MAPPING THE POSTGLACIAL SUBMERGENCE OF EASTERNMOST BAFFIN ISLAND, NUNAVUT, CANADA

At the eastern margin of the Laurentide Ice Sheet (LIS), eastern Baffin Island has a complex history of postglacial glacio-isostatic adjustment and relative sea level. The eastward dipping raised shoreline gradients on southwestern Cumberland Peninsula led Dyke (1979, Arctic & Alpine Research 11: 179-202) to infer their continuation below present sea level, thereby suggesting continuous postglacial submergence farther east on the peninsula. Miller (1975, PhD dissertation: University of Colorado) added evidence to this conceptual model with his single-trace profiles of submerged deltas 32-38 m below sea level along northern Cumberland Peninsula. Since Miller’s discovery, despite extensive research on Quaternary raised shorelines in the region, few submerged shorelines have been documented to help constrain this postglacial lowstand. Only recently has seabed-mapping technology advanced to a point where the submergence model for eastern Cumberland Peninsula can be substantially tested.

Multibeam sounding was used to search the fiords and coastal waters of eastern Cumberland Peninsula for submerged deltas. Along the northeastern coast seven submerged ice-contact deltas were discovered and mapped in high-resolution at present depths ranging from 19 to 45 m. The eastward gradient of the submerged shorelines projected along a west-east transect is similar to that of the raised shorelines in the southwest, though less pronounced, and confirms Dyke’s conceptual model for submergence of the eastern peninsula. From the linear eastward gradient, the deposition of the submerged deltas is interpreted to have been approximately synchronous. Though these deltas were not dated, their deposition is constrained to <10 ka BP (radiocarbon time scale) by recessional LIS ice margins on the peninsula. The pulse in deglacial meltwater and sediment necessary for delta progradation, at the point when LIS and local alpine glaciers had receded to the fiord-heads, was sourced from the subsequent recession after the Cockburn readvance ca. 9.6 ka BP. High priority for future work is to determine bracketing ages for the lowstand from cores of prodelta bottomsets and delta topsets. With an age of deposition, these deltas can provide index points to constrain the submerged sea-level history of eastern Cumberland Peninsula.