January 30. Fossil record

TAPHONOMY

biocoenosis: living assemblage

thanatocoenosis: assemblage after death and decay (during biostratinomy)

taphocoenosis: fossil assemblage that is preserved (after fossil diagenesis)

life assemblages = autochthonous thanatocoenoses

death assemblage = allochthonous taphocoenoses

time-averaging: assemblage is accumulation of mixture of successive populations

DEGREE OF DISLOCATON

1. life assemblages: retain life orientation; e.g. bivalves joined, echinoderms complete
2. neighborhood assemblages: assemblages disturbed by in original habitat; e.g. bivalves separate, but breakage and abrasion rare; adjacent beds have similar composition; no mixing with other communities
3. transported assemblages: broken abraded shells with species from adjacent communities

DESTRUCTION AT SEDIMENT SURFACE

• bioerosion
• caused by fungi, algae, sponges, barnacles, bivalves, echinoids, worms, bryozoans
• bore into or excavate shells
• produces fine sediment
• sediment production nearly equal to rate of biomineralization
• fragmentation in quiet offshore environments is correlated with degree of bioturbation; function of biological, not physical, factors
• dissolution
• rare at sed/water interface in shallow marine settings b/c saturated with CaCO₃
• setting must be fresh or brackish to corrode or dissolve
• increasing depth coupled with increasing oxidation of organic matter causes CO₂ to increase, which dissolves carbonate
• increased pressure and decreased temperature are secondary effects on carbonate solubility