堆積環境の復元 : 熊本県人吉盆地西域に分布する人吉層を例として

概要

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The result of sedimentary study of the western part of the Hitoyoshi Basin in southern Kyusyu, are given in the present article mainly from the viewpoint of the sedimentary environment. K-Ar age evidence suggests that the Hitoyoshi Formation is Late Pliocene in age. The formation is lithologically divided into two members. The lower member shows very rapid changes in vertical facies, namely, conglomerate, tuff breccia, sandstones and tuffs in ascending order. This shows a lacustrine environment. From the lithological characters and sedimentary strucuture, the member is considered to be sediments of fan-delta plain or braided-river. The upper member is composed mainly of slightly strarified siltstones, yielding plant fossils and with intercalations of sandstone, tuff and diatomite. This represents the later depositional stage of the formation and filling up of the lake basin with sediments. Furthermore, brief notes on teaching materials development about stratum of Earth Science Education are added.
2007-11-30