Chronological Study of Fluvial Terraces along the Jusu River, Eastern Korea

Abstract

A series of fluvial terraces is well developed along the Jusu River flowing into the eastern side of the Taebaek Mts., Korea. Among these terraces, the development of the most well-preserved lower terraces were examined in connection with the climatic and sea-level changes since Last Interglacial by an investigation into the deposits and longitudinal profiles of the terraces. The results are as follows.Main lower terraces can be classified into two, the Sankye I terrace of Last Glacial age and the Okgye terrace of Last Interglacial age.The Sankye I terrace is accumulation one, and is distributed in the upper reach. The longitudinal profile of the terrace could be continuously connected to that of the buried valley floor formed at the low sea-level of Last Glacial age. The terrace deposits is a valley-fill under the periglacial environment, and mainly consists of poorly sorted angular and subangular boulder. The gravels are partly weathered for granite but unweathered for limestone.The Okgye terrace is distributed in the lower reach. The relative height above the present river floor slightly increases downstream. The terrace deposits mainly consists of well sorted and subround cobble to boulder, which is intensively weathered to be friable or has weathering rinds of 1.5-2.0 centimeters in thickness. The terrace deposits is overlain by a pseudogleyed red soil, which is regarded as a paleosol formed under a warm-wet environment of Last Interglacial age. From the above facts, the Okgye terrace is inferred to be formed at high sea-level prior to Last Glacial age, probably to be of Last Interglacial age.By extrapolation, the Okgye terrace is estimated to be 17-19 meters above sea-level at the river mouth, approximating the altitude of the ancient shoreline.