Lithostratigraphy and Depositional Environments of the Vaqueros and Upper Sespe/Alegria Formations, Hondo Field, Santa Barbara Channel, California

Abstract The Vaqueros, Sespe, and Alegria Formations are important oil and gas reservoirs in the area of the Santa Barbara Channel. At Hondo field, which is located about 40 km west of Santa Barbara and 9 km offshore, ten exploratory wells and five development wells have been drilled into these formations. The interpretation of data obtained from these wells, including a cored section from the OCS 190-2 well, suggests that Sespe and Alegria strata in the Hondo area were deposited in a deltaic environment during the Oligocene Epoch and that Vaqueros strata formed in an inner shelf setting during a late Oligocene and early Miocene transgression. Vaqueros deposition ended abruptly when rapid subsidence and deepening related to incipient basin formation terminated shallow marine sedimentation in the area. Gradation of the Vaqueros Formation into deep-water deposits of the overlying Rincon Formation, as interpreted from well logs, occurs vertically over just a few meters.