Formation Of Fossils Flashcards
Outline exceptional preservation in Amber
Tree resin that has been hardened and preserved. Flowed from trees, accumulated on trunk, animals get caught in it. Hardened by chemical reactions-tells us what was present in ancient forests
What type of exceptional preservation can be seen displayed in Scandinavia?
Amber formed by resin of extinct pine Pinus succinifera used for jewellery-gold of the north
Outline exceptional preservation in tar pits
Hydrocarbons migrate to surface to form poop of asphalt, water accumulated on top, animals lured in and become trapped
Outline processes of exceptional preservation in the Burgess Shales
Cambrian age, found in Canadian Rocky Mountains, snapshot into evolution of life on Earth, animals all extinct but soft parts preserved replaced by clay mineral. Found trilobites, crabs, velvet worms- totally soft bodies so wouldn’t have known about its existence without
Define Benthonic
Creature that lives in it on sediment substrate in sea floor
Define infaunal
Organism lives in sediment, usually in a burrow
Define epifaunal
Organism lives on sediment substrate
Define sessile
Organism does not move around on substrate, may be attached or free lying
Define vagrant
Organism moves around on sea floor, may be a scavenger it predator
Define pelagic
Organism lives in water column
Define Nektonic
Organism actively swims in the water column
Define pelagic
Floats in the water column to wherever the current will take it
Define mechanism of replacement
Original material slowly dissolved and substituted with another, most common Is aragonite to calcite- polymorphs as calcite is more stable. Typically replaced with another mineral present in the groundwater
Define mechanism of silicification
Percolating groundwater rich in SO2 moves through the rock. Minerals crystallise out I solution to full pores and voids in the rock, may be space left behind by dissolves material or in pores within mineral-often in bone or wood
Define mechanism of pyritisation
Replacement of original material by iron pyrites. In anoxic environments with only sulfur bacteria present, use sulfur to respire, reduces sulfur to bisulphate, reacts with iron to iron pyrites, then replaces the fossil material. Common in deep sea of swamps
Where in the world are important exceptionally preserved fossils found?
Burgess shales in Canada, Cambrian Changjiang formation in China, Cambrian Soom Shales in South Africa, Ordivician Herefordshire Lagerstatten, Silurian Solenhofen Limestone, Germany
What are the types of trace fossils?
Tracks on bedding planes, soft sediment
Trails on soft sediment, made by whole or parts of organism
Burrows soft sediment, dwelling, locomotion or protection
Borings stuctures in wood or Rick, hard substrate
Excrement fecal pellets, covered quickly so high sedimentation
Root structures woody impression in rocks or lignite, shallow marine, terrestrial
What are the main types of preservation?
Replacement Silicification Pyritisation Carbonisation Mould and cast formation
How can dinosaur tracks give us information about the animal that made it?
Shape of soft parts
Patterns of scales on the skin
Weight, estimated by size and length and depth
Running/walking speed
Outline mechanism of carbonisation
Occurs during burial, overlying rock increases temperature and pressure, squeezes out volatiles, given off as gas, increasing carbon content. Fossils left as thin layer of carbon within mudstone or shales
Define mechanism of mould and cast formation
Fossils dissolved out of rock they are in, leaving void in the rock. Breaking rock open would show external mould, imprint of fossil, internal mould formed if fossil filled with sediment before burial, cast made if void filled with another material
What is a fossil?
Remains of a living organism, mostly formed from hard parts, can be body fossils or trace fossils
What factors affect the type of fossilisation
Original composition Energy levels Transport distance Rapidity of burial Amount of oxygen Size if sediment Diagnosis Composition and acidity of groundwater
What is a derived fossil?
Organisms originally preserved in older sedimentary layer are eroded, transported and deposited in younger later. Rounded and broken due to transport
How can fossil assemblages indicate paleoenvironments
Thick shells, ribbed, attachment mechanism, broken fragments indicate high energy
Thin shells, wise shells, complete specimens indicate low energy
What is an assemblage?
More than one fossil type found in a rock
What us a defeats assemblage and how is it recognised?
Accumulation of fossils after death, transported and broken then deposited, not in their living position
Broken and fragmented
Sorting of shells by size
Alignment to currents
Mixture of organisms not generally found in same environment
What is a life assemblage and how is it recognised?
Fossils found in living positions eg in reef community or in burrow. Have not been transported, complete and in position they lived in
What is exceptional preservation?
Fossils have fine details or soft parts preserved
What are the ideal conditions for exceptional preservation to occur?
Rapid burial in soft sediment Burial in low energy conditions Lack of oxygen pH is acidic No scavenging animals
Why may fossil record be biased?
Generally only hard parts preseved, some fossils may be entirely soft parts, better preservation in marine conditions
Where in Britain can exceptionally preserved fossils be found?
Charwood forest in Leicestershire, Cnidaria, 575Ma related to corals
What is a trace fossil?
Tracks trails and burrows left behind by ancient organism, provide glimpse of nature and behaviour and help interpret paleoenvironments
How are trace fossils formed?
Organism walks across fine soft substrate, leaves imprint
Footprints infilled with sediment before destroyed, may be seen on base of i filling sediment layer
