Taphonomy & Preservation
• The fossil record is very incomplete
• Biased
• fossil record contains ~ 250,000 species
• ~ 1.5 million living plant and animal species
• fossils represent only 5% of total living forms!
• 14 phyla of animals only 9 are abundant as fossils
Taphonomy & Preservation
• 2 points to consider……
• (1) fossil record is very incomplete; why?
– must make a distinction between incompleteness and inadequacy
• (2) the same processes that inhibit preservation can provide information
concerning the environment of deposition
Taphonomy - the study of fossil Preservation
• 3 subdivisions
• Necrology - how did it die?
• Biostratinomy - sedimentary and biological interactions
• Diagenesis - types of preservation
Biostratinomy
• Many German contributions
• Can apply uniformitarian/actualistic approach
• decay, disarticulation, disintegration (the 3 D’s)
• Biological and sedimentological factors
Biostratinomy - biological
• biological factors
• bacterial decay
• Scavengers
• borers and encrusters
• biological factors don't end with burial - bioturbation
• biological destruction inhibited by low dissolved oxygen
Biostratinomy - mechanical
• mechanical factors -- breakage and abrasion caused by environmental
disturbance
- high energy environments
- Chave (1964) tumbling experiments Biostratinomy - chemical
• chemical factors -- dissolution
- skeletal dissolution can occur at sed/water interface or down under sediment
- different skeletal materials have different stabilities in different environments
- example:
- in acidic environs -- arag < calcite; silica and apatite very stable
- in alkaline environs -- silica not stable
Biostratinomy - transport
• post-mortem transport
• very few body fossils are preserved in situ
• some fossils can't be preserved in life position
• differential transport (teeth versus bones)
• most sessile, benthic organisms don't get transported too far……how
can you detect transport?
Biostratinomy - transport
• Detecting post mortem transport
• find a fossil in a 'wrong' depositional environ
• see signs of breakage and disarticulation or sorting
Biostratinomy - transport
• transport can lead to
• Sorting
– size sorting -- mechanical separation on basis of density
– shape sorting -- different shapes transport better
• Orientation
– alignment -- elongated fossils align to currents; can get paleocurrent
direction
EX: cephs & crinoid stems
– up/down orientation -- shells will flip to stable concave down in a
current
- imbricate, on-edge shell deposits
• internal sedimentation of shells
– not well understood; draft infilling of shells
• prefossilization (doesn't fit in well with the biostratinomic processes)
– sometimes buried organisms that are partially fossilized are reworked
and unburied again
Biostratinomy – burial
• Rates of burial
• burial is usually slow and gradual
• when really slow can get a lag or time-averaged assemblage or a death
assemblage
• rapid or catastrophic burial can happen due to storms, turbidites, volcanic
eruptions; can lead to:
• life assemblage -- whole community at one point in time preserved together
Types of Fossil Assemblages
• biocoenosis
• thanatocoenosis
• taphocoenosis
(how do you tell the 3 apart?)
- life orientations -- fragile organisms well preserved in life orientation
- refugee communities -- escape burrows