Fossils

Created by

Christian Walker

Cards (24)

What is pyritisation?
When the original shell is replaced by pyrite
Why do peat and tar preserve fossils?
They both slow down decay processes
Nektonic 
Organism actively moves/swims in the water
What is replacement?
The original mineral is dissolved atom by atom and replaced by another
Planktonic 
Organism floats in the water column
What is an external mould? 
An imprint left on the surrounding rock by the outside of the organism
Vagrant 
Organism moves around to look for food
Benthonic 
Organism lives on or in the sediment on the ocean floor
What is a facies?
The characteristics of a rock, produced by its environment of deposition, that allow it to be distinguished from rocks deposited in an adjacent environment
What is an internal mould? 
Formed when sediment gets into a shell and preseves the imprint of the inside of the shell
What is a trace fossil?
Evidence of an organisms activity
Epifaunal 
Organism lives on the sediment
What is the principle of uniformitarianism?
The present is the key to the past
What is the law of faunal succession?
Fossils occur in a definite unchanging order in the geological record
Infaunal 
Organism lives in the sediment (a burrower)
What conditions does pyritisation require?
Anoxic conditions
What is a cast? 
A replica of the original fossil
What is carbonisation? 
When organisms are preserved as a thin film of carbon. Common with plants
What is a facies association?
A group of facies that occur together and represent one depositional environment. E.g Desert facies association
Sessile 
Organism is fixed to one place
Which two fossils are good zone fossils?
Graptolites and Ammonites
What two fossil groups are really good zone fossils?
Ammanoids and graptolites
What reasons are there for fragmented fossils?
Death assemblages
Scavengers
Catastrophic events
Why can you find ammonite fossils that are mostly large in areas?
High availability of food
Lack of predators
Low infant mortality
Death assemblages
Juveniles somewhere else