, within larger gaps, within much larger gaps, etc.