The Holocene Destruction of the Tumannaya River Delta and the Formation of Shallow Gas Accumulations along the Shelf in the Western Part of Peter the Great Bay (Sea of Japan)

Abstract

This paper reports on results of bathymetric and seismoacoustic studies of the shelf in the western part of Peter the Great Bay. Five flooded coastlines, formed in the Late Pleistocene–Holocene, were revealed on the shelf. It was found that a significant part of the shelf is occupied by a zone of irregular sedimentation. This zone is underlain by an erosion surface buried under sediments of ebb–flood tidal deltas in the areas of active sedimentation and is exposed on the seafloor within the area of active modern erosion. The abrasion and formation of the irregular sedimentation zone on the shelf intensified about 11 500–11 700 years ago. Acoustic anomalies, associated with gas occurrences in sediments and gas plumes in the water column, were recorded on the shelf of the bay. Types of anomalies were classified, and a map of their areal distribution was compiled. It is concluded that the trigger mechanism that provides gas migration into sediments and to the water column is associated with a group of factors: the change of the postglacial sea level and abrasion processes, as well as the meteorological and hydrological regimes.