충남 공주 제민평야 충적층의 퇴적구조

Abstract

This study investigated the sedimentary structure of the Jemin Plain alluvial (17.2~31.5 m a.s.l.), developed in the whole area of the Jemin Stream banks in Gongju, Chungnam. The research was done by carrying out facies analysis, grain size analysis, radiocarbon dating and stratigraphic interpretation of the Plain’s trench materials and exploratory holes drilled on the alluvial plain. Results showed that the thickness of the Plain alluvial was between 2.2 and 14 m. Furthermore, the altitude above sea level of the river bed (buried valley bottom) in the coldest period of the Last Glacial of the Jemin Stream (a tributary of the Geum River) was found to between 3.2 and 28 m. The alluvium of the Plain was largely classified into the Lower layer, the Middle layer and the Upper layer. The Lower layer was composed of gravel in the most part and of a thin layer of peat. This basal gravel layer was deposited in the coldest period of the Last Glacial. The Middle layer mostly consisted of silt and contained a sandy gravel layer, an organic layer and a cultural layer. The Middle layer was formed by flooding in the Post-Glacial age. The Upper layer was mostly composed of silty sand and also contained a sandy silt layer and a buried layer. These silty sand and sandy silt layers were formed by flood and mass movement after the longitudinal profile of the Jemin Stream reached an equilibrium state in the late Post-Glacial age. The buried layer was an artificially dumped layer made to reduce damages caused by river flooding in the modern ages.