Two late Pleistocene marine transgressions of contrasting character are recorded by deposits of the Arctic coastal plain. Deposits of the oldest transgression extend from Harrison Bay west to near Barrow and contain a fauna that documents interglacial conditions. Five thermoluminescence (TL) dates on the marine deposits average 127 Ka and indicate a correlation with oxygen isotope stage 5e. Sedimentary structures characteristic of the swash zone occur at altitudes within the commonly accepted range (6 ± 4 m) for eustatic high sea level at that time, showing that this part of the coastal plain has been tectonically stable for the past 125,000 years.

Deposits of the youngest transgression are glaciomarine sediments that contain ice-rafted erratics of Canadian provenance. They compose the Flaxman member of the Gubik Formation and occur locally along the Beaufort Sea coast and inland to altitudes of about 7 m. TL dates on these sediments suggest that the Flaxman transgression occurred between 70 and 80 Ka and is correlative with deposits dated to this interval that are exposed near sea level on the North Carolina coastal plain. However, the deep-sea oxygen-isotope record is commonly interpreted to indicate that sea level was below its modern position at that time. The present altitude of the Flaxman deposits cannot be attributed to tectonism because their distribution includes the part of the coastal plain determined to be tectonica ly stable for the past 125 Ka. Isostatic depression and subsequent elevation are unlikely considering the correlative deposits of North Carolina. This paradox could be explained if enormous volumes of floating glacial ice were produced by the rapid breakup of a large part of the Laurentide ice sheet, and recent work indeed suggests that the Hudson Bay lowlands were ice free at this time.

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