COSMOGENIC EXPOSURE DATING VERTICAL TRANSECTS IN THE FIORD LANDSCAPE OF NORTHEASTERN BAFFIN ISLAND: INSIGHTS INTO GLACIAL EROSION

Fourteen new ¹⁰Be exposure ages collected from two elevational transects in fiords in the Clyde Region, northeastern Baffin Island help to elucidate the efficiency of glacial erosion. In the Ayr Lake valley, eight ¹⁰Be ages were obtained from samples collected during the ascent of a 520-m-high vertical fiord wall (340-860 m asl) at a site that was deglaciated by the Laurentide Ice Sheet (LIS) ~13 ka. All samples from the fiord wall are within 2 S.D. of the deglaciation age, or are younger, indicating post-glacial spalling. Lack of inheritance in the wall surface, including a sample only 30 m below the summit, indicates that the wall was completely cosmogenically reset (ie, experienced >2 m of glacial erosion) during the last glaciation. A ¹⁰Be age of 50.0±1.2 ka on a horizontal surface at the 860 m asl summit indicates that the cliff-top was not glacially-eroded during the Last Glacial Maximum (LGM). At a second site in outer Clyde Inlet, bedrock/erratic pairs were collected from 175, 375 and 500 m asl along the shoulder of a peninsula that protrudes into the fiord. Erratics provide a deglaciation age for the peninsula of ~10 ka. Bedrock at the lower two sites is sculpted and striated, but the summit of the peninsula does not appear to have been glacially modified. However, nearby summits up to 700 m asl have deglacial-age erratics that overlie weathered bedrock, indicating that LGM ice covered the summit of the peninsula. The bedrock at all three elevations, ranging from ~25 to ~35 ka, has not been completely cosmogenically reset, which requires less than 2 m of glacial erosion during the LGM. These results reveal that: 1) striated bedrock is not always cosmogenically reset, 2) vertical fiord walls in the Clyde Region are probably cosmogenically reset to their tops, and 3) in landscapes that were differentially eroded, exposure dating of erratics, not bedrock, can provide the most accurate information regarding glacial chronology.