Formation Of Fossils Flashcards Preview

Geology F795 > Formation Of Fossils > Flashcards

Flashcards in Formation Of Fossils Deck (34):

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?

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
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