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西沙群岛生物碳酸盐的成因和沉积:来自活体仙掌藻的证据 总被引：1，自引：0，他引：1
A recent island survey reveals that the Xuande Atoll and the Yongle Atoll in the Xisha Islands can be classified into one of two systems: the depleted atoll system and growth atoll system; the survey also indicates that the decreased area of several shoals is an unbearable burden for the Xisha Islands, of which the largest island area is 2.13 km2 and the minimum elevation is 1.4 m. According to a survey on the ecological characteristics of Halimeda in the Laolongtou breaker zone of Shidao Island in the Xisha Islands, the green and white living Halimeda are collected,the isotopic ages of 14 C contained in the Halimeda are shown to be 27 years and 55 years, respectively, and carbonate mainly occurs in five types, i.e., luster, segment, sand, sand grain, and marl in the formation. The Halimeda segments mainly provide the carbonate sediments of long-term biogenic deposits in the reef environment and the annual productivity per area is 60–100 g/m2; the characteristics of the microstructure of the Halimeda are analyzed, the aragonite raphide carbonate is deposited and enriched in the cortexes, medullas and cysts, and the Halimeda generally contain major elements such as C, O, Ca, Cl, Mg, K, Na, S and Al, and are rich in trace elements such as tellurium(Te), rhodium(Rh) and strontium. It is believed that the Halimeda grow slowly,including the biotic community of reef corals in the reef areas, thus they possess an environmental remediation capacity, but it takes much time to remedy the environment, and it is necessary to make the law to protect the diversity and vulnerability of the Xisha marine ecology, the ecology of the reef community and the island environment in a scientific way. As indicated in the survey, under the background of global warming and sea-level rise, the discovery of large amounts of Halimeda in the Laolongtou sea area is significant for the natural increase of the depleted atoll system of the Xuande Atoll, while the Halimeda segments represent the primary form of the fossil Halimeda, of which the species can be identified and preserved in great numbers under geological conditions. The Miocene was discovered in large amounts in the Xichen-1 well, therefore the study on the characteristics and mechanism of Halimeda carbonate sediments plays a pivotal role in the formation and construction of organic reefs in the South China Sea as well as oil and gas exploration. 相似文献
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针对南黄海海域油气勘探缺乏揭示古生界钻井样品资料的窘况,对邻近陆区2个典型露头剖面进行了调查研究。这2个剖面分别为南京幕府山的下古生界寒武系陆相泥岩和安微巢湖的上古生界二叠系海相灰岩,都呈深灰黑色;前者是当前下扬子陆区页岩气勘探重点研究层系;后者出露面积较大,似臭鸡蛋味浓烈,为含硅碳酸盐岩,俗称"臭灰岩"。通过系统油气地球化学测试,证实其均为优质烃源岩;岩石物性测试结果表明,后者还可为优质储集岩。由于古生代下扬子地块具有地台性质,沉积体系向南黄海海区自然延伸沉积,因此,利用这些来自陆区露头地质剖面的珍贵样品推测,二者均可作为南黄海盆地尤其是南部坳陷的潜在主力烃源岩,以期为相应的油气勘探评价提供借鉴。 相似文献
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典型的前陆盆地一般位于造山带和稳定克拉通之间的狭长槽地,而南黄海盆地则主要为华北—扬子地块陆陆碰撞及后期太平洋系构造运动叠加形成的"再生"陆内前陆盆地,因此具有其"特殊性"。虽然南黄海前陆盆地经过多期构造运动叠加改造及破坏,但仍然保存了比较完整的楔顶、前渊、前隆及隆后各带,故划分了各带分布的位置,认为其楔顶沉积带位于千里岩隆起、前渊带位于北部坳陷东北凹、前隆带位于其乳山凸起、隆后沉积带位于乳山凸起与中部隆起间;并从地震、沉积、构造3方面分析了各带的结构构造和沉积特征。 相似文献
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Halimeda is one of the major reef-building algas in the middle Miocene of Xisha, and one of the significant reefbuilding algas in the algal reef oil and gas field of the South China Sea. However, there have been few reports regarding the characteristics of mineral rocks, reservoir porosity and permeability layers, and sedimentationdiagenetic-evolution of fossil Halimeda systems. The present paper briefly introduces the relevant studies on chlorophyta Halimeda and the research status of oil and gas exploration. Through the 1 043 m core of the Xichen-1 well, we studied the characteristics of the mineral rocks and porosity and permeability of the middle Miocene Halimeda of the Yongle Atoll, identified and described the segments of fossil Halimeda, and pointed out that most of the segment slides are vertical sections in ovular, irregular or long strips. The overwhelming majority of these fossil Halimeda found and studied are vertical sections instead of cross sections. In this paper, knowledge regarding the cross sections of fossil Halimeda is reported and proven to be similar with the microscopic characteristics of modern living Halimeda; fossil Halimeda are buried in superposition; it is shown that there are different structures present, including typical bio-segment structure, and due to its feature of coexisting with red alga, tying structure, twining structure and encrusting structure are all present; and finally, it is suggested to classify the fossil Halimeda into segment algal reef dolomites. In addition, all of the studied intervals are moderately dolomitized. Secondary microcrystalline-dolosparite dominates the original aragonite raphide zones,and aphanitic-micrite dolomite plays the leading role in the cortexes and medullas; in the aragonite raphide zones between medulla and cysts, secondary dissolved pores and intercrystalline pores are formed inside the segments, and algal frame holes are formed between segments; therefore, a pore space network system(dissolved pores + intragranular dissolved pores—intercrystalline pores + algal frame holes) is established. Segment Halimeda dolomite has a porosity of 16.2%–46.1%, a permeability of 0.203×10–3–2 641×10–3 μm2, and a throatradius of 23.42–90.43 μm, therefore it is shown to be a good oil and gas reservoir. For the reasons mentioned above, we suggest building the neogene organic reef-modern reef sedimentation-diagenetic-evolution models for the Xisha Islands. 相似文献
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南黄海盆地是中国海域历经54年勘探至今尚未实现工业油气发现的唯一大型含油气盆地,特别是29年前发现的白垩系黑色页岩含轻质油,属于页岩油范畴。分析了南黄海盆地白垩系勘探研究现状,提出白垩系主要分布于盆地北部,有8口井钻遇,K1系红浦口组,K2系黑泰州组,与苏北盆地近似;在最新地震测线上表现为顶蚀,与古/新近系及下伏侏罗系均呈不整合接触,斜层状分布,残留沉积,部分构成次凹的特征。通过近海灵山岛露头调查、剖面实测和包括常规生油岩有机质丰度、类型、成熟度、等离子质谱、U-Pb同位素年龄等测试,发现下白垩统多套深灰黑色含煤泥岩层,发育Ⅰ型和Ⅲ型干酪根,自由烃0.02~0.07mg/g或为零,生油潜力0.06~0.03mg/g或为零,残留有机碳1.85%~1.99%或0.70%~0.84%,氧指数4及超过10,属于2类烃源岩,分别生烃和二氧化碳气。总体认为南黄海盆地白垩系具有一定资源前景,值得开展深入分析。 相似文献
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