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ABSTRACT: Case Studies, Santa Maria Province, California

K. J. Bird, P. H. McClellan, T. R. Bruns

Seismic-reflection records and well data are being analyzed to provide a subsurface geologic framework for the U.S. Geological Survey's Santa Maria project. This project, jointly sponsored by the Evolution of Sedimentary Basins and Onshore Oil and Gas Investigations Programs, is a basin-evolution study focusing on the geologically complex and tectonically active south-central California margin. The area embraces several basins and basin fragments: the Santa Maria (on and off shore), Pismo, Huasna, Sur, Santa Lucia, and western Santa Barbara-Ventura basins. These basins have many similarities, including generally synchronous formation at approximately the end of the Oligocene, basin development on a complex assemblage of Mesozoic tectonostratigraphic terranes, and basin fi l consisting of Neogene clastic marine and nonmarine deposits, minor volcanic rocks, and organic-rich biogenous deposits of the Monterey Formation. Despite these similarities, basin origins and paleogeographies are controversial and uncertain.

Large petroleum resources, collectively more than 1 billion bbl of oil, and a long exploration history primarily are responsible for an abundance of subsurface information in these basins. However, since the early 1950s, relatively few published studies have provided subsurface documentation. We are constructing a network of well-correlation sections, supplemented where possible with seismic-reflection data and synthetic seismograms, which integrate surface with subsurface geology, one basin with another basin, and onshore with offshore regions.

Offshore seismic records offer an opportunity for improved stratigraphic understanding, including the discrimination of tectonic from eustatic sea level patterns by calibrating the stratigraphy penetrated in wells with the seismic-reflection records. Subsurface information will contribute to facies studies and paleogeographic reconstructions necessary to test hypotheses of basin origins.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990