GEOL 337 Lecture Notes - Baltic Amber, Gaseous Fire Suppression, Taphonomy

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What is a Fossil?
-a fossil is any object that provides evidence of prehistoric life (over 6000
years ago)
-shells, bones, or other hard parts
-mineral placement of bodies or skeletons
-biological impressions in rock
-tracks, trails and burrows
-chemical compounds dianostic of specific groups of life (chemofossil)
Why Study Taphonomy?
-fossils are selective
-some are more easily preserved
-some parts of organisms are easier to preserve (skeleton vs soft parts)
-some environments preseve fossils better than others (offshore vs beaches)
-some environments, skeletons can be moved witihn or between communities
-taphonomy controls the fidelity of the local fossil record
-understanding taphonomy can provide important environmental information
How are Fossils Preserved?
A) Unaltered soft parts
-no change to organic tissue except the loss of water
-three processes: frozen (Pleistocene mammoth), mummified (Eocene wood
"Fossil Forest"), conservation trap (baltic amber)
B) Altered Soft Parts
-soft parts are preserved but has been altered
-carbonized body parts, soft tissues replaced by pyrite, soft body impressions
-two processes: anoxia/stagnation, rapid burial/obrution
-fossil lagerstaten (exquisite preservation of soft tissues)
C) Unaltered Hard Parts
-original hard parts
D) Altered Hard parts
Argonite or HMC CaCO2 orthorhombic -> LMC CaCO3 Hexagonal)
Silica -SiO2-H2O > Quartz SiO2
Fine crystal -> coarse crystals
-Carbonization of Organic Skeletons
heat and pressure drive off the volatiles from organic skeletons
leaves a thin film of carbon: black (coal) or or silvery (graphite)
infilll of porous skeletons with mierals that percipitate out of fluids
fresh water environmend typically mineralized with silica (wood,
dinosaur bones)
marine environment is typically mineralized with calcite
dissolution of skeleton while precipitating a new mineral:: dolomite,
silica, pyrite
E) Leached Fossils
-the organism was filled with material and leached away leaving a mold
-on the outside of the fossil is the external mold, inside is the internal mold
F) Biogenic Structures
-Biostratification structures (stromatolites)
threadlike cyano bacteria grow upwards through sediment as
carbonatemud and sand are trapped
certain parts grow faster, creating mounds on the ground
very common during the Pre-Cambrian, now limited to a few harsh
-Trace Fossils (tracks, trails burrows, borings)
bonds with certain requirement for O2 biosynthesis
chemical evidence of when sponges or their acestors first appeared
Biostratinomy: From Death to Final Burial
a) Disarticulation (least energy) - breaking up of parts
b) Abrasion - a tumbling environment, pourous things abrade much quicker
c) Reorientation - currents reorient the organism to a more kydrodynamically
stable position waves will orient them opposingly, current will orient
them uniformally
d) Transportation (most energy)
1) fidelity oif the local fossil record
2) understanding taphonoy can provide important environmental information