Quaternary geology and glacial history of Bylot Island, Northwest Territories

Abstract

The Quaternary geology of Bylot Island records glaciation by regional ice sheets and by local mountain glaciers, and marine and glaciomarine sedimentation around its margins. The geological evidence for the last major foreign glaciation, Eclipse glaciation, is widespread in surficial deposits and landforms and is used as a basis for recognition of other glacial events and for establishing their relative ages. Four distinct foreign glaciations are recognized. The oldest and most extensive, named Baffin glaciation, occurred prior to a period of interglacial weathering, named Salmon River interglaciation, and ice could have moved northward across the topographic divide of Bylot Island. During the later Eclipse glaciation, ice was less extensive, although it fully occupied the channels around the island and attained elevations of 270 to 370 m a.s.l. from 10 to 20 km inland on the south coast, and 500 to 600 m a.s.l. against the northern coastal mountains. Eclipse glaciation occurred prior to 43 000 radiocarbon years ago and is older than marine shells having amino acid ratios (D-alloisoleucine to L-isoleucine) of 0.20 to 0.25. Evidence of the younger Button glaciation is restricted to coastal areas of Bylot Island below 140 m a.s.l., and foreign ice was restricted to the marine channels and was likely floating. Button drift is bounded stratigraphically by shells having amino acid ratios of about 0.15 and 0.10. Cape Hatt glaciation is of Late Wisconsinan or early Holocene age during which time ice extended across Baffin Island to the northern mouth of Milne Inlet. Three periods of native glaciation are known. The oldest, named Bylot glaciation, was most extensive and covered most of the island prior to Baffin glaciation. Late during Eclipse glaciation, native glaciers that had been dammed on the island by foreign ice underwent major expansion as part of Aktineq glacial phase as they re-established normal outward directions of flow. Modern glaciers appear to be either stationary at, or retreating from, Neoglacial maximum positions attained within the last 100 years that represent their greatest extent since Eclipse glaciation. Five periods of change in relative sea level are recognized, the oldest of which predates Salmon River interglaciation and is represented in sections by marine sediments containing in situ shells with amino acid ratios of 0.55 to 0.60. Younger marine sediments of pre-Eclipse age occur in two stratigraphic sections and contain shells having amino acid ratios of about 0.4 to 0.35. Surficial marine sediments of pre-Holocene age are related to periods of higher relative sea level subsequent to Eclipse glaciation and to Button glaciation. They contain shells having amino acid ratios of about 0.2 and 0.1, respectively. Eclipse marine sediments may extend to 90 m a.s.l. near Canada Point. On northern Bylot Island, Button marine sediments extend to 35 m a.s.l. Holocene emergence is 100 mat the southern end of Milne Inlet, 80 mat Cape Hatt, 50 to 60 m near Pond Inlet townsite, and 35 to 45 m on southern Bylot Island. No raised Holocene marine sediments are known on northern Bylot Island and there the modern coast appears to be submerging.