Late Wisconsinan erosion and eolian deposition, Summer Island area, Pleistocene Mackenzie Delta, Northwest Territories: optical dating and implications for glacial chronology

Abstract

The Summer Island area of the Pleistocene Mackenzie Delta, western Canadian Arctic, is thought to have been last glaciated during the Early Wisconsinan (>35 ka), with a suggested Late Wisconsinan (~13 ka) glacial limit located ~80–100 km to the south. Cryostratigraphic observations in the Summer Island area identify eolian and fluvial sediments overlying an erosion surface. On Summer Island, eolian sand occurs within sand wedges, the tops of which are contiguous with an eolian sand sheet deposited on a formerly bare ice surface. This paleo-ice surface is attributed to fluvial erosion, and that in turn is attributed to proglacial meltwater activity. The age of erosion is inferred to be shortly before ~14 ka, determined by optical dating (using infrared stimulation of luminescence from feldspar) of the eolian sand wedges. This ~14 ka meltwater erosion is significantly north of the generally accepted limit of Late Wisconsinan glaciation in this coastal area, suggesting that ice last covered the whole of Richards Island near the end of the Late Wisconsinan, rather than in the Early Wisconsinan, as previously thought.