Coarse Terrigenous Fraction at IODP Site 1308, North Atlantic: Evidence For Changing IRD Sources Through Last 300ky

Integrated Ocean Drilling Program (IODP) Expedition 303 obtained ocean floor sediment cores from the North Atlantic, including Site 1308 at 50N 24W. These cores contain coarse terrigenous material, known as Ice Rafted ( IRD), which deposited by melting icebergs that had carried continental rock fragments and traversed the North Atlantic before melting. The abundance and composition of this IRD have been used as a proxy to understand the locations and history of glaciation on landmasses that border the North Atlantic. In this study, 78 samples were analyzed to produce an IRD record to ~288,000 years before present (ka), with an average spacing between samples of ~4 ky. IRD abundances within these samples vary from 0.1 to 12.23%. The IRD composition is dominated by a relatively constant content of unstained quartz (~55%). The second-most abundant IRD grain is volcanic glass, whose average abundance increases upsection. Iron-stained quartz is the third-most abundant grain type; its abundance reaches a maximum at ~88ka, with abundance in younger sediments. Variations in the abundances of individual IRD grain types appear to define three stratigraphic intervals with distinctive IRD assemblages; these are: ~73-0 ka – 55% qtz, 30-40% volc. glass, 5% Fe-stained qtz. ~150-73 ka – 55% qtz, 30% volc. glass, ~10% Fe-stained qtz. ~288-150 ka – 55% qtz, 10% volc. glass, ~7% Fe-stained qtz, ~10% rock frags. These compositional variations suggest that older IRD was supplied from a wider range of source regions, possibly indicating more geographically widespread glaciation.Shell Oil Corp