Abstract

A 240-cm thick coarse carbonate sand layer was recovered by piston coring from 4,000 m of water east of the steep (14 degrees -60 degrees ), high relief (4-5 km) Bahama Escarpment. Most of the sediment was derived from the adjacent shallow-water Bahama carbonate platform. The deposit consists of four units (from bottom to top): (I) a basal unit (7-8 cm thick) intensely mined with the underlying hemipelagic sediment; (II) a 72-cm thick inversely graded section; (III) a massive, non-graded unit 125 cm thick; and capped by (IV) a normally graded unit 35 cm thick. Contacts between all units are gradational and the top of the deposit is flat and sharp. Units I-III are interpreted to have been deposited by modified grain flow. Interstitial muds are believed to have aided in support of the flow by adding some matrix strength. The normal grading in unit IV may have resulted from increased turbulence with overlying waters and the transition from grain flow to turbidity current at the top of the flow. This is the first report of a modern modified grain flow deposit from the deep sea.

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