For the increasing number of oil geologists who are studying the submerged shelves of Southern California in order to unravel the bedrock structure, a knowledge of where to look on the sea floor to find bedrock outcrops is highly desirable in saving exploration time and expense. Knowledge of the topography of the shelves is thus required.

The submerged shelf between Point Conception and Santa Barbara is considered. Cross sections of the shelf show that the Recent marine sediment or "overburden" which rests on the bedrock commonly forms a lens-shaped deposit. Within the surf zone, this sediment lens varies from zero to a few feet thick. It thickens offshore to an average of about 40 feet, but in places to more than 100 feet, then usually tapers off to a few feet or less in thickness near the outer edge of the submerged shelf. Isopach charts of overburden aid in conveying the nature of the sediment lens.

The bedrock of the shelf is traversed by numerous canyons and gullies probably Late Pleistocene in age. These have subsequently been alluviated by continental sediment and later by marine sediment so that no topographic expression of them is evident on the ocean floor. These features are illustrated on the submarine bedrock contour charts.

The common giant kelp which forms the extensive kelp beds along this coast (Macrocystis pyrifera Linnaeus) is commonly considered to be a good criterion for the presence of bedrock outcrops. This is now known to be partly erroneous, and it is shown that the kelp grows equally well in thick overburden of mud and fine sand. However, by observing the plant density from aerial photography, it can be determined whether the algae is growing on bedrock or in thick sediments.

End_of_Article - Last_Page 2062------------