八尾層群の堆積環境について : いわゆるGreen Tuff地域の中新統に関する堆積環境の研究(その1)
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概要
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In general, the middle Miocene formations in the so-called "Green tuff" region were deposited on the eroded land surface in an early stage of Miocene transgression., Thus, the sedimentary environment was variable, as shown by the refletion of the faunas and facies., In this paper, the relationship between the faunas and facies in the Yatuo group, and the sedimentary environment are discussed., The Yatuo group consists of four formations, namely, Nirehara, Iwaine, Kurosedani and Higasibessho, in ascending order., The distribution, stratigraphy and rock facies of these formations in the Yatuo area are shown in figures 1, 2 and 3., The litho-facies of the Nirehara and Kurosedani formations is variable as shown in the figures., Generally speaking, the maximum size of the grains in the deposits of the two formations is in the lower portions of the conglomerates which are distributed in the central part of the mapped area., The grains decrease in size in all directions therefrom., The rock facies and fossil occurrence reflect the sedimentary environment of the Kurosedani formation, as is shown by the terrestrial boulder conglomeratic facies containing drift-wood fragments, and which grades into a marine muddy facies characterized by marine animals which live in a deeper sea of normal salinity., The alternations of sediments between the terrestrial boulder conglomerates and marine mudstones contain abundant brackish shallow sea forms mixed with terrestrial ones., From the above mentioned facts, it can be said that the boulder conglomerates of the Nirehara and Kurosedani formations are ancient deltaic deposits., Close resemblance is seen in the sedimentary environments of the two formations., The Iwaine formation consists of thick volcanics as a result of rapid accumulation of volcanic products., The faunas and facies of the Higasibessho formation show that it was deposited in a deeper sea of normal salinity., An evolutional change is observed in the structural movement between the Kurosedani and Higasibessho.,
- 日本地質学会の論文
- 1955-11-25