Sedimentary records of paleoenvironmental changes during the last deglaciation in the Ulleung Interplain Gap, East Sea (Sea of Japan)

The Ulleung Basin in the East Sea (Sea of Japan) is a semi-enclosed basin surrounded by shallow sills and straits. Detailed observation of X-radiographs and thin sections of core sediments from the Ulleung Interplain Gap reveals five mud facies: laminated mud, crudely laminated mud, homogeneous mud, bioturbated mud and laminated Mn-carbonate mud. The laminated and homogenous muds were most likely deposited from turbidity currents, whereas the bioturbated and crudely laminated muds were formed by pelagic/hemipelagic sedimentation under oxic and anoxic bottom-water conditions, respectively. The laminated Mn-carbonate mud occurs at the lithologic boundary between the turbidite and hemipelagic laminated mud (last glacial) and the pelagic bioturbated mud (Lateglacial to Holocene). Mn-carbonates were formed at the sediment–water interface, probably reflecting an abrupt change in bottom-water oxygenation caused by sea-level rise during the last deglaciation. Profiles of redox-sensitive elements also support an anoxic to oxic change of bottom-water conditions during this period.