GEOL 102 Historical Geology

Spring Semester 2017
Fossils and Fossilization

Some general ways of describing organisms' life habits:
Trophic Level: where is the organism in the food web?

Mobility: does the organism move?

If in water, where in the water/sediment column is it?

Fossils: The physical traces of past life.

Or, more fully, a fossil is any remain of an ancient organism or its behavior preserved in the rock record.

Fossils are the only direct evidence of past life, although indirect evidence exists in the form of the phylogenetic and biogeographic distribution of modern organisms.

The study of the preservation of fossils is called taphonomy.

Two major types of fossils:

Trace fossils are, essentially, biologically-generated sedimentary structures. They include:

Preservation of trace fossils is just like other sedimentary structures: must have rapid burial, and preserved by lithification of the rock itself.

Body fossils: can be preserved in a variety of ways.

In general, only organisms with hard parts can be preserved: shells, bones & teeth, wood, etc.

Main hard part mineralogies/biochemistries:

But many organisms have NO hard parts, and are only preserved in rare instances.

Most hard parts are not solid material, but porous. Pore space is occupied by organic material in life. Upon death, organic material begins to decay.

Modes of preservation:

Different organisms have different potential for fossilization.

Plants a special case: different organs (leaves, stems, trunks, fruit, flowers, seeds, pollen, etc.) are only very rarely preserved together. Each part generally given its own species name!

Many fossils were transported by currents betweeen their death and their burial. These are said to be allochthonous ("other [place] buried"). However, some organisms might get buried in place (in situ, to use the Latin phrase), and are said to be authochthonous ("same [place] buried").

Once in awhile there are depositional settings which preserve extremely fine details or soft tissues that are not commonly preserved in fossils. These are known by the German word for "bonanza": Lagerstätten (singular "Lagerstätte"). Lagerstätten give us great insight into the diversity and anatomy of past life.

To Lecture Notes.

Last modified: 17 January 2017