HOGE, BRADLEY EARLE, Rice University, Houston, TX

ABSTRACT: Comparisons of the Phanerozoic Biodiversity Curve Against Paleoclimate: Suggestions of Forcing Agents and Causal Relationships

Mass extinction rates, background extinction rates, and speciation rates have been estimated. There is also data on the frequency of bolide impact, flood basalts, glaciation, and orogenic volcanism. Biodiversity curves generated by models using these parameters can provide guidelines for further study into possible effects on paleodiversity.

A simple one-box model, with biodiversity having an input from speciation and an output to extinction, is offered. Biodiversity is initially set to one, representing the biodiversity present at the beginning of the Cambrian. Extinction is the sum of background extinction and mass extinction rates. Speciation is a background rate, relative to the background extinction rate, and delayed radiations, accelerated relative to the intensity of mass extinction events. Mass extinction rates are determined by combining climate and extinction susceptibility curves that are allowed to fluctuate through time. Susceptibility generally decreases with time, due to aging taxa and widening of geographic ranges, but rises following extinctions. Climate fluctuates according to volcanic, glacial, and impa t driven changes in air and ocean temperature, eolian dust, and ocean pH. Each climate parameter is scaled between zero and one to compare their relative contributions to extinctions. Simulations are run for 570 m.y. at 1 m.y. iterations.

The model suggests that major extinction events are strongly influenced byextended, orogenic, volcanism. Impacts and flood-basalt events can contribute, or cause intermediate and minor extinctions depending on their severity and frequency. Glaciation is important only when combined with other agents.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.