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| index | Vol. 50 | 1 | 2 | 3 | 4 | 5/6 | 7 | 8 | 9 | 10 | 11 | 12 | Japanese Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Geochemical study on the composition and degradation processes of organic matter during early diagenesis: A case study in the sediments from the offshore area of the western part of Hokkaido, Japan
Minako TERASHIMA(retired from Mineral and Fuel Resources Department, GSJ) , Masatoshi KOMIYA(Mineral and Fuel Resources Department GSJ) , Shigeru TERASHIMA(Geochemical Department, GSJ) , Yoshio INOUCHI(Faculty of Science, Ehime University) and Kikuo KATOInstitute for Hydrospheric-Atmospheric Sciences, Nagoya University)
1999
vol. 50 (5/6), P. 307-319
6 figs
Keywords: Japan Sea, organic carbon, nitrogen, sulfur, n-alkane, n-fatty acid, n-alcohol, δ13C
Abstract: Total organic carbon, nitrogen, sulfur, δ13C, n-alkane, n-fatty acid, n-alcohol, and n-hydroxy acid were analyzed within surface sediments and core collected from the offshore area of the eastern part of Hokkaido. The accumulation and degradation processes of organic matter are discussed on the distribution of the organic constituents. Organic constituents of the surface sediments were generaly higher in Okusiri basin and lower in Matsumae plateau. Organic contents in the sediments were consistent with the grain size of sediments, that is, organic contents were larger in clay than in silt. The facts that higher ratios of C/N, lower ratios of L/H, smaller values of δ13C suggest the larger suppry of terrestrial higher plants in Okushiri basin. Though L/H ratios and CPI of n-alkane and n-fatty acid were scattered in the surface sediments, the average values were higher in n-fatty acid than in n-alkane. It is conceivable that the precursor and preservation processes of n-alkane are different from those of n-fatty acid. The vertical distribution of total organic carbon and total nitro-gen contents were fluctuated remarkably in core 1100 and 1217, it is conceivable that the sedimentary conditions altered strikingly with time. Though the total organic carbon and total nitrogen contents of core 1217 were within the approximately similar values, the vertical fluctuation of total sulfur presumably showed the changes of sedimentary conditions. The vertical distributions of n-alkane and n-fatty acid of core 1101 show increasing trend of higher molecular coumpunds with depth, except for the lowest two samples. The results indicate diagenetic changes of organic matter progressed in core sediments. The lowest two samples showed the predominace trend of lower molecular coumpounds in n-alkane and n-fatty acid. It seems that the unstable lower molecular compounds were presurved under anoxic conditions, as up and/or down layer showed the enrichment of organic carbon and sulfur. δ13C of core 1101 and 1217 decrease gradualy with depth. This indicates that the contibution of terrestrial organic matter increased with depth.
Palaeotemperature assessment of the northern Japan Sea using alkenone in the sediment cores
Masatoshi KOMIYA(Mineral and Fuel Resources Department, GSJ)
1999
vol. 50 (5/6), P. 321-327
4 figs
Keywords: alkenone, paleotemperature, Japan Sea, sediment
Abstract: Alkenones were analyzed for the sediment cores collected from the northern Japan Sea, and fluctuation of paleo-SST (paleotemperature) were estimated from their composition. The estimated-SST from the sample near the top of each sediment core is consistent with observed modern SST. The sample collected from northern slope of Matsumae plateau indicates that estimated paleotemperature were relatively high throughout the maximum period of the last glacial time. After that, the paleotemperature were once decreased, and then increased toward the end of the glacial time. This fluctuation pattern generally resembles to the results of the other studies on several core sediments from a southern part of the Japan Sea. The fluctuation of paleotemperature from the sample collected from Japan Basin, north west of Matsumae plateau, is relatively large, and suggesting at different environmental fluctuation at this location.
Biomarkers of various bound forms in Neogene sediments, Yashima, Akita, NE Japan
Masanobu YAMAMOTO(Mineral and Fuel Resources Department GSJ)
1999
vol. 50 (5/6), P. 329-359
20figs, 9tables, 1appendix-fig
Keywords: biomarkers, bound lipids, chemical degradation, NiB desulfurization, Yashima, Akita, Neogene, petroleum source rock
Abstract: Biomarkers were analyzed in various bound fractions released by sequential chemical degradations of sedimentary organic matter in diatomaceous - argillaceous rocks from the Neogene Onnagawa, Funakawa and Tentokuji Formations, Yashima, Akita, NE Japan. Biomarker distributions indicate the contributions of diatoms, dinoflaggelates, higher plants, heterotrophic bacteria and/or cyanobacteria, chemoautotrophic bacteria and anaerobic bacterivorous ciliates to the organic matter in samples. A remarkable difference is observed in the distributions of n-fatty acids and w-hydroxy-n-fatty acids between free and ester-, amide- and glyceride-bound forms. This is attributed to the differences between land and aquatic organic matters in the history of chemical degradations suffered before deposition. High amount of sulfur-bound lipids are encountered characteristically in the samples deposited in anoxic environment. Differences are observed between free and sulfur-bound fractions in the distributions of n-alkanes, acyclic isoprenoids, hopanoids and steroids. These presumably result from the variations of precursor compounds with different functionalities in source organisms. Several source and maturity indicators show different values between free and sulfur-bound forms. Diagenetic changes of some source indicators such as pristane/n-heptadecane likely result from the release of sulfur-bound lipids from higher-molecular-weight organic matter by thermal cracking.
Paleoceanographic controls on the deposition of Neogene petroleum source rocks, NE Japan
Masanobu YAMAMOTO(Mineral and Fuel Resources Department GSJ) , Yoshio WATANABE(Mineral and Fuel Resources Department GSJ) and Mahito WATANABE(Mineral and Fuel Resources Department GSJ)
1999
vol. 50 (5/6), P. 361-376
10figs
Keywords: organic geochemistry, biomarkers, petroleum source rocks, diatomaceous sediments, Onnagawa Formation, Neogene, upwelling, Tohoku Trough, NE Japan
Abstract: Paleoceanographic reconstruction was conducted on the Middle Miocene-Pliocene Tohoku Trough where the petroleum source beds were deposited. The decrease of dinosterane/sterane ratio at 10.5 Ma indicates that both diatoms and dinoflaggelates were abundant during 12-10.5 Ma, and that diatoms became dominant after 10.5 Ma. This suggests that the supply of dissolved silica to surface water became to be constant after 10.5 Ma. High C27/C29 sterane ratio during 9-5 Ma suggests the enhanced productivity. This presumably resulted from intensified local upwelling induced by increased wind stress. The bioturbation degree shows the gradual bottom water oxygenation during 10-6 Ma. This likely resulted from (1) the decreased inflow of Pacific OMZ water by the shallowing of sill depth or (2) the sinking of oxygen-rich water to the deeper part of basin. These suggest a drastic paleoenvironmental change at 9 Ma from the anoxic basin with highly stratified water column to the suboxic basin with circulated water and regional upwelling. Fair to good potential for petroleum source rocks occurs through middle and upper parts of the Onnagawa Formation in Yashima area. The environment where the middle Onnagawa Formation was deposited was a stratified anoxic basin, which favored the preservation of marine organic matter. The upper Onnagawa Formation was deposited in the ventilated basin that was characterized by high primary production due to a local upwelling and relatively reducing benthic water, which accelerated the accumulation of marine organic matter
Origin of unusual hydrocarbon ratio gases in Japan:compositional change due to bacterial degradation
Shun-ichiro IGARI(Geochemistry Department,GSJ)
1999
vol. 50 (5/6), P. 377-381
2 figs, 1 table
Keywords: natural gas, bacterial degradation, unusal hydrocarbon ratio
Abstract: Some natural gases from Niigata, Yamagata and Akita region have unusual hydrocarbon ratios. These "unusual gases" have higher ethane/propane, ethane/n-butane, iso-butane/n-butane and lower propane/iso-butane ratios compared to "normal gases". Igari and Sakata (1988) inferred that the unusual ratios were caused by the chromatographic effect of sediments during migration of the gases. Sakata (1991) and Igari (1998) measured ethane and propane carbon isotopic ratios of natural gases from Niigata and Akita. Igari and Sakata (1992) simulated migration effects using gas chromatograph whose column was packed with various minerals and rocks. The results of these experiments show unusual hydrocarbon ratios arenot caused by chromatographic effect. Especially, for gases from the Kubiki gas field in Niigata, unusual hydrocarbon ratio is inferred to be caused by bacterial degradation
Carbon isotope analysis of natural gas components using a gas chromatograph/combustion/mass specrometer (GC/C/MS)
Nobuyuki KANEKO(Mineral and Fuel Resources Department, GSJ) , Tatsuo MAEKAWA(Geochemistry Department, GSJ) , Shun-ichiro IGARI(Geochemistry Department, GSJ) and Susumu SAKATA(Geochemistry Department, GSJ)
1999
vol. 50 (5/6), P. 383-393
9 figs, 1 table, 1appendix
Keywords: GC/C/MS, carbon isotope, natural gas, carbon dioxide, hydrocarbon, analytical condition
Abstract: Conditions of gas chromatograph/combustion/mass specrometer(MAT252 GC/C) to analyze compound-specific carbon isotope ratio of natural gas components including carbon dioxide and hydrocarbons were examined. Combustion furnace temperature higher than 900℃ was required especially for methane analysis. Appropriate temperature and split ratios of injection were 180℃ and 1/10-1/20, respectively. Amplified signal of m/z 44 of objective peaks must be between 2-7V. On these conditions, standard deviation of standard pure methane gas analyses were 0.08‰. GC temperature and pressure programs for individual gas components were designed to archieve baseline separation of peaks and rapid analyses. By applying this method to natural gas samples, we confirmed very high reproducibility of the isotopic values
Conditions and performance of GC/C/MS for carbon isotopic analyses of high molecular-weight hydrocarbons
Susumu SAKATA(Geochemistry Department, GSJ) , Nobuyuki KANEKO(Mineral and Fuel Resources Department, GSJ) , Masatoshi KOMIYA(Mineral and Fuel Resources Department, GSJ) and Tatsuo MAEKAWA(Geochemistry Department, GSJ)
1999
vol. 50 (5/6), P. 395-404
6 figs, 4 tables
Keywords: carbon isotopic composition, n-alkane, GC/C/MS, analytical chemistry
Abstract: Conditions and performance of GC/C/MS for compound-specific carbon isotopic analyses of high molecular-weight hydrocarbons were examined using the pure reagents of C16 to C34 n-alkanes whose values of d had been determined by conventional techniques. By the method of calibration assigning the d value of carbon dioxide from the mixing volume (external standard), a systematic error (D 〜 -1.0 ‰) was observed for those of the n-alkanes. When assigning the d value of regular C18 n-alkane (internal standard), accuracy of the isotopic analyses was greatly improved, although there remained a trend of drift in which values of D became more negative with the increasing number of carbon in the n-alkanes. When assigning the d value of two (or more) n-alkanes whose retention times were widely apart, the drift disappeared, and high accuracy was obtained from the measurements. Precision for the isotopic analyses was found to improve with the increasing height of peaks in m/z 44 signal traces, and high precision was observed for the analyses in which peaks were higher than 2 V. Under the conditions in this study (with the emission current at 1.00 mA, and the VISC completely opened), the contents of n-alkanes giving a 2 V-peak were 7 to 14 nmol in carbon, with higher contents required for n-alkanes with larger numbers of carbon. By closing the VISC during the measurement, sensitivity for the analysis may increase approximately 2-fold with no deterioration in its accuracy
Evaluation of oil-generation potential on coals from Japan and foreign countries
Yuichiro Suzuki(Mineral and Fuel Resources Department, GSJ) and Keizo Fujii(Faculty of Education, Shizuoka University)
1999
vol. 50 (5/6), P. 405-420
14 figs, 4 tables
Keywords: coal, Japan, source rock potential, Tertiary, biomaker, diterpenoid, conifer, non-marine oil
Abstract: Several coals from Tertiary Basins in Japan, Tertiary and Mesozoic Basins in China and Tertiary Kutei Basin in Indonesia were examined for oil-source rocks. Japanese coals were plotted between type II(exinite) and type III(vitrinite) kerogen evolution paths on van Krevelen diagram. Their property is caused by the degradinite, a maceral on the coal petrography, which has the elementary property of exinite group and which contents has good correlation with H/C and O/C. After these calculated regression formulas, H/C and O/C of the pure vitrinite, i.e.degradinite free, on several Japanese coals were estimated. They were plotted in hydrogen richer area than typical type III pathways. Calorific values and O/C, volatile matter contents and H/C show good correlation respectively, so that the calorific value and volatile matter content cross-plotted diagram was used for evaluation for oil-source rock potentials of Japan, China and Indonesia coals. All Tertiary coals have higher values in volatile matter contents ,which have positive relation with H/C ,than Mesozoic coals in China. These properties of Tertiary coals which are similar as the results on van Krevelen diagram were derived from hydrogen richer original plants materials of Tertiary coals than that of Mesozoic coals. The occurrence of diterpenoids in Japanese coals indicate the contribution of coniferous trees. Diterpenoids were comprised in coals from Gippsland Basin in Australia, where oil from coals is produced. Conifer rich type coals as Gippsland, Basin coals, which have high potentials of oil-generation, are assumed to be widespread in Northern Hemisphere
A new statistical approach to marine gas hydrate resources appraisal
Yoshio Watanabe(Mineral and Fuel Resources Department, GSJ)
1999
vol. 50 (5/6), P. 421-430
3 figs, 2 tables
Keywords: resources assessment, marine gas hydrate, play, probability, statistical method
Abstract: A new approach to statistical resource appraisal method of marine gas hydrate is hypothetically discussed based on the scarce accumulation of actual production wells. On the proposed method, both the existence probability of the gas hydrate deposit and its controlling parameters of volumetric yield of deriving methane gas are statistically dealt. Within the prospecting field given by hydrate stability conditions, the estimated yield will be given by probability distribution curve which enables us to set respective appraisal on geologic, economic, and politic point view. The conventional methods would always give a fixed value based on the linear function of volumetric estimates, which caused the indefinite errors. The proposed method will give the flexibilities of judgement based on the distribution of probabilities of the given estimate by the cumulative probability distribution, with known and controlled error derivatives during the estimate
