Milankovitch Forcing of Continental Monsoons Across the Equator of Pangaea

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Abstract ATM-9317227 Olsen, Paul E. Kent, Dennis V. Columbia University Title: Milankovitch Forcing of Continental Monsoons Across the Equator of Pangaea This award is directed at an examination of Milankovitch forcing of climate in the equatorial zone of Late Triassic and earliest Jurassic Pangaea. The recording medium consists of lacustrine rocks laid down in Early Mesozoic rift valleys preserved in eastern North America that can now be shown to cover a latitudinal range from 6.5o straddling the paleoequator. These lacustrine rocks consist of lake level cycles that recorded Milankovitch forcing of monsoonal precipitation over the interval from about 230 to 199 Ma. This work will extend the high-resolution cyclostratigraphy, magnetostratigraphy, and paleolatitudinal framework developed in the Newark basin coring project backward in time and laterally in geography through the study available cores and outcrop in six additional rift basins. This will result in a time-geography- climate matrix which will address three specific problems: 1) regional trends in the climate of equatorial Pangaea as it drifted northward about 10o; 2) the doubling of the frequency of precession cycle forcing around the equator; and 3) the apparent broadening of the humid belts in the latest Triassic-Early Jurassic. The first and last of these are important for refining tests of global climate models of Pangaea. The second is of generic interest, reflecting general processes of Milankovitch forcing expected in tropical regions of any age but most readily addressed by study of these unique sequences.