Paleoweathering and paleoclimatic condition inferred from paleosol facies in the Miocene Seto Porcelain Clay Formation in the Setouchi Geologic Province, central Japan

Abstract

Paleosol descriptions and sedimentary facies analysis were performed for the Miocene Seto Porcelain Clay Formation in Toyota City, Aichi Prefecture, to reveal the paleoweathering conditions after deposition. The sedimentary facies analysis suggests that deposition occurred mainly in a lacustrine, backswamp floodplain of a meandering river channel. Three paleosol horizons have been described and compared with modern soils. Histosol-like and inceptisol-like paleosols reflect the local topography and sedimentary features related to drainage conditions, vegetation cover, and sedimentation rate. Conversely, the vertic ultisol-like and ultisol-like paleosols were developed on a gently sloping terrace. The vertic ultisol-like paleosol is characterized by an illuviated clay-rich B horizon (Bt horizon, argillic horizon), pedogenic slickensides, hummock-and-swale microtopography showing gilgai microrelief, and festoon-shaped horizons showing mukkara subsurface structures. Vertic paleosol indicates the typical soil type, suggesting that the climatic conditions in this period were warm and humid with pronounced seasonality.