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1.
周炼  周红兵  李茉  王峰 《地球科学》2007,32(6):759-766
通过对扬子克拉通古大陆边缘不同时期沉积岩的Mo同位素进行测定,结合Mo微量元素组成,对古大陆边缘Mo的自生作用规律进行了研究,并根据Mo丰度对原始有机碳堆积速率进行了计算.结果表明,其原始有机碳堆积速率在0.17～0.67mmol/m2/day之间.利用已建立的现代大陆边缘δ98Mo与有机碳埋藏速率模型,对该区不同时期沉积岩的有机碳埋藏速率进行恢复.结果表明,扬子克拉通显生宙不同时期沉积岩的有机碳埋藏速率有较大的变化范围(0.43～2.87mmol/m2/day),并与原始有机碳堆积速率具有明显的相关性,因此,δ98Mo有可能成为评价有效烃源岩的潜在指标.  相似文献   

2.
The Late Permian Dalong Formation in Hubei, Hunan, Guizhou and Guangxi in South China could be subdivided into several sedimentary types according to the lithology, indicative of the great spatial variations of both the lithology and sedimentary facies. The Dalong Formation deposited during the highest transgression of Late Permian, in particular under the anaerobic and suboxic conditions, which shows a strong linkage with the hydrocarbon source rocks. The Dalong Formation has some favorable properties such as hydrocarbon source rocks, including the sediments deposited in highest transgression sea level, the deep slope sedimentary environments and the low sedimentary rate, which raises the importance of the investigations on the sedimentary features, the geochemical properties and their relationship with the oil potential. __________ Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 774–780 [译自: 地球科学—中国地质大学学报]  相似文献   

3.
On the geobiological evaluation of hydrocarbon source rocks   总被引：1，自引：0，他引：1  
Hydrocarbon source rocks are characterized by the hydrocarbon discharge, and the alteration and variation in organic compositions and organic content due to the enhanced thermal maturation. These variations throw constraints on the application of the conventional inversion evaluation of hydrocarbon potential by assessing the residual organic matter left in source rocks. Geobiology, probing the interaction between the life system and the earth system, provides new principles in deciphering the whole dynamic processes related to the organic evolution history from living biomass to organic burial. Geobiological subdisciplines, including molecular geobiology, geomicrobiology, geoecology and biogeochemistry, offer new methodology and techniques to estimate the paleoproductivity, depositional organics and organic burial capacity and their components. Geobiofacies, newly proposed herein, is terminologized to define the geobiological dynamic processes through the combination of biofacies with organic facies and sedimentary facies, and expressed by the biohabitat types, paleoproductivity, depositional and preserved organics. Geobiofacies is identified as a useful means to create the geobiological evaluation system, which in turn rectifies the conventional evaluation system for the marine source rocks. __________ Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 727–740 [译自: 地球科学—中国地质大学学报]  相似文献   

4.
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5.
The calci-mircobialite is a special carbonate buildup, which is formed due to the activities of different kinds of microbes. Abundant microfossils preserved in the microbialite show the high-level productivity during deposition, while characteristic sedimentary minerals and geochemical compositions suggest an anoxic marine environment for organic burial. The high-level productivity and anoxic sedimentary environment favor the efficient preservation of organic matter and thus the formation of source rocks. On these points, microbialites could be one of the potential hydrocarbon source rocks, awaiting further geobiological investigation and exploration. Precambrian and some of the great transitional stages in Phanerozoic are critical periods when microbialites were well developed. Widespread microbialites have been found in North and South China. Bitumen observed in many outcrops of Precambrian and late Devonian microbialites further raises the possibility of the calci-microbialite as a potential hydrocarbon source rock. __________ Translated from Earth Science-Journal of China University of Geosciences, 2007, 32(6): 797-802 [译自: 地球科学-中国地质大学学报]  相似文献   

6.
By combining the carbon cycle model with the records of carbonate and organic (kerogen) carbon isotope, this paper presents the calculation of the fraction of organic carbon burial (f org) of beds 23–40 at the global boundary stratotype section and point (GSSP) of the Permian-Triassic boundary at Meishan, Zhejiang Province. The resulting calculation produces two episodes of f org maxima observed to occur at beds 23–24 and 27–29, which respectively corresponds to the two episodic anoxic events indicated by the flourish of green sulfur bacteria. Two episodic f org minima occurred at beds 25–26 and 32–34, generally coincident with the flourish of cyanobacteria (bed 26 and upper part of beds 29 to 34) as shown by the high value of 2-melthyhopnoanes. It appears that the f org is related to the redox conditions, with greater f org values observed under the reductive condition. The relationship between f org and the total organic carbon (TOC) content was complex. The f org value was low at some beds with a high TOC content (such as bed 26), while high observed at some beds with a low TOC content (e.g. bed 27). This association infers the important contribution of primary productivity to the TOC content. The original organic burial could be thus calculated through the configuration of the function of the primary productivity and f org, which can be used to correct the residual TOC measured today. This investigation indicates that compiling the organic-inorganic carbon isotopes with the carbon cycle model favors to understand the fraction of organic carbon burial, providing information for the reconstruction of the coupling among biota, environments and organic burial. Journal of China University of Geosciences, 2007, 32(6): 767–773 [译自: 地球科学—中国地质大学学报]  相似文献   

7.
Understanding the dynamics of organic matter in modern marine water columns greatly favors the geobiological evaluation of hydrocarbon source rocks. Biolipids could make great contribution to petroleum hydrocarbons due to their comparable chemical components and the slightly refractory characteristics of biolipids during the microbial/thermal degradation. A variety of environmental factors such as temperature, CO2 and salinity could affect the biochemical contents in microorganisms. As a result, microorganisms living in a changing environmental condition might have a different contribution to the petroleum formation. Organic carbon flux is shown to bear a positive correlation with the primary productivity only within a certain range of biomass volumes in a specific biohabitat. Furthermore, organic matter is degraded much quickly in a water column with oxic conditions. Therefore, the anoxic condition, along with the enhanced biological productivity, would be one of the significant factors in the formation of high-quality hydrocarbon source rocks. The formation of biofilms and microbial mats favors the preservation of sedimentary organic matter by decreasing the degradation rate of organic matter. Identification of biofilms and microbial mats in sedimentary rocks will thus greatly help to understand the depositional processes of organic matter finally preserved in hydrocarbon source rocks. __________ Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 748–754 [译自: 地球科学—中国地质大学学报  相似文献   

8.
Northeast Sichuan basin is a Mesozoic-Cenozoic basin in the northern margin of the Yangtze plate which has a complex tectonic background and hydrocarbon accumulation history. By means of the analysis method of wave processes, major cycles of sedimentary wave process in this basin have been studied. The results show that there are five-order cycles corresponding to 760, 220, 100, 35 and 20 Ma respectively, two first-order sedimentary cycles (220 Ma) and four secondorder sedimentary cycles (100 Ma). The authors find that the second-order sedimentary cycles are well matched with reservoir formation cycles through studying the relationship between second-order sedimentary cycles and reservoir formation cycles, and divide three reservoir formation cycles in this basin. __________ Translated from Journal of Jilin University (Earth Science Edition), 2007, 37(3): 513–518 [译自: 吉林大学学报(地球科学版)]  相似文献   

9.
Metazoan fossils in the Gaojiashan Biota are famous for being well preserved and may provide new insights into the early evolution and skeletonization of Metazoans. We are studying the isotopic compositions of organic and carbonate carbon from a sequence of sedimentary rocks at the Gaojiashan section, northern Yangtze Platform, Shaanxi Province of China. Organic carbon isotope values display a range between –30.8‰ and –24.7‰ with clear stratigraphic variations. Carbonate carbon isotope data vary between 0.1‰ and +6‰. Positive δ13C values from sediments with Gaojiashan biota reflect temporal variations in carbon turnover, i.e. an increasing in photosynthetic carbon fixation followed by an increasing subsequent fractional organic carbon burial, and that related to bio-radiation such as increasing algae, bacteria, and original creatures productivity in biomass. These secular variations are interpreted to reflect perturbations of the regional carbon cycle, specifically changes in the fractional burial of organic carbon, and discuss the relationship between Gaojiashan biota and paleoenvrionmental variation.  相似文献   

10.
To decipher the origin of oxygen-deficient shelfal deposits is significant for tracing the distribution of marine source rocks and interpreting the evolution of depositional environment. The origin of the Middle Permian Chihsia Formation in South China remains a puzzle for long with its evident oxygen-deficient features but diverse benthos. This paper shows a typical Chihsian depositional rhythm composed of the massive and the laminated limestones with ecological and geochemical features. Massive bioclastic limestone from the rhythm was aerobic in paleoxygenation condition indicated by both the ecological and geochemical features. However, a contradictory oxygenation was inferred for the “laminated” counterpart from the rhythm, with the ecological signal being aerobic and the geochemical one being anoxic. The difference in ecological and geochemical indications was interpreted as the instability of paleoxygenation condition in shelf environments, caused by an enhanced paleoproductivity. Rhythmic occurrence of the oxygen-deficient condition might have been stemmed from paleo-Tethyan paleocurrents flowing across South China. __________ Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 789–796 [译自: 地球科学—中国地质大学学报]  相似文献   

11.
The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South China, documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata, exquisitely preserved fossils have been discovered： the Weng＇an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng＇an section of a carbonate platform （shelf of the Yangtze Platform, Guizhou Province） from the Songtao section and Nanming section of a transition belt （slope of the Yangtze Platform, Guizhou Province） and from the Yanwutan section （basin area of the Yangtze Platform, Hunan Province）. Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon （mean δ^13Corg = -35.0‰） from the uppermost Nantuo Formation are followed by an overall increase in δ^13C up-section. Carbon isotope values vary between -9.9‰ and 3.6‰ for carbonate and between -35.6‰ and -21.5‰ for organic carbon, respectively. Heavier δ^13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity （such as the Weng＇an biota）. The δ^13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin, reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.  相似文献   

12.
The redox sensitive elements, molybdenum (Mo) and uranium (U), in marine sediments from the latest Permian Dalong (大隆) Formation at the Shangsi (上寺) Section, Northeast Siehuan (四川), South China, were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine their response to a range of redox conditions, and to estimate the organic carbon burial rate. On the basis of the correlation between authigenic Mo abundance and organic carbon content in modern oceans, the organic carbon burial rates were calculated for the rocks at Dalong Formation, ranging from 0.48-125.83 mmol/(m2-d), which shows a larger range than the mineralization rate of organic carbon at the continental margins (1.6-4.23 mmol/(m2.d)). The Zr-normalized Mo and U abundances show large fluctuations in the entire section. The maxima of Zr-normalized Mo abundance and thus the maxima of the organic carbon burial rates were observed at the interval between the 155th and 156th beds (404-407 m above the base of Middle Permian). A decrease (the minimum) in U/Mo ratios is present in this interval. It is speculated that the oxygen-limited conditions and ultimately anoxia or euxinia may develop within this depth interval. In contrast, an enhanced enrichment of Zr-normallzed U abundance is found, in association with less enrichment in Zr-normnllzed Mo abundance in the interval from the I51st to 154th beds (395-404 m above the base of Middle Permian), inferring the dominance of a suboxic/anoxic depositional condition (denitrifying condition), or without free H2S. The presence of small quantities of dissolved oxygen may have caused the solubilization and loss of Mo from sediments. It is proposed that the multiple cycles of abrupt oxidation and reduction due to the upwelllng at this interval lead to the enhanced accumulation of authigenic U, but less enrichment of Mo. A decrease in the contents of U, Mo, and TOC is found above the 157th bed (407 m above the base of Middle Permian), in association with the enhanced U/Mo ratio, suggesting the overall oxic conditions at the end of the Dalong Formation.  相似文献   

13.
Gravity driven mass-flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western Argentine Basin. In this study we present geochemical data from a total of 23 gravity cores. Pore-water SO4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane (AOM). The different shapes of SO4 profiles (concave, kink- and s-type) can be consistently explained by sedimentary slides possibly in combination with changes in the CH4 flux from below, thus, mostly representing transient pore-water conditions. Since slides may keep their original sedimentary signature, a combined analysis and numerical modeling of geochemical, physical properties, and hydro acoustic data could be applied in order to reconstruct the sedimentary history. We present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day. The results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep-sea, depositing high amounts of reactive compounds. The high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by AOM. For the total region we estimate a SO4 (or CH4) flux of 6.6 × 1010 moles per year into the zone of AOM. Projected to the global continental slope and rise area, this may sum up to about 2.6 × 1012 moles per year. Provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1.2 × 1012 moles per year as previously estimated. Thus, AOM obviously contributes very significantly to the regulation of global sulfur reservoirs, which is hitherto not sufficiently recognized. This finding may have implications for global geochemical models, as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time.  相似文献   

14.
A significant change in composition was recorded in late Oligocene sediments from the northern South China Sea. This abrupt event coincided with the seafloor spreading axis jump across the Oligocene/Miocene boundary, leading to sedimentation breaks and slumps as well as obvious changes in sediment geochemical composition, and representing the greatest tectonic activity in the South China Sea region since the Oligocene. Through this tectonic event, the sedimentary environment in the Baiyun sag area transformed from a continental shelf in the late Oligocene to a continental slope since the early Miocene, the provenance of the sediments changed from neighboring areas to the hinterland of the South China block, and the sea level rose since the early Miocene in the area. Therefore, this abrupt change event has a profound influence on the evolution of petroleum offshore in the northern South China Sea. __________ Translated from Geology in China, 2007, 34(6): 1022–1031 [译自: 中国地质]  相似文献   

15.
边缘海沉积物是海洋重要的碳储库,其内部的碳循环主要是由有机质矿化分解过程来驱动的。有机碳进入边缘海沉积物后,矿化分解为溶解无机碳(DIC)进入沉积物孔隙水并扩散到上层水柱,参与海洋系统碳循环;同时还有部分DIC与钙镁等离子结合形成自生碳酸盐,保存于沉积物碳库。从生物地球化学角度探讨有机质埋藏机制和效率,在此基础上重点综述沉积物硫酸盐还原、产甲烷和甲烷厌氧氧化过程的耦合机制,以及有机质矿化对自生碳酸盐形成的影响等方面的研究进展,以期加深对陆架边缘海沉积物在全球碳循环收支平衡中的作用及其气候环境效应的认识。  相似文献   

16.
Continental margin sediments are important ocean carbon repository, and the internal carbon cycle is mainly driven by the mineralization processes of sedimentary organic matter. Most organic carbon is transformed to Dissolved Inorganic Carbon (DIC) by mineralization processes after being delivered to continental margin sediments, and DIC from pore water diffuses into the upper water column and participates in the ocean carbon cycle. At the same time, some DIC combines ions such as Ca2+ and Mg2+ and precipitates as authigenic carbonate minerals so that carbon is stored in the deposits. Based on the biogeochemical study of the mechanism and efficiency of organic matter burial, we discussed the interaction among sulfate reduction, methanogenesis and anaerobic oxidation of methane, and the effect of organic mineralization on the formation of authigenic carbonate. By reviewing the above-mentioned aspects, we can obtain a better understanding of the role of continental margin sediments in the global carbon cycling budgets as well as its climate and environmental effects.  相似文献   

17.
We have measured U in benthic incubation chambers, sediment pore waters, and in sediments along the California continental margin. Sedimentary U uptake rates, based on a combination of sediment pore water profiles and benthic incubation chambers, generally agree with those predicted from sediment accumulation rate data. This agreement supports the view that most of the continental margin sedimentary U is delivered by diffusion across the seawater-sediment boundary. The average rate of authigenic U accumulation for all the sites examined here is ∼−0.2 nmol cm-2 y-1, which is consistent with published global estimates of sedimentary U uptake. In addition, the accumulation rate of U in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate. These relationships highlight the potential utility for the U accumulation rate as a proxy for these processes.  相似文献   

18.
The stable isotope compositions of sedimentary organic carbon and content of organic carbon for sediment cores recovered at two sites (sites 724C and 725C) during Ocean Drilling Program (ODP) Leg. 117 on the Oman continental margin are used to document variability of the monsoon winds for the past 350 ka. Although both sites have a mean δ13C value of -20.1‰, three zones depleted in13C are observable at site 724C during isotope stages 3, 8 and 10, while only one zone is recognizable at site 725C. Increased coastal upwelling during isotope stage 3 owing to intense SW monsoon winds resulted in higher concentration of CO2 in the water column causing the formation of organic matter that was depleted in13C. The other two zones deposited during oxygen isotope stages 8 and 10, which are also characterized by low values of organic carbon, nitrogen and C/N ratios, could be attributed to the dilution by terrestrial material derived from paleosol by transported by northwester lies. Because of utilization of13C enriched dissolved CO2 during the last glacial maximum Holocene sedimentary organic materials are depleted in13C relative to the the fomer. The content of residues organic carbon (ROC) is higher at site 724C (with an average of 2.3 ± 1.2%) relative to site 725C, which averages to 0.9 ± 0.4% probably because of differences in the degree of preservation. Organic material deposited at site 725C has undergone more degradation relative to site 724C as reflected by a systematic downcore decrease in13C resulting from a loss of13C enriched organic compounds. Owing to lack of good chronology at site 725C, a zone that is characterized by low δ13C values it could not be correlated with the other three zones observed at Site 724C.  相似文献   

19.
To understand the potential mechanism of marine extremophiles participating in the formation and the evolution of hydrocarbon resources in marine extreme environments, some typical kinds of extremophiles and their distributions in marine hydrothermal and cold vents are discussed and evaluated respectively. The potential relationship between extremophile activities and hydrocarbon resources in marine extreme environments are then discussed in details. It could be now preliminary concluded that archaea and bacteria are the two main kinds of extremophiles in marine extreme environments. The dominating microbe communities in hydrothermal vents are heterotrophic zymogens, sulfate reducers and methanogens, while the ANME-2 group (Methanosarcinales) surrounded by sulfate-reducing bacteria and ANME-1 group dominate in cold vents. Marine extremophiles would be able to use CH4 and H2S to synthesize energy for metabolism and to support food chains for other unique macrobiota nearby, which together present a high abundance but a low diversity with distinct characteristics of horizontal and vertical distributions. Marine extremophiles might play an important role either directly or indirectly in the processes of hydrocarbon formation and subsequent alteration, and could indicate the evolution of hydrocarbon resources in marine extreme environments. Our research thus has a great significance both in theoretical approach of potential hydrocarbon resources formed by marine extremophile activities and in practical exploration of the potential hydrocarbonsource sedimentary layers formed in the Earth history or the potential strata in southern China. __________ Translated from Earth Science—Journal of China University of Geosciences, 2007, 32(6): 781–788 [译自: 地球科学—中国地质大学学报]  相似文献   

20.
A petrochemical analysis was undertaken of peridotitic xenoliths in volcanic rocks that erupted from the Paleozoic to the Cenozoic within the eastern part of the North China craton, and the peridotites as tectonic intrusion in the Early Mesozoic from the Sulu orogen. The results show that the cratonic mantle, which was refractory and existed when the kimberlites intruded in the Paleozoic, had almost been replaced by the newly accreted fertile lithospheric mantle during the Mesozoic-Cenozoic. The erosion, metasomatism, and intermingling caused by the accreted asthenospheric material acting on the craton mantle along the weak zone and deep fault (such as the Tanlu fault) in the existing lithosphere resulted in the lithospheric thinning at a larger scale 100 Ma ago (but later than 178 Ma). The largest thinning would be in the Eogene. The upwelling asthenospheric material transformed into accreted lithospheric mantle due to the asthenospheric temperature falling in the Neogene (leading to relatively slight lithospheric incrassation), and finally accomplished mantle replacement. The peridotitic body in the Sulu orogen represents the products spreading from the modified cratonic lithospheric mantle. Translated from Earth Science—Journal of China University of Geosciences, 2006, 31(1): 49–56 [译自: 地球科学—中国地质大学学报]  相似文献   

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