River terrace in the Tsuyama basin, Okayama Prefecture, Southwest Japan <Articles>

The distribution of river terrace was studied in the Tsuyama basin, Okayama Prefecture, in order to understand the historical development of landforms. The Tsuyama basin as well as Miyoshi, Syoubara and Niimi basin is located to the south of the E-W trending Chyugoku axial mountains. In the south of the Chugoku axial mountains, three kinds of the low-relief surface are commonly known as the Kibi surface(450–600 m), the Sera surface(300–450 m)and the Setouchi surface(60–200 m). It is generally understand that the basin areas are formed by gentle folding of the Kibi surface. In the Tsuyama basin, four kinds of the river terrace are recognized: I-surface(250–300 m); II-survace(210–250 m); III-surface(150–200 m); IVsurface (100–130 m). Comparing the level of the river terrace and hills in the Tsuyama basin and that of the low-relief surface distributed to the south of the basin, the river terrace was genetically formed eroding the Sera surface. This means that the basin had been continuously formed after the formation of the Sera surface as well as the Miyoshi-Syobara basins