Chapter 5- Fossils, Preservation, and Dating Flashcards
Fossil
describes any trace of past life, may be parts of/whole organisms or traces such as burrows and footprints
organism
individual life form, animal/plant/fungus/bacteria, may be single or multi cellular. can be preserved as fossils
Body Fossil
hard parts of an organism, ie skeleton or shell
Replacement
atom by atom substitution of one mineral for another
Dissolution
the process whereby minerals that make up the fossils are dissolved away and removed in solution by groundwater
taphonomy
study of the entire process of fossilisation to when it’s discovered
Mould
the impression of the outside or inside of a fossil
cast
an in-filled fossil void, usually with another mineral
Factors affecting fossilisation (8)
Original composition, energy levels, transport distance, rapidity of burial, amount of oxygen, size of sediment, diagenesis, compaction
Silicification
occurs when percolating groundwater is rich in silica dioxide
Carbonisation
occurs during burial
Pyritisation
occurs in an anaerobic environment containing live sulfur bacteria
Benthonic
organism lives in or on sediment substrate of the sea floor
Infaunal
organism lives in the sediment, usually in a burrow and typically filter feeds
Example of a benthonic infaunal organism
Bivalve clam
Epifaunal
organism lives on the sediment substrate
Example of a benthonic epifaunal organism
bivalve oyster
Vagrant
organism moves around on the sea floor, typically a scavenger or predator
Example of a benthonic vagrant organism
regular echinoid
sessile
organism does not move, some are attached to the substrate, others lie on the sea floor, most filter feed
example of a benthonic sessile organism
bivalve mussel
pelagic
organism lives in the water column, typically in the surface layer
planktonic
organism that floats in the water current usually a filter feeder
Pelagic Planktonic orgaism
graptolite
Nektonic
organism that actively swims in the water column, typically scavenger or predator
example of a pelagic nektonic organism
ammonite
extant
organisms are still alive today
extinct
organisms are no longer alive today
Death assemblage
collection of organisms found in a different place and position than they occupied in life, ie collection of disarticulated shells
Disarticulated
organisms found as fragments, ie seperate shells or parts of trilobites
Life Assemblage
a collection of organisms found within sediments in the same position they would have occupied in life, in bivalve in a burrow
Geopetal structures
allow us to see the way up of a rock, ie coral or bivalve in life position
Derived fossil
fossil that has been weathered out of one rock and deposited in another, different fossils may give conflicting dates
Ornament
expressed on the surface of the fossil, such as ribs, tubercles, spines, and growth lines
Robustness
ability of a fossil to resist abrasion, robust forms are more likely to be preserved whole or with minimal damage
Articulated
organisms found whole or connected, as in life
Littoral zone
high energy area between high and low tide
anoxic/ anaeorbic conditions
lack oxygen and are unsuitable for life
Trace fossils
formed by benthonic infaunal and epifaunal organisms, aquatic or terrestrial. preservation potential is poor
Tracks
footprints of an organism makes when it moved along the sediment
Trails
impressions of animals which were travelling, could have formed due to part or all of the animal dragging along the substrate
Resting traces
a type of trail formed by the animal at rest
terrestrial
refers to anything formed on land
bioturbation
refers to burrowing or working the sediment in a way that disrupts the bedding. caused by activity of living organisms
substrate
name given to sediment/rock on the sea floor
Vertical burrow
skolithos
u-shaped burrow
diplocraterion
branching burrow
thalassionoides
trilobite resting trace
rusophycus
trilobite walking trace
cruziana
borings
structures formed in rock or wood
