Terraces of three stages are distributed on the foot of Mt. Yoneyama, along the coast of the Sea of Japan, Central Honshu. Characteristic reddish layers are found within the higher terrace deposits. In some place, the reddish layer lies unconformably on the Tertiary basement, while in the other place, sandy beds are intercalated between the reddish layer and the basement. On the other hand, the reddish layers are related with the upper soil horizons in the following two ways. The one is that the recent A horizon, with or without the transitional brownish soil layer beneath it, is developed on the reddish layer, while the other is that the A-C solum derived from the reddish layer, is covered with the dune sand deposit which had also differentiated to the considerably matured soil profile. The ferric oxides responsible for the reddish hue (2.5 YR in the MUNSELL'S color notation) of these layers, seem to be very stable, judging from the fact that the hue persists over 2 months under the incubation treatment with starch. The reddish layers are dominated by the clay fraction (-2μ), the SiO_2/R_2O_3 mol ratio of which tends to be somewhat lower than those of the adjacent layers, and contents of free A1- and Fe-oxides of the formers relatively higher than the latters, though the type of weathering of the reddish layers does not seem to be so strongly allitic. One of the most important factors of the genesis of these soil layers may be the high content of clay in their parent materials, which may have prevented from free drainage and resulted in reduction and solvation of free iron compounds. After the upheaval of the terraces, water regime may have turned to be well-drained, and facilitated to oxidize ferrous iron. Then, the limonitic coating of clay particles may have gradually altered to the hematitic compounds. The parent material of these layers is supposed to have deposited during Riss/Wurm interglaciation, and the red weathering to have taken place mainly in Wurm I/Wurm II interstadial age, though it seems that the weathering has gone on progressively up to today.
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