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Volume 30 (1996)
- Issue 6 Pages 323-
- Issue 5 Pages 261-
- Issue 4 Pages 201-
- Issue 3 Pages 139-
- Issue 2 Pages 71-
- Issue 1 Pages 1-
Volume 30, Issue 4
Displaying 1-4 of 4 articles from this issue
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Hodaka Kawahata, Nobuhisa Eguchi1996 Volume 30 Issue 4 Pages 201-215
Published: August 20, 1996
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSIt has been suggested that late Quaternary variability in atmospheric CO2 concentrations may have resulted from variations in the nature of biogenic sedimentation. In this paper we present 262 kyr time series for the mass accumulation rates of organic carbon (MAROC), carbonate (MARCarbonate), and biogenic opal (MARopal) of the Eauripik Rise, the western equatorial Pacific. The MAROC record exhibits a general trend of higher values during glaciation time; Stage 2, Stage 3, Stage 4, Stage 6 and late Stage 8 except middle Stage 5. A weak correlation between MAROC and MARopal as well as MARCarbonate is attributed to the oligotrophic character of the western Pacific in the Eauripik Rise area. Spectral analysis of organic carbon contents displays eccentricity, obliquity and precession-related peaks. The presence of 23-kyr periodicity indicates a possible link between organic carbon burial and trade winds associated with insolation.View full abstractDownload PDF (3653K) -
Che Abd. Rahim Mohamed, Hisashi Narita, Koh Harada, Shizuo Tsunogai1996 Volume 30 Issue 4 Pages 217-229
Published: August 20, 1996
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSSediment cores were obtained at six stations in the region from the continental slope to the oceanic basin across the northern Japan Trench and analyzed for the natural radionuclides, 238U, 234U, 232Th, 230Th and 210Pb. The subsurface sediment was enriched in authigenic uranium-containing minerals and the layer with the maximum concentration tended to be deeper with increasing distance from the coast to the basin. The subsurface layer of the hemipelagic sediments seems to be a significant sink for the oceanic uranium. The activities of 210Pb did not decrease monotonically with depth, indicating the sliding of bottom sediments from the shallower seabed towards the trench. The sediment accumulation rate increased from the continental slope towards the trench and was the largest of 7.3 mm/yr at a station in the trench. The sedimentation fluxes of excess 210Pb and excess 230Th in the study area were also the largest in the trench and one to two orders of magnitude larger than their deposition fluxes predicted if all the nuclides are removed only from the overlying water column. This higher fluxes are partly due to the so-called boundary scavenging effect, namely the accelerated removal process at the boundary, but mostly due to the sporadic events of sliding of sediments once deposited on the shallower seabed.View full abstractDownload PDF (2991K) -
Andrew Turek, Cheong-Bin Kim1996 Volume 30 Issue 4 Pages 231-249
Published: August 20, 1996
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSThe Korean peninsula is part of the Sino-Korean platform and is composed of Precambrian to Holocene rocks. It can be divided into three cratonic blocks, the Nangrim massif of North Korea, and the Gyeonggi and Ryeongnam massifs of South Korea. The Precambrian rocks in the Ryeongnam massif are dominantly plutonic, while in the Gyeonggi massif the metasedimentary rocks are dominant. This Precambrian basement is overlain by Phanerozoic rocks and intruded by Mesozoic plutonic rocks. This study reports U-Pb zircon ages for Precambrian rocks in the southwestern Ryeongnam and southwestern Gyeonggi massifs. The oldest rocks in both massifs belong to the Gneiss complex which is composed of migmatitic and other gneisses, metasedimentary rocks, and mafic plutonic rocks. In the Ryeongnam massif the Gneiss complex is intruded by granite and porphyroblastic orthogneisses. The Kurye granite gneiss has an age of 2120 and 2113 Ma. The Chailbong granite gneiss is younger, having an age of 1923 Ma. The porphyroblastic gneisses were probably emplaced in at least two episodes. The older ones are dated at 1945, 1935, and 1928 Ma, and a younger porphyroblastic gneiss has an age of 1890 Ma. In the Gyeonggi massif the Gneiss complex is intruded by two granite orthogneisses. The Seosan granite gneiss has an age of 1766 Ma and the Hongseong granite gneiss is 687 Ma old. The age for the Hongseong granite gneiss is a lower concordia intercept age, the upper intercept indicates derivation from a ca. 3 Ga protolith.View full abstractDownload PDF (4628K) -
Hajime Mita, Ryusuke Shigematsu, Akira Shimoyama1996 Volume 30 Issue 4 Pages 251-260
Published: August 20, 1996
Released on J-STAGE: April 08, 2008
JOURNAL FREE ACCESSWater-extractable dicarboxylic acids (C3–C9) were detected in sediments of a stratigraphic sequence from Miocene to Pliocene in the Shinjo basin, Japan. Contents of these acids in the sediments ranged from 0.01 to 10 n mol g–1, showing generally succinic acid the most abundant of all. The saturated normal dicarboxylic acids generally showed a decrease in contents with an increase of carbon numbers in their molecular distribution patterns. Unsaturated acids exhibited strong predominance of cis isomer over trans one with the C4 and C5 acids in the lower part of the sequence. Optical isomers of branched dicarboxylic acids, especially, methylsuccinic acid and 2-methylglutaric acid were present in racemic mixtures in the lower part of the sequence. The depth profile of the contents of the saturated normal dicarboxylic acids as well as their molecular distribution patterns was different from that of monocarboxylic acids (C3–C9) in the same sediments (Shimoyama et al., 1991), suggesting different chemical forms of the two kinds of the carboxylic acids in the sediments.View full abstractDownload PDF (2421K)
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