Trace fossils

Define the term 'trace fossils' and briefly outline their use in palaeoenvironmental analyses.

Trace fossils are also referred to as…

ichnofossils

What are trace fossils?

a fossil record of the activity of an organism rather than they’re remains

what are trace fossils evidence of?

Activity of an organism

Preservation shows/ depends on

how the trace fossils and how the organism interacts with the sediment

Endogenic traces

made within; organism burrowing into the sediment

Exogenic traces

not in full relief/ epirelief; made on the surface

Traces can be:

• full relief: burrow preserved in 3 dimension; only endogenic

• epirelief: on top of bed

• hyporelief: on base of bed; most common; common in interbedded sand and muds

Resting trace

• common

• series of scratches

• organism leaves a hollow - filled with sediment

• left by multiple organism e.g. snails, trilobites

Repichnia

• walking/crawling trace

• bilobed structure - series of scratch marks/ drag marks

Cubichnia

• restring trace

• cubare = to lie down

Domichnion

living burrow

Diplocraterion

escape trace

Paschinia

• surface feeding trace

• series of infinite loops

• try not to come back on themselves

• cover as much area as possible

Fodinichnia

• mining feeding trace

• worm punching into sediment

• animals living close to sediment water-face

• try to avoid previoisly ingested sediment

Agrichnia

• cultivation trace

• characteristic of deep waters

• organism creates a series of chambers to harvest algae from

Utility of trace fossils

• helps identify pre-Cambrian - Cambrian boundary: base of Cambrian defined by appearance of Phycodes

• diversity throughout the phanerozoic

• helps us understand behaviour of ancient organisms

Trace fossils can be used as…

environmental indicators

how can trace fossil be used as environmental indicators

communities of trace fossils can determine the environment

What do Thalassonoides indicate?

Typical of littoral deposits; beachfront deposits; shallow water deposits

4 classic marine ichnofacies

1. Nereites

2. Zoophycos

3. Cruziana

4. Skolithos

what does the skolithos ichnofacies indicate

indicates highly mobile seafloor/ substrate floor

what do the Psilonichnus and Scoyenia describe?

marginal marine and freshwater occurrences or communities of trace fossils

glossifungites ichnofacies

substrate dependant forms: shallow water

Trypanites ichnofacies

substrate dependant; boring into limestone;

Teredolites ichnofacies

substrate dependant; boring into wood

marine ichnofacies are related to…

• Sediment type

• Water depth

• rate of deposition

what are the controls on distribution of trace fossils?

1. Avg. grain size of the sediment

• Affects sediment ingesting burrowers

• Organisms that requires particular sediment

• Filter feeder avoid fine sediment particles

 

2. Sediemt stability

• Glossifungites and Trypanites ichnofacies depend upon firm and lithified substrates

 

3. Water content

• Affect the consistency of the sediment

 

4. Chemical conditions

• O2 levels - absent in anoxic conditions

what is tierring

the number of levels exploited by organisms; organisms producing trace fossils