More than 180 radiocarbon age determinations on cores from the basins off southern California yield rates of deposition of sediments ranging from 5 to 180 cm/1,000 years, with greater rates for nearshore than offshore basins. These rates are comparable to those which occurred during the Pliocene Epoch in the now-filled and oil-rich Ventura and Los Angeles basins. They were computed from ages based on total organic carbon. Radiocarbon ages based on associated foraminiferal carbonate are commonly greater than ages of total organic carbon, a difference attributed to redeposition of foraminiferal tests onto the basin floors from surrounding higher areas. Fine-grained carbonate and total carbonate also have greater ages than total organic carbon, but the age differences are less than those of foraminiferal carbonate. Greater ages of carbon extractable with benzene are typical in nearshore basins and are attributed largely to redeposited tar from known nearshore seeps. Surface sediments now being deposited have a mean radiocarbon age of 2,500 years, but a completely satisfactory explanation for such an old age is still lacking.

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