Growth Patterns of a Miocene Turbidite Complex in an Active-margin Basin, Yowlumne Field, San Joaquin Basin, California

Michael S. Clark, John D. Melvin, and Marc Kamerling

The upper Miocene Yowlumne sandstone was deposited as a Iobate, northward-prograding turbidite complex, in eight or more stages, along the tectonically active southern margin of the San Joaquin basin, Califomia. This prolific sandstone, which has produced most of the 100 MMBL of oil attributed to Yowlumne field, is one of several different, discontinuous reservoirs that make up the Stevens sandstone, a deep-marine clastic facies of the Miocene Monterey Formation. The Yowlumne reservoir is a lens-shaped, complex-layered sandstone body with evidence of channeling and erosion within the body. However, because seismic markers bounding this body are not truncated by it, and merge on the margins of the body, the reservoir does not incise underlying strata.

Pressure data, 3D-seismic, and detailed well log correlations indicate lens-shaped, Iobate sandstone layers within the Yowlumne reservoir that downlap to the north and are separated by thin shales. These layers represent separate permeability pathways that are in pressure communication over geologic time (thousands of years) but become weakly compartmentalized during rapid reservoir draw down (tens of years). Two layers form a left-stepping (westward), shingled complex that resulted from lateral shifting of turbidite depositional Iobes. A second, younger, left-stepping complex of five layers is located basinward (northward) from the first and represents a basinward shift of deposition. A third, even younger complex may be located basinward from the second. Most likely, left-stepping geometries represent lobe switching influenced by Coriolis forces, and basinward-stepping geometries represent progradation controlled by accommodation.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California