Fossils

Types of Fossils

Body fossils- The remains of an organism, even if chemically replaced

Trace fossils-  Evidence of an activity by a living thing, such as footprints or burrows

Chemical- Chemical evidence of life, such as products in the rock record that do not occur apart from life or the altered products of such chemicals

Types of Chemical Fossils

Biomarkers- chemical evidence of specific types of life

Isotopic fractionation- Preferential use of one isotope by living things can concentrate those isotopes

Types of Fossilization

Unaltered- Original mineralogy preserved

Permineralization-highly porous material like plant stems or bone have spaces filled with minerals like calcite or silica

Types of Fossilization pt. 2

Pyritization- May overgrow fossil preserving it. Often associated with low oxygen environments. Pyrite can oxidize to hematite when exposed to air and preserve fossils in red rust hues

Recrystalization- Hard parts may shift to a more stable mineralogy during diagenesis

Carbonization-rapid burial can preserve a fossil as a thin film of carbon

Molds

Molds are impressions made by body fossils

Internal molds (also called Steinkerns) are made by filling the inside of a shell

Casts

Casts are made by filling external molds, replicating the shape in new material

Index Fossils

Index fossils are diagnostic of a particular geologic time

Bryozoans

Colonial marine animals with a variety of skeleton shapes

Cnidaria (Corals)

Two types during Devonian: Tabulate and Rugose

Most Tabulate corals are colonial and many Rugose corals are solitary, however you tell them apart based on the form of the corallite and its septa