ABSTRACT
A better understanding of the Miocene geologic history of the southern Salinian block is aided by a stratigraphic and paleoenvironmental study of the Monterey Formation. Extensive subsurface and surface data enable construction of isopach, paleobathymetric, age-relationship, and paleogeographic maps that document the depositional history of the Monterey Formation. Isopach maps show that the formation ranges up to 1,400 m (4,500 ft) thick beneath Cuyama valley. Other areas of maximum accumulation occur in the northwest Caliente Range and the Indian Creek area. Offset of isopachs north of Barrett Ridge suggests approximately 15 km (9 mi) of post-middle Miocene right slip on the San Juan fault.
Age-relationship maps of the upper and lower contacts of the Monterey Formation for the area from Cuyama Valley to the northern La Panza Range indicate that both the top and base of the formation become younger toward the northwest—the base ranging from Saucesian to Relizian and the top from Relizian to Mohnian. Paleobathymetric maps, based on the distribution of benthic Foraminifera, are plotted on four time slices: late Saucesian, Relizian, Luisian, and early Mohnian. These maps also indicate that the Cuyama basin filled from the southeast to the northwest, and they reflect the migration of maximum subsidence in that direction during the Miocene.
The relationship of general stratigraphy to structural features in the Cuyama basin shows that certain faults and anticlines were active during the deposition of the Monterey Formation. Specifically, the Cox fault zone and South Cuyama anticline show evidence of such movement, beginning in the early Miocene, which affected the distribution of the formation. These relationships reflect an episode of structural deformation preceding the late Neogene episode associated with movement on the San Andreas fault system, and they may be related to the earliest activity on this system.
