Strat i Graphy and Fossils
Transcript of Strat i Graphy and Fossils
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STRATIGRAPHY ANDFOSSILS
Vertical Stratigraphic Relationships
Stratigraphy Vertical relations in rocks
Sedimentary Rocks Strata
Time lines Bedding planes; fossil data
Law of Superposition
Principle of Inclusions
Unconformities
Law of Fossil succession (later)
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Lateral Relationships
Sedimentary Rocks Principle of Lateral Continuity
Sedimentary rock layers extend outward inall directions until they terminate.
Terminations
Edge of depositional basin
Later erosion of portion of basin
Truncation by faults
Pinching out
Lateral gradation
Sedimentary Facies
Different adjacent environments producedifferent rocks and fossil assemblages
P. 83, Figure 5.7
Marine Transgressions and Regressions
Transgression rise in sea level or sinking
of land Regression Lowering of sea level or rise of
land
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Walthers Law
The facies seen in a conformablevertical sequence will also replace oneanother laterally
P. 84, figure 5.9
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Transgress ion/ Reg r essionANI MATI ON
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Reasons for Sea Level Change Amount of water frozen in glaciers
Rates of Sea Floor Spreading Rapid spreading, high heat flow causes
ridges to rise and displace water ontothe continents causing universaltransgression
Slower spreading, lower heat flow,causes ridges to subside, increased
volume of ocean basins causes universalregression.
FOSSILS
What is a fossil?
Remains of a living thing
How are living things preserved?
Taphonomy = Preservation of livingthings
Basics of most preservationHard Parts
Burial
Interactions with rocks and solutions
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Modes of Preservation Unaltered remains (soft parts)
Permineralization
Recrystalization
Dissolution and Replacement
Mold and cast, concretions
Silicification and pyritization
Trace Fossils
Unaltered Remains
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Soft Part Preservation
Marrella Most abundant organism in Burgess Shale
Soft Part Preservation
Anomalocaris
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Permineralization
By permineralization, hard parts
can become more dense and
durable than the original wood
or bone
Recrystallization
CalciteAragonite
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Mold and Cast
Dissolution and internal mold -Steinkern
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Concretions
Pyritization
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Trace Fossils
Biostratigraphy
The use of fossils to date rocks andput rocks in stratigraphic order.
Geologic Range of a fossil: The age atwhich a fossil appears (bottom ofrange) to the age at which it becomesextinct (top of range); depicted as a
vertical bar.Example: Lingula spp. Range =Cambrian to Recent
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Using Geologic Ranges Finding one fossil with a known range
means the rock can be any age withinthat range
Finding fossils with overlappingranges means that the rocks are theage of the overlap of the ranges.
Principle of Fossil Succession
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