9405772 Bralower Investigation of some of the most topical problems in Mesozoic paleoceanography, paleobiology and tectonics are currently limited by the lack of an accurate and precise time scale. Pertinent examples include estimating rates of evolution of fossil organisms and the factors that control them, accumulation rates of organic matter and their relationship with oceanic anoxia, and sea floor spreading and oceanic crustal production rates and their paleoclimatic significance. We propose to significantly improve the precision of the Late mesozoic time scale by investigating the U-Pb zircon geochronology of Lower Cretaceous tuffs and bentonites from the Great Valley Group, Northern California. Because the biostratigraphically with calcareous nannofossils, the pelecypod, Buchia and time scale, and indirectly to a chronostratigraphy for the entire Late mesozoic (Late Jurassic to Late Cretaceous) interval. In addition, tighter absolute age control will allow narrower constraints to be placed on the periodicities of sedimentary cycles, thus enhancing the applicability of cyclostratigraphy as a stratigraphic tool.
