琵琶湖深層ボーリング資料からみた近江盆地の構造運動と堆積環境

概要

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The sinking rates of the different parts of Lake Biwa can be calculated based on the marker tephras and their depth in the four deep drillings in and near the lake. Two sites of the drilling have high sinking rate as large as 0.8mm/year, and other two sites have slow rates as large as 0.5mm/year. On the other hand, modem structural units in the Omi basin can be estimated by the topography, geology and active fault systems. There exist many small quadrilateral units of which sides are as long as a few kilometers in the Omi basin. New tectonic movement started about 400,000years ago, and the differential sinking of the structural units have been played a basic roll to form the present Omi sedimentary basin and its topography which include Lake Biwa. Strong subsidence and poor sediment supply formed deep water environment such as northern Iake of Lake Biwa., and weak sinking or strong sinking with abundant sediment supply caused the shalIow lake or fIuvial environments for a Iong time such as southern lake of Lake Biwa and Koto plain, east-side plain of Lake Biwa.
滋賀県立琵琶湖博物館の論文