Improving Quaternary tephrostratigraphy and cryptotephrostratigraphy of Hole ODP797B in the Japan Sea: Inserting globally correlated tephra ages into deep-sea sediments in a semi-closed sea

We investigated deep-sea sediments corresponding to the last 1.2 Ma in Hole ODP797B in the northern Yamato Basin, Japan Sea, and refined the tephrostratigraphy. We correlated tephras and cryptotephras with terrestrial and marine tephras using glass shard major- and trace-element compositions and by referring to the reported tephrostratigraphy of marine sediments in the Japan Sea and NW Pacific, marine–terrestrial sequences on the Oga Peninsula (northern Honshu), and Lake Suigetsu lacustrine sediments (central Honshu). We identified tephras from the Japan arcs (NE Japan, Izu-Bonin, and Kyushu arcs) corresponding to marine isotopic stages (MISs) 1–21 by referring to the tephrostratigraphy and δ 18 O stratigraphy of Holes U1437B and C9001C and core MD012422 in the NW Pacific. These tephra horizons are consistent with the reported bio- and magnetic horizons. We also correlated tephras from Ulleungdo and Changbaishan volcanoes to well-dated tephras in Lake Suigetsu and Japan Sea sediments by their shard chemistries and stratigraphic levels relative to Japan arc tephras. Further, we suggested that a Changbaishan tephra in the MIS 8 segment of Hole ODP797B occurs in the MIS 8 segment of Hole C9001C, and an Ulleungdo tephra in the MIS 12 segment of Hole ODP797B occurs in MIS 12 terrestrial sediment (lignite) on the Oga Peninsula. The Ulleungdo and Changbaishan tephras can potentially serve as time markers in Middle Pleistocene sediments of the Japan arcs and NW Pacific, where they are not common, once the tephra correlation uncertainties caused by multiple tephra candidates with similar shard chemistries are improved.