--> Biological Sensing of Primary Environmental Changes Related to Milankovitch Climate Cyclicity: Examples from a Cretaceous Greenhouse World, by E. G. Kauffman; #90986 (1994).

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Abstract: Biological Sensing of Primary Environmental Changes Related to Milankovitch Climate Cyclicity: Examples from a Cretaceous Greenhouse World

Erle G. Kauffman

Milankovitch climate cycles have had a pervasive effect on marine deposition and paleoceanography at parasequence and finer scales in icehouse and greenhouse worlds. Cyclic changes in sedimentation are expressed as variations in carbonate: siliciclastic ratios, grain size, and storm/turbidite deposition. Oceanographic changes involve sea level, stratification, and chemical composition (salinity, oxygen). These cyclic changes had a profound effect on environmentally sensitive marine organisms, providing ecologic signatures for climate cyclicity in trace and body fossil associations. Whereas diagenetic processes may subsequently modify physical and chemical expressions of climate cycles, primary biological signals are commonly preserved and comprise the best sensors for climate change. ell-studied examples from hemipelagic to shoreface facies of the Western Interior Cretaceous basin, North America, and from carbonate platform facies of northeastern Mexico and Texas support this contention. In all examples, ecological and taxonomic diversity increase as substrates become firmer and stabilize, and decrease relative to expansion of chemically deleterious aquatic environments along ecological stress gradients in both wet/cool and warm/dry phases of the climate cycles. Rapidly changing community structure and trophic strategies reflect these climatic gradients; from two to seven or more paleocommunities have been identified in consistently ordered sequences through single facies suites reflecting Milankovitch climate cycles. Ecological diversification generally decreases up ection from wet to dry climate phases in nearshore siliciclastic and shallow carbonate platform settings, but increases upsection in hemipelagic clay to carbonate cycles. Sequence boundaries and systems tracts can also be identified biologically within Milankoviotch climate cycle deposits.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994