Research Technical Report

Grain Size, Organic Carbon, and CaCO3 of Surface Sediments from the Southern Monterey Bay Continental Shelf Seafloor

Edwards, B.D., J.V. Gardner, and M.D. Medrano (1997)

In: S.L. Eittreim (editor), Southern Monterey Bay Continental Shelf Investigations: Former Fort Ord Restricted Zone. U.S. Department of the Interior, U.S. Geological Survey, Open File Report 97-450. p. 22-75.

ABSTRACT

Forty-six coring sites were occupied on the continental shelf south of Monterey Canyon as part of the Fort Ord Restricted Zone (FORZ) study. The recovered sediment was evaluated for geological, geochemical, and geotechnical characteristics. The data show surface sediment grain size to decrease offshore with clearly developed nearshore sand bodies and a midshelf/ outer shelf mud belt. These findings are consistent with the view that finer-grained sediment (e.g., flood sediment) from the Salinas River either bypasses the inner shelf and is deposited at mid- to outer shelf depths or bypasses the shelf entirely and is deposited in the adjacent Monterey Canyon. Organic carbon and calcium carbonate contents are generally unremarkable except in the exposed bedrock area north of the Monterey peninsula (high backscatter on the SIMRAD EM-1000 data) where CaCOa values are >30%. Photographs taken simultaneously with the cores show bioturbation and physical structures that are typical of mid-latitude terrigenous shelf environments.