2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 5
Presentation Time: 3:00 PM


COULTHARD, Roy D., Earth and Atmospheric Sciences, Univ of Alberta, 1-26 Earth Sciences Building, Edmonton, AB T6G 2E3, DAVIS, P. Thompson, Department of Natural & Applied Sciences, Bentley University, 175 Forest St, Waltham, MA 02452-4705, BRINER, Jason P., INSTAAR, Univ of Colorado, Boulder, CO 80309-0450 and MILLER, Gifford H., INSTAAR and Geological Sciences, Univ of Colorado, Boulder, CO 80309-0450, roy.coulthard@ualberta.ca

The extent of the Laurentide Ice Sheet (LIS) on eastern Baffin Island during the Last Glacial Maximum (LGM) has been debated for over 40 years. Early work predicted the LIS inundated the Baffin Island coast, terminating at the continental shelf break. This “big ice” model was largely discredited by Løken’s (1966) discovery of undisturbed pre-LGM sediments in the 80 m asl Aston Delta on the coastal foreland south of Inugsuin Fiord.

Two extensive raised marine shorelines were observed on the Aston Lowland: a 80 m asl marine limit shoreline that can be traced for 30 km northward from the Aston Delta; and a 25 m asl shoreline that extends for 45 km parallel to the 80 m beach. Nine 14C ages confirm the pre-LGM depositional age (>54,700 yrs BP) of the Aston Delta and 80 m shoreline. However, lateral meltwater channels that cross the delta and lowland indicate the area was inundated by minimally erosive cold-based ice subsequent to the delta’s deposition. These channels drain to the 25 m shoreline, and outline the retreat of three glaciers that inundated the coastal lowlands but were insufficiently thick to overwhelm the outermost coastal summits. Ice-transported molluscs in till collected from the surface of the Aston Delta returned a 14C age of 36,490 yrs BP, a limiting age for the advance of the LIS. Cosmogenic exposure ages on erratic boulders indicate the LIS retreated from the outer coast between about 13 and 15 ka (cal). Seven basal lake core 14C ages from the Aston Lowland and Clyde Foreland indicate that the outer coast was deglaciated before 12 ka (cal).

Our study indicates that an extensive, but thin LIS covered the Aston Lowland during the LGM, terminating beyond the modern coast. Ice advanced after 36 ka BP, and retreated before 12 ka (cal). The preservation of older Quaternary sediments and landforms indicates that the most distal part of the LIS was composed of minimally erosive cold-based ice during the LGM and earlier glaciations. Erosive, warm-based ice was probably restricted to the major fiords during these glacial episodes. This new model suggests that much of the eastern Baffin Island landscape is ancient in origin and has not been substantially modified during several glacial cycles. Late Quaternary glacial climate was probably too cold and dry to support large, warm-based ice sheets along the outer Baffin Island coast.