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Foraminiferal Biofacies in Soda Lake Shale Member, Vaqueros Formation, Cuyama Basin, California

Martin B. Lagoe

Analysis of foraminiferal faunas from the Soda Lake Shale Member of the Vaqueros Formation in the Cuyama basin provides insights into the depositional history of that area. Sections from the type area (Carizo plain), the southeastern Caliente Range, wells in Cuyama Valley, and outcrops in the Sierra Madre Range and Hurricane Deck yield foraminifera belonging to four major biofacies: (1) the Florilus costiferum biofacies (FCB) (outer neritic to upper bathyal water depths), (2) the Uvigerinella obesa biofacies (UOB) (upper bathyal to upper middle bathyal), (3) the agglutinated species biofacies (ASB) (bathyal undifferentiated), and (4) the Gyroidina solidanii biofacies (GSB) (lower middle bathyal). The distribution of these biofacies yields an informal biostratigraphic subd vision of the Soda Lake Shale Member, with the GSB dominating the lower part of the member in many sections and the UOB in the upper part. The FCB and ASB are of more limited extent. The occurrence of these biofacies in the Sierra Madre Range and Hurricane Deck indicates that units formerly assigned to the Branch Canyon Formation are equivalent to the Vaqueros Formation as defined in Cuyama Valley.

Recognition of these relationships helps define major variations in bathyal depositional environments within the Soda Lake Shale Member and its lateral equivalents. These environments include outer shelf, slope, and basin plain (both muddy and sandy facies). All faunas examined are indicative of the Saucesian Stage (lowermost Miocene). No diagnostically Zemorrian (Oligocene) assemblages were found.

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