The late Cretaceous to Neogene formations are widely distributed in the northern area along the Itoigawa-Shizuoka Tectonic Line (abbreviation, I. S. T. L.). On the west side of the I. S. T. L., they are divided into five formations in ascending order, which are Akahageyama sandstone formation, Ipponmatsuyama tuff breccia formation (abbreviation, Ipponmatsuyama formation), Ishizaka rhyolite formation, Yamamoto formation and Imai formation. They unconformably cover the Palaeozoic formations, the early Jurassic Kuruma Group and serpentinite. The Akahageyama sandstone formation is mainly composed of arkosic sandstone with intercalation of conglomerate and mudstone. The Ipponmatsuyama formation is divided into two members; the lower part is composed of andesitic pyroclastic rocks, and the upper part is garnet bearing dacitic pyroclastic rocks. The Ipponmatsuyama formation is only distributed in the Omi limestone area. The Ishizaka rhyolite formation is mainly composed of rhyolite welded tuffs with intercalation of conglomerate and non-welded tuff. It is widely distributed in the Omi limestone area and the Yokokawa area, and unconformably overlies the pre-Cretaceous basemental rocks. The Yamamoto formation consists of andesitic pyroclastic rocks. The Imai formation is mainly composed of acidic volcanic rocks carrying marine molluscus. The lithofacies of the Akahageyama sandstone formation, Ipponmatsuyama formation and Ishizaka rhyolite formation are respectively correlative to the Shiritakayama sandstone-conglomerate formation, Oyashirazu volcanic rock formation and Sasagawa welded tuff formation which are distributed in the Oyashirazu area. Fission track age determination of the late Cretaceous to Paleogene igneous rocks in the northern area along the I. S. T. L. was carried out by using " external detected method". Dating results are as follows; Akahageyama sandstone formation, Ok-An: 94.2±5.9Ma, Ipponmatsuyama formation, Ipl57 d: 66.4±2.4 Ma, Ishizaka rhyolite formation, I-2 (type locality): 54.7±1.9 Ma, Azakiri A: 74.8±2.9 Ma, Sasagawa welded tuff formation, F-2: 55.7±2.3 Ma, Omi granite, Oh-Or: 92.7±5.9 Ma, garnet porphyrite, Da-O4: 62.2±3.5 Ma. The above mentioned stratigraphy and ages indicate that the late Cretaceous to Neogene igneous activity in the northern area along the I. S. T. L. is divided into four periods. They are as follows; 1) the plutonic activity in the early late Cretaceous of Omi granite, 2) the local andesitic volcanism from the end of late Cretaceous to early Paleocene characterized by the Ipponmatsuyama formation, 3) the wide acidic volcanism from the late Paleocene to early Eocene characterized by the Ishizaka rhyolite formation, 4) the middle Miocene volcanism of the so-called "Green-Tuff" Movement.

抄録全体を表示

Late Pleistocene to Holocene sediments in central Kinki district, which are mainly distributed in separated basins, i.e. Osaka, Kyoto, Nara and Omi Basins, are composed of unconsolidated gravels, sands and clay with frequent intercalations of volcanic ash layers. In this paper, the volcanic ash layers found in these sediments are lithologically and petrographically investigated, and correlation of volcanic ash layers is discussed based on the stratigraphic position, and lithologic and petrographic properties. The study has revealed that five volcanic ash layers are widely traceable and are available as stratigraphic time-markers. They are Heianjingu and Kitoragawa volcanic ash layers in the Lower Terrace deposits (late Pleistocene), and Sakate, Minato and Yoko-oji volcanic ash layers in the Alluvial deposits (latest Pleistocene to Holocene), in ascending order. Heianjingu volcanic ash layer which is one of the most useful key beds, is intercalated in the upper part of the Lower Terrace deposits and its correlatives. This layer about 10 cm thick is composed of yellowish white to pinkish white and medium to coarse grained ash. It consists chiefly of glass (mainly H-type shards with index of 1.498-1.501; mode 1.500), with trace amounts of plagioclase, orthopyroxene (γ=1.702-1.735), amphibole and clinopyroxene. Kitoragawa volcanic ash layer which occurs about 10 cm above Heianjingu ash layer, is composed of white and fine to medium grained ash. The average thickness is about 1 cm. This ash consists of phenocrysts and T-type glass shards with index of 1.502-1.504 (mode 1.503). The commonest phenocrysts are of plagioclase, followed in order of abundance by amphibole and orthopyroxene (γ=1.700-1.710; mode 1.704-1.708). Sakate volcanic ash layer intercalated in the lowermost part of the Alluvial deposits, is about 10 cm thick, and is composed of yellowish white and medium to fine grained ash. This ash consists of phenocysts, and C- and T-type glass shards with index of 1.498-1.504 (mode 1.500). The phenocrysts are of plagioclase and amphibole (mainly green hornblende), with a few crystals of biotite. Minato volcanic ash layer intercalated in the lower part of the Alluvial deposits, is about 2 cm thick, and is composed of white to grey and fine to medium grained ash. It consists of T-type glass shards with index of 1.521-1.526 (mode 1.522-1.523) and phenocrysts. The phenocrysts are of feldspar, with a few crystals of biotite, amphibole and clinopyroxene. Yoko-oji volcanic ash layer which is one of the most useful key beds, is intercalated in the middle part of the Alluvial deposits. This layer about 5 cm thick is composed of light red to yellowish brown and medium grained ash. It consists mainly of pale brown H-type glass shards with index of 1.507-1.515 (mode 1.510-1.512), with trace amounts of plagioclase, orthopyroxene (γ=1.700-1.717; mode 1.705-1.711), clinopyroxene and amphibole.

抄録全体を表示

Three elephant molars from the Pleistocene were found in Niigata Prefecture and reported by MATSUMOTO et al. (1968) have been re-examined. These molars were identified by MATSUMOTO et al. (1968) as Loxodonta (Palaeoloxodori) yabei, L. (P.*) tokunagai junior (=Palaeoloxodon naumanni), but morphological and stratigraphical studies have identified these molars as being from an archtipal mammoth. Specifically, this morphological study identified the Monzen specimen as Mammuthus protomammonteus. In comparison with the measurement of molars of the genus Mammuthus in Europe by MAGLIO (1973), the Monzen specimen is similar to M. armeniacus. This shows that the progression of stages in the development of genus Mammuthus is similar to Europian counterpart. Meanwhile a geological survey has revealed that the Mitama specimen occured in a SK030 bed (1.30 m. y. B. P.), which is the key bed of the most upper part of the middle Formation in the Uonuma Group. Therefore the importance of this specimen to discussion is that the meridionalis type shifted into the armeniacus type in Japan.

抄録全体を表示

This paper describes the stratigraphy and geologic structure of the Ashigara group distributed along the Sakawa River, Kanagawa Prefecture. The contents are summarized as follows: 1. The Tanzawa group distributed in the reported area consists of the Araizawa lapilli tuff (Tanzawa Research Group, 1975) of the Yozuku formation, the Asase lapilli tuff of the Hirayama formation, the Mushizawa tuff (new name) and the Takamatsu tuff (new name) of the Hirayama formation, and the Furoyama basalt, in ascending order. 2. The Ashigara group consists of six formations, namely, Doyama, Dai, Seto, Tsuburano, Hatazawa and Shiozawa formations, in ascending order. These formations, all newly named, are conformable with one another. 3. The Ashigara group is unconformably overlain by the Yamakita group and younger sediments. The younger sediments are divisible into the Suruga gravel, the Hakone ejecta and the Fuji mud flow. 4. Pyroxene andesite dikes being abutted by the overling Yamakita group, and hornblende andesite dikes intruding the former dikes are found in the reported area. 5. In the southern part of the reported area occurs the Yaguradake quartz diorite which cuts the Hatazawa formation and forms a chilled margin. 6. The Ashigara group differs in strike, dip, facies and thickness between the east limb and the west limb of the Minasegawa flexure axis (new name), which trends in a NW-SE directions. In the east limb the strata are dippring steeply to the north due to the Yamakita flexure (new name) trending E-W, whereas the west limb is represented by the Ashigara flexure (new name) having a NNE-SSW axis, and the strata on the west side are dipping steeply to the west. 7. The faults developed comprise three systems, as distinguished by their formative stages. They are; the NE-SW〜NNE-SSW system in the Tanzawa group, the NNE-SSW and WNW-ESE〜EW system in the Ashigara group, the E-W trending Kannawa fault cutting both groups, and the NNE-SSW〜NW-SE system cutting the Kannawa fault. The Kannawa fault, striking E-W, is a reverse fault plunging to the north at a high angle, and up-thrusting southward. 8. The geologic age of the Ashigara group, inferred from the fossils of planktonic Foraminifera, Mollusca and Stegodon, ranges from late Pliocene of the Neogene Tertiary to early-middle Pleistocene of the Quaternary.

抄録全体を表示