Sand beds which mainly consist of massive, consolidated and well-sorted sand are observed along the coast of the Japan Sea and are thought to be Pleistocene dunes. The writers call these dunes the “Ancient Dunes” in contrast with “Recent Dunes” of the Holocene epoch. The Ancient Dunes can be classified into two groups: the older “Ancient Dunes I” and the other “Ancient Dunes II” according to the different ages of formation.
The Ancient Dunes I consists of grey, massive and consolidated medium sand, the lower part of which is occasionally aqueous, and is overlying on the middle terrace deposits almost conformably, although partly unconformably. The dunes of this group are found all along the coast of the Japan Sea from North Kyûshû to Aomori Prefecture, the northernmost of Honshû.
The Ancient Dunes II consists of pale yollow fine sand with crepe-like texture, which is a characteristic feature of loessy sand. The dunes of this group are distributed at Yasuoka in Yamaguchi Prefecture and south of it while, along the northern coasts they are not found. There is brown weathered clay or volcanic ash overlying the Ancient Dunes I, which may be the equivalent to them in age.
The stratigraphic relation between the sand beds of the Ancient Dunes and the terrace deposits or volcanic ash deposits suggests that the Ancient Dunes I and II are correlated to the Riss-Würm interglacial and the Würm glacial stages respectively. They are thought to have been formed the marine regression in glacial ages.
