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The Cuyama basin is located in the southern portion of the Salinian block of coastal California, a distinctive geologic terrane underlain by granitic and gneissic basement and surrounded by areas underlain by Franciscan basement. This basin is one of several discrete, middle Cenozoic basins that formed a continental borderland in the coastal California province during the Miocene. The regional stratigraphy of the Monterey Formation and associated rocks within this area illustrates the character of an inboard basin (immediately adjacent to the primary strandline) within this borderland. The formation is lithologically and stratigraphically complex, as illustrated by regional cross sections and stratigraphic maps. It varies widely in thickness, up to 4,500 ft (1,400 m), ref ecting variable subsidence within the basin. Thinning over anticlines and the Cox fault zone suggests structural movement occurred contemporaneously with sedimentation, beginning in the late Saucesian (early Miocene). The age of the Monterey Formation also varies within the basin, becoming younger to the northwest. This relationship plus paleobathymetric maps representing 4 early to middle Miocene time slices (late Saucesian, Relizian, Luisian, and early Mohnian) shows that areas of maximum subsidence migrated from southeast (Cuyama Valley) to northwest (northern La Panza Range). Schematic paleogeographic maps constructed on the same 4 time slices illustrate that the depositional history of the basin reflects these subsidence patterns and various depositional controls. Late Saucesian-Rel zian (early Miocene) time is characterized by relatively low sea level, maximum subsidence in the southeast, and basinal sedimentation varying from calcareous biogenous sediments to sandy submarine fan deposits. Luisian-early Mohnian (middle Miocene) patterns reflect high sea level, maximum subsidence in the northwest, and basinal sediments of a calcareous or siliceous biogenous nature. Finally, the entire southern Salinian block shoaled to shallow marine or nonmarine conditions by the end of Mohnian (late Miocene) time. Variations of tectonic, paleo-oceanographic, and paleogeographic controls on basinal sedimentation over a period of 10 m.y. ultimately dictated the character of the Monterey Formation, including its potential as a source bed for hydrocarbons.
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