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STRATIGRAPHY AND FOSSILS

Vertical Stratigraphic Relationships

Stratigraphy – Vertical relations in rocksSedimentary Rocks – StrataTime lines –Bedding planes; fossil dataLaw of SuperpositionPrinciple of InclusionsUnconformitiesLaw of Fossil succession (later)

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Lateral Relationships –Sedimentary Rocks

Principle of Lateral Continuity –Sedimentary rock layers extend outward in all directions until they terminate.Terminations

Edge of depositional basinLater erosion of portion of basinTruncation by faultsPinching outLateral gradation

Sedimentary Facies

Different adjacent environments produce different rocks and fossil assemblagesP. 83, Figure 5.7

Marine Transgressions and RegressionsTransgression – rise in sea level or sinking of land

Regression – Lowering of sea level or rise of land

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Walther’s Law

The facies seen in a conformable vertical sequence will also replace one another laterallyP. 84, figure 5.9

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Transgression / RegressionANIMATION

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Reasons for Sea Level Change

Amount of water frozen in glaciersRates of Sea Floor Spreading

Rapid spreading, high heat flow causes ridges to rise and displace water onto the continents causing universal transgressionSlower spreading, lower heat flow, causes ridges to subside, increased volume of ocean basins causes universal regression.

FOSSILS

What is a fossil?Remains of a living thing

How are living things preserved?Taphonomy = Preservation of living things

Basics of most preservationHard Parts

BurialInteractions with rocks and solutions

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Modes of Preservation

Unaltered remains (soft parts)PermineralizationRecrystalizationDissolution and Replacement

Mold and cast, concretionsSilicification 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 and put rocks in stratigraphic order.Geologic Range of a fossil: The age at which a fossil appears (bottom of range) to the age at which it becomes extinct (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 within that rangeFinding fossils with overlapping ranges means that the rocks are the age of the overlap of the ranges.

Principle of Fossil Succession

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