Surface sediments on southwestern Grand Bank are composed mostly of sand, with local admixtures of mud and gravel. Most sediments are enriched with biogenic calcium carbonate, primarily barnacle valves with lesser amounts of mollusk, echinoid, and foraminifera fragments. In contrast to similar carbonate-rich sediments reported from other high-latitude areas, available data indicate that the barnacles were deposited in very shallow water during the last Würm regression. The other carbonate components, being fresher in appearance, may be younger in age.Apparently neither glaciers nor their melt waters extended far enough south on Grand Bank during the last Würm glaciation to dilute these carbonate-rich sediments with terrigenous debris. Similarly, the Holocene influx of fluvial terrigenous sediment appears to have been minor, because of both the lack of major river runoff and the active current regime in the area.

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