Stratigraphy and chronology of Holocene tephras from Ulleungdo volcano (South Korea) distributed in and around the Sea of Japan

Ulleungdo is a volcanic island located 130 km east of the Korean Peninsula. The alkaline tephra named Ulleung-Oki (U-Oki) has played an important role as an essential time marker of the early Holocene, especially in paleoenvironmental research in and around the Sea of Japan. During the early-middle Holocene, at least three pumiceous tephras (U-4, U-3, and U-2 in ascending order) covered the island. Therefore, multiple Ulleung tephras are expected to distribute in and around the Sea of Japan. In order to accurately identify and correlate the tephras, it is necessary to consider stratigraphic/chronologic position as well as geochemical/petrographic characteristics. We review previous studies on Holocene tephras from the Ulleungdo volcano, and discuss fundamental methods of tephra correlation and problems for tephrochronology. There is a possibility to revise and fine-tune the stratigraphy of the Holocene tephras from the volcano. The chemical composition of volcanic glass shards is a useful tool for evaluating mixtures of multiple layers. The heavy mineral composition can be also used to identify tephra units. In order to reveal distribution of each tephra unit to a high degree of certainty, characteristics such as heavy mineral and the chemical compositions of each unit must be determined in greater detail.