Sediments of the sea floor of the Alpha Rise, 500 mi north of Point Barrow, Alaska, were cored to a depth of about 3 m below the sea-sediment interface beneath Ice Island T-3, where the ocean is slightly deeper than 2,000 m. The sediments contain about 80 percent clay and silt, the remainder being fine sand. They are either gray or brownish gray in color, the brown color being caused mainly by the oxidation of ferrous monosulfide. Although organic matter seems plentiful, it is of colloidal size and amounts to about 3 percent of the sediments. The clay minerals present are mica (both muscovite and biotite), mixed-layer mica and organic matter, vermiculite, chlorite (two polytypes), together with quartz, feldspar, and, in some samples, dolomite. The predominant clay mineral are mica and mixed-layer micas. Chlorite commonly is present, but vermiculite is scarce. Dolomite appears to be authigenic, but the micas, most of the chlorite, quartz, and feldspar are detrital. The mixed-layer mica with organic matter is authigenic.

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