Quaternary glaciation of central Banks Island, NT, Canada

The glacial geology and geomorphology of central Banks Island record the extent and dynamics of the northwest Laurentide Ice Sheet (LIS) during Late Wisconsinan glaciation. Additional stratigraphic exposures document Mid Quaternary environmental changes. Detailed mapping and a new chronology indicate that the island was inundated by the northwest LIS during the Late Wisconsinan. The maximum limit of the ice sheet was offshore on the Beaufort Sea shelf, one of several source regions for floating glacier ice that scoured the Arctic Ocean sea floor to a depth of 450 m. Ice sheet retreat was underway by ∼14 cal ka BP when an ice stream withdrew rapidly from M'Clure Strait. A readvance or stillstand 13.75–12.75 cal ka BP resulted in deposition of widespread controlled moraines, comprising the Jesse moraine belt on eastern Banks Island and adjacent Victoria Island. This deposit records predominantly cold-based ice margins giving way to polythermal bed conditions, which were conducive to widespread deposition of controlled moraines and ice stream bedforms. The expansion of warm-based thermal regimes in the northwest LIS followed ice sheet withdrawal from M'Clure Strait and western Amundsen Gulf, suggesting a re-equilibration of regional ice divides in response to rapidly changing ice sheet margins and surface gradients. These reconstructed ice sheet dynamics provide new constraints for assessing the sensitivity of the northwest LIS to past changes in climate and sea level. Stratigraphic exposures at Morgan Bluffs on eastern Banks Island comprise an archive of Mid to Late Quaternary environmental change. New, detailed sedimentological analyses and stratigraphic investigations negate the previously reported climatostratigraphy, which involved multiple glacial-interglacial cycles. Instead, three distinct intervals of sedimentation are now recognized. The first records the progradation of a delta, followed by aggradation of a braided river valley perhaps ∼1 Ma ago. The second documents a glacier advance across a former marine delta more than 780 ka ago. The third succession is interpreted to record sedimentation by an ice-contact delta into an ice-dammed lake during the last deglaciation, ∼12.75 cal ka BP. The revised stratigraphic framework adds important new terrestrial observations to a sparse and fragmentary dataset of Arctic environmental change.