Cores recovered during Leg 19 permit a preliminary synthesis of late Cenozoic sedimentation in the Bering Sea and extreme north Pacific Ocean. In addition, the material contributes to the growing store of data aimed at deciphering the complex interactions between tectonism and sedimentation along active continental margins. Many of the deposits, until now characterized only by acoustic properties on seismic reflection profiles (Ewing et al., 1965; Scholl et al., 1968 and in press; Scholl and Hopkins, 1969; Grim and McManus, 1970; Ludwig et al., 1971b), have been directly observed and can be used in further interpretation of the acoustic data (see Scholl and Creager, this volume). The Bering Sea includes the northernmost of the deep marginal basins associated with the dominantly convergent plate boundaries on the northern and western sides of the Pacific Ocean. It differs from other Pacific marginal basins in that the terrigenous fraction of the basin deposits is generated in high-latitude areas largely underlain by permafrost. The processes of chemical weathering, typical of temperate and tropical zones, are severely restricted, and seasonal variations in runoff and sediment contribution to the basin are extreme (Lisitsyn, 1966). In addition to the volcanic and terrigenous components of the sediments, the high biogenic productivity of the region results in the deposition of significant (indeed, vast) quantities of siliceous microorganism remains. Although silicoflagellates and radiolarians are present, diatom frustules comprise almost all of the siliceous biogenic fraction. Carbonate horizons, some of which are composed of calcareous nannoplankton remains, also occur and indicate at least local deposition above the carbonate compensation depth. The complex suite of sediments in the region, then, directly reflects the interaction of oceanic and continental margin sedimentation mechanisms, as well as the influence of nearby active volcanos. Overall, the Miocene to Holocene sediments of the Bering Sea are dark greenish gray hemipelagic muds with local significant quantities of intercalated sand and volcanic ash.

Buldir Depression is a large, rectilinear basin that lies on the northern edge of the Aleutian Ridge and is aligned with the arcuate chain of active volcanoes on the ridge crest. The depression appears to be a volcanic-tectonic feature, which began to form in Late Tertiary time and which is still forming. It is a graben formed by extensional rifting and accompanied by contemporaneous volcanism on the Aleutian Ridge. Subsidence rates for the depression are estimated at 20–70 cm/1,000 years. Sediments in the depression are 300 m thick and are probably pelagic and turbidite deposits of Pleistocene age. The turbidites were apparently derived from the plateau area of the Aleutian Ridge surrounding the depression. Older sediments on the northern slope of the Aleutian Ridge have a maximum thickness of 550 m and are deformed and slumped toward the Bering Sea. These sediments are postulated to overlie a mid-flank terrace on the northern Aleutian Ridge that titled to the north during the formation of Buldir Depression.