Study of the Upper Sand Layer in the Late Quaternary Sediments of Japanese Alluvial Lowlands.

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Younger, soft sediments in the deltaic and coastal lowlands are called "Chuseki-so", which were deposited in the period since the last glacial maximum. Deposition of the sediments has been closely related to the post glacial transgression. Especially, the upper sand layer in the "Chuseki-so" has characteristics of sedimentay features in relation to the sea-level changes and landform evolution of the lowlands. The upper sand layer in the present coastal zone of barrier type lowland consists of relatively thick sediments, deposited since relatively earlier periods in the Holocene. The sediments in the deltaic type lowlands and in the inland region of the barrier type lowlands mainly deposited in the period of ca. 5,000-3,000 yrBP, and the sediments in the coastal zone of the deltaic type lowlands mainly deposited after ca. 2,000 yrBP.