Study on Quaternary Geological Characteristics of Echigo Plain

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The stratigraphy of Quaternary deposits of the Echigo Plain was examined and correlated with that of the surrounding areas. Especially, the subsurface strata in the plain were made clear stratigraphically. The new stratigraphical division and the geologic age of them were established. They are divided into the Nishiyama Formation, the Haizume Formatin, the unnamed Middle Pleistocene, the Kanbara Group, Buried terrace deposits, the Nishikanbara Formation, the Shirone Formation, and the Kurotori Formation in ascending order. Nest, the preliminary study on the history of Quaternary sedimentary environment was carried out in relation to relative sea-level change. After the latest Pliocene, the coastal line was moved northward step by step. In Echigo Plain, depositional sites composed of coastal plain-delta system deposits spread out since late Middle Pleistocene age. At Holocene age, the Echigo Plain was formed with sand dunes under rising sea level. Especially, in this study the history o … More f Quaternary sea level changes in the east-central area of the Sea of Japan, and the geological characteristics were examined as followings.1) The Quaternary sedimentary basin of the Echigo Plain was a part of the basin since middle Miocene age. It is very characteristic to deposit Quaternary marine and terrestrial sediments more than 3,500m in thickness. The depositional basin has continued since Early Miocene time. 2) The Quaternary basin was divided into uplift and subsiding areas at middle Middle Pleistocene age. The strata consist of shallow marine and fluvial deposits with many kinds of animal and plant fossils. The repeated sea level changes during Late Cenozoic were in detail recorded on the Quaternary around the Echigo Plain. 3) The basin surrounded by rising mountains and hills is a large-scaled subsiding area with growing fault zones in east and west sides. 4) Water-soluble gas and iodine included in groundwater are very useful for fuel and material resources. They are extracted from strata which are composed of bay-delta-gravelly river system deposits, but the land subsidence was caused by pomping groundwater. Less