New Data on the Geological Development of the Southern Part of the East Siberian Sea in the Late Pleistocene–Holocene

New data are presented on the geological sequence, composition, and genesis of Late Pleistocene–Holocene deposits in the southern part of the East Siberian Sea (Long Strait to Chaun Bay). Basic materials were collected during a marine geological expedition by the A.P. Karpinsky Russian Geological Research Institute (VSEGEI) carried out in 2018 for geological mapping of sheets R-56–R-60. Research included sub-bottom profiling, side-scan sonar survey and multibeam echo sounder, sediment sampling (box corer and gravity corer). Processing and interpretation of geophysical data and study of sediment cores, including layer-by-layer grain-size, geochemical, diatom, and palynological analysis, as well as radiocarbon dating, were used to update the knowledge on reconstruction of the geological development of the region and refine the palaeoclimatic and palaeogeographic characteristics of the natural environment in the Late Pleistocene–Holocene. During the Sartan Cooling within the off-shore study area, continental conditions prevailed, but no seafloor landforms or any sediments formed by glacial activity were found, since erosional processes dominated at that time. Sediments accumulated within shallow freshwater lakes (possibly thermokarst in origin), river valleys, and semienclosed lagoons. Since the end of Pleistocene, the sea level rose irregularly, as evidenced by characteristic seafloor landforms (longshore bars, underwater terraces, foredeltas, etc.). Holocene sedimentation is characterized by high facial diversity, low sedimentation rates, and weak sorting of sedimentary material.