Changes in the silt- and clay-size mineralogy of sediments at Ocean Drilling Program site 645B, Baffin Bay

Abstract

Site 645B, Ocean Drilling Program (ODP) leg 105, was cored in 2010 m water depth off the eastern margin of Baffin Island. A 279 m core was dated as extending back to ca. 2 Ma. Samples of sediment were analyzed for their silt- and clay-size mineralogy using X-ray diffraction techniques. Constrained cluster analysis on these data defined three units, which indicated that significant changes in mineralogies occurred at approximately 75 m below sea floor (bsf) (ca. 0.5 Ma) and 155 m bsf (ca. 1.15 Ma). These boundaries coincide closely with units IA–IB and IB–II as designated in the ODP shipboard reports, and which were based on detrital carbonate and sand contents. Unit II (1.2–2 Ma) is characterized by zero clay-size calcite and high amounts of clay-size smectite and silt-size mica. Unit IB (0.5 – 1.15 Ma) is noteworthy for the first presence of clay-size calcite, high amounts of detrital dolomite, and a peak in clay-size kaolinite. The uppermost unit IA (0–0.5 Ma) is characterized by consistently high values of clay-size dolomite and sand. Compared with sediments on the adjacent eastern Baffin Island shelf and fiords, the sediments at ODP site 645B are enhanced in the amounts of carbonate, smectite, and kaolinite, and depleted in both silt- and clay-size mica and feldspar. This pattern suggests a limited supply of sediment is transported from Baffin Island into Baffin Bay.