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Two re-entrants or troughs extending from the Arctic basin into the northern Kara Sea, an epicontinental sea on the Eurasian continental shelf, were sampled during the summer of 1965. The program was limited to depths exceeding 100 fm.

Distinct sedimentary zones exist in the westernmost trough which is open toward the southwest. These zones are expressed most strongly by the chlorite-kaolinite clay-group distribution which reflects a mixture from two distinct sources. The chlorite clays enter from the southwest and are dispersed northward along the eastern margin.

The sedimentary zones depend more on the bottom relief, currents, and source than on the absolute water depth. The zones trend north-south, paralleling the dominant currents which consist of a north-flowing near-surface current on the east side and a south-flowing bottom current on the west. The zonation is shown on maps of clay-group facies, water content, insoluble residue, and organic carbon. Similar zonation is suggested by the distribution of the grain size, the composition of the sand-size clastic grains, and foraminiferal populations.

In terms of relative amounts, the easternmost zone or slope is characterized by a low water content, and abundant chloritic clays, sand, and Foraminifera. The deposits at the foot of the slope have a high water and organic-carbon content, little chloritic material, and the greatest amounts of soluble material, though they contain few Foraminifera. The trough-floor sediments are characterized by an intermediate water content, low amounts of organic carbon, a very low chloritic content, and varying amounts of soluble material. The easternmost trough, which is open only to the Arctic, does not contain distinct sedimentary zones, nor does it have a recognizable current pattern.

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