97 New Perspectives on Beringian Paleoecology, Paleoclimate, and Paleoceanography

This session will showcase the use of new sedimentary records and analytical techniques to augment reconstructions of Beringian and North Pacific Gateway paleoclimate and paleoecology and elucidate the role of terrestrial and marine linkages.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 303C

Luminescence Dating of Late Quaternary Sediments on the Eastern Side of the Nushagak Peninsula, Southwestern Alaska

Paper number: 97-3
Program: Technical Sessions
Time: 8:40 AM – 8:55 AM

Authors

Abstract

Wave-cut exposures (kilometers long, >10 m tall) along the east side of the Nushagak Peninsula in southwestern Alaska reveal a consistent stratigraphy.  Dense diamicton of the Nushagak Formation is locally exposed near sea level.  Sediments of the Flounder Flat complex fill shallow basins in the upper Nushagak Formation and are interpreted to record thaw lakes filled by prograding deltas that were buried by an eolian sand sheet during a transition to colder conditions.  The organic-rich Etolin complex overlies the Flounder Flat and represents a moist tundra environment.  A layer of loess known as the Igushik formation caps the sequence, and records a return to colder, drier conditions.  Efforts in the 1990s using thermoluminescence and amino-acid racemization suggested that the Nushagak sediments were deposited late in Marine Isotope Stage (MIS) 5, whereas conventional radiocarbon dating of dispersed organics concluded that the Etolin complex was >30,000 years old and the Igushik loess was from the Last Glacial Maximum (LGM).  Although not directly dated, the inference was that the Flounder Flat complex accumulated during MIS 4.  In August 2024, new samples were collected from separate exposures spanning 2.5 km along the shoreline for Single Aliquot Regenerative dose (SAR) luminescence dating of quartz and Post Infrared/Infrared (PIR/IR) dating of K-feldspar separates.  Duplicate preliminary ages for quartz and feldspar from individual samples agree within uncertainty and suggest that the Flounder Flat complex actually accumulated during the LGM between ~24 and 20 ka.  In contrast, two samples of dispersed organic matter from the overlying Etolin complex yielded Accelerator Mass Spectrometry (AMS) 14C ages of 31.5 and 40 cal ka BP, matching the existing non-finite conventional ages.  Given the consistency of our results on both quartz and feldspar from multiple samples collected from separate exposures, our explanation for this discrepancy is that 14C ages on dispersed organics in these sediments are artificially old due to contamination from inorganic carbon.  Our preliminary luminescence results suggest that the Flounder Flat-Etolin-Igushik sequence reflects a dynamic late-glacial climate with considerable variability superimposed on the general transition from glacial to interglacial conditions.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412456

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