琵琶湖深層試錐からみた中期更新世 (中期更新生,その時代と環境--東海・伊勢湾周辺地域を例として)

概要

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Drilling core samples of Lake Biwa sediments of 200m and 1000m thick obtained from the lake bottom and the east coast are correlated to the Pleistocene strata distributed in the Kinki district, using volcanic ash layers and paleomagnetic polarity data. The 200m core sample composed of clay sediments with some volcanic ashes has provided various data of tephrostratigraphy, paleomagnetism, biostratigraphy and geochemistry covering the last 0.5m.y. These records are suggested to be usefull as a reference data to investigate the Pleisotcene in the Kinki district. A significant key for the correlation is a volcanic ash layer which has a fission track age of 0.17m.y. and remanent magnetization of reversed polarity. This volcanic ash layer occurs in the horizon of the Biwa I event of the 200m core sample. The layer is also found in the Kobiwako Group on the northwest coast of Lake Biwa, and between the marine clays Ma 10 and Ma 11 of the Osaka Group in the Akashi area. According to this correlation, type of topographic surfaces in the Kinki district can be divided into three fundamental shapes (Fig. 13). It is implied that the marine facies and topographic flat planes were formed in accordance with the sea level change by the global climatic oscillation.
日本第四紀学会の論文