Formation of fossils Flashcards
What is a fossil
Fossils are the remains of living organisms
What are body fossils
Skeletal remains or ‘hard parts’ of the organism
Apart from body fossils what is the other main type of fossil and what does that include
Trace fossil
Including tracks, trails and burrows
What are the factors that affect fossilisation
Original composition Energy levels Transport distance Rapidity of burial Amount of oxygen Size of sediment Diagenesis
What are the types of preservation
Replacement (where minerals are substituted)
Silicification (When percolating ground water rich in silica dioxide moves through the rock, the minerals in the groundwater crystallise out of solution and fill any pores or voids)
Pyritisation (replacememnt of original material by iron pyrites, commonly occurs in deep sea environments)
Carbonisation (occurs during burial as the overlying mass of rockks increases the pressure and temp, allowing volitile gases within the organic material to be driven off, this increases the carbon content overall)
Mould cast formation ( moulds are formed when fossils are dissolved out of the rock they are in, usually made of CaCO3. Casts are formed when the void is infilled with another mineral, such as iron pyrites or sillica)
What is exceptional preservation of fossils
Mean that the fossils have very fine detail or the remains of soft tissue are preserved
What are the ideal conditions for exceptional preservation to take place
Rapid burial in a protective medium such as soft, fine clay
Burial in low energy conditions
Lack of oxygen
Low pH (high acidity slows down decay)
Methods of exceptional preservation (Amber)
Amber is tree resin that has been hardened and preserved, when resin was warm in the sun it flowed down the trunk, animals were trapped by the resin and later flows buried the animal, the amber is formed from the resin of the extinct pine tree, Pinus succinifera.
Methods of exceptional preservation (Tar)
Tar pits formed when hydrocarbons that had migrated upwards formed pools of asphalt, water accumulated on top of the tar creating a water hole which enticed animals, animals that became trapped attracted other animals that also became trapped, THE MOST FAMOUS TAR PIT IS RANCHO LE BREA IN CALIFORNIA, most famous species caught is smilodon.
Methods of exceptional preservation (The Burgess Shale)
Was discovered in the Canadian rocky mountains in 1909 by Charles Walcott) the fossils are of Cambrian age and offer a snap shot to evolution to life on earth, examples trilobites and lace crabs.
Methods of exceptional preservation (The Solenhofen Limestone, Germany)
Jurassic limestone contained a bird-like animal called Archaeopteryx) unlike all birds this animal had a full set of teeth, claws on its wings, a flat sternum and a long bony tail However its feathers, wings, furcula and reduced fingers are all characteristics of modern birds.
What is a trace fossil
A fossil that provides glimpses into natural behavior, they can also help us interpret palaeo-environment
Types of trace fossils
Tracks, trails, burrows, borings and excrement (coprolites)
How to make a trace fossil
When the trace by the organism is made it need to be filled in by sediment before they are destroyed by some cause.
What is an assemblage
Many types of fossils in one rock
