Fossilization

Reading: Chapter 3

Background

Skeletal materials - see Fossilization lab

Terms:

preservation potential - likelihood that an organism will become a fossil

scavenger - organism that eats dead organisms; usually reserved for multicellular organisms

decomposers - organisms that break down dead organisms; essentially very small scavengers

concretions - areas of localized cementation in sedimentary rock, often formed around organic material

biofacies - the total recognizable fossils content of a designated portion of a stratigraphic unit

anoxic - lacking oxygen. Anoxic environments often are deep water, or very still water, or water with a lot of organic material - the oxygen has been used up in decomposition

artifact - an observation that is a product of the observational process, or of something other than the process under observation.

Biological Classification:

Kingdom, Phylum (plural, phyla), Class, Order, Family, Genus, Species

Key Questions:

1. How do fossils form?

A. What are the processes of fossilization?

key terms:

permineralization

recrystallization

replacement

carbonization

impressions

trace

B. What are the conditions that lead to fossilization?

Evidence of the organism must escape biological destruction.

What kinds of biological agents destroy evidence or organisms?

What key factors limit biological destruction?

Evidence of the organism must survive mechanical destruction.

What environmental agents destroy evidence of organisms?

What sedimentary environments are the best for preserving fossils?

What sedimentary environments are the worst for preserving fossils?

Evidence of the organism must survive chemical destruction.

What factors are the most important in determining whether a fossil survives diagenesis?

2. How does differential preservation affect the information carried in the fossil record? How does it affect our ability to ask and answer scienctific questions about ancient organisms and communities?

A. What characteristics of organisms increase the probability of fossilization?

B. What characteristics of environments increase the probability of fossilization?

(look at the examples of Lagerstatten. What aspects of the environment allowed such extrordinary preservation?)

C. In a typical fossil assemblage, what information is preserved? What information is lost?

Assessment

1. Short Answer

Describe two of the ways in which organisms are preserved in an altered state. What organisms are likely to be fossilized in each of these ways?

A crab dies on the seafloor. Identify the major agents of biological and mechanical destruction that would prevent the crab from becoming a fossil. Describe a scenario by which the crab could become a fossil.

What conditions permit exceptional preservation, even of soft-bodied creatures? Give two examples of such exceptional preservation.

2. Essay

Selective preservation changes the information available from the fossil record. Explain how we expect the record to be altered: which organisms and environments will be underrepresented? Which organisms and environments will be overrepresented? Be sure to give reasons and examples for each of your answers.

Geology 105 - Paleontology
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