WHITE, LISA D., Department of Geosciences, San Francisco State University, San Francisco, CA

ABSTRACT: Age and Paleoceanographic Significance of the Santa Cruz Mudstone in the Bodega and Santa Cruz Basins, Marin and Santa Cruz Counties, California

The upper Miocene Santa Cruz Mudstone is a siliceous mudstone sequence of considerable thickness in the Bodega and Santa Cruz basins of north-central California. Equivalent to the upper Monterey Formation in other Neogene basins of California, the Santa Cruz Mudstone is separated from the Monterey Formation by the Santa Margarita Sandstone. Because the siliceous mudstones have been diagenetically altered to the opal-CT silica phase, diatoms are poorly preserved in the mudstones, and age investigations of the Santa Cruz Mudstone have therefore been limited. Diatoms are more moderately preserved in cyclically interbedded carbonate concretions and beds that have been sampled from the Bolinas (Marin County) and Davenport (Santa Cruz County) sections of the Santa Cruz Mudstone. A detailed ge evaluation of the Santa Cruz Mudstone using diatom biostratigraphy is in progress. Sedimentation rates are being estimated and compared between the Bodega and Santa Cruz basins. Preliminary sedimentation rates reflect the high detrital content of the Santa Cruz Mudstone and support a more proximal setting of both basins during the late Miocene. Finally, age estimates and sedimentation rates for the sections will be applied to stratigraphic cycles in order to determine their paleoceanographic significance.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.