奈良三笠山附近の地質 : 特に火山活動の年代について
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概要
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The age of the small andesite knolls such as Mts., Mikasa and Kasuga, which fringe the eastern brink of the Nara Basin, has now become fairly clear by the writer's field survey, the results are: The stratigraphic sequence in this area from the older to the younger is:(1) "Fujiwara" Formation (Marine doposits, F_2-F_3)(2) "Jigokudani" Formation (Fresh-water deposits, ? F_3-G-H_1; rich in endocarps of Styrax obassioides MIKI.,)(3) "Shirakawaike-Saho" Formations (Fresh-water deposits, I_1-I_2?)(4) Upper gravel beds (J-K) Three tectonic lines of north to south trend prevail, these govern the distribution of the sediments and the arrangement of the volcanics., Concerning the geologic age of the "Mikasa-andesite", the important facts confirmed are: a) Over and under the lava, some parts of the "Shirakawaike-Saho" F., exist and the sheet-formed "Mikasa-andesite" is inserted concordantly in the sediments., b) Gravels of the Mikasa-andesite, though not abundant, are contained in the middle and upper parts of "Shirakawaike-Saho" F., c) The lower part of the "Shirakawaike-Saho" F., is rich in its yield of the so-called "Metasequoia-flora", such as Metasequoia disticha (HEER) MIKI, Picea Koribai MIKI, Juglans megacinerea CHANEY etc., From the above-mentioned facts it was concluded that, the horizon of "Mikasa-andesite" occupies the lower part of the "Shirakawaike-Saho" Formations, which may be assigned to Plio-Pleistocene (I_1).,
- 日本地質学会の論文
- 1954-11-25