The Last Interglacial to Glacial Transition, Togiak Bay, Southwestern Alaska

Abstract

An 18-m-high coastal bluff at Togiak Bay (northwestern Bristol Bay, southwestern Alaska) exposes marine, lacustrine, fluvial, glacial, volcanic, and organic deposits that record the ∼50,000-year-long transition from the peak of the last interglaciation to the early Wisconsin glaciation. The base of the section is dominated by stratified sand and silt extending up to 4.3 m above sea level; marine diatoms are present, and pollen assemblages are characterized by relatively high percentages of Picea, Alnus, and Betula and low percentages of Poaceae and Cyperaceae. The marine sediment was probably deposited during the peak of marine oxygen-isotope stage (OIS) 5e. An infrared stimulated luminescence (IRSL) age of 151,000±13,000 yr from near the base of the exposure is permissive of this correlation. The marine sand and silt are overlain by 0.8 m of peaty silt with diatoms that record a transition from marine to lacustrine conditions. During this interval, Poaceae and Cyperaceae dominate the pollen assemblages, and Picea and shrubs are nearly absent, suggesting that herb tundra occupied the landscape. This interval probably encompasses OIS 5d on the basis of the herb tundra and an IRSL age of 119,000±10,000 yr from 60 cm below the marine/lacustrine transition. The organic mud is overlain by 3.1 m of stratified sand and organic silt that apparently record shallowing of the lake; reappearance of spruce and shrubs (=OIS 5c?); and subsequent deepening of the lake (=OIS 5b?); followed by aggradation of a floodplain (=OIS 5a?), which was dry at the time basaltic lava buried the site. Thermoluminescence analyses on lava-baked sediment indicate that the eruption occurred 70,000±10,000 yr ago. Sometime thereafter, but prior to 53,600 14C yr B.P. an outlet of the Ahklun Mountains ice cap advanced over the site and deposited ∼7 m of bouldery ice-contact drift. The sedimentary sequence contains at least four tephra beds. Major- and trace-element chemistry provide a basis for correlating two of the tephras with tephra beds at nearby sites. The tephras, luminescence ages, and correlations with marine isotope stages provide the geochronological control to place the Togiak Bay section into a global context. The site serves as an important new reference section for late Pleistocene paleoenvironmental change in eastern Beringia.

Geoarchaeology of the Kostenki–Borshchevo sites, Don River Valley, Russia

“…This preheat, similar to previous studies (e.g., Kaufman et al, 1996Kaufman et al, , 2001Forman, 1999;Forman and Pierson, 2002;Forman et al, in press;Nowaczyk et al, 2002;Ollerhead et al, 1994;Stokes, 1992;Watanuki and Tsukamotto, 2001), is effective in largely circumventing an unstable luminescence component (e.g., anomalous fading; Wintle, 1973) associated with laboratory irradiation. Tests on luminescence signal stability were preformed by comparing changes in luminescence emissions for an additive dose between 0.8 and 1.6 kGy after preheating at 160°C for 10 hours and storage for 24 hr, separate aliquots were measured immediately and after storage at 25°C for 30 to 40 days (Table XI).…”

Late Pleistocene mountain glaciation in Alaska: key chronologies

“…3) is dated in several locations across the range. In the southern Ahklun Mountains, Kaufman et al (2001a) report a thermoluminescence (TL) age of 70 AE 10 ka on lava-baked sediment that underlies penultimate drift and provides a maximum-limiting age on the glaciation. Manley et al (2001) report a minimum 14 C age of 39.9 ka on organic material that overlies Arolik Lake drift.…”

“…Previous studies have emphasised evidence for 'out-of-phase' glaciations in Beringia (e.g. Brigham-Grette, 2001;Kaufman et al, 2001a). Glaciers in northeastern Siberia and western Alaska expanded onto the continental shelf several times during the Middle Pleistocene.…”

Ce3+‐Centric Organic Pollutant Elimination by CeO2 in the Presence of H2O2

“…Despite the frequency of large, relatively proximal eruptions, however, few regional tephra deposits have been described in the region. Previous work on coastal bluffs around Bristol Bay revealed multiple Quaternary tephra deposits interbedded with loess, peat and glacial–marine sediment (Kaufman et al ., 2001). The most prevalent and thickest of these is the Aniakchak tephra, which forms a widespread mid‐Holocene marker across western Alaska (Riehle et al ., 1987; Begét et al ., 1992).…”