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Volume 105, Issue 1
Displaying 1-7 of 7 articles from this issue
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Yasuhiro Takashimizu, Fujio Masuda, Masaaki Tateishi1999 Volume 105 Issue 1 Pages 1-12
Published: January 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Upper Pleistocene (the last interglacial period) of the Makinohara Upland, Shizuoka, Japan, is divided into four formations, and constructed from a drowned valley, estuary, beach-shoreface and an alluvial system. These comprise one depositional sequence. Grain-size characteristics of each facies are clarified in this study. The assemblages of each facies can be classified into two types (closely and scattered distributed groups) based on 3-D diagrams (arithmetic mean versus standard deviation versus mud content). Fluvial deposits of LST have poorly sorted fine sand, whereas fluvial deposits of HST have well sorted coarse sand. In the beach-shoreface system, grain-size gradually fines and mud content increases, from the beach to the lower shoreface. In the drowned valley- estuary system, estuary mouth bars have higher arithmetic mean values than the bay-head delta. Both environments have moderate standard deviation and mud content values. Central bay floor (central basin) and drowned valley have high arithmetic mean and mud content values, and low standard deviation values. Seaward barrier have intermediate arithmetic mean values, low standard deviation and mud content values. These facts indicate that 1) terrigenous coarse sediments were trapped in the bay-head delta and were not transported to the central basin, 2) seaward coarse sediments were not transported into the central basin (tidal inlet is an exception). The horizon of the MFS have high arithmetic mean and mud content values compared with other similar facies. Grain-size characteristics differ between the tsunami deposits in the relict barrier and drowned valley. The tsunami deposits in drowned valley include numerous suspended (from landward and/or seaward) load by oscillationary currents along the paleo-valleys, whereas the tsunami deposits in relict barriers consist of offshore sands and erosion of the barrier itself.View full abstractDownload PDF (1464K) -
Yasuyuki Kakihara1999 Volume 105 Issue 1 Pages 13-24
Published: January 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSA large amount of andesitic volcanic rocks are widely distributed in northern Hokkaido. These volcanic rocks have formed a high topography with flat surface, and therefore have been called "flat lavas". The "flat lavas" distributed around the Hakodake area to the east of Bifuka town, northern Hokkaido are divided into three units in ascending order ; the Sakkuru andesites, Otoifuji andesites and Hakodake lavas. Each andesitic unit is composed of lava flows and debris flow deposits and, their maximum thickness is about 400 m for the Sakkuru andesites, more than 40 m for Otoifuji andesites and about 500 m for the Hakodake lavas. Field observations revealed that three volcanic units are interfingered with the middle Miocene Onnenai Formation composed of fluvial and shallow sea deposits. This suggests that the lavas and debris flow deposits were formed on the flat fluvial plains and subsequently buried in a relatively shallow depth due to subsidence of the basin. The present stratigraphical results are good consistent with the previously obtained radiometric ages of 10∼14 Ma for the volcanic rocks in this area. After eruption of the Hakodake Lava, the volcanic and sedimentary rocks in the area may have been uplifted by tectonic movement accompanied by NS trending faulting and folding. A very short period of erosion on the subaerial ground seems to have resulted in preservation of flat plains consisting mainly of lava flows in the Hakodake area.View full abstractDownload PDF (1908K) -
Yasu'uchi Kubota1999 Volume 105 Issue 1 Pages 25-44
Published: January 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSVoluminous Plio-Pleistocene andesitic volcanism with "flood andesite" is characteristic of the three arc-junctions of the Japanese Islands. This paper aims to clarify the nature of the volcanism and to reconstruct the geometry of volcanic basins in central Japan, the junction of the Northeast Japan, Southwest Japan and Izu-Ogasawara arcs.Surveyed area is situated on the southwest side of the Lake Suwa, where the Plio-Pleistocene Enrei Formation has accumulated up to 900 m in thickness. The Enrei Formation is divided into four stratigraphic units (23 subunits). Individual units become more mafic upward in phenocryst composition (predominant phenocrysts are hornblende→orthopyroxene and clinopyroxene→olivine), volcanism ceases at the end of each unit, and the four units show an overall more felsic tendency upward. Large ratio of lava flows of the formation can be attributed to the high rate of effusion that would have supplied thick lava flows with large potentials of flow distances.The formation has accumulated the three tilted basins arranged subparallel. These were formed through northwestward syn-sedimentary tilting of three basement blocks bounded by antithetic faults. Each sedimentary basin shows that the comparative altitudes of the individual basement blocks tend to decrease northwestward, so that the extents and maximum depths of the titled basins conversely increase in the same direction. This regularity provides important restriction to the formative mechanism of the tilted basins that through forming the Enrei Formation the individual basement blocks tend to tilt and subside northwestward and three main longitudinal faults mutually have antithetic displacement.View full abstractDownload PDF (3576K) -
Yodai Nakamura, Tomowo Ozawa, Takami Nobuhara1999 Volume 105 Issue 1 Pages 45-60_2
Published: January 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe stratigraphy and molluscan fauna of the lower part of the Miyazaki Group distributed in the Aoshima area, southern Kyushu, were reexamined on the basis of the new biostratigraphic and paleontologic evidence. The Miyazaki Group in this area is lithologically divided into the Boroishi, Kaichigo, Gonoharu, Janokawauchi, Aoshima and Tano Formations in ascending order. The upper part of the Gonoharu Formation and the Janokawauchi Formation can be assigned to planktonic foraminiferal Zone N. 16 of Blow (1969), while the Aoshima and Tano Formations can be assigned to Zone N.17-N.18. Although the geologic age of the lower two formations could not be determined because of poor preservation of planktonic foraminiferal fossils, the fining-upward lithologic sequence caused by the increase of the bathymetrical depth and the occurrence of the tropical to subtropical molluscan fossils from the Kaichigo Formation suggest that these formations may have deposited in Zone N. 16 when the global marine transgression was recorded.The molluscan fauna of the upper Miocene Kaichigo Formation consists of the Megacardita taiwanensis-Donax sp. assemblage and the Amusium cf. pleuronectes-Amussiopecten sp. A assemblage. These assemblages have never been reported in the Neogene of Japan. The diagnostic species of these assemblages such as Megacardita taiwanensis, Amusium cf. pleuronectes have been known from the Miocene strata in Taiwan. On the other hand, the molluscan fauna of the uppermost Miocene to lower Pliocene Tano Formation consists of the characteristic species of the Zushi Fauna of central to southwest Japan. The molluscan fauna of the Tano Formation differs in species composition from that of the Kaichigo Formation. In fact, several genera such as Amussiopecten and Megacardita are represented by different species between these two formations. In this paper, the Kaichigo Fauna is newly proposed for a late Miocene tropical to subtropical molluscan fauna prior to the Zushi Fauna.View full abstractDownload PDF (3830K) -
Yuko Tomita, Katsuki Kurokawa1999 Volume 105 Issue 1 Pages 63-71
Published: January 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSA late Pliocene widespread volcanic ash layer in central Japan was detected both on the Pacific Ocean side and the Sea of Japan side. The Habutaki I ash layer in the Osaka Group and the Minamidani 1 ash layer in the Tokai Group around Ise Bay were correlated to the MT 2 ash layer in the Himi Group around Toyama Bay and also the Arg-2 ash layer in the Nishiyama Formation of the Niigata region. They are waterlaid airfall ash layers of 13-150 cm in total thickness. These ash layers are placed in the Gauss chron and are assumed to be about 2.7 Ma in age. They commonly consist of fine-grained vitric ashes and dominant in bubble-wall type glass shards. The mineral association is characterized by high-quartz, orthopyroxene and hornblende, and chemical composition of glass shards is also coincident, namely SiO2=79.5-81.5%, TiO2=0.18-0.28%, Al2O3=11.5-12.4%, FeO=0.95-1.15%, MnO<0.08%, MgO=0.13-0.19%, CaO=0.70-0.88%, Na2O=1.1-2.0% and K2O=2.7-4.0% on water-free basis. The Minamidani 1 ash was also so far correlated to the Arigaya I ash layer in the Kakegawa Group around Suruga Bay. The name of the Habutaki I-MT 2 ash layer is proposed as the general name of these widespread ash layers. The ashfall area of the Habutaki I-MT 2 ash attains 430 km×280 km in central Japan.View full abstractDownload PDF (2731K) -
Hidemi Tanaka, Takayuki Higuchi, Naoto Tomida, Koichiro Fujimoto, Tomo ...1999 Volume 105 Issue 1 Pages 72-85
Published: January 15, 1999
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThis paper describes distribution, deformation and alteration of the brittle fault rocks from the borehole which penetrated into the Nojima Fault. This fault was activated during the 1995 Hyogoken-Nanbu earthquake (M 7.2) which caused great disasters in the southern part of Kobe City and the northern area of Awaji Island. The active-fault drilling was performed by the Geological Survey of Japan (GSJ) at Nojima Hirabayashi, northwest of Awaji Island and was successful by penetrating the core of the Nojima Fault at 625 m depth.The GSJ core consists of granodiorite including six shear zones, MSZ (main shear zone : 625 m depth), USZ, LSZ-1, LSZ-2, CZ-1 and CZ-2. The former two shear zones are in the hangingwall and the others are in the footwall respectively of the Nojima fault. We have recognized from the core observation that the fault rocks are formed mainly by pulverization and/or alteration. Thus, we proposed a diagram for classification of the fault rocks in the core, on the basis of the degree of pulverization and alteration. Density of cracks and shear surfaces is adopted as pulverization index (plotted on x axis).Relative amounts of residual mafic minerals are selected to represent the degree of alteration (plotted on the y axis). Each axis is divided into four grades and standard samples are selected to represent each intersection point (i.e., 0-0, 0-1, 1-1...3-3.) for classification by unaided eyes.Shear zones are classified into the following three types by using this diagram. Three shear zones, MSZ, USZ and LSZ-1 are characterized by sequential arrangement from the core to margin, of fault gouge, fault breccia, weakly altered and deformed rocks, and host rock. This fault rock distribution is referred to as pulverization - alteration series. The other two shear zones, CZ-1 and CZ-2, are characterized by non-altered- and random-fabric- cataclasites and are referred to as pulverization series. The rest, LSZ-1 is characterized by the complete substitution of the host rock minerals to clay minerals with little pervasive deformation, which is referred to as alteration series. Both pulverization and alteration are characteristic features for formation of fault rocks especially in main shear zone in the hanging wall. In contrast, either pulverization or alteration effect is apparent in separate shear zones in the footwall.View full abstractDownload PDF (3275K) -
—an example of continental growth and evolution evidence at an Archean continental crust—Shoichi Kiyokawa, Asahiko Taira, Tim Byrne1999 Volume 105 Issue 1 Pages I-II
Published: 1999
Released on J-STAGE: November 26, 2010
JOURNAL FREE ACCESSThe middle Archean (3.25-3.20Ga) coastal Pilbara Terrane was formed by an immature oceanic island arc-continent collision [D1: 3.15-3.05Ga] and was deformed by regional intraplate strike-slip deformations [D2: 3.0-2.95Ga; D3: 2.90-2.80Ga] (Kiyokwa and Taira, 1999; Kiyokawa et al., submit). The immatured oceanic island arc unit of the Cleaverville-Roebourne Supercomplex tectonically overthrusts the granitecontinental shelf metasedimentary Karratha Supercomplex (see cross section) (Kiyokawa and Taira, 1998). D1 thrust deformation evidences, such as klippen structure, imbricated thrust piles and a basal decollement with quartz mylonite, are well preserved in the complexes boundary. On the other hand, the D2 event identified regional strike-slip deformations (eg. reactivated quartz mylonite, steep axis asymmetric fold) and the D3 deformation locally preserved at the terrane boundary with mylonite shear zone [Sholl shear zone]. These deformations are identified as formation of a juvenile continent and stabilization of early continent in Middle Archean.View full abstractDownload PDF (2992K)
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