CLAY-MINERALS AS INDICATORS OF SOURCES OF TERRIGENOUS SEDIMENTS, THEIR TRANSPORTATION AND DEPOSITION - BERING BASIN, RUSSIAN-ALASKAN ARCTIC

Cluster analysis of clay mineral abundances in surficial sediments from 52 stations revealed the presence of four station cluster groups within the Bering Basin and contiguous eastern Aleutian Trench/Forearc. These results can be explained using two end-members of terrigenous clay mineral sources, and their admixtures. The first end-member, Cluster Group I, consists of the highest (average) concentration of illite (48%) and chlorite plus kaolinite (40%) and lowest of expandable minerals (12%). In contrast, the second end-member, Cluster Group Iv, has the highest concentration of expandable minerals (43%) and lowest concentrations of illite (30%) and chlorite plus kaolinite (27%). The Group I assemblages come from two regions: the eastern Aleutian Trench/Forearc and the northwestern margin of the Bering Basin off Koryak Mountains, east Siberia. Clays in the former region are derived primarily from the meta-sedimentary and meta-volcanic rocks of the Chugach Mountains with infiltrations from Alaska Peninsula, and are transported from the southeastern Kodiak Shelf of the Gulf of Alaska to the trench/forearc by the Alaska Current/Alaskan Stream. Similar clays are derived from the Koryak Mountains. Group IV clays, located within the Komandorsky and Bowers Basins and Unmak Plateau, originated from the Mio-Pliocene andesites and basalts of the eastern Kamchatka Peninsula and Aleutian Islands, respectively. It is postulated that Group II clays in the southcentral Aleutian Basin and Bowers Ridge/Basin area, and Group III clays in the northern Aleutian Basin, are mixtures obtained primarily from terrigenous sources of Group I and IV. The distribution patterns and boundaries of the cluster groups reflect the dispersal pathways of clays from the primary sources and the extent of their mixing by regional and local surface currents and mesoscale gyres/eddies. Presumably, the minor infiltration of Anadyr River clays into Group III is a result of clay transport by episodic turbidity currents. Most of the clays derived from the Alaska mainland and Russia proper do not reach the Bering Basin as these clays are trapped within the Bering Sea shelf.