EARLY AND MIDDLE MIOCENE FORAMINIFERAL PALEOENVIRONMENTS, SOUTHEASTERN SAN JOAQUIN BASIN, CALIFORNIA

Shallow-water foraminiferal species are an important, but neglected, component that is critical for reconstruction of the Miocene depositional, tectonic, and paleoceanographic history of the San Joaquin Basin. This study utilizes Miocene foraminifera from a range of paleoenvironments (shelf to slope) to aid in unraveling the history of the southeastern San Joaquin Basin. During the early Miocene the southeastern San Joaquin Basin returned to normal marine conditions (ca. 18 Ma) as evidenced by the transition from braided streams to deltaic deposits of the middle Olcese Sand, followed by deposition of inner shelf sands and outer shelf silts of the upper Olcese Sand. The initial phases of middle Miocene basin evolution (ca. 16 Ma) consisted of deposition of shallow marine silts of the Round Mountain Silt, followed by basin subsidence and accumulation of pelagic, diatomaceous slope deposits. The final stages of basin development during the middle Miocene (ca. 14 Ma) included shoaling that returned the basin to shelf depths. -from Author