Aminostratigraphy of Pliocene-Pleistocene high-sea-level deposits, Nome coastal plain and adjacent nearshore area, Alaska

Amino acid epimerization ratios (alle/Ile) measured in 295 fossil molluscan shells of three genera provide a basis to evaluate the number and relative timing of high-sea-level events represented by deposits blanketing the Nome coastal plain and adjacent nearshore area, northwestern Alaska. Six periods of high relative sea level were distinguished; some are recognized only by redeposited shells rather than in situ bio- or lithostratigraphic units. On the basis of a new empirical model of parabolic epimerization kinetics and an assumed age of 3.2 m.y. for the oldest Beringian aminozone (the approximate age of the initial submergence of Bering Strait), the estimated length of time represented by the three Beringian highstand was followed in the late Pliocene or early Pleistocene by a lengthy period of nonmarine deposition during which local valley glaciers advanced onto the coastal plain at least once. Relative sea level apparently did not again surpass that of today until the middle Pleistocene Anvilian transgression, the oldest higher-than-present stand of the Pleistocene, yet considerably younger than previously thought. Glaciers overran the Nome coastal plain at least once following the Anvilian transgression, incorporating abundant shells into their drift. The drift is notched by a shoreline formed during the Pelukian transgression of the last interglaciation. -from Author