HAY, WILLIAM W., University of Colorado, Boulder, CO, and with GEOMAR, Kiel, Germany; DAVID POLLARD and STARLEY THOMPSON, National Center for Atmospheric Research, Boulder, CO; KEVIN M. WILSON, Consultant, Oklahoma City, OK; and MICHAEL SCHULZ and CHRISTOPHER N. WOLD, GEOMAR, Kiel, Germany

ABSTRACT: Using a Climate Model to Infer Conditions of Sediment Accumulation

Simulation of climatic conditions on and near the continent of Pangaea for the Early (Scythian) and Late (Carnian) Triassic using a new Atmospheric Global Circulation Model (AGCM), GENESIS offers insight into the conditions under which terrestrial and shelf sedimentation occurred. GENESIS is an AGCM developed from the National Center for Atmospheric Research (NCAR) Community Climate Model expressly to facilitate modeling of paleoclimates. Among other refinements GENESIS includes infiltration of precipitation into a variety of soil types and layers, the effects of two levels of vegetation (grass and trees) of many different types, and ocean heat transport. Iterating atmospheric processes every 1.5 hours, it reproduces diurnal as well as seasonal cycles.

The simulation suggests that Pangaea had climatic regimes more rigorous than anywhere on Earth today. In the model, the climate is dominated by large (up to 70 degrees C) seasonal temperature variations and monsoonal conditions that extend over the entire globe. The widespread occurrence of redbeds in the Triassic becomes more readily understood in the context of a continental climates with extreme diurnal and seasonal temperature variations, and extreme seasonal distribution of rainfall. The distribution of evaporites in rift valleys well off the equator is also a product of the extremely arid conditions that are suggested by the model. Equatorial rainfall is concentrated on the western margin of the supercontinent. Seasonal coastal upwelling would result from seasonally reversing co st-parallel winds alongboth the Gondwanan and Laurasian margins.

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