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Volume 119, Issue 3
Displaying 1-6 of 6 articles from this issue
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Takashi Nanjo, Keiichi Sasaki, Hiroki Matsuda2013 Volume 119 Issue 3 Pages 155-170
Published: March 15, 2013
Released on J-STAGE: July 03, 2013
JOURNAL FREE ACCESSThe carbon and oxygen isotope compositions of carbonate sediments can be used to reconstruct sea-level changes and the diagenetic processes that have affected the sediments, primarily as isotope depth profiles through shallow-marine carbonate successions can identify stratigraphic horizons that underwent subaerial exposure-related meteoric diagenesis, even within intervals where sedimentary features diagnostic of subaerial exposure have been eroded away.
The Upper Pleistocene Ryukyu Group of Kikai Island, Kagoshima Prefecture, Japan, consists of reefal sediments that were deposited during high-amplitude and short-termed glacioeustatic sea-level changes prior to the last interglacial. These sediments are thought to have undergone repeated subaerial exposure, although no sedimentary evidence for this exposure has been observed. The carbon and oxygen isotope compositions of two borehole cores (STb-1 and STb-2) drilled in the northeastern part of Kikai Island were determined to identify subaerial exposure surfaces (SESs) within the Ryukyu Group, and to determine precisely the nature of Late Pleistocene sea-level changes in this area.
Correlations with adjacent outcrops indicate that the sediments within the STb-1 and STb-2 cores were deposited at approximately 62-52 ka. Carbon and oxygen isotope composition, lithology, mineral composition, and diagenetic textural data enabled the identification of three SESs in STb-1 and two in STb-2. The stratigraphic position of SESs within the sediments enabled the division of the STb-1 and STb-2 cores into four depositional sequences that were deposited during highstands corresponding to IS (Interstadial)-14-IS-17 stages of the ice core oxygen isotope curve. This study shows that carbon and oxygen isotope data can enable the identification of SESs and the reconstruction of high-resolution sea-level changes over intervals of a few thousand years. This method is useful for the construction of detailed sea-level change curves and the characterization of depositional sequences.View full abstractDownload PDF (8538K) -
Kiyoyuki Shigeno, Futoshi Nanayama, Yusuke Sudo, Tsumoru Sagayama, Tak ...2013 Volume 119 Issue 3 Pages 171-189
Published: March 15, 2013
Released on J-STAGE: July 03, 2013
JOURNAL FREE ACCESSAn active barrier system is present in Akkeshi Bay and a lagoonal area along the Pacific coast of eastern Hokkaido, Japan. This rare feature consists of a so-called lagoon (the Akkeshi-ko lagoon), a flood tidal delta, a barrier, and a tidal inlet that leads into the outer sea of Akkeshi Bay and the Pacific Ocean. Large oyster reefs were living on the flood tidal delta until their sudden extinction in the early 1980s. The processes involved in the formation of this barrier system during a postglacial transgression period are not well understood. Here, we use sedimentological, paleontological, and radiocarbon dating methods to analyze Holocene drillcore obtained from the Akkeshi fishing port in 2009 and borehole log data previously obtained from public works around the Akkeshi lowlands. The data obtained from both drillcore and borehole logs indicates that: (1) postglacial transgression occurred in this area some 11,400 years ago and reached 50 m below the present sea water level, with the barrier system in the study area established 8800 years ago. (2) The preservation of this barrier system is due to the stable sea level in this area. The sea level has been constant for the past 5500 years, and has led to the development of oyster reefs on the tidal flood delta. (3) The current topographically distinctive barrier system has been affected by sudden uplifts associated with giant earthquakes. These events occur every few hundred years, with the barrier undergoing prolonged but relatively rapid post-earthquake subsidence at about 1 cm/year, as observed after a giant 17th century earthquake.View full abstractDownload PDF (7039K) -
Chika Iwata, Atsushi Kamei, Katsuhiko Iwata, Tomoyuki Shibata, Asuka M ...2013 Volume 119 Issue 3 Pages 190-204
Published: March 15, 2013
Released on J-STAGE: July 03, 2013
JOURNAL FREE ACCESSThis study investigates the geology, petrology, and geochronology of the Abire granodiorite, which lies in the Okuizumo district, within the San'in zone of the Southwest Japan arc. The Abire intrusion is one of a number of large batholiths in the district, and is mainly composed of hornblende-biotite granodiorite. In its northern part, the Abire intrusion contacts the Yokota intrusion. Both intrusions are locally mingled, with a small quartz-dioritic stock at their boundary. In its southern part, the Abire intrusion is adjacent to the Ryukoma intrusion, but the boundary between these two bodies is gradational. These geological features suggest that all of these plutonic bodies formed at almost the same time. The Abire intrusion yields a Rb-Sr whole-rock isochron age of 60.5 ± 6.3 Ma, with an initial Sr isotopic ratio (SrI) of 0.70531 ± 0.00013. This age is very close to a previously reported age of the Yokota intrusion (59.6 ± 5.5 Ma from RbSr WR; SrI = 0.70484 ± 0.00022). These ages are compatible with the geological evidence. However, the Abire and Yokota intrusions solidified from different magmas, because their SrI values differ. This suggests that several large magma chambers in molten state coexisted in this region during the Paleozoic. SiO2 contents of the Abire intrusion range from 68.1 to 73.4 wt.%. The intrusion belongs to the I-type magnetite series, and is classified geochemically as a volcanic arc granitoid. Major and trace elements generally show marked differentiation trends on Harker diagrams, although chondrite-normalized rare earth element patterns change little with varying SiO2 content. The major cause of this geochemical feature lies in the small degree of differentiation observed, and in the weight proportions of the fractional assemblage (plagioclase: alkali feldspar: hornblende: biotite: apatite: zircon = 28.7: 31.6: 24.5: 14.7: 0.5: 0.1) during fractional crystallization; this assemblage leads to bulk distribution coefficients near unity for the rare earth elements.View full abstractDownload PDF (7360K) -
Keita Suzuki, Kunihiro Sakai, Tohru Ohta2013 Volume 119 Issue 3 Pages 205-216
Published: March 15, 2013
Released on J-STAGE: July 03, 2013
JOURNAL FREE ACCESS
Supplementary materialFourier and fractal analysis methods have allowed new advancements in determining the shape of sand grains. However, the full quantification of grain shapes has not as yet been accomplished, partly due to the difficulties in interpreting the results of Fourier analysis, and partly because fractal dimension changes are somewhat dependent on the measuring techniques used. This study focuses on the application of a method that integrates elliptic Fourier and principal component analysis methods (elliptic Fourier-PCA). This method reduces the number of extracted variables and enables a visual inspection of the results of Fourier analysis, an approach that facilitates the understanding of the sedimentological significances of the results obtained using this technique. The application of this Elliptic Fourier-PCA technique to sand grains collected from fluvial, beach, and glacial environments produced particle descriptors such as elongation index (EF1) and multiple bump indices (EF2, EF3, and EF2 + EF3). These descriptors indicate that glacial, beach, and fluvial sediments contain particles with shapes similar to circles, ellipses, and cylinders, respectively. A modified pixel dilation (mPD) method was used for fractal dimension analysis, primarily as a simple model experiment proved that the mPD method enabled better detection of the degree of surface smoothness than traditional boxcounting methods. Mean (FD) and coefficient of variation of fractal dimension (FDCv) values decrease from glacial to fluvial and beach particles, indicating that glacial particles retain rugged surfaces, whereas beach particles have smoother and more even surfaces due to increased abrasion. Of the grain shape indices used during this study, the FD and EF1 variables are key shape proxies that enable differentiation between sedimentary environments, with an FD-EF1 plot allowing the effective discrimination of particles derived from fluvial, beach, and glacial environments.View full abstractDownload PDF (3075K)
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Fumio Kobayashi2013 Volume 119 Issue 3 Pages 217-221
Published: March 15, 2013
Released on J-STAGE: July 03, 2013
JOURNAL FREE ACCESSFusuline fossils are uncommon and are generally poorly preserved in rare limestone blocks within a Jurassic accretionary complex in the Kambara Mountains of Niigata Prefecture, Japan. The poor preservation of fossils in this area is due to the thermal effect of intrusion of Late Cretaceous to Paleogene granites. Middle Permian (Guadalupian) fusulines such as Yabeina kaizensis Huzimoto, Neoschwagerina sp., Chusenella sp., Dunbarula sp., and Sichotenella ovoidea (Sosnina) were obtained from three limestone float boulders in the western Kambara Mountains. These fossils are paleobiogeographically important and will be used in further research to reconstruct the oceanic plate stratigraphy of the Kambara and other mountains along the Japan Sea side of northeast Japan.View full abstractDownload PDF (3362K) -
Toshio Yasui2013 Volume 119 Issue 3 Pages 222-225
Published: March 15, 2013
Released on J-STAGE: July 03, 2013
JOURNAL FREE ACCESSEdmund Naumann, a geologist employed by the Japanese government in the early Meiji period, visited Shikoku Island for geological investigation in 1883. At that time, two medical doctors named Otsuka and Teshima asked him to judge the quality of coal in the Ryoseki area of Kochi Prefecture. Little was known about Teshima until after a recent discovery of his grave and the remains of his house, which was used as a hospital and a private school in and around Ryoseki . He is identified Yoshinaga and was 53 years old at the time.View full abstractDownload PDF (1989K)
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