LAST INTERGLACIAL (ISOTOPE STAGE 5) GLACIAL AND SEA-LEVEL HISTORY OF COASTAL CHUKOTKA PENINSULA AND ST. LAWRENCE ISLAND, WESTERN BERINGIA

Abstract

Study of glacial and marine sequences along the outer coast of Chukotka Peninsula, Bering Strait, is the basis for major revisions of the regional stratigraphy. The Val’katlen Suite at its type section at the mouth of the Enmelen River records the youngest high sea stand of the last interglaciation on Chukotka Peninsula. Marine deposits and glacial diamicton stratigraphically below the type section record, respectfully, the peak of the last interglacial (marine oxygen-isotope substage 5e) and rapid glacierization of the coastal mountains probably during substage 5d or 5b. Correlative deposits recording a similar sequence of intra-stage 5 events, but once thought to be of early and middle Pleistocene age, include the Upper and Lower Pinakul’ Suite at Cape Pinakul’ and marine deposits near the Nunyamo River on the Gulf of Anadyr, based upon amino-acid analyses, biostratigraphy, and supporting geochronology. These deposits enclose warmer-than-present faunas and floras comparible to last interglacial Pelukian marine deposits found along the coast of Alaska. The last major advance of glacial ice from Chukotka Peninsula across Anadyr Strait and onto St. Lawrence Island was likely initiated during the later part of stage 5 based on our reinterpretaion of the stratigraphy at Cape Pinakul’, near the Nunyamo River, and on northwestern St. Lawrence Island. Chukotkan ice probably reached St. Lawrence Island sometime during oxygen-isotope stage 4. Ice extend across Chukotka during the LGM was very imited.