Characterization and correlation of cryptotephras using major-element analyses of melt inclusions preserved in quartz in last interglacial marine sediments, southeastern Shikoku, Japan

Although sediments underlying marine terraces in SE Shikoku, southwest Japan, contain no visible tephra layers, late Pleistocene cryptotephras were detected in a paleosol within the sediments. The cryptotephras contained little or no glass, but they were characterized through major-element analyses of glass preserved as melt inclusions in quartz grains extracted from the paleosol. The analyses enabled correlation of the cryptotephras with known eruptives from volcanoes on Kyushu, namely the Kikai-Tozurahara tephra (MIS 5.2–5.3), the Aira-Tn tephra (28.6 cal ka), and the Kikai-Akahoya tephra (7.5 cal ka). These correlations enabled dating of the marine terrace surface known as the Murotomisaki 1 surface in SE Shikoku as being older than MIS 5.2–5.3, probably MIS 5.5 in age. In the absence of glass or mafic minerals because of weathering, the analysis of melt inclusions in resistant quartz grains demonstrably provides a powerful method for characterizing cryptotephras to facilitate their correlation and thus their application as a linking and dating tool.