[H-CG25] Earth surface processes related to deposition, erosion and sediment transport

[HCG25-P04] Paleosol and paleoenvironment of the Lower Pleistocene Bushi Formation in Iruma City,Saitama Prefecture,Japan

*Haruki Sugiyama¹ (1.Shinshu Univ.)

Keywords:Soil, Paleoenviroment, Pleistocene, Paleosol

The Lower Pleistocene Bushi Formation, which is distributed around Iruma River in Iruma City, Saitama Prefecture, consists of fluvial and marine deposits. This study focuses on the sedimentary facies and paleosol formation to reconstruct paleomorphology and paleoenvironments. The sedimentary facies analysis suggested that most parts of the Bushi Formation were deposited in predominated flood plain and back marsh environments around the meandering river. Such environments changed into estuarine environments. In addition, several paleosol horizons were recognized in the flood plain and back marsh deposits. The paleosols were classified by 5 pedofacies that were correlated to the present soil classification. As a result, entisol and inseptisol, both are kinds of immature paleosol, were recognized. These immature paleosols indicate the deposition in the cumulative environments in deposition with large accommodation space and in poor drainage environments.