ABSTRACT

Facies relations between deep and shallow-marine to continental deposits in the Eocene-Oligocene sequence of the Santa Ynez Mountains, California, have been studied in detail. The rocks studied include the Anita, Sierra Blanca, Juncal (with Camino Cielo Member), Matilija, Cozy Dell, and “Coldwater” formations. The topmost unit of the Eocene-Oligocene sequence, the nonmarine Sespe Formation, was not included in this study.

In landward sequence, the facies recognized include turbidites and marine lutites, proximal turbidites, shallow-marine, coastal, and continental facies. These are present in 2 major regressive sequences. In the first, the Juncal-Matilija sequence, thin-bedded turbidites and marine lutites are overlain by, and are laterally equivalent to, very thick proximal turbidites which pass upward into shallow-marine and coastal sands. The major sand accumulations are in the basin-margin shallow-marine, coastal, and proximal-turbidite facies. The second regression, the Cozy Dell-Sespe sequence, lacks significant proximal-turbidite deposits, but has extensive shallow-marine and coastal deposits. Facies distribution and stratigraphic sequence are explained as responses to the interplay of depositional and structural processes.

Detailed stratigraphic mapping has clarified correlation in the Eocene sequence of the Santa Ynez Mountains. Micropaleontology is used in support of correlations and bathymetric interpretations. Stratigraphic and paleontologic data resolve a biofacies problem in the lower to upper Narizian interval and clarify definition of the Eocene-Cretaceous boundary. Bathymetric interpretations based on comparison of fossil assemblages with modern Gulf of Mexico fauna are in better agreement with depths of deposition interpreted from lithologic data than interpretations based on comparison with modern assemblages in the Pacific Ocean off California.

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