Abstract: Southern California Basins - An In Depth View by Manned Submersible

By

John E. Warme

Marine basins of the Continental Borderland off Southern California have long been regarded as oil fields in-the-making. They provide models for understanding adjacent producing areas such as the Los Angeles and Ventura Basins. The varied water depths and submarine geology of the Borderland also provide a spectrum of natural conditions for investigating many problems in marine geology and paleoecology that directly bear on resource exploration.

Studies now being conducted at Rice University are concerned with bottom conditions across the Borderland--particularly water depth, bottom topography, sediment type and organic content--as they relate to the distribution of larger sea bottom- dwelling animals. Life on the bottom is a measure of physical conditions there, and such conditions also determine the fate of organic matter in the surface sediments. The interrelationships between the organisms and the organic matter on which they feed are, however, only poorly understood.

The purpose of this work is (1) to determine the usefulness of bottom animals as signatures of present conditions in the basins, which include oxygen, organic contents and pollution levels; and, (2) to evaluate the potential of the faunas as paleoecological indicators. Determination of some faunal indicators is an important step in identifying ancient deep water strata: because they rarely include larger shelled animals capable of fossilization. But deep water strata does exhibit assemblages of distinctive biogenic sedimentary structures (trace fossils) left behind by burrowers. The burrowing organisms are dominated by soft-bodied animals such as worms and crustaceans, but little is known about their burrow patterns. The widely used paleobathymetric trace fossil zonations of Seilacher and other workers were devised from land-based stratigraphic sections and never have been tested in modern deep-sea sediments. It is important to couple modern-ancient deep water investigations while resource exploration is moving into deeper water and at a time when the Deep Sea Drilling Project is providing true oceanic samples for study.

In order to explore the presently developing record in the California basins large volume box cores that recover undisturbed portions of the seabed are used. The box cores can be cut on shipboard, yielding undisturbed slices that are sealed and stored for sedimentary analyses and radiographic inspection. Use of manned submersibles allows in situ selection of core sites and rock samples, as well as providing high-resolution visual observation and photography. Motion pictures are a primary tool by which to record submarine data.

Submersible dives using Lockheed's Deep Quest provide direct observation and sampling from depths of 1000 to 6700 feet. Motion pictures document conditions on the Coronado Escarpment and Fan Valley, the Son Diego Trough, the San Clemente Basin, and the western escarpment of Forty-mile Bank. Although basin floors vary in depth, the San Diego Trough (4000') and San Clemente (6900') harbor abundant large animals. The San Clemente Basin is silled at 6000', but contains prolific life to the bottom. In contrast, other studies in the San Pedro (3000') and Santa Barbara (2000') basins show them to be faunally poor or lifeless in some areas. Judging from the distribution and density of animal life it appears that neither depth nor distance from shore controls critical oxygen levels or food resources.

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