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GY 112L: Earth History Lab

Week 5: Fossil Preservation

Instructor: Dr. Douglas W. Haywick

UNIVERSITY OF SOUTH ALABAMA

Today’s Agenda

1) Types of fossils 2) Types of fossil preservation

Types of Fossils

Body Fossils: Actually physical remains of a beastie (shell, skeleton, tests, bones, eggs, feathers, scales, wood etc.)

175 million year old “bird” Archiopteryx sp.

Types of Fossils

Body Fossils: Actually physical remains of a beastie (shell, skeleton, tests, bones, eggs, feathers, scales, wood etc.) Trace Fossils: Evidence that a beasties once lived in a particular environment.

Source: www.humboldt.edu/.../MakingFossils.html

50 million year old bird footprints

Trace Fossils (Ichnofossils)

Ichnology: The study of trace fossils

• Burrows: mostly vertical passages made in soft sediment.

• Feeding Traces: mostly horizontal paths made on top of sediment

• Borings: mostly vertical passages made in solid material (wood, rock)

• Encrustation: attachment of fossils on top of hard materials (e.g. worm tubes)

• Coprilite: fossil turds

Body Fossils

How does something get fossilized?

•Possess hard body parts •Die “peacefully” •Get buried quickly •Stay buried •Avoid oxygen (anaerobic environment) •Get “fossilized”

Modes of Fossil Preservation

Most fossils in the rock record were deposited in marine environments. Most are composed of CaCO3


Most fossils in the rock record were deposited in marine environments. Most are composed of CaCO3 Two major mineral forms: Calcite and Aragonite


Aragonite Calcite More soluble Less Soluble


Unaltered (Pristine) Aragonite


Unaltered (Pristine) Aragonite Chalky Aragonite

Partially dissolved


Unaltered (Pristine) Aragonite a “hole” or mold

Completely dissolved


Molds and Casts External Mold: Impression of the outside of a shell.



Molds and Casts External Mold: Impression of the outside of a shell. Internal Mold: Impression of the inside of a shell.



Molds and Casts External and Internal Molds: Impression of the inside and outside of a shell.


Molds and Casts Cast: an filled-in external mold


Molds and Casts Cast: a filled-in external mold

source: http://paleo.cc/casts/yuep3.jpg


Mineral Replacement

Original shell/skeleton material (calcite/aragonite) replaced by other minerals: Dolomite, chert, pyrite, phosphate, hematite, calcite etc.

Source: http://gpc.edu/~pgore/myphotos/fossils/cast&mold.jpg


Petrifaction

Originally porous materials (wood or bone) are replaced by silica, and the original pore space is filled by silica (perimineralization)

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Concretions

Fossils are encased in nodules that protect them from compaction (leaves, shells). When split open, you get an impression of both sides of the beastie

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Carbonization

Soft organic materials (leaves, graptolites, worms) are preserved as a thin (black to brown) carbon film in sedimentary rocks. Requires anaerobic conditions



“Entombment”

Soft organic remains (insects) are preserved in amber (fossil tree sap)

Today’s Lab 1) Lot’s of fossils, lots of short questions

Next Time Lab 7 Paleozoic Rocks and Fossils

Lab 6 is a bonus opportunity

GY 112/112L: Earth History

Week 5: Fossil Preservation

Instructor: Dr. Doug Haywick [email protected]

This is a free open access lecture, but not for commercial purposes. For personal use only.

university of south alabama · types of fossils body fossils: actually physical remains of a...

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