Formation Of Fossils

Question 1

Outline exceptional preservation in Amber

Answer 1

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

Question 2

What type of exceptional preservation can be seen displayed in Scandinavia?

Answer 2

Amber formed by resin of extinct pine Pinus succinifera used for jewellery-gold of the north

Question 3

Outline exceptional preservation in tar pits

Answer 3

Hydrocarbons migrate to surface to form poop of asphalt, water accumulated on top, animals lured in and become trapped

Question 4

Outline processes of exceptional preservation in the Burgess Shales

Answer 4

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

Question 5

Define Benthonic

Answer 5

Creature that lives in it on sediment substrate in sea floor

Question 6

Define infaunal

Answer 6

Organism lives in sediment, usually in a burrow

Question 7

Define epifaunal

Answer 7

Organism lives on sediment substrate

Question 8

Define sessile

Answer 8

Organism does not move around on substrate, may be attached or free lying

Question 9

Define vagrant

Answer 9

Organism moves around on sea floor, may be a scavenger it predator

Question 10

Define pelagic

Answer 10

Organism lives in water column

Question 11

Define Nektonic

Answer 11

Organism actively swims in the water column

Question 12

Define pelagic

Answer 12

Floats in the water column to wherever the current will take it

Question 13

Define mechanism of replacement

Answer 13

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

Question 14

Define mechanism of silicification

Answer 14

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

Question 15

Define mechanism of pyritisation

Answer 15

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

Question 16

Where in the world are important exceptionally preserved fossils found?

Answer 16

Burgess shales in Canada, Cambrian 
Changjiang formation in China, Cambrian 
Soom Shales in South Africa, Ordivician 
Herefordshire Lagerstatten, Silurian 
Solenhofen Limestone, Germany

Question 17

What are the types of trace fossils?

Answer 17

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

Question 18

What are the main types of preservation?

Answer 18

Replacement 
Silicification
Pyritisation
Carbonisation 
Mould and cast formation

Question 19

How can dinosaur tracks give us information about the animal that made it?

Answer 19

Shape of soft parts
Patterns of scales on the skin
Weight, estimated by size and length and depth
Running/walking speed

Question 20

Outline mechanism of carbonisation

Answer 20

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

Question 21

Define mechanism of mould and cast formation

Answer 21

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

Question 22

What is a fossil?

Answer 22

Remains of a living organism, mostly formed from hard parts, can be body fossils or trace fossils

Question 23

What factors affect the type of fossilisation

Answer 23

Original composition
Energy levels 
Transport distance
Rapidity of burial
Amount of oxygen 
Size if sediment 
Diagnosis
Composition and acidity of groundwater

Question 24

What is a derived fossil?

Answer 24

Organisms originally preserved in older sedimentary layer are eroded, transported and deposited in younger later. Rounded and broken due to transport

Question 25

How can fossil assemblages indicate paleoenvironments

Answer 25

Thick shells, ribbed, attachment mechanism, broken fragments indicate high energy
Thin shells, wise shells, complete specimens indicate low energy

Question 26

What is an assemblage?

Answer 26

More than one fossil type found in a rock

Question 27

What us a defeats assemblage and how is it recognised?

Answer 27

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

Question 28

What is a life assemblage and how is it recognised?

Answer 28

Fossils found in living positions eg in reef community or in burrow. Have not been transported, complete and in position they lived in

Question 29

What is exceptional preservation?

Answer 29

Fossils have fine details or soft parts preserved

Question 30

What are the ideal conditions for exceptional preservation to occur?

Answer 30

Rapid burial in soft sediment 
Burial in low energy conditions
Lack of oxygen 
pH is acidic 
No scavenging animals

Question 31

Why may fossil record be biased?

Answer 31

Generally only hard parts preseved, some fossils may be entirely soft parts, better preservation in marine conditions

Question 32

Where in Britain can exceptionally preserved fossils be found?

Answer 32

Charwood forest in Leicestershire, Cnidaria, 575Ma related to corals

Question 33

What is a trace fossil?

Answer 33

Tracks trails and burrows left behind by ancient organism, provide glimpse of nature and behaviour and help interpret paleoenvironments

Question 34

How are trace fossils formed?

Answer 34

Organism walks across fine soft substrate, leaves imprint

Footprints infilled with sediment before destroyed, may be seen on base of i filling sediment layer