有孔虫化石群からみた日本の古第三系

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There have been many discussions concerning the Danian, whether it is Cretaceous or Paleogene. The problems are not discussed or documented in this paper, but the modern tendency is to place the Danian at the base of the Paleogene, because of the distinct faunal break-disappearance of Cretaceous Globotruncana and appearance of Tertiary Globigerina-at the base of the Danian. Such Danian planktonic foraminiferal assemblage was first found in the Cretaceous formation of Nemuro, Hokkaido. Asano reported on the occurrence of Globigerinoides sp. (cf. G. trilocauhnoides Plummer), Globigerina pseadobaalloides Plummer, Globigerina daubjergensis Bronnimann, Globigerina corn ressa Plummer associated with many benthonic Foraminifera from the Choboshi formation at Ochiishi, Nemuro which had been considered to he Upper Cretaceous from the megafossils contained in it. (Table 1) On the other hand, Yoshida who studied the Cretaceous Formainifera from Urahoro, Tokachi-gun stated that the foraminiferal assemblage from the so-called Cretaceous formation near the provincial boundary between Tokachi and Kushiro may be correlated with that of the Paleocene of Venezuela. More recently, Iwamoto reported on the occurrence of Globorotalia pseudonsenardii Belli, a typical Paleocene planktonic Foraminifera, from the Chippomanai formation, south of Akkeshi, which was also previously referred to Upper Cretaceous. Another type of Paleocene Globorotalia was found in the limestone of the Setogawa group, Shizuoka Prefecture by Saito. These evidences suggest that Paleocene (including Danian) deposits are distributed in Japan, although they are local at present, and it is desirable that detailed stratigraphical studies of those areas should be carried out. Well-defined Eocene and Oligocene formations are well developed in many coal-fields of Hokkaido, Kyushu and Honshu, but they are rather limited in occurrence, being of nonmarine or coal-bearing facies in most places. There is another type of Paleogene formations in the Outer Zone of Southwest Japan, just south of the "Undifferentiated Mesozoic". They are called locally by different names, such as Kinan, Murotohanto or Nichinan groups. This type of Paleogene is considered to be geosynclinal, having rock-characters similar to those of the undifferentiated Mesozoic belt which is incorporated in forming a zonal structure. In most cases, there is an unconformity between the Paleogene and Cretaceous rocks, and a typical epeirogeny exists at the Cretaceo-Tertiary boundary. The Wakayaman movement of Hanzawa in the Outer Zone of Southwest Japan took place in this period and is related to the genesis of the Median Line which is one of the most outstanding features in the geologic structures of the Japanese Islands Arc. This tectonic line always appears as a system of faults and runs from the Fossa Magna westward to Kyushu passing through the western side of the Akaishi Mountains, northern part of Wakayama Prefecture, and northern part of Shikoku. The much deformed Senonian-Maastrichtian series and the crystalline schists on the south and north sides of the Median Line respectively are covered with the Lutetian series of the Ishizuchi Mountains of Shikoku. Therefore, it is older than Lutetian in age at least in its first activity. In Eocene time, the transgressive sediments except for the Outer Zone of Southwest Japan, were deposited on the erosion surface of the Cretaceous and older rocks in the lowland areas and characterized with a warm water fauna, such as Aturia, Nuvnmvdites, Discocyclina, Plectofrondicularia or with the warm and humid flora, such as Woodwardia, Musophyllum, Sabalites, etc. 'Near the end of the Eocene, widespread uplift took place in the larger parts of Japan (Fukuokan Movement of Hanzawa) and is represented by an unconformity in many districts, as shown in the tables (2, 5, 6). The Oligocene transgression commenced with basal conglomerates in some places, but is more restricted in distribution than the Eocene. The climate of the Oligocene in Japan was rather cool as shown by the fauna from the Asagai formation in the Johan coal-field or Momijiyama formation in Hokkaido. The upper half of the Oligocene is missing in almost every part of the Japanese Islands. This period is represented by the Pre-Kishima (Pre Aquitanian) crustal deformation of Saito. According to him, the characters of this movement are represented by the transverse faults of the Median Line and it is said that the Itoigawa-Shunto Line, adjacent to the Fossa Magna was formed by this movement. At the basal part of the Kishima group in the Karatsu coal-filed, Kyushu, there has been found the Catal5sydrax dissimilis Zone, a good datum-plane of the lower part of the Aquitanian. Therefore, if the Aquitanian should be included in the Miocene, the Japanese Neogene is represented from the basal part of the Rishima group and its correlatives.
東北大学の論文
1962-11-26

有孔虫化石群からみた日本の古第三系

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東北大学 | 論文

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