Surface sediment from the inner continental shelf and island beaches in the Sitka Sound area contains between 94 and 37 percent by weight carbonate, the remainder being silicate rock fragments and minerals. Sand-sized pumice is a minor constituent. These sediments are bi- and polymodial coarse skewed gravelly sands. Mud is present in trace amounts and is mostly carbonate. The carbonates are biogenic; sand-sized grains are fragmented skeletons of barnacles, echinoids, bryozoans, and mollusks. Sand-sized carbonate minerals are mostly low Mg-calcite with high Mg-calcite and aragonite as minor constituents. Aerial reconnaissance in the Sitka Sound area suggests that these carbonates are more widespread than formerly supposed.

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