Pre-Late-Wisconsin glacial history, coastal Ahklun Mountains, southwesternAlaska - new amino acid, thermoluminescence, and Ar-40/Ar-39 results

New stratigraphic and geochronologic data from the Togiak Bay area of south western Alaska indicate that glaciers advanced from the southern Ahklun Mou ntains at least three and as many as six times prior to the late Wisconsin. The oldest glaciations are represented by glacial-marine sediment in coast al exposures on Hagemeister Island. The extent of amino acid (isoleucine) e pimerization in fossil molluscs indicates that at least one, and possibly f our, older middle Pleistocene glacial intervals are represented, with age e stimates spanning similar to 500-280 ka and averaging similar to 400 +/- 10 0 ka. The youngest glacial-marine drift on Hagemeister Island may correlate with the eruption of the Togiak tuya. A new Ar-40/Ar-39 age on basalt that overlies pillow lava indicates that the volcano erupted through glacial ic e at least 300 m thick 263 +/- 22 ka. The youngest drift in the region over lies the Old Crow tephra (140 +/- 10 ka) and a 70 +/- 10 ka basaltic lava f low dated by thermoluminescence analysis of underlying baked sediment. The drift delimits flat piedmont lobes that spread out onto the continental she lf and terminated > 100 km from their source areas during the early Wiscons in (sensu late). The glacial-geologic evidence suggests that major expansio ns of glaciers were out of phase with global ice volume. (C) 2000 Elsevier Science Ltd. All rights reserved.