富士川上流地域の西八代層群の層序

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The geosynclinal sediments (Late Cenozoic) which comprise much Volcanic products, are developed in the South Fossa Magna, Central Japan, and are intensively deformed by later crustal movements., In this paper, the Nishiyatsushiro group, one of the representatives of these sediments, is described and some problems are discussed., 1 The group consists mainly of pyroclastics and mudstone-rich alternations, and is divided into the following four formations: (Shizukawa group).,.,.,.,.,.,.,.,.,unconformity (?).,.,.,.,.,.,.,.,.,Nishiyatsushiro group Shimobe formation.,.,.,.,.,.,.,.,.,mostly of an alternation of sandstone and mudstone with fine conglomerate beds., The upper part is cut off by a fault., Daigoyama formation.,.,.,.,.,.,.,.,.,basic (lower) and acidic (upper) pyroclastics, sandstone and mudstone., The lower part consists of basalt and basic tuffaceous sandstone, and the upper of pumiceous tuff, sandstone and mudstone., Ichinose formation.,.,.,.,.,.,.,.,.,mostly of mudstone and alternated acidic tuff., Alkaline olivine basalt occurs in the lowest part as thin lavas and sheets., Furusekigawa formation.,.,.,.,.,.,.,.,.,mostly of basic lavas and pyroclastics with thin tuffaceous sandstone and mudstone., The base is unknowxn., (in descending order) Besides the above, two mudstone members are intercalated between the Daigoyama formation and the Shizukawa group, but their stratigraphical position remains unsettled., 2 In the area where the group is exposed, igneous activities are represented in the following sequence in ascending order., 1) A large amount of tholeiitic (pigeonitic according to H., KUNO) basalt acompanied with a small quantity of alkaline olivine basalt (in the upper horizons)., 2) Subordinate amount of acidic tuff alternating with mudstone and other sediments., 3) Acidic intrusives 4) Calc-alkalic (hypersthenic according to H.,KUN0) andesite eruptives (in the shizukawa group)., It is remarkable that similar sequences of igneous activities and associated sediments are found in the other areas within the South Fossa Magna regions., 3 The group is probably Miocene in age., There are few fossils except Sagarites and small foraminifers., 4 Alteration of the igneous rocks is comparatively slight., The texture of the rocks and most of the rock-forming minerals are fairly well preserved., However, all of olivine and some of hypersthene and plagioclase are altered., Iron saponite is most conmon as a secondary mineral., Chlorite, prehnite and epidote appear in the tuff only in the southeastern part contiguous to the area of many intrusive bodies which are not shown in the map.,
日本地質学会の論文
1955-06-25

富士川上流地域の西八代層群の層序

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