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Volume 107, Issue 3
Displaying 1-6 of 6 articles from this issue
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Kazuyoshi Moriya, Hiromichi Hirano2001 Volume 107 Issue 3 Pages 199-214
Published: March 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Cretaceous deposits distributed in the Chikubetsu area, northwestern Hokkaido, are lithostratigraphically divided into the underlying Upper Yezo and the Hakobuchi Groups. They form an asymmetrical anticlinal structure, whose axis has a NNW-SSE trend and plunges to the NNW with an axial-plane fault. The Upper Yezo Group is subdivided into two formations, the underlying Middle Haborogawa Formation (over 450 m thick) and the Upper Haborogawa Formation (about 800 m). The former consists of mudstone, sandy mudstone and muddy sandstone with frequent intercalations of thin sandstone, while the latter of a coarsening upward sequence is composed of dark gray mudstone, bioturbated sandy mudstone and light gray muddy sandstone, and cross-bedded gray or bluish gray glauconitic sandstone in ascending order. The Hakobuchi Group is represented by the Pankezawa Formation (135-170 m thick), which is redefined in this study. It consists of dark gray mudstone, gray or bluish gray sandstone and parallel or cross laminated tuff in ascending order. The Upper Yezo Group is unconformably overlain by the Hakobuchi Group. Based on the stratigraphic distribution of ammonoids and inoceramids, the Middle Haborogawa Formation and the lower part of the Upper Haborogawa Formation are correlated to the Santonian, and the upper part of the Upper Haborogawa Formation and the Pankezawa Formation to the Campanian to the Maastrichtian. A time gap between the Upper Yezo Group and the Hakobuchi Group seems not to be large.View full abstractDownload PDF (1831K) -
Futoshi Nanayama, Yasuhiro Doi, Naoko Kitada, Keiji Takemura, Yuichi S ...2001 Volume 107 Issue 3 Pages 215-221
Published: March 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSBorehole and seismic-reflection data provide no evidence for recent activity of the Suminoe flexure, a branch of the Uemachi fault system near Osaka since 14, 000 14CyBP. Using cores from six boreholes, we studied the sedimentology, paleontology, micropaleontology, tephrochronology, and radiocarbon age of late Quaternary deposits on the flexure. We also made an S-wave seismic reflection survey to check the architecture of these deposits. The architecture of these units shows that the average vertical slip rate on the flexure has not exceeded 0.2 m/ky, and that the most recent faulting predates 14, 000 14CyBP. The Holocene deposits further shows that relative sea level was about -19 m at 8, 500 14CyBP, and that it rose rapidly between 8, 500 and 6, 000 14CyBP.View full abstractDownload PDF (1346K) -
Michio Takami, Yujiro Nishimura, Tetsumaru Itaya2001 Volume 107 Issue 3 Pages 222-227
Published: March 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSK-Ar ages of illite rich fraction have been determined for pelagic claystone near the Permian-Triassic boundary from the Jurassic-earliest Cretaceous accretionary complexes in Gifu and Okinawa areas, Japan. The Early-Middle Triassic pelagic claystones give 181.5±3.8 Ma, 184.4±3.9 Ma, and 190.2±4.1 Ma (Early Jurassic), whereas the latest Permian pelagic claystone, 233.4±4.9 Ma (Middle Triassic). These ages are younger than the depositional ages of the protoliths and older than the accretion ages of the complexes. Time-lags between the depositional age and K-Ar age are ca. 15 m.y. for the latest Permian claystone and ca. 50-60 m.y. for the Early-Middle Triassic claystones. These results suggest that K-Ar ages represent average ages of K-bearing clay minerals such as illite and/or illite-smectite mixed layer which formed during illitization in the process of diagenesis on an oceanic crust and subsequent regional metamorphism within a subduction zone. The age relation between depositional age and K-Ar age depends on a mixing of older and younger illite which formed during illitization, and a partial Ar depletion from illite during regional metamorphism.View full abstractDownload PDF (955K) -
Mieko Uchiyama, Muneki Mitamura, Shusaku Yoshikawa2001 Volume 107 Issue 3 Pages 228-236
Published: March 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSThe Osaka sedimentary basin is a tectonic subsidence basin. The basement rocks of the Osaka Plain in the northern part of the Osaka sedimentary basin has been broken into two major blocks called West and East Osaka blocks by the Uemachi Fault trending north to south. The Osaka Plain consists of 1, 000-2, 000 m thick Quaternary sediments. Tectonic movements of the basement blocks are estimated by detailed study of the geological section of the Osaka Plain. This section is drawn by the reviewing and compiling deep drilling cores, borehole logs and depth sections of the seismic reflection surveys. The thickness of sediments and the difference of distribution levels of marine clay as time markers indicate the tectonic movements of these basement blocks and the Uemachi Fault. The two basement blocks have been tilting separately, but both have continuously subsided as one basin since ca. 1.2 Ma. The northern part of this basin has subsided from ca. 1.2 Ma to 0.4 Ma with the subsiding rate of 0.7-0.5 m/ky. And then, the subsidence rate has moderated to 0.5-0.2 m/ky.View full abstractDownload PDF (1404K) -
Makoto Kawamura, Hayato Ueda, Mitsuru Nakagawa, Takayuki Katoh, the R ...2001 Volume 107 Issue 3 Pages 237-240
Published: March 15, 2001
Released on J-STAGE: April 11, 2008
JOURNAL FREE ACCESSHigh P/T metamorphic minerals are found from a Late Cretaceous accretionary complex (Ganpi-yama Complex) separately occurring within a serpentinite mass in the Kamuikotan Zone of the Sorachi-Yezo Belt, Hokkaido. The complex was previously referred to as the "undivided Hidaka Supergroup". The Yon-no-sawa Unit, a major member of the complex, is composed of deformed alternation of siliciclastic sandstone and mudstone, greenstones and chert. Sodic pyroxenes coexisting with quartz are found from greenstone, and metamorphic aragonite from sandstone and greenstone. The finding of these high P/T metamorphic minerals suggests that the Ganpi-yama Complex has, at least, a metamorphic affinity to the Kamuikotan Zone. An exact tectonostratigraphic correlation of the complex, however, is still open to the argument.View full abstractDownload PDF (998K) -
Hirokazu Maekawa, Hiroo Inokuchi, Tetsuji Enomoto2001 Volume 107 Issue 3 Pages V-VI
Published: 2001
Released on J-STAGE: November 26, 2010
JOURNAL FREE ACCESS
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