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Facies and Preliminary Depositional Environments of Vaqueros Formation, Southeastern Cuyama Valley, California

George A. Freitag, A. Eugene Fritsche

Rocks mapped as Vaqueros Formation in the southeastern Cuyama Valley crop out in two separate belts: (1) north of the Ozena fault, near Santa Barbara Canyon, and (2) a more easterly sequence that extends to the San Andreas fault in the Pattiway Ridge area. The Vaqueros Formation is principally a marine clastic unit; in the Santa Barbara Canyon area, it conformably overlies the nonmarine Simmler Formation and is conformably overlain by the marine Saltos Member of the Monterey Formation. In the Pattiway Ridge area, it is unconformable on the Simmler Formation and is conformably overlain by the nonmarine Caliente Formation.

In the Santa Barbara Canyon area, the Vaqueros Formation consists generally of light-brown, structureless to medium-bedded, fine to coarse sandstone, with local pebble- and Pecten miguelensis-filled channels and some interbedded reddish-brown mudstone. Chert and fossiliferous mudstone occur locally at the base of the unit. Rare cross-bedding indicates westward paleocurrents. Turritella inezana, Pecten miguelensis, Ostrea howelli, and Balanus sp. are common. Thickness averages 65 m and is fairly constant throughout the Santa Barbara Canyon area. In the Pattiway Ridge area, the Vaqueros Formation consists generally of laminated to thin-bedded, dark-gray to brown mudstone, which grades upward to light-brown to white, structureless to medium-bedded sandstone. Fossils are rare, but include Ostrea eldridgei and Isurus sp. Thickness (from east to west) ranges from 0 to 50 m along the Sand Andreas fault to over 240 m near Cuyama Valley.

The marine to nonmarine transition represented by the Vaqueros and Caliente Formations in the Pattiway Ridge area is indicative of a nearshore (probably deltaic) environment of deposition. The nonmarine to marine transition represented by the Simmler and Vaqueros Formations in the Santa Barbara Canyon area is also attributed to a nearshore or deltaic environment. The reddish-brown mudstone interbedded in the marine Vaqueros at Santa Barbara Canyon indicates nonmarine delta-plain to overbank deposition along a fluctuating shoreline. Altogether, the Vaqueros Formation in southeastern Cuyama Valley records an eastward(?) marine transgression over a westward-flowing deltaic system.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.