Paleoenvironmental history of post-Toya Ash tephric deposits and paleosols at Iwate Volcano, Japan, using aeolian dust content and phytolith composition

Abstract

Abstract Physicochemical, mineralogical, and geochemical analyses of post-Toya Ash (90–130 ka) tephric and aeolian deposits at the foot of Iwate volcano, northeastern Japan, revealed the accumulation of deposits of long-range aeolian dust transported from the Asian continent and interstratified with the tephric deposits. Oxygen isotopic ratios of quartz in the 1–10μm fractions from two paleosols formed in the aeolian units (Shibutami cracked layers) are +16.2 and +17.0‰, consistent with this fine-grained quartz being of an aeolian origin. The accumulation of Asian aeolian dust onto tephric deposits in northeastern Japan was dominant in the cold stages of the Last Glacial period (20–34 ka and 50–70 ka). We determined the changes in vegetation and climate by using opal phytolith distribution in the tephra and aeolian deposits and associated paleosols. Similarly, we interpreted the paleoenvironmental history of the tephric deposits by relating the vegetation history to the dust flux and fossil periglacial phenomena (i.e. involution) observed on tephra beds. The paleoclimate sequence obtained coincides closely with the marine oxygen isotope curves, indicating that opal phytolith analysis is useful in determining the Interglacial/Glacial-cycle recorded in aeolian and tephric deposits.