Sedimentology of deep-water carbonate diamictons in Baffin Bay

In Baffin Bay, situated between Greenland and the Canadian Arctic Archipelago, dozens of conspicuous beds consisting of detrital carbonate mud, sand, and gravel mixtures occur in Pleistocene strata recovered by various drilling projects. These beds have been interpreted as ice-rafted debris, with the implication that they record large scale-calving events. Petrographic examination of the sand and gravel fractions reveals carbonate clasts with a range of carbonate textures, Paleozoic fossils, and dolomitization styles that correspond to potential source regions in Canada and Greenland. However, the processes involved their formation within an otherwise carbonate-poor, siliciclastic-dominated, deep-water setting remain poorly constrained. Here, we use core descriptions, high-resolution core photographs, X-Ray images, petrography, and other data archived in the online IODP Laboratory Information Management System (LIMS) to characterize the deposits. Carbonate beds show variability in sedimentological expression, including differences in upper and lower contacts (sharp vs. gradational) and occurrence as isolated beds or compound sequences featuring carbonate-rich laminae that grade into or out of thicker units. Internal structures range from massive, to coarsening upward, and laminated. Comparison of the stratigraphic distribution of detrital carbonate beds between very closely spaced cores shows that only a few of the thickest beds can be correlated, indicating limited lateral continuity. Results are most consistent with dump deposits derived from melting of icebergs calved from the sediment-rich base layers of glacial ice streams overlying regions of carbonate bedrock. Such icebergs have the potential to release cold, dense mixtures of sediment and water that have the potential to sink rapidly to the seafloor and form localized deposits that thin laterally. Sedimentary structures suggest that some deposits were later transported downslope or reworked by bottom currents. These unique carbonate diamictons, linked to distinct source regions, provide a distinctive record of Pleistocene glacial dynamics in Baffin Bay.