Middle Holocene Marine Sedimentation on the Southwestern Coastal Margin in Primorye, Russia

A comprehensive study of marine sediments deposited on the southwestern margin of the Primorye region (near the settlement of Khasan) allowed us to consider in detail the paleogeography of the coast in the second half of the Atlantic Period of the Holocene, about 6500–6000 BP/7400–6800 cal BP. Marine environment sedimentation, as a result of the development of postglacial oceanic transgression, began around 6500 BP/7400 cal BP. A shallow marine gulf formed on the coastal accumulation plain, into which flowed the Tumannaya (Tumangan) River, the largest in the Sea of Japan Basin. The estuarine area of the river created an avalanche sedimentation environment in the bay, which developed at an average rate of 16–24 mm/year. The final sedimentation phase, which occurred after 6200 BP/7100 cal BP, did so at a time when the sea transgression slowed and sea level reached its maximum height of +1 m in this coastal area. The distribution of multispecies broadleaved forests predominated by oak and with increased participation of thermophilic hornbeam in the area adjacent to the coast at this time clearly indicates optimal climatic conditions. The end of marine sedimentation occurred around 6000 BP/6800 cal BP. It did not resume for a long time, until the middle of the Sub-Atlantic Period of the Holocene.