Paleozoic and Mesozoic Systems in the Central Area of the Kii Mountains, Southwest Japan

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Other Title
  • 紀伊山地中央部の中・古生界
  • 紀伊山地中央部の中・古生界-1-大普賢岳地域
  • キイ サンチ チュウオウブ ノ ナカ コセイカイ 1 ダイフゲンダケ チイキ
  • Paleozoic and Mesozoic systems in the central area of the Kii Mountains, Southwest Japan (Part 1) geology around Mt Daifugen district, Nara prefecture
  • その1.大普賢岳地域
  • (Part 1) Geology around Mt. Daifugen District, Nara Prefecture

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The geologic sequence in the eastern part of Mt. Daifugen, Nara Prefecture, is subdivided into following three formations, namely the A, the B and the C formations. The A formation (450 m + in thickness) consisting of sandstone, mudstone and their alternation closely resembles lithologically the sequences belonging to the northern marginal part of the Shimanto Major Belt. The B formation (180 to 450 m in thickness) is composed of a large amount of greenstones, chert, limestone and mudstone, and yields abundantly fossils such as fusulinids and hexacorals (Table 1) from "limestone blocks" of pebble to boulder size which are contained in these greenstones. The hexacorals, which have newly been discovered from this formation, are of Late Triassic age. The C formation (700 m + in thickness), conformably overlying the B formation, is made up of chert and sandstone, intercalated with thin greenstone masses. The B and the C formations may be correlated with some part of "the Sambosan Group" which occupies the southern margin of the Chichibu Belt. Although the age of the B formation has been said to be Paleozoic, both the B and the C formations are at least Late Triassic or younger in geologic age because of the occurrence of the hexacorals from the B formation. The geologic relationship between the A and the B formations is considered to be a fault contact with a gentle dip nearly parallel to their bedding planes. This inferred fault corresponds to the Butsuzo tectonic line.

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