[H-CG22] Earth surface processes related to deposition, erosion and sediment transport

[HCG22-P03] Paleoenvironmental restoration with paleosols
-The Paleogene Shiromizu group, Iwaki Formation, Joban Area, Northeast Japan-

*Sugiyama Haruki¹, Kohki Yoshida¹ (1.Shinshu University)

Keywords:Paleoclimate, Paleosol, Soil

The Paleogene Japanese Islands are known to have been located off the east coast of Eurasia before the formation of the Sea of Japan. The formation of the Sea of Japan and the Central Highland placed the present-day Japanese islands in climatic conditions with a strong maritime influence. The formation of the Sea of Japan and the Central Highland occurred between the Neogene and the Quaternary, and the Palaeogene climatic conditions in the Japanese Islands were very different from those of today. In this study, paleoenvironmental reconstructions were performed on paleosols developed from the Iwaki Formation of the Shiramizu Group, and the paleoenvironments and climatic conditions of the Japanese Islands at that time were investigated. The sedimentary facies analysis suggests that the sedimentary environment in the study area was deposited on the gravelly rivers and floodplains of meandering rivers. Such environments were transformed into shelf environments. In addition, several paleosol horizons were recognised in the minor channel deposits of gravel rivers, floodplain deposits of meandering rivers and back marsh deposits. In this study, each paleosol was contrasted with current soil classifications. As a result, entisols, inseptisols and ultisols were recognized. Ultisol is a kind of highly weathered paleosol, whereas entisol and inseptisol are kinds of immature paleosol. Ultisol is generally formed in warm and humid climates. Therefore, the presence of ultisol indicates that the study area had warm and wet climatic conditions.