All issues
Volume 107, Issue 8
Displaying 1-5 of 5 articles from this issue
- |<
- <
- 1
- >
- >|
-
Kenya Ono, Makoto Takeuchi2001 Volume 107 Issue 8 Pages 481-495
Published: August 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe sedimentation of the Motodo Formation and the evolution of the sedimentary basin were analyzed. The Motodo Formation occurs in the Hida-gaien Tectonic Zone, Fukui Prefecture, central Japan, and it consists mainly of conglomerate. It was analyzed on the basis of sedimentary facies, clast compositions of conglomerate, distribution of maximum clast size and paleocurrent direction.This formation is divided into three members, the Nakajima Tuff Breccia Member, the Wasadani Conglomerate Member and the Kumokawa Conglomerate Member in ascending order. Six sedimentary facies have been identified and include Facies A (crudely stratified conglomerate), Facies B (stratified sandstone), Facies C (lenticular conglomerate), Facies D (andesitic volcanic conglomerate), Facies E (disorganized conglomerate) a nd Facies F (andesitic tuff breccia). Facies A, Facies B, and minor Facies C accompanied with Facies D in the Kumokawa Conglomerate Member represent deposits in a sheetflood (hyperconcentrated flood-flow)-dominated middle alluvial fan. Facies E in the Wasadani Conglomerate Member represents deposits in a debris-flow-dominated proximal alluvial fan. Facies F in the Nakajima Tuff Breccia Member represents andesitic pyroclastic flow deposits. Debris flow deposits (Wasadani Conglomerate Member), mainly supplying granitoid, rhyolite and hornfels clasts from the north or south, transfer upward, east and west to sheetflood deposits (Kumokawa Conglomerate Member) mainly supplying sandstone and mudstone from the west to the east.A debris-flow-dominated proximal alluvial fan developed transverse to the basin axis, and a sheetflood-dominated slope of middle alluvial fan facies formed parallel to the basin axis. This feature suggests that the Motodo Formation was deposited in a strike-slip basin or a rift basin with andesitic volcanism.View full abstractDownload PDF (3899K) -
Masamichi Shiono, Itaru Koizumi2001 Volume 107 Issue 8 Pages 496-510_4
Published: August 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Thalassiosira trifulta group has few morphological features as observed in the LM (light microscope) that allow its evolution to be traced. This study and our previous studies described this diatom group in detail based on LM and SEM (scanning electron microscope) observations, and distinguished three subgroups, the Thalassiosira frenguelliopsis subgroup, the Thalassiosira oestrupii subgroup, and the Thalassiosira bipora subgroup. Here we define the stratigraphic ranges of the species which were defined in the T. trifulta group by integrating LM and SEM observations on samples from deep-sea cores in the northwestern Pacific Ocean. The detailed SEM observations of fultoportulae (both operculate and trifultate) and small pore-like structure in the valve centre (occluded areola in our previous studies) provide a reliable classification based on the phylogenetic evolution. Thalassiosira bipora f. marginata n. f., Thalassiosira bipora f. minima n. f., Thalassiosira bipora f. prima n. f., Thalassiosira oestrupii f. vetus n. f., Thalassiosira praeoestrupii f. juvenis n. f., and Thalassiosira mesopora n. sp. are described and assigned to the T. trifulta group. Four events concerning the differentiation and evolution of this group during the intervals of 5.7-5.4 Ma, 5.3-4.8 Ma, 3.4-3.2 Ma, and 2.5-2.2 Ma are defined and discussed.View full abstractDownload PDF (4811K) -
Shin-ichi Kagashima, Toshiaki Shimura2001 Volume 107 Issue 8 Pages 515-530
Published: August 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Late Cretaceous to Paleogene Iwafune granitoids of are distributed around the border between Niigata and Yamagata Prefectures, Japan. The Budo Mountains is located in northern part of Niigata Prefecture and is exposed in an area covering more than 250 square kilometers. It consists of Iwafune granitoids, which are divided into six lithological types ; porphyritic biotite granite (PBG), biotite granite (BG), garnet two-mica granite (GTMG), two-mica granite (TMG), quartz diorite (QD) and granodiorite (GD). The six rock types can be assigned to three rock groups on the basis of petrological observations as follows : biotite granite group (BG-group ; PBG and BG), and tow-mica granite group (TMG-group ; GTMG and TMG) and diorite group (D-group ; QD and GD).Most of the granitoids in this area are attributed to BG-group. This group is composed of quartz, plagioclase, potassium feldspar, biotite and minor amounts of accessory minerals. Especially, the PBG contains potassium feldspar megacrysts and sometimes shows schlieren layering owing to the concentration of biotite and plagioclase. BG-group has medium SiO2 content ranging from 69 to 77 weight percent and is peraluminous.Modal and bulk chemical compositions show that BG-group has curved trend. Mass balance calculation indicates that the BG-series magma can be derived from common parental magma through two-stage fractional crystallization of potassium feldspar, biotite and plagioclase. The first stage is characterized by plagioclase- and biotite-rich fractionation, and the second stage is characterized by fractionation of biotite and potassium feldspar more than plagioclase.View full abstractDownload PDF (2782K) -
Masayuki Ehiro, Daishi Nogi, Kei Mori, Goichi Kawashima, Noritoshi Suz ...2001 Volume 107 Issue 8 Pages 531-534
Published: August 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSScleractinian corals were discovered from the limestone conglomerate distributed along the Shimochizawa River, west of Fukushi in the Kuzumaki-Kamaishi Belt (Jurassic accretionary complexes), Northeast Japan. These corals give the first evidence for Mesozoic limestone body present in the belt. The limestone conglomerates are lenticular in distribution pattern and interbedded in the thick bedded chert slab. They can be traced from the Shimochizawa River, trending NNW, to the north of Kita-Kawame over a distance of about 6 km.View full abstractDownload PDF (711K) -
Shusaku Yoshikawa, Hideo Yamazaki, Jun Inoue, Muneki Mitamura, Shinji ...2001 Volume 107 Issue 8 Pages 535-538
Published: August 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe explosion of a plutonium atomic bomb over Nagasaki city took place on 9 August 1945. After the explosion, a cloud formed, which passed over the Nishiyama district, where 'black rain' fell. Thus, the Nishiyama reservoir, located approximately 3 km from the hypocenter, received the heaviest radioactive fallout from the Nagasaki atomic bomb. Sediment samples were collected from the bottom of the Nishiyama reservoir in 1999 and analyzed for their 137Cs, 241Am and charcoal concentrations. The stratigraphic distribution of 137Cs and charcoal clearly indicate that the 'black rain' horizon is recognized in the Nishiyama reservoir sediments. The 'black rain' horizon contains anthropogenic radionuclides (137Cs and 241Am) and charcoal in high concentrations.View full abstractDownload PDF (797K)
- |<
- <
- 1
- >
- >|