Submarine Tar Mounds, Santa Barbara County, California: GEOLOGICAL NOTES

Abstract

Submarine tar mounds occur in 3 localities: the Point Conception area, Coal Oil Point near Goleta, and off Carpinteria. Tar is most abundant near Point Conception where a sheet of tar covers at least 1/4 sq mi and forms a 10-12-ft scarp at its seaward edge. E. of the Point, mounds range up to 100 ft in diam and 8 ft in height. They are irregularly distributed along an E.-W. trend of faulted anticlines and are localized along fractures in shale. Most of the mounds have roughly circular outlines, rise abruptly from the sea floor, and then slope upward gradually toward a vent at the central high point. The mounds are accumulations of small discrete masses of tar in the form of flows. Tar is extruded slowly from the vent. As dated by late Quaternary changes in sea level, the tar mounds are believed to have accumulated since the sea floor was submerged about 9000 yr ago.