Amino acid age estimates of marine terraces and sea levels on San Nicolas Island, California

Abstract

Fourteen marine terraces rising to an elevation of 274 m have been mapped on San Nicolas Island, California. The lowest terrace is ∼105 000 yr old, on the basis of amino acid ratios in fossil mollusks slightly lower than those from the ∼120 000 yr old, uranium-series dated second terrace. The age estimate and present elevation of the lowest terrace, along with an assumption of constant uplift rate, indicate a paleo–sea-level estimate of −10 to −12 m at about 105 000 B.P., supporting the general Barbados model of sea-level history. The fourth and fifth terraces probably represent separate high sea-level stands during the same interglacial complex ≥400 000 B.P. The eight and tenth terraces have amino acid ratios near equilibrium and imply ages of ≥600 000 yr. Collectively, the data suggest long-term average Quaternary uplift rates of 0.2–0.3 m/1000 yr.