ISLA CALAFIA,THE FIFTH SANTA BARBARA CHANNEL ISLAND?

A 2km long high-relief segment on the topographic crest of the Oak Ridge-Mid Channel Anticline (ORMCA) in the Santa Barbara Channel was likely an island during the late Pleistocene low stand, at 18 ka. We informally name the feature "Isla Calafia". High-resolution (vertical resolution <1m) topographic data for ORMCA suggests that coastal erosion occurred on Calafia during the last ice age. Landforms that are apparently present include sea stacks, sea cliffs, and shoreline platforms that rim the elevated area of Calafia. The most western sector of ORMCA is an actively growing anticline with pristine fold scarps, fault scarps, and cross faults that segment the structure. A prominent fault scarp is associated with the Mid Channel fault, a steeply north dipping structure in the hanging wall of the south dipping Oak Ridge fault. Seismic reflection data linking surface and sub-surface features indicates that the vertical rate of deformation due to faulting is approximately 0.5m/ky. The rate of vertical deformation produced by folding is about 2m/ky. The crest of ORMCA is marked by several surface pits ranging from about 100 to 200 meters in diameter. These are assumed to be gas emission pits. Stable isotopic data of foraminifera from four push cores taken near the crest of ORMCA suggests the influence of isotopically light methane in the sediments and water column. The planktonic foraminifera assemblages in a gas-emission pit indicate glacial age of surface sediments, with deposition during a sea level low stand. This may suggest the age of formation of he pit. Also present on ORMCA are conspicuous features of unknown origin. They are about the same size as the gas emission pits, but are positive features that may be tar or mud mounds.