AMINOSTRATIGRAPHIC CORRELATIONS AND PALEOTEMPERATURE IMPLICATIONS, PLIOCENE PLEISTOCENE HIGH-SEA-LEVEL DEPOSITS, NORTHWESTERN ALASKA

Multiple periods of Late Pliocene and Pleistocene high sea level are r ecorded by surficial deposits along the coastal plains of northwestern Alaska. Analyses of the extent of amino acid epimerization in fossil molluscan shells from the Nome coastal plain of the northern Bering Se a coast, and from the Alaskan Arctic Coastal Plain of the Chukchi and Beaufort Sea coasts, allow recognition of at least five intervals of h igher-than-present relative sea level. Three Late Pliocene transgressi ons are represented at Nome by the complex and protracted Beringian tr ansgression, and on the Arctic Coastal Plain by the Colvillian, Bigben dian, and Fishcreekian transgressions. These were followed by a length y period of non-marine deposition during the Early Pleistocene when se a level did not reach above its present position. A Middle Pleistocene high-sea-level event is represented at Nome by the Anvilian transgres sion, and on the Arctic Coastal Plain by the Wainwrightian transgressi on. Anvilian deposits at the type locality are considerably younger th an previously thought, perhaps as young as Oxygen-Isotope Stage 11 (ap proximately 410,000 BP). Finally, the last interglacial Pelukian trans gression is represented discontinuously along the shores of northweste rn Alaska. Amino acid epimerization data, together with previous paleo magnetic measurements, radiometric-age determinations, and paleontolog ic evidence provide geochronological constraints on the sequence of ma rine deposits. They form the basis of regional correlations and offer a means of evaluating the post-depositional thermal history of the hig h-sea-level deposits. Provisional correlations between marine units at Nome and the Arctic Coastal Plain indicate that the temperature diffe rence that separates the two sites today had existed by about 3.0 Ma. Since that time. the effective diagenetic temperature was lowered by a bout 3-4-degrees-C at both sites, and the mean annual temperature was lowered considerably more. This temperature decrease was largely accom plished by the close of the Fishcreekian = Beringian III transgression (ca. 2.5-2.1 Ma). Since then, intervals of warm temperature must have been extremely brief. These data suggest that the steep latitudinal t emperature gradient and the frigid temperatures that characterize the high latitudes of Alaska today are ancient features of Arctic climate.