Abstract: Macropaleontology of Eocene Marine Rocks. Upper Sespe Creek Area, Ventura County, Southern California
Richard L. Squires
Eocene marine rocks in the upper Sespe Creek area are, in ascending stratigraphic order, the Matilija Sandstone, Cozy Dell Shale, and Coldwater Sandstone. Macrofossils in the upper part of the Matilija Sandstone are sparse and preserved as molds. They are shallow- marine gastropods (e.g., Turritella uvasana uvasana) and bivalves transported by turbidity currents into deeper waters. Cozy Dell Shale macrofossils are moderately sparse and preserved as molds. Species in siltstone/mudstone are in situ and form deep-water communities dominated by either starfish (e.g., Astropecten matilijaensis), brittle stars, or the bivalve Delectopecten. Locally, raninid crabs and the ichnofossil Gyrolithes are present. Species in the informal Circle B sandstone member in the middle of the Cozy Dell Shale are a few shallow-marine bivalves and scaphopods transported by turbidity currents into deeper waters. Coldwater Sandstone macrofossils are locally common, and most have been transported and concentrated by nearshore processes. At a few localities, some fossils are in situ and form a community dominated by the gastropod Turritella uvasana uvasana and the bivalves Venericardia (Pacificor) clarki clarki, "Crassatella" collina, Striostrea? tayloriana, and Isognomon (Isognomon) Clarki. At one locality, there is a mud flat community dominated by the spatangoid echinoid Schizaster diabloensis and nuculanid bivalves.
All of the macrofossils used in this study are indicative of the macroinvertebrate "Tejon Stage" and are assigned to the middle Eocene part of this stage on the basis of the latest medial Eocene-age constraint of the rodent-bearing basal part of the nonmarine Sespe Formation that interfingers with the Coldwater Sandstone.
AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994