107-3 Provenance and Timing of Pleistocene Detrital Carbonate Beds in IODP Sites U1603 and U1604 on the NW Greenland Margin: Implications for Ice Sheet Dynamics in Baffin Bay

Session: Sedimentary Geology Division/SEPM Student Research Poster Competition: Dynamics of Stratigraphy and Sedimentation

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IODP Expedition 400 drilled multiple sites along the northwest margin of Greenland to investigate the Cenozoic evolution of the Greenland Ice Sheet. Pleistocene slope deposits at Sites U1603 and U1604 contain dozens of conspicuous beds of yellow- to reddish-brown detrital carbonate mud with outsized clasts of limestone, dolostone, and other lithologies. Similar deposits recovered in piston cores near the Canadian Arctic Archipelago have been interpreted as the products of ice-rafting from the region of Lancaster Sound, where ice streams were underlain by carbonate bedrock. To investigate the origin, timing, and significance of these beds, their sedimentology, stratigraphic distribution, and sand-gravel (>150 µm) fractions were characterized in Sites U1603 and U1604. Analysis of their stratigraphic distribution shows that although several prominent beds correlate between the sites, many are not laterally extensive. Outsized clasts were examined after wet sieving via standard point counting under a binocular microscope and in thin section for rounding, sphericity, and composition using visual estimation diagrams. They are typically angular to subrounded with low sphericity, consistent with glacial transport. Exceptions are spherical, frosted quartz grains interpreted tentatively as aeolian. Compositions are dominated by quartz and sedimentary rocks, notably limestone and dolostone, along with igneous and metamorphic rocks, cherts, and other accessory minerals. At both sites, the proportion of sedimentary clasts decreases upward from ~60-90% to ~30-80%. At the same time, the proportion of carbonate clasts within the sedimentary fraction increases from ~30-80% to ~40-100%. Aeolian quartz relative to total quartz additionally peaks as high as ~27-28% at both sites. These trends may reflect prolonged erosion of bedrock by ice streams and temporal variability in source regions of ice streams. Similarities with detrital carbonate beds from western Baffin Bay suggest a shared provenance, likely Paleozoic carbonate units exposed in Lancaster Sound. Owing to their relatively distal positions from potential source regions, Sites U1603 and U1604 may contain a more episodic record of carbonate ice rafting than do more proximal sites. Whereas major iceberg discharge events may have produced regionally extensive deposits that reached Sites U1603 and U1604, smaller-scale events produced isolated sediment dumps from individual icebergs that terminate laterally. These results contribute to understanding potential spatiotemporal variation in Laurentide and Greenland ice sheet extents, outlets, and drainage patterns through the Pleistocene. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6529

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