A Review of Late Quaternary Deep-sea Tephras Around Japan

Abstract

Studies on late Quaternary deep-sea tephras are briefly reviewed in oceans and seas of the world and around the Japanese islands. A great number of modern research has been carried out on deep-sea tephra layers especially in the eastern Mediterranean Sea, Atlantic Ocean, Caribbean Sea and Pacific Ocean. Researches focus on the magnitude and type of individual explosive volcanism, the mechanism of deposition of tephra, correlation of macroscopic tephra layers and biostratigraphic dating of tephra, and resulted in disclosing several explosive volcanic eruptions of extraordinarily great magnitude such as the eruption of Campanian Y 5 ash in the Mediterranean, Los Chocoyos ash around Central America, Wairakei ash around New Zealand and Toba ash in the Bengal Bay and Indian Ocean.In deep-sea sediments around the Japanese islands there are numbers of tephra layers, which are characterized and identified by petrographic and chemical methods. In the Sea of Japan six tephra layers have been identified, three of which are alkalic and are the products of major plinian eruptions of two volcanoes situated on and near the Korean Peninsula: Baegdusan and Ulreung-do. The other three are subalkalic and are corelated with large-scale eruptions from caldera volcanoes in Kyushu: Kikai, Aira and Aso. They are recognized not only in the Sea of Japan but also in the East China Sea and northwest Pacific Ocean, together with widespread tephras derived from Ata and Kikai calderas. All of them are co-ignimbrite ash fall deposit, and well dated by radiometric and stratigraphic methods. Palaeooceanography of late Quaternary around Japan are successfully studied with the aid of such widespread and time-marker tephras. There remain several tephras unidentified around Japan. In addition detailed volcanological and interdisciplinary studies of deep-sea tephras will be one of the problems to be studied in near future.