Stratigraphy and Palaeoenvironments of Richards Island and the Eastern Beaufort Continental Shelf during the Last Glacial-Interglacial Cycle

摘要

The Pleistocene lithostratigraphy exposed on northern Richards Island comprises seven units that correlate with the offshore seismostratigraphy of the eastern Beaufort Continental Shelf. Land-sea correlations, cryostratigraphic observations and proxy indicators of environmental change provide a record of palaeoenvironmental history that commences before the last glacial-interglacial cycle. After the high sea-level stand of the Last (Sangamonian) Interglaciation, marine regression exposed a large area of the eastern Beaufort Shelf to cold subaerial conditions and permafrost aggradation. Northward progradation of a braided river system was abruptly replaced by aeolian activity, probably as a result of diversion of the palaeo-Porcupine River by the advancing Laurentide Ice Sheet during the Late Wisconsinan. Glaciation of Richards Island by the Mackenzie palaeo-ice stream was brief (sometime between ~22 000 and 16 000 cal. yr BP), and deglaciation had certainly commenced by 14300 cal. yr BP and perhaps by ~16 000 cal. yr BP or earlier. Major fluvial erosion during the Last Glacial-Interglacial Transition incised cross-shelf valleys and formed a regional erosion surface. The Holocene marine transgression trimmed some of the erosion surface and offshore, covered it with marine deposits.