Collaborative Research: (GRGC) Testing the Hypothesis of a Cretaceous Supertethyan Climate Zone in the Caribbean Province

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9418081 Johnson This proposal focuses on testing the stability of cretaceous climates in the Caribbean Province by analyzing integrated high- resolution stratigraphic, sedimentologic, paleobiologic and geochemical data, in conjunction with climate simulations, to test the hypothesis of a warmer and more saline core tropical climate zone - Supertethys (Kauffman and Johnson, 1988) - and to define its temporal and spatial characteristics. Tests will be made along two north-south transects spanning the entire Cretaceous paleotropics and its margins, plotted on the Caribbean plate reconstructions of Pindell and Barrett (1990), and will utilize a series of three time slices representing different stages of Cretaceous climate-ocean history (Late Albian, Early Turonian, Early Maastrichtian). These time slices will span the interval for which paleobiogeographic and reef diversity data (Johnson, 1993; 1994, in press) propose two episodes of development and an intervening period of collapse of Supertethys. One transect will extend from New Mexico through west Texas, Mexico, Central American and western Venezuela (Fig.1); the second will extend from Oklahoma through central Texas, and Greater Antilles, Trinidad, the Dutch, West Indies, and eastern Venezuela to northern Brazil (Fig.1). For each time slice, detailed facies analyses of shallow water platform sequences will be used to independently determine areas of net evaporation, upwelling , etc. Stable isotope analyses of unaltered rudisted bivalve shell material, early marine cements, and foraminifer tests where available, will allow definition of relative sea surface (photic zone) temperature/salinity, and characterization of north to south thermal gradients. Paleobiological data along the transects will include species and generic dispersion maps, taxonomic and ecologic analyses of community composition and structure, statistically predicted latitudinal diversity gradients, and analyses of pal eobiogeographic dispersion, dispersal pathways, and the taxonomic composition and boundary characteristics of paleobiogeographic units. A partial stratigraphic and paleobiologic data base exists for each transect and time slice, enhancing the efficiency of the proposed research. Integration of these data sets for each time slice will allow identification, and where present, characterization of the supertropical Caribbean climate zone (Supertethys), its dynamic evolution during the Cretaceous greenhouse interval, its effect on the evolution, diversification, and extinction of tropical organisms/ecosystems, the structure and chemistry of tropical Cretaceous seas, and the evolution of Cretaceous paleoclimates. These data will be directly applied to testing and modifying Cretaceous climate simulations generated using the Semtner-Chervin eddy-resolving ocean general circulation model (Semtner and Chervin, 1988) and the GENESIS atmospheric general circulation model (Pollard and Thompson 1993a,b) for these same time intervals.