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Masters Thesis

Depositional environments and paleogeography of the Miocene Painted Rock Sandstone Member of the Vaqueros Formation in the southeastern Caliente Range, San Luis Obispo County, California

The Painted Rock Sandstone Member of the Miocene Vaqueros Formation crops out discontinuously along the anticlinal Caliente Range. The study area is in the southeastern portion of this northwest-trending range, in San Luis Obispo County, California. The Painted Rock Sandstone thickens rapidly to the west; thicknesses from five measured sections range from less than 100 m in the east to more than 1,600 m in the westernmost and type section. The eastern sections coarsen from the underlying bathyal deposits of the Soda Lake Shale to the overlying continental deposits of the Caliente Formation. The western section initially coarsens from the underlying shale through a repetitive series of coarsening upward cycles, and then fines upward to the overlying Monterey Formation. Petrology and paleocurrent data suggest an easterly provenance across the then inactive San Gabriel and San Andreas faults. The member is composed of laminated, cross-bedded, and structureless sandstone, mudstone, and local conglomerate. This variation in lithology made it possible to divide the member into twelve lithosomes. The lithosomes have been interpreted to represent a westward-prograding, fluvialdominated delta and include channel, point bar, crevasse splay, marsh, delta front, interdistributary bay, and prodelta or shelf environments. In the eastern part of the area, the delta is part of a complete progradational cycle from deep marine to continental deposits. The western sequence records progradation followed by retrogradation due to increased subsidence or a decrease in sediment supply.

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