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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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