Depositional environments and paleogeography of the coldwater formation, upper Sespe Creek, Ventura County, California

The Coldwater Formation, exposed in upper Sespe Creek, north of Ojai, Ventura County, California, is a regressive sequence of upper Eocene marine deposits that are underlain by the marine Cozy Dell Shale and overlain by the nonmarine Sespe Formation. Stratigraphic analysis of rocks of the Coldwater Formation reveals that they are composed of ten lithosomes. One additional lithosome was designated for the underlying Cozy Dell Shale (lithesome A) and one for the overlying Sespe Formation (lithesome L). The marine deposits include lithosomes A (greenish-gray siltstone with thin-bedded, fine-grained sandstone), B (yellowish-green, medium- to fine-grained sandstone), C (laminated, fossiliferous, medium-grained sandstone), D (grayish-green, bioturbated, fine-grained sandstone), E (cross-bedded, medium-to-coarse-grained sandstone), F (structureless, coarse-grained sandstone), G (yellowish-green siltstone, fossiliferous in some beds), H (fossiliferous, medium-grained sandstone), I (grayish-green claystone), J (interbedded green and red siltstone), and K (coralline-algae-bearing, conglomeratic sandstone). Lithosome L represents nonmarine deposition (red, green, and yellow siltstone and pebbly coarse-grained sandstone). Two depositional systems existed during deposition of the Coldwater Formation: a wave-dominated shoreline in the east and a tide-dominated shoreline toward the west. These two systems interfingered in the North of Hartman Ranch area. An upper delta plain marsh environment with small leveed channels (lithosomes J and L) existed to the north of these systems throughout deposition of the Coldwater Formation.