Paleogeography of Monterey Formation, Cuyama Basin, California

The Cuyama Basin is one of several discrete, middle Cenozoic basins that formed a continental borderland in the coastal California province during the Miocene. The Monterey Formation is lithologically and stratigraphically complex. It varies widely in thickness, up to 4,500 ft (1,400 m), reflecting 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, becoming younger to the northwest. Areas of maximum subsidence migrated from southeast (Cuyama Valley) to northwest (northern La Panza Range). Schematic paleogeographic maps constructed on 4 time slices illustrate that the depositional history of the basin reflects these subsidence patterns and various depositional controls. Late Saucesian-Relizian (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.--Modified journal abstract.