Continental Shelf Structure and Sediments of Gulf of Anadyr: ABSTRACT

Abstract

Interpretation of continuous seismic reflection profiles indicates that the continental shelf of the northwestern Bering Sea is underlain by up to 1 km of Tertiary End_Page 2492------------------------------ and Quaternary sediments that were deposited in a basin formed by the subsidence of a lithified and folded Mesozoic basement complex. This Anadyr basin is evidently an extension of the depression containing up to 3 km of Tertiary strata below the Anadyr Lowland on the west of the Gulf of Anadyr. A basement sill extends eastward from the southwest corner of the gulf; apparently, the sill is the continuation onto the shelf of the Koryak Mountain structural province. Tertiary layers generally are little deformed over the basement sill, thus it is suggested that this broad arch has been in existence throughout the Tertiary. If the thick Tertiary deposits of the Anadyr, Bristol, Norton, and Chukchi basins are shallow marine in origin, the extent of an exposed Bering Sea shelf during the Te tiary may not have been as great as previously thought. Some draining of the shelf is suggested, however, near the end of Tertiary time by a distinct erosional unconformity below Quaternary sediments in the northwestern part of the Gulf of Anadyr. On seismic profiles Quaternary sediments appear to be highly deformed across parts of the Anadyr shelf. These deformed Quaternary deposits are ascribed to continental ice encroachment on the shelf, and they define the outer limits of ice advance during the maximum glaciation as lying approximately along a line from St. Lawrence Island to a point 150 km east of Anadyr Bay, then south roughly parallel with the coast. Buried erosion surfaces and stream channels within the Quaternary sediments are evidence of sea-level fluctuations during that time. Present bathymetry and the sediments and fauna of 1-m cores suggest a sea level stillstand at approximately -75 to -80 m. Lack of suitable material precludes dating of this stillstand. End_of_Article - Last_Page 2493------------