Historical Geology

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Historical Geology
Lecture 3 Fossilization
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Historical Geology
Outline
I Taphonomy II The Fossil Record A) Controls on
Fossil Record Completeness B) Mineral
Composition of Hard Parts C) Fossil
Preservation 1) Body Fossils a) Altered
Hard Parts b) Unaltered Remains c) Preserv
ed Soft Tissue 2) Trace Fossils 3) Chemical
Fossils III Information from the Fossil
Record A) Paleoecology B) Paleoclimate C) Pa
leogeography D) Biodiversity
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Historical Geology
Taphonomy
the study of all that has happened to organisms
from the moment of death to final preservation as
a fossil.
Taphonomic Processes

• necrolysis
• biostratinomy
• diagenesis

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Historical Geology
Fossilization Common Mineral Compositions of Hard
Parts

• calcium carbonate CaCO3
• aragonite
• calcite
• silica SiO2
• calcium phosphate Ca3(F, Cl, OH)(PO4)3

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Historical Geology
The Fossil Record

• Body Fossils
• Altered Hard Parts
• Unaltered Remains
• Preserved Soft Tissue
• Trace Fossils
• Chemical Fossils

Trilobite Tracks
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Historical Geology
Fossil Preservation Altered Hard Parts

• permineralization
• replacement
• recrystallization

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Historical Geology
Fossil Preservation Permineralization
permineralization - the process of fossilization
wherein the original hard parts of an animal have
additional mineral material deposited in their
pore spaces.
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Historical Geology
Fossil Preservation Replacement
replacement - substitution of inorganic matter
for the original organic constituents of an
organism during fossilization.
Petrified Wood
Florissant Fossil Beds National Monument, Colorado
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Historical Geology
Sponge
Fossil Preservation Replacement
Phosphatization
replacement by Ca3(F, Cl, OH)(PO4)3
Silicification
replacement by SiO2
shark vertebrae
Brachiopod
Ammonite
Pyritization
replacement by FeS
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Historical Geology
Fossil Preservation Recrystallization
Same minerals New mineral structure Loss of detail
Aragonite
Calcite
Increasing crystal size
Rugose coral
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Historical Geology
Fossil Preservation Unaltered Remains

• amber
• tar
• freezing
• mummification

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Historical Geology
Fossil Preservation Unaltered Remains
amber
tar
freezing
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Historical Geology
Fossil Preservation Preserved Soft Parts

• mineral plating
• impressions
• replacement
• carbonization

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Historical Geology
Fossil Preservation Preserved Soft Parts
phosphatization - replacement of low phosphate
apatite with high-phosphate apatite
mineral plating
Aphaesia
Markuelia secunda phosphatized embryo
soft tissue impression
fern leaf
Dickinsonia
Spriggina
Bengston and Zhao, 1997
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Historical Geology
Fossil Preservation Preserved Soft Parts
carbonization - the conversion of the organic
material of a plant or animal to a thin film
of carbon.
Insect
Isograptus
Palm frond
Didymograptus
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Historical Geology
Fossil Preservation Trace Fossils

• tracks
• trails
• burrows
• borings
• eggs and nests
• gastroliths
• fossilized feces (coprolites)
• root paths
• casts and molds (?)

ichnology - the study of plant and animal traces.
Implicit in this definition is that the traces
made by plants and animals reflect some sort of
behavior while living (biogenic).
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Historical Geology
Fossil Preservation Trace Fossils
Advantages
Long Time Range Abundance Common In-situ
Occurrence Preservation Potential Excellent
Environmental Indicators
Disadvantages
One trace maker can make multiple traces Many
trace makers can make identical traces
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Historical Geology
Fossil Preservation Trace Fossils on Bedding
Planes
track - a set of discrete footprints
Dinosaur Tracks
Australopithecus afarensis
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Historical Geology
Fossil Preservation Trace Fossils on Bedding
Planes
trail - continuous trace, usually formed by the
whole body of a travelling or resting worm,
mollusc or arthropod
Trilobite
A crawling trace B resting trace C dwelling
trace D grazing traces E feeding traces
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Historical Geology
Fossil Preservation Trace Fossils within Sediment
burrow - structures formed within soft sediment
by moving grains out of the way, either for
locomotion, dwelling, protection or feeding
vertical burrows
ichnofossil Paleocastor
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Historical Geology
Fossil Preservation Trace Fossils within Sediment
horizontal burrows
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Historical Geology
Fossil Preservation Trace Fossils within Sediment
boring - structures formed in hard substrate by
cutting right through the grains, either for
protection, dwelling, carbonate extraction or
even for feeding purpose (bioerosion).
Ordovician ichnofossil Trypanites
Cretaceous ichnofossil Gastrochaenolites
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Historical Geology
Fossil Preservation Trace Fossils - Excrements
fecal pellets (or strings) - small pellets or
strings of excrement, usually of less than
10 mm length coprolite - fossil feces, probably
an amalgamation of pellets in many cases
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Historical Geology
Fossil Preservation Trace Fossils - Other
Nest and eggs of a Therizinosaur or Segnosaur
root paths
Plesiosaur gastroliths (stomach stones)
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Historical Geology
Fossil Preservation Molds and Casts
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Historical Geology
Fossil Preservation Molds
mold - an impression made in the earth or rock
material by the exterior or interior of a fossil
shell or other organic structure.
Internal Molds
External Molds
Bivalves
Gastropods
Subprionocyclus normalis
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Historical Geology
Fossil Preservation Casts
Coleoptera curulionidae
Tree trunk
Keichousaurus hui
secondary rock or mineral matter that fills a
natural mold, producing a replica of a fossil
shell or skeleton.
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Historical Geology
Fossil Preservation Casts and External Molds
Step a burial of a shell Step b
dissolution leaving a cavity, a mold Step c
the mold is filled by sediment forming a cast
Brachiopod
Trilobite
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Historical Geology
Information from the Fossil Record

• Paleoecology
• Paleoclimate
• Paleogeography
• Biodiversity

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Historical Geology
Information from the Fossil Record Paleoecology
and Paleoclimate
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Historical Geology
Information from the Fossil Record Paleoecology
and Paleoclimate
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Historical Geology
Information from the Fossil Record Paleoclimate
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Historical Geology
Information from the Fossil Record Paleogeography
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Historical Geology
Information from the Fossil Record Biodiversity