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1.
硫酸盐-甲烷转换带(SMTZ)是海洋富甲烷沉积环境中重要的生物地球化学分带,其内发生的甲烷厌氧氧化反应(AOM)通常能影响多种自生矿物(碳酸盐类、黄铁矿、重晶石和石膏等)的形成过程。本文选取南海东北部天然气水合物赋存区GMGS2-16站位的58个沉积物样品,对其中发育的自生矿物进行了类型、含量、分布、显微形貌和稳定同位素研究。GMGS2-16站位岩心沉积物中主要发育碳酸盐类、黄铁矿和石膏3类自生矿物,亦发现单质硫颗粒的存在。自生矿物含量分布变化较大,存在多个富集层位。自生碳酸盐类均为块状,具极负的δ~(13 )C值(-37.3‰~-51.7‰VPDB)和较重的δ~(18 )O值(3.13‰~4.95‰VPDB),指示其为甲烷碳源,即AOM成因。自生黄铁矿主要呈不规则块状、棒状-管状和生物充填状,δ~(34 )S值变化范围为-41.7‰~27.1‰VCDT,其中δ~(34)S值异常正偏很可能与大量甲烷流体上涌至SMTZ内加强AOM反应有关。多层AOM成因的自生碳酸盐类与δ~(34)S值异常的自生黄铁矿产出层位基本吻合,共同指示了研究站位曾发生过多期次甲烷渗漏事件,可能与研究站位天然气水合物藏失稳存在一定联系。自生石膏主要呈棱柱状和透镜状,偶见黄铁矿-石膏共生体,初步推测自生石膏可能与水合物形成过程中的排离子效应和(或)沉积环境氧化还原条件改变导致的黄铁矿氧化有关。因此,海洋沉积物中碳酸盐类-黄铁矿-石膏自生矿物组合对探讨古海洋甲烷渗漏事件和天然气水合物藏的演化具有重要指示意义。 相似文献
2.
天然气水合物目前已经成为世界范围的一个研究热点，而我国的天然气水合物研究起步则相对较晚，通过阅读国内外有关文献，总结了天然气水合物在海底的分布特征，聚集和形成机制，产状及其形成机理，甲烷羽的形成过程，天然气水合物在沉积物中的聚集位置通常有两种情况：一是较浅的沉积物（海底以下几米）中，受控于泥底辟，泥火山，断层等；二是较深的沉积物（海底以下几十米，甚至更深）中，受控于流体，当断层延伸至海底时，通常在水合物聚集处的上部发现甲烷羽，天然气以溶解气，游离气或分子扩散的形式运移，在温，压适宜的沉积物中，即水合物稳定带内聚集并形成水合物，水合物的形成过程是：最初形成晶体，呈分散状分布于沉积物中，之后逐渐聚集，生长成结核状，层状，最后形成块状，在细粒的浅层沉积物中，通常以较慢的速度生长，形成分散状的水合物；而在粗粒沉积物中，水合物通常呈填隙状，并且这种产状可能位于较深层位中，我国南海在温度，压力，构造条件，天然气来源等方面都能满足天然气水合物的形成条件，并且在南海也发现了一些水合物存在的标志，如似海底反射层（BSR）以及孔隙水中氯离子浓度的降低。因此，天然气水合物在我国南海海域可能有很好的前景。 相似文献
3.
海底天然气渗漏是海洋环境中广泛分布的自然现象,在世界各大洋中都有发现。海底渗漏可以极大地改变海底地貌特征,形成多种与之相关的微地貌类型。海底渗漏和天然气水合物的赋存具有密切的关系,海底渗漏区常伴有埋藏浅、饱和度高的天然气水合物。对南海东北部陆坡海域浅地层剖面、多波束测深和地震反射剖面等资料进行综合研究,识别出海底麻坑、海底丘状体、大型海底圆丘、泥火山等与海底天然气渗漏有关的微地貌类型,且麻坑、海底丘状体／大型海底圆丘、泥火山微地貌分别代表了浅覆盖层快速天然气渗漏、浅覆盖层中等速度天然气渗漏和厚覆盖层快速天然气渗漏3种天然气渗漏模式。以海底丘状体微地貌及声空白反射特征的浅层天然气聚集带,成为块状水合物最理想的发育场所,这可能成为南海北部陆坡勘察块状水合物的重要识别标志。 相似文献
4.
南海东北部陆坡海底微地貌特征及其天然气渗透模式 总被引：1，自引：0，他引：1
海底天然气渗漏是海洋环境中广泛分布的自然现象,在世界各大洋中都有发现。海底渗漏可以极大地改变海底地貌特征,形成多种与之相关的微地貌类型。海底渗漏和天然气水合物的赋存具有密切的关系,海底渗漏区常伴有埋藏浅、饱和度高的天然气水合物。对南海东北部陆坡海域浅地层剖面、多波束测探和地震反射剖面等资料进行综合研究,识别出海底麻坑、海底丘状体、大型海底圆丘、泥火山等与海底天然气渗漏有关的微地貌类型,且麻坑、海底丘状体/大型海底圆丘、泥火山微地貌分别代表了浅覆盖层快速天然气渗漏、浅覆盖层中等速度天然气渗漏和厚覆盖层快速天然气渗漏3种天然气渗漏模式。具有海底丘状体微地貌及声空白反射特征的浅层天然气聚集带,成为块状水合物最理想的发育场所,这可能称为南海北部陆坡勘察块状水合物的重要识别标志。 相似文献
5.
《海洋地质与第四纪地质》2017,(6)
自生黄铁矿是渗漏甲烷发生甲烷厌氧氧化和硫酸盐还原作用的产物之一,是海底甲烷渗漏活动的有效示踪剂。南海神狐海域是我国天然气水合物研究的重点区域,对神狐海域柱状沉积物中自生黄铁矿含量、分布、形貌等特征进行研究,结果发现自生黄铁矿的含量随深度增加而递增,存在两个异常富集峰段:在第一个黄铁矿富集峰段,黄铁矿以长条状为主,外形较粗,微晶形态以草莓状黄铁矿为主,且粒径均一;在第二个峰段主要以细长的条状黄铁矿为主,由带外壳结构的草莓球颗粒组成,晶粒大小不一,存在二次生长现象。另外还发现胶黄铁矿与自生黄铁矿共生。这些特征反映神狐海域沉积物中存在多期次的甲烷渗漏事件,高通量的甲烷渗漏发生在较浅的层位,可能发生甲烷的有氧氧化而变成缺氧环境,有利于黄铁矿富集在第一个峰段;较低的甲烷渗漏发生在较深的层位,甲烷厌氧氧化和硫酸盐还原作用而形成大量的黄铁矿保存在第二个峰段。因此,神狐海域沉积物中自生黄铁矿的异常富集可以作为地质历史时期甲烷渗漏通量和期次的指示矿物之一。 相似文献
6.
X-射线衍射和扫描电镜观察表明,采自南海北部琼东南盆地的沉积物样品中有天然气水合物和甲烷渗漏指示意义的自生碳酸盐、硫酸盐和草莓状framboids黄铁矿,自生矿物组合和显微结构特征与冷泉沉积物类似,属微生物成因。沉积物孔隙水化学组分分析结果显示,随着埋藏深度加深,SO42-,Ca2+,Mg2+和Sr2+浓度明显降低,Mg2+浓度与Ca2+浓度和Sr2+浓度与Ca2+浓度的比值急剧增加,这些地球化学特征与世界上天然气水合物产区的浅表层沉积物孔隙水中离子浓度异常吻合较好,暗示采样站位深部可能有油气或天然气水合物藏。 相似文献
7.
西沙海槽潜在天然气水合物成因及形成地质模式 总被引：10，自引：0，他引：10
西沙海槽具备良好的热解成因气及断层通道、深部异常压力等运移条件,分析海底表层沉积物所含甲烷气来源可以很好地指示潜在天然气水合物成因.西沙海槽海底表层沉积物所含甲烷气以热解成因气为主,可能混有少量生物成因气.表层沉积物所含甲烷气为断层渗逸-自由扩散作用双重运移结果,主要有3种来源：（1）直接来自于下部断层通道中气态烃的释放;（2）来自于动态变化的水合物分解,再由渗滤作用或沿浅部微小断层向上运移;（3）来自于原地少量的生物气.不同地区有不同的气体来源,这是海底表层沉积物甲烷高值区与下部断层相关性较大而与BSR区域并非完全一致的原因.甲烷气来源及运聚条件综合分析表明,潜在天然气水合物以热解成因为主,为断层-渗滤综合地质模式. 相似文献
8.
对南海北部陆坡柱状沉积物样品总有机碳、总硫含量,以及其中的自生黄铁矿形貌、含量进行分析．结果显示,沉积物中黄铁矿（FeS2）、总有机碳（TOC）、总硫（TS）的质量分数分别为0～0,71％、0．37％～1．18％、0．04％～0．81％;黄铁矿和总有机碳、总硫的含量随深度加深逐渐增大,达到峰值后不断减少,三者的分布趋势基本一致;扫描电镜下观察到黄铁矿主要以莓球状集合体和八面体微晶形貌产出,局部层位亦发现管状、生物内膜状和立方体状黄铁矿晶体．表明该区浅表层环境为缺氧环境,硫化物主要以黄铁矿形式产出,其成因与有机质的厌氧氧化作用有关,而甲烷的厌氧氧化作用也可能促使自生黄铁矿的加速形成．莓球状黄铁矿占主导亦指示一种强还原性的缺氧微环境．黄铁矿富集的缺氧环境与下伏地层中天然气水合物分解释放的甲烷有关,为天然气水合物在该区的勘探提供一定的科荤依据． 相似文献
9.
10.
用地球化学方法勘查中国南海的天然气水合物 总被引：7，自引：0，他引：7
天然气水合物是一种未来新型能源,赋存于低温高压环境下的海洋沉积物中,但也可形成于大陆永久冻土带中。天然气水合物资源量巨大,具有经济和环境上的研究意义。近年来,国际上己对天然气水合物的产况、分布和形成机理开展了大量研究,但国内这方面的工作还刚刚开展。对中国南海的调查表明该区存在天然气水合物赋存的有利地质条件、温压条件和富含有机质的沉积条件。在南海的许多海区还发现了指示天然气水合物存在的地震标志(BSR)。介绍了在南海天然气水合物勘查中的地球化学异常标志。这些地球化学异常的产生可能与天然气水合物的形成或分解过程有关。研究内容包括沉积物中气体含量(主要为甲烷和乙烷),甲烷的碳同位素,孔隙水中阴离子(Cl^-、SO4^2-等)、阳离子(Ca^2 、Mg^2 、Ba^2 、Sr^2 ,B^3 和NH4^ 等)浓度和δ^18,δD,δ^11B,及^87Sr／^86Sr等同位素组成,此外还对海底沉积物的热释光特征和紫外、可见、近红外反射光谱特征开展了探索性研究。通过进一步加强理论和实验研究,结合地球物理和地球化学资料,在不远的将来将会在南海发现和圈定天然气水合物矿藏。 相似文献
11.
南海神狐海域沉积物自生黄铁矿和石膏S同位素特征及对甲烷渗漏强度的示踪 总被引：1，自引：1，他引：0
The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments.Anaerobic oxidation of methane(AOM) coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment,including pyrite and gypsum.Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor(cmbsf) in the entire core sediment of HS328 from the northern South China Sea.Most pyrites are tubes consisting of framboidal cores and outer crusts.Gypsum aggregates occur as rosettes and spheroids consisting of plates.Some of them grow over pyrite,indicating that gypsum precipitation postdates pyrite formation.The sulfur isotopic values(δ~(34) S) of pyrite vary greatly(from –46.6‰ to –12.3‰ V-CDT) and increase with depth.Thus,the pyrite in the shallow sediments resulted from organoclastic sulfate reduction(OSR) and is influenced by AOM with depth.The relative high abundance and δ~(34) S values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone(SMTZ).The sulfur isotopic composition of gypsum(from–25‰ to –20.7‰) is much lower than that of the seawater sulfate,indicating the existence of a 34 S-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR.Pyrite oxidation is controlled by ambient electron acceptors such as MnO_2,iron(Ⅲ) and oxygen driven by the SMTZ location shift to great depths.The δ~(34) S values of gypsum at greater depth are lower than those of the associated pyrite,revealing downward diffusion of 34 S-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate.These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral,which will be favor to the formation of gypsum.Overall,the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities,and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage. 相似文献
12.
Submersible investigations with the ROV Victor 6000 of some pockmark structures on the seafloor of the Congo deep-sea fan
have shown that they are active venting sites of methane-rich fluids, associated with abundant fauna and carbonate crusts.
Moreover, methane hydrates have been observed both outcropping and deep in the sediments in the centre of the “Regab” giant
pockmark. Authigenic carbonates, mostly calcite sometimes mixed with aragonite, are cementing the sedimentary matrix components
and fauna; diatoms are abundant but only as moulds, indicating that biogenic silica dissolution occurred in situ synchronous
with carbonate precipitation. The occurrence of diagenetic barite and pyrite in some carbonate crusts demonstrates that they
can be formed either within the sulphate/methane transition zone or deeper in sulphate-depleted sediments. The oxygen isotopic
compositions of the diagenetic carbonates (3.17–6.01‰ V-PDB) indicate that precipitation occurred with bottom seawater mixed
with a variable contribution of water from gas hydrate decomposition. The very low carbon isotopic compositions of the diagenetic
carbonates (−57.1 to −27.75‰ V-PDB) demonstrate that carbon derives mostly from the microbial oxidation of methane. 相似文献
13.
Variations of methane induced pyrite formation in the accretionary wedge sediments offshore southwestern Taiwan 总被引：4，自引：0，他引：4
Yee Cheng Lim Saulwood Lin Tsanyao Frank Yang Yue-Gau Chen Char-Shine Liu 《Marine and Petroleum Geology》2011,28(10):1829-1837
The accretionary wedge of offshore southwestern Taiwan contains abundant deposits of gas hydrate beneath the sea floor. High concentrations of methane in pore waters are observed at several locations with little data concerning historical methane venting available. To understand temporal variation of methane venting in sediments over geologic time, a 23-m-long Calypso piston core (MD05-2911) was collected on the flank of the Yung-An Ridge. Pore water sulfate, dissolved sulfide, dissolved iron, methane, sedimentary pyrite, acid volatile sulfide, reactive iron, organic carbon and nitrogen as well as carbonate δ13C were analyzed.Three zones with markedly different pyrite concentration were found at the study site. Unit I sediments (>20 mbsf) were characterized with a high amount of pyrite (251–380 μmol/g) and a δ13C-depleted carbonate, Unit II sediments (15–20 mbsf) with a low pyrite (15–43 μmol/g) and a high content of iron oxide mineral and Unit III sediments (<10 mbsf) by a present-day sulfate–methane interface (SMI) at 5 m with a high amount of pyrite (84–221 μmol/g) and a high concentration of dissolved sulfide.The oscillation records of pyrite concentrations are controlled by temporal variations of methane flux. With an abundant supply of methane to Unit I and III, anaerobic methane oxidation and associated sulfate reduction favor diagenetic conditions conducive for significant pyrite formation. No AOM signal was found in Unit II, characterized by typical organically-limited normal marine sediments with little pyrite formation. The AOM induced pyrite formation near the SMI generates a marked pyrite signature, rendering such formation of pyrite as a useful proxy in identifying methane flux oscillation in a methane flux fluctuate environment. 相似文献
14.
《Marine Geology》2005,216(4):265-274
Magnetic susceptibility measurements on near-surface sediment cores from the North Cascadia accretionary sedimentary prism show that seismic blanking or wipe-out zones in the upper few hundred metres of sediments are associated with a prominent low magnetic susceptibility signature. Seismic blanking and low magnetization are both attributed to high upward methane flux within a vent zone, as evidenced by the presence of massive gas hydrate within the cores. Sedimentological analysis of these cores also reveals the presence of authigenic pyrite within the areas of magnetic susceptibility lows. This phenomenon is suspected to be produced by the reducing environment associated with the high upward methane flux and increased bacterial activity within the topmost sediments, resulting in diagenesis of highly magnetic detrital minerals such as magnetite into nearly non-magnetic pyrite. These low magnetic susceptibility zones may produce magnetic anomalies with a magnitude of 10–35 nT near the seafloor. Such anomalies might be detected using high-resolution near-bottom magnetometers to provide a means of mapping zones of methane venting. 相似文献
15.
海底甲烷缺氧氧化与冷泉碳酸盐岩沉淀动力学研究进展 总被引：9，自引：0，他引：9
海底缺氧带甲烷氧化作用是一个重要的甲烷生物地球化学过程,已被许多地球化学现象所证实。甲烷缺氧氧化有效地减少了渗漏到海水和大气中的甲烷通量,但目前仅有的数据还不能很好地限定甲烷缺氧氧化在全球甲烷循环和全球碳循环中的作用。甲烷缺氧氧化的机理还存在争议,很可能是一个“反甲烷生成”过程。在许多天然气渗漏发育区域,由于甲烷缺氧氧化作用引起环境碱度的增加而沉淀冷泉碳酸盐岩,在海底表层沉积物中形成块状碳酸盐岩结壳。但冷泉碳酸盐岩生成所需的物理化学和生物地球化学条件在很大程度上还不清楚。数值计算表明,孔隙水中溶解足够量的甲烷、冷泉渗漏强度适中、较小的生物扰动作用有利于冷泉碳酸盐岩的生成,而过高的沉积速率则抑制冷泉碳酸盐岩结壳的生成。因此,海底发育冷泉碳酸盐岩可以指示天然气渗漏系统的演化特征。 相似文献
16.
Irina Popescu Gilles Lericolais Nicolae Panin Marc De Batist Hervé Gillet 《Geo-Marine Letters》2007,27(2-4):173-183
This study is a synthesis of gas-related features in recent sediments across the western Black Sea basin. The investigation
is based on an extensive seismic dataset, and integrates published information from previous local studies. Our data reveal
widespread occurrences of seismic facies indicating free gas in sediments and gas escape in the water column. The presence
of gas hydrates is inferred from bottom-simulating reflections (BSRs). The distribution of the gas facies shows (1) major
gas accumulations close to the seafloor in the coastal area and along the shelfbreak, (2) ubiquitous gas migration from the
deeper subsurface on the shelf and (3) gas hydrate occurrences on the lower slope (below 750 m water depth). The coastal and
shelfbreak shallow gas areas correspond to the highstand and lowstand depocentres, respectively. Gas in these areas most likely
results from in situ degradation of biogenic methane, probably with a contribution of deep gas in the shelfbreak accumulation.
On the western shelf, vertical gas migration appears to originate from a source of Eocene age or older and, in some cases,
it is clearly related to known deep oil and gas fields. Gas release at the seafloor is abundant at water depths shallower
than 725 m, which corresponds to the minimum theoretical depth for methane hydrate stability, but occurs only exceptionally
at water depths where hydrates can form. As such, gas entering the hydrate stability field appears to form hydrates, acting
as a buffer for gas migration towards the seafloor and subsequent escape. 相似文献
17.
C. K. Paull P. G. Brewer W. Ussler E. T. Peltzer G. Rehder D. Clague 《Geo-Marine Letters》2002,22(4):198-203
The scientific community is engaged in a lively debate over whether and how venting from the gas-hydrate reservoir and the Earth’s climate is connected. The various scenarios which have been proposed are based on the following assumptions: the inventory of methane gas-hydrate deposits is locally enormous, the stability of marine gas-hydrate deposits can easily be perturbed by temperature and pressure changes, enough methane can be released from these deposits to contribute adequate volumes of this isotopically distinct greenhouse gas to alter the composition of oceanic or atmospheric methane reservoirs, and the mechanisms exist for the transfer of methane from deeper geologic reservoirs to the ocean and/or atmosphere. However, some potential transfer mechanisms have been difficult to evaluate. Here, we consider the possibility of marine slumping as a mechanism to transfer methane carbon from gas hydrates within the seafloor into the ocean and atmosphere. Our analyses and field experiments indicate that large slumps could release volumetrically significant quantities of solid gas hydrates which would float upwards in the water column. Large pieces of gas hydrate would reach the upper layers of the ocean before decomposing, and some of the methane would be directly injected into the atmosphere. 相似文献
18.
C. K. Paull W. Ussler III T. Lorenson W. Winters J. Dougherty 《Geo-Marine Letters》2005,25(5):273-280
Gas hydrates are common within near-seafloor sediments immediately surrounding fluid and gas venting sites on the continental
slope of the northern Gulf of Mexico. However, the distribution of gas hydrates within sediments away from the vents is poorly
documented, yet critical for gas hydrate assessments. Porewater chloride and sulfate concentrations, hydrocarbon gas compositions,
and geothermal gradients obtained during a porewater geochemical survey of the northern Gulf of Mexico suggest that the lack
of bottom simulating reflectors in gas-rich areas of the gulf may be the consequence of elevated porewater salinity, geothermal
gradients, and microbial gas compositions in sediments away from fault conduits. 相似文献
19.
Xiang Rong Li Tiegang Yang Zuosheng Yan Jun Cao Qiyuan College of Marine Geosciences Ocean University of China 《海洋学报(英文版)》2003,(1)
Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to the bottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corresponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, dominated by Cassidulina carinata , Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispi-da, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4) lower continental slope- trough b 相似文献
20.
Multichannel seismic reflection data from the continental margin of western India suggest the potential presence of fluid
expulsion features, which may or may not be associated with gas hydrates. No typical bottom simulating reflector was observed
on the reflection seismic section. As a result we look for other evidence in seismic sections in a small corridor of the western
continental margin of India in order to establish the presence of gas hydrates. We study features including venting through
the seafloor, pockmarks, sea floor collapse, faults acting as migration paths for fluid flow, transparent gas-charged sediment,
reduction in amplitude strength, diapirism and mud-volcano. Presence of all these gas-escape features on a seismic section
implies the probable presence of methane within the zone of hydrate stability field. 相似文献