Depositional environments of the Yukon Delta, northeastern Bering Sea

Abstract

The Yukon River provides approximately 90% of the sediment presently entering the northeastern Bering Sea. Most of that sediment is initially deposited in Norton Sound, a broad, microtidal embayment typically less than 20 m deep. The shallowness of the depositional basin has allowed extensive reworking of the deltaic sediments by a variety of processes. These include waves, Tidally and wind-induced currents, and oceanic currents, as well as processes associated with the movement and deformation of sea ice. The relative importance of these processes varies systematically throughout the year. The seasonal variability is best described by the definition of an ice-dominated, river-dominated. and storm-dominated regimen. each consisting of a characteristic suite of geologic processes. The morphology of the Yukon Delta also reflects the climatic extremes of this high-latitude, epicontinental sea. The subaqueous profile of the delta differs from most previously described deltas in that the shoreline is separated from the prograding margin of the delta by a 'sub-ice platform' which is typically 2-3 m deep and extends up to 25 km offshore. The platform is crossed by a series of 'sub-ice channels' which extend up to 25 km beyond the mouths of the major distributaries. The platform and associated subaqueous channels are related to the presence of shorefast ice which fringes the delta for half of the year. and appear to be characteristic of ice-dominated deltas formed in high-latitudes.