Biostratigraphy PDF

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Summary

Lecture notes on biostratigraphy from Marine Geology. ...

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MSCI 304: Biostratigraphy Definition: Rock/sediment units correlated based on fossils present in the strata. William Smith (1793) (English)  Recognized that fossils show the relative ages of sedimentary rocks.  Principle of faunal succession (Smith): -Sedimentary strata in an outcrop contain fossils in a definite sequence and same sequence can be found at other locations. Therefore, relative age can be determined by correlating fossils from distant outcrops.  Led to birth of paleontology (one of most important sources of information about Earth history) Phylogeny – tracking living organism’s evolution  

Populations that can interbreed and produce fertile offspring are defined as a single species (biological species concept) Can’t try to breed fossils

Morphology – physical similarities 

Use physical similarities of a group of fossils to determine relatedness

The Ideal Fossil for Biostratigraphy:     

Organism lived in all depositional environments all over world Abundant Easily preserved hard parts Organism frequently developed new, distinct species Does not exist!

Barriers to the Ideal Fossil Rate of speciation

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frequency with which new species evolve and replace former species Some show little speciation over long periods of geologic time Some of higher rates are mammals, reptiles, fish (every 1-3 million years) But these less common than marine molluscs (~1 million years) Some ammonites and trilobites (~1 million years) Use multiple species!

Depositional Environment     

Marine better than continental Rapid burial better than slow burial Low energy better than high energy Anoxic better than oxic (carbonization) Result is bias to marine fossils

Mobility of Organisms 

Planktonic and nektonic better than benthic (they move around)

Abundance and Size   

Must be abundant enough to easily find in the rocks Smaller organisms tend to be more numerous Microfossils (used commonly in cores for biostratigraphy)

Preservation Potential   

Few organisms ever preserved as fossils, so record of life incomplete Need hard parts and ability to withstand erosion/breakdown Stratigraphic record is incomplete (erosion, unconformities)

Biozones  

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Fundamental unit of biostratigraphy (like ‘formation’ for lithostratigraphy) Intervals of geological strata that are defined on the basis of their characteristic fossil taxa, as opposed to a lithostratigraphic unit which is defined by the lithological properties of the surrounding rock. Types of biozones: range zone, concurrent range zone, partial range zone, assemblage zone, acme zone

Index Fossils     

Can pinpoint specific time all by itself Criteria: Easily recognizable Existed for short period of time Widespread distribution...