Origin and Paleogeographic Development of Tertiary Cuyama Depositional Basin, Southern California: ABSTRACT

Abstract

The Cuyama depositional basin of southern California originated during the latest Oligocene and early Miocene as a chain of small interior-drainage basins that filled rapidly with the nonmarine alluvial-fan, flood plain, and lacustrine deposits of the Simmler, Plush Ranch, and Vasquez Formations and their associated volcanics. During the early Miocene, the ocean transgressed rapidly eastward across this chain of small basins, and as they filled they became united into one large, narrow basin that was confined to the northern part of the area. The basin deepened to bathyal depths and the mountains to the south subsided, allowing the ocean to transgress southward and greatly enlarge the area of the basin. Following expansion and deepening, a large delta prograded westward into the northern part of the basin and began to fill it. During the latest early Miocene, subsidence occurred and the ocean began a second transgression, and most of the basin became occupied by basin-plain deposits. Near the beginning of the middle Miocene, westward progradation of the delta was renewed. Progradation continued until about 13 Ma, when the San Gabriel fault began to move and clockwise rotation of some parts of the basin began. Tectonic deformation of the region during themore » Pliocene and early Pleistocene created the Soledad, Cuyama, and San Rafael structural basins out of the Miocene Cuyama depositional basin. The depositional and paleogeographic history of many California basins has been misunderstood because of the confusion of the depositional basin with the structural basins that were created postdepositionally, and understanding will come only through careful stratigraphic and paleogeographic analysis.« less