Nearshore Conglomerates of Vaqueros Formation, Westernmost Santa Ynez Range, California: ABSTRACT

Abstract

The Vaqueros sequence in this area can be divided into three lithofacies. The basal facies (facies A) consists of inversely graded, matrix-supported, boulder to pebble-conglomerates. These conglomerates are angular, nonfossiliferous, and laterally persistent. The middle facies (facies B) is characterized by nongraded to normally graded, sandy, cobble to pebble-conglomerate. Pectens, oysters, gastropods, and clams are abundant in this facies and individual beds have sharp bases and burrowed tops. Small-scale lenticular bedding and reworked lenses of fossil material are common throughout. Facies C (the upper facies) is dominated by extensively bioturbated, locally cross-bedded, pebbly coarse sandstone. Pebble imbrication throughout the sequence, channel orientations in facies B, and cross-bedding in Facies C record paleoflows to the east and the southeast. Pebble lithologies and sandstone composition indicate a dominant Franciscan-assemblage provenance for the entire sequence. These facies represent deposition in proximal (facies A) and distal (facies B and C) fan-delta and braid-delta environments. Facies A conglomerates record braided fluvial deposition, facies B conglomerates record channel-mouth deposition, and the sandstones of facies C record deposition in shoreface to inner shelf environments. The sequence of strata documents local sedimentary response to complexly intertwined tectonic and eustatic events. The deepening-upward sequence described here was deposited onmore » the southern flank of the then-emergent Santa Maria basin (the Paleotrench-slope break.) during a late Oligocene-early Miocene eustatic sea level rise and suggests an eastward dipping paleoslope for the western margin of the late Oligocene-early Miocene Western Transverse Range province.« less