Historical Geology Lecture 3 Fossilization. Historical Geology ITaphonomy IIThe Fossil Record A)Controls on Fossil Record Completeness B)Mineral Composition

Historical Geology

Lecture 3

Fossilization

Historical Geology

I TaphonomyII The Fossil Record

A) Controls on Fossil Record CompletenessB) Mineral Composition of Hard PartsC) Fossil Preservation

1) Body Fossilsa) Altered Hard Partsb) Unaltered Remainsc) Preserved Soft Tissue

2) Trace Fossils3) Chemical Fossils

III Information from the Fossil RecordA) PaleoecologyB) PaleoclimateC) PaleogeographyD) Biodiversity

Outline

Historical GeologyTaphonomy

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

Historical GeologyFossilization

Controlling Factorsbody construction (hard parts)

environment

predationDeath

Scavenging

Decayof softtissues

Decre

asin

g p

robab

ility

100%

?%

Continuous removal of “potential” fossils

The probability of preservation depends on the anatomy and habitat of theorganism—marine organisms with hard parts are most likely to be preserved

AbrasionAnd

transport

Burial

FinalPreservation

Historical GeologyFossilization

Common Mineral Compositions of Hard Parts

calcium carbonate CaCO3

aragonite

calcite

silica SiO2

calcium phosphate Ca3(F, Cl, OH)(PO4)3

Historical GeologyThe Fossil Record

Body Fossils

Altered Hard Parts

Unaltered Remains

Preserved Soft Tissue

Trace Fossils

Chemical Fossils

Trilobite Tracks

Historical GeologyFossil Preservation

Altered Hard Parts

permineralization

replacement

recrystallization


Permineralizationpermineralization - the process of fossilization wherein the originalhard parts of an animal have additional mineral material deposited in their pore spaces.


Replacementreplacement - substitution of inorganic matter for the original

organic constituents of an organism during fossilization.

Florissant Fossil BedsNational Monument, Colorado

Petrified Wood


Replacement

Brachiopod

Sponge

Silicification

Pyritization

Ammonite

replacement by FeS

replacement by SiO2

Phosphatizationreplacement by Ca3(F, Cl, OH)(PO4)3

sharkvertebrae


RecrystallizationSame mineralsNew mineral structureLoss of detail

Aragonite Calcite

Increasing crystal sizeRugose coral

Fossil PreservationUnaltered Remains

Historical Geology

amber

tar

freezing

mummification


Unaltered Remains

amber

tar

freezing

Fossil PreservationPreserved Soft Parts

Historical Geology

mineral plating

impressions

replacement

carbonization

Historical GeologyFossil PreservationPreserved Soft Parts

phosphatization - replacement of low phosphate apatite with high-phosphate apatite

Markuelia secunda

phosphatized embryo

Bengston and Zhao, 1997

Aphaesia

Dickinsonia Spriggina fern leaf

soft tissue impression

mineral plating

Historical GeologyFossil PreservationPreserved Soft Parts

carbonization - the conversion of the organic material of a plant or animal to a thin film of carbon.

Didymograptus

Isograptus

Insect

Palm frond


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).


Trace Fossils

Advantages

Long Time RangeAbundanceCommon In-situ OccurrencePreservation PotentialExcellent Environmental Indicators

Disadvantages

One trace maker can make multiple tracesMany trace makers can make identical traces

Fossil PreservationTrace Fossils on Bedding Planes

Historical Geology

track - a set of discrete footprints

Australopithecus afarensis

Dinosaur Tracks

Fossil PreservationTrace Fossils on Bedding Planes

Historical Geology

trail - continuous trace, usually formed by the whole body of a travelling or resting worm, mollusc or arthropod

TrilobiteA : crawling traceB : resting traceC : dwelling traceD : grazing tracesE : feeding traces


Trace Fossils within Sedimentburrow - structures formed within soft sediment by moving grains out of the way, either for locomotion, dwelling, protection or feeding

vertical burrows

ichnofossil Paleocastor


Trace Fossils within Sediment

horizontal burrows

Fossil PreservationTrace Fossils within Sediment

Historical Geology

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


Trace Fossils - Excrementsfecal pellets (or strings) - small pellets or strings of excrement,

usually of less than 10 mm lengthcoprolite - fossil feces, probably an amalgamation of pellets in many

cases

Historical GeologyFossil PreservationTrace Fossils - Other

Plesiosaur gastroliths (“stomach stones”)

root paths

Nest and eggs of a Therizinosaur or

Segnosaur


Molds and Casts


Moldsmold - an impression made in the earth or rock material by the

exterior or interior of a fossil shell or other organic structure.

Subprionocyclus normalis

Gastropods

Internal Molds External Molds

Bivalves


Casts

secondary rock or mineral matter that fills a natural mold, producing a replica of a fossil shell or skeleton.

Coleoptera curulionidae

Keichousaurus hui

Tree trunk

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


Casts and External Molds

Trilobite

Brachiopod

Historical GeologyInformation from the Fossil Record

Paleoecology

Paleoclimate

Paleogeography

Biodiversity


Paleoecology and Paleoclimate


Paleoecology and Paleoclimate


Paleoclimate


Paleogeography


Biodiversity

Documents

Historical Geology Lecture 3 Fossilization. Historical Geology ITaphonomy IIThe Fossil Record A)Controls on Fossil Record Completeness B)Mineral Composition