南沙海槽南部海区表层沉积物的碳酸盐沉积特征   总被引：5，自引：1，他引：5  

陈忠  古森昌  颜文  刘芳文 《海洋学报》2002,24(5):141-146

南海的深海碳酸盐沉积及溶解作用包含极其丰富的信息,既由于陆源物质供应而关系到陆地风化作用速度及气候问题,又通过海水生产力和碱度涉及大气CO₂含量的变化[1～2].南沙海槽位于加里曼丹岛西北部大陆坡与南沙台阶之间,构造上处在南沙海槽北断裂和南沙海槽南断裂之间的断堑带,南沙台阶有众多的海山、礁盘与槽谷,东南坡直下南沙海槽,其坡度变化为5°47'-2°23'-1°57'[3].研究区为7°Ｎ以南至曾母暗沙浅滩、112°E以东至加里曼丹岛西北大陆坡的海区,本文称之为南沙海槽南部海区.  相似文献   

南海西沙海槽的碳酸盐结壳及其对甲烷冷泉活动的指示意义   总被引：5，自引：3，他引：5  

陈忠  黄奇瑜  颜文  陈木宏  陆钧  王淑红 《热带海洋学报》2007,26(2):26-33

冷泉碳酸盐岩是指示南海北部可能发育天然气水合物的重要证据之一。对在西沙海槽采集到的冷泉碳酸盐结壳颗粒进行了形貌、稳定同位素等的研究,讨论和揭示了冷泉碳酸盐结壳的形成机理及其与甲烷冷泉活动的关系。结果表明,碳酸盐结壳具有多孔结构,冷泉矿物为文石和重晶石,文石呈针状,含量为39.5%—46.6%,重晶石呈矮柱状,含量为15.6%—21.2%,它们均是从流体中沉淀出来的。重晶石的δ34S值为23.47‰—26.32‰,表明硫同位素发生正漂移,属于与冷泉流体有关的成岩成因重晶石。文石的碳同位素轻度亏损,δ13C值为-13.30‰—-29.59‰,主要来源于热解成因气,但结合了少量正常海水的溶解碳,δ18O值为2.32‰—3.74‰,指示碳酸盐结壳形成时的温度为3.5—9.7℃。研究表明,碳酸盐结壳形成于流体活动缓慢的环境,是深部富含Ba2 的甲烷冷泉流体向上排放和喷溢,在近海底遇到向下渗漏的富含SO42-海水,发生缺氧甲烷氧化反应沉淀出文石,流体中剩余的重34S的SO42-与Ba2 形成重晶石,因此,碳酸盐结壳是西沙海槽存在甲烷冷泉活动的证据。研究结果为进一步开展该海域潜在天然气水合物的调查和研究提供了新证据。  相似文献   

冲绳海槽北部CS1孔岩石磁学特征及其早期成岩作用的影响   总被引：2，自引：0，他引：2  

葛淑兰石学法  吴永华李德贵  熊应乾SAITO Yoshi 《海洋学报》2005,27(6):56-64

以2～4cm为间隔，对冲绳海槽北部的CSH1孔岩心（17．36m）进行了岩石磁学研究．根据岩心上部的两个特征火山灰层和浮游有孔虫组合分析建立了钻孔的时间框架，沉积物底部年龄可能为50ka．除了在三个火山灰层和近表层向下的快速降低外，整个钻孔磁学参数的变化甚小，未能反映出50ka来的气候变化．与大多数沉积物不同，该钻孔大多数层位的S值（S=-IRM-0.3T/SIRM，它代表了低矫顽力磁性矿物的含量）小于0.9，指示钻孔沉积物中存在相当比例的高矫顽力磁性矿物．代表性沉积物样品的磁化率-温度（K-T）曲线除了存在580℃磁铁矿的居里温度之外，还显示200-350℃的居里温度，指示样品中存在铁硫化物（胶黄铁矿-磁黄铁矿）．这与加热过程中有刺鼻的臭味、加热后的沉积物变黑对铁硫化物的指示相吻合．自生成因的铁硫化物的存在以及表层磁性参数的快速降低，都明确表明沉积物遭受了早期成岩作用．除了三个火山灰层以外钻孔的其他层位无特征磁学变化，表明沉积物后来受到的改造作用强烈，磁学参数所蕴含的原始气候信号被破坏．在这一系列氧化-还原过程中消耗了沉积物中的有机质和水溶液中的硫酸盐，造成了沉积物中铁、锰元素的重新溶解和沉淀等．  相似文献   

冲绳海槽DGKS9603孔细粒沉积物元素组合特征及其意义   总被引：8，自引：3，他引：8  

熊应乾  刘振夏 《海洋学报》2004,26(2):61-71

通过对冲绳海槽DGKS9603孔柱样高密度取样,提取样品中小于2μm的黏土粒级组分,利用ICP-AES进行常、微量元素含量分析后,再经多种方法处理数据,发现该孔沉积物物源时段分明:距今45～43ka以生物源作用为主,距今43～41ka以火山作用为主,距今41.0～11.2ka以陆源作用为主,距今11.2～0.0ka以生物源作用为主.元素和氧化物含量的垂向变化主要受古气候、古环境变化的影响.DGKS9603孔沉积物元素地球化学特征清晰地记录了E3,YD,H1,LGM,H2,H3,H5七次变冷事件,并表明该孔很可能受到了A,B,C三次火山事件的影响.  相似文献   

A preliminary study on microtextures, structures and mineralizing processes of hydrothermal chimneys in Mariana Trough     

Zhang Deyu 《海洋学报(英文版)》1996,15(4):469-492

Ａ　ｐｒｅｌｉｍｉｎａｒｙ　ｓｔｕｄｙ　ｏｎ　ｍｉｃｒｏｔｅｘｔｕｒｅｓ，ｓｔｒｕｃｔｕｒｅｓ　ａｎｄ　ｍｉｎｅｒａｌｉｚｉｎｇ　ｐｒｏｃｅｓｓｅｓ　ｏｆ　ｈｙｄｒｏｔｈｅｒｍａｌ　ｃｈｉｍｎｅｙｓ　ｉｎ　Ｍａｒｉａｎａ　ＴｒｏｕｇｈＺｈａｎｇＤｅｙ...  相似文献   

A Deep-sea Channel in the Northwestern Mediterranean Sea: Morphology and seismic structure of the Valencia Channel and its surroundings   总被引：2，自引：0，他引：2  

Belen Alonso  Miquel Canals  Alberto Palanques  Jean-Pierre Rehault 《Marine Geophysical Researches》1995,17(5):469-484

The 400 km long Valencia Channel occupies the axis of the Valencia Trough in the Northwestern Mediterranean. Four different types of seismic reflection profiles were used to analyze the morphology and structure of the Valencia Channel with regard to the role played by both margins, Balearic and Iberian, of the Valencia Trough. From a detailed morphoseismic analysis of the Valencia Channel, its upper, middle, and lower courses can be characterized as follows: (1) in the upper course, tributaries are short and only slightly incised, with recent mass-transport deposits occurring on the adjacent continental slopes; (2) in the middle course, the channel deepens, and tributary valleys merge into it; and (3) the lower course begins after a sudden change in the direction of the channel, has a meandering path, is flanked by levees, and is fed by some valleys.During the Pliocene and Quaternary, at least four erosional and filling phases are observed in seismic profiles of the lower course of the Valencia Channel. The varying intensity of mass-transport processes and associated retrogressive slumping, which are related with fluctuations in sediment supply and relative sea-level changes, have played a major role in the formation, maintenance and deepening of the Valencia Channel. In addition to these sedimentary processes, a basement tectonic control and some morphostructural features affect the direction of the Valencia Channel locally.  相似文献   

Oblique rifting in the Havre Trough and its propagation into the continental margin of New Zealand: Comparison with analogue experiments     

Vladimir Benes  Steven D. Scott 《Marine Geophysical Researches》1996,18(2-4):189-201

The Havre Trough is opening by oblique back-arc rifting which is propagating into the continental margin of New Zealand at the Taupo Volcanic Zone. Variations of deformational style along the rift axis have been investigated by comparison with analogue experiments which incorporate brittle and ductile rheologies and are scaled for gravity. Based on the results of the analogue experiments, we present a tectonic model for oblique rifting in the Havre Trough, which involves the rheological contrast between oceanic and continental lithosphere and the oblique geometry of the continental margin of New Zealand with respect to the regional rift trend. The model shows that the continental margin, which is weaker than both oceanic and continental lithosphere, cannot support large shear stresses. The two lithospheres can be decoupled during extensional events along the marginal shear and, depending on the continental margin orientation, this shear can modify the regional stress field. A heterogeneous stress field will rotate normal stresses to be perpendicular or parallel to the margin. As the two lithospheres decouple during extension, the rift grabens and internal faults of the oblique rift system propagate normal to the marginal shear. This model explains the oblique trend of the Havre Trough's tectonic fabric and its relationships to the Vening Meinesz Fracture Zone which represents the oceanic/continental lithospheric boundary.As the Havre Trough rift propagates into the continental margin, rheological differences between oceanic and continental lithosphere result in variations in distribution of strain along the rift axis. Extension of oceanic sub-arc lithosphere is localized into a single rift graben. At the transition into continental rifting, the zone of extension widens into a number of rift grabens forming complex indentations into the margin. This change in deformation style is consistent with analogue experiments as well as other natural examples and results from the contrast in lithospheric rheology and its influence on the process of strain localization.  相似文献   

图像边缘检测方法在地震剖面同相轴自动检测中的应用研究   总被引：4，自引：2，他引：4       下载免费PDF全文

李红星  刘财  陶春辉 《地球物理学进展》2007,22(5):1607-1610

为了提高地震剖面的信噪比和分辨率,使同相轴容易识别和追踪,便于地震资料解释,应用图像边缘检测方法检测地震剖面的同相轴.通过对比各种边缘检测方法对地震剖面的边缘检测效果,确定使用Canny算子对地震剖面进行边缘检测.但边缘检测的结果是灰度突变区域的包络线,并不能直接作为同相轴检测结果.根据地层反射同相轴灰度值较大这一特性,提取强灰度包络线的中轴作为同相轴的检测追踪结果,得到了正确的同相轴检测结果.并经过消除检测结果中的斑点边缘后,使同相轴显示更加清晰.  相似文献   

Peak earthquake response of structures under multi-component excitations     

Zach Liang  George C. Lee 《地震工程与工程振动(英文版)》2007,6(4):357-370

Accurate estimation of the peak seismic responses of structures is important in earthquake resistant design. The internal force distributions and the seismic responses of structures are quite complex, since ground motions are multi- directional. One key issue is the uncertainty of the incident angle between the directions of ground motion and the reference axes of the structure. Different assumed seismic incidences can result in different peak values within the scope of design spectrum analysis for a given structure and earthquake ground motion record combination. Using time history analysis to determine the maximum structural responses excited by a given earthquake record requires repetitive calculations to determine the critical incident angle. This paper presents a transformation approach for relatively accurate and rapid determination of the maximum peak responses of a linear structure subjected to three-dimensional excitations within all possible seismic incident angles. The responses can be deformations, internal forces, strains and so on. An irregular building structure model is established using SAP2000 program. Several typical earthquake records and an artifi cial white noise are applied to the structure model to illustrate the variation of the maximum structural responses for different incident angles. Numerical results show that for many structural parameters, the variation can be greater than 100%. This method can be directly applied to time history analysis of structures using existing computer software to determine the peak responses without carrying out the analyses for all possible incident angles. It can also be used to verify and/or modify aseismic designs by using response spectrum analysis.  相似文献   

Spatial-temporal changes of Tianjin urban spatial morphology from 1978 to 2004     

CAI Bofeng  ZHANG Zengxiang  LIU Bin  ZHOU Quanbin 《地理学报》2007,17(4):500-510

Taken fractal dimension, compact ratio, urban centroid and urban principal axis as the urban spatial characteristic indices, Tianjin city’s urban area is investigated in the last 26 years in a quantitative perspective, and its traits and changes during different periods are also analyzed. It is clear that these indices can not only scientifically and explicitly assess the urban morphology, urban direction and its changes and trends, but also uncover long-term effects of economy and urban planning on urban morphology.  相似文献