Lithostratigraphy and depositional environments of the Vaqueros Formation in Hondo field, Capitan field, and the western Santa Ynez Mountains, California

The Santa Ynez Mountains and the adjacent offshore areas are situated on the northwest edge of the western Transverse Range province. Oligocene-lower Miocene strata in this province record complex interactions among local and regional eustatics and local and regional tectonics and shed light on the sedimentary and tectonic history of this poorly understood region. Correlation of lithofacies units in Oligocene-lower Miocene Vaqueros Formation outcrops the Santa Ynez Mountains with Vaqueros cores from the Hondo and Capital fields leads to the delineation of three major facies tracts within the offshore and coastal areas: fan-delta conglomerates, shoreline sandstones and conglomerates, and inner shelf sandstones. Vaqueros strata at both Hondo and Capital fields are part of the inner shelf sandstone facies tract. Outcrops of the inner shelf facies typically consist of amalgamated packets of locally burrowed, cross-bedded, gravelly sandstones. In outcrop, bioturbation is most common near the tops of the cross-bed sets. In Hondo field a thinner, more basinward portion of this facies is characterized by bioturbated medium- to coarse-grained sandstones. Both in outcrops and at Hondo the base of the Vaqueros is marked by a sharp grain-size change and by a change from interbedded fluvial/deltaic strata below (the Alegria/Sespe formations) to innermore » shelf strata above (the Vaqueros Formation). The inner shelf facies tract represented by these three localities, fines, thins, and becomes more pervasively bioturbated in the present-day offshore direction suggesting a similar shoreline polarity however, the Oligocene-early Miocene paleogeography is more complex. Facies tracts present in outcrop in the western Santa Ynez Mountains become thinner and coarser in the present-day westerly direction and record deposition on a topographically and geomorphically complex shoreline.« less