formation of fossils Flashcards
replacement
original material is dissolved atom by atom and substituted with anther material. it can occur where ground water has another mineral present within it like hematite.
what does replacement most commonly occur with?
Arogonite to calcite
silicification
percolating ground water rich in silica dioxide moves through the rock. the mineral crystallises out of solution to fill any pores or voids.
what does silicification tend to preserve?
it fills the pores in bones. sells and wood
pyritisation
Replacement of original material with pyrite. It takes place when the environment has no oxygen and the only organisms alive are sulphur bacteria. The sulphur bacteria use sulphur to respire which reduces the sulphur and causes it to react with any iron present forming pyrite.
where does pyritization usually occur?
deep sea environments or swamps
carbonisation
organic material (usually plants) is subjected to increased het and pressure. This forces volatiles to be driven off and increases the carbon content which essentially preserves the material as a carbon film
moulds
moulds are formed when fossils are dissolved out of the rock they are in. This leaves a void which preserves the external features of the organism. sometimes if the organism was filled with sediment before burial and then dissolved a mould of the internal features is preserved.
casts
formed if a new mineral in the void (mould)
what factors affect fossilisation? x7
diagenesis transport energy levels sediment size composition oxygen amounts speed of burials
fossils
the preserved remains of living organisms or the traces of those organisms when they were alive.
body fossils
the hard parts of a whole or fragmented organisms. They represent the skeletal remains
traces fossils
these are traces of animal life such as tracks, burrows or fossilised dung
