Paleoweathering condition in middle Miocene to early Pliocene period in Japanese Island; From paleopedology and chemistry of muddy sediments

Hatano, Nozomi*; Yoshida, Koki*; Sasao, Eiji; Kubota, Mitsuru; Adachi, Yoshiko*

In Japanese Islands, the middle Miocene to Pliocene fluvial formations include aluminous clayey horizons. These formations can be a useful to reconstruct of weathering conditions. Description of paleosols and geochemical research were carried out in the middle Miocene (10-11 Ma) and the early Pliocene (3-4 Ma) sediments in central Japan in order to illuminate the weathering condition. The major elemental geochemistry shows that the Miocene sediments were supplied from severe weathered sources with CIA values of 80-94. The Pliocene sediments show the CIA values of 72-90 showing the relatively weak weathering condition. The weathering condition in the middle Miocene to Pliocene in Japanese Islands may be affected by the influence of warm water current and initiation of the Eastern Asian monsoon. The middle Miocene period is considered to have been under the intenser weathering condition than one in the early Pliocene period.