Late Pleistocene - Holocene transgressive sedimentation in deltaic and non-deltaic areas of the Northeastern Bering epicontinental shelf

Abstract

The distribution of late Pleistocene and Holocene surface sediments on the northern Bering Seafloor is patchy and dependent upon locations of seafloor bedrock and pre-late Pleistocene glacial debris, late Holocene river sediment influx, and modern strong bottom currents. Seafloor vibracores and high-resolution profiles record two different sedimentary environments in the northern Bering shelf: late Pleistocene-Holocene shoreline transgression (<16.000 years BP) in Chirikov Basin, and Holocene deposition from the Yukon River in Norton Sound. Lag gravels remain exposed on the margins of Chirikov Basin where the transgression of the late Pleistocene-Holocene shoreline reworked pre-Quaternary bedrock and Pleistocene glacial moraines. In central Chirikov Basin. the transgressive deposits cover Pleistocene limnic peaty mud of emergent shelf deposition. In places, a few centimeter thick basal transgressive facies of pebbly Medium or fine sand is left above which is a widespread sheet of thin (< lm) inner-shelf fine-sand facies. Water circulation patterns have inhibited deposition of Holocene Yukon River silt over trangressive sand and lag gravels of Chirikov Basin. About 10.000 BP. a rapid marine transgression caused the deposition of a basal nearshore facies of thick storm-sand layers in marine silt over the Pleistocene freshwater peaty mud of Norton Sound. This has been covered by an offshore bioturbated silt. A younger progradation of thick storm-sand lavers and Holocene brackish-water silt (up to 14 m) in southern Norton Sound has been deposited since a shift of the active Yukon Delta into its present position about 2.500 BP.