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QIN Zhiliang,WU Shiguo,WANG Dawei,LI Wei,GONG Shaojun,MI Lijun,SPENCE George. 2015. Mass transport deposits and processes in the north slope of the Xisha Trough, northern South China Sea. Acta Oceanologica Sinica, 34(9):117-125
Mass transport deposits and processes in the north slope of the Xisha Trough, northern South China Sea
南海北部西沙海槽北侧陆坡块体搬运沉积体系的发育特征及演化
Received:September 23, 2014  Revised:December 16, 2014
DOI:10.1007/s13131-015-0608-9
Key words:South China Sea  mass transport deposits  submarine slides  gravity flow  deepwater channel system
中文关键词:  南海  块体搬运沉积体系  海底滑坡  重力流  深水水道体系
基金项目:
Author NameAffiliationE-mail
QIN Zhiliang Tianjin Research Institute for Water Transport Engineering, Ministry of Transport, Tianjin 300456, China  
WU Shiguo Laboratory of Marine Geophysics and Deep Sea Georesource, Sanya Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China swu@sidsse.ac.cn 
WANG Dawei Laboratory of Marine Geophysics and Deep Sea Georesource, Sanya Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China  
LI Wei Laboratory of Marine Geophysics and Deep Sea Georesource, Sanya Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China  
GONG Shaojun Tianjin Exploration Center of Marine Geology, Tianjin 300170, China  
MI Lijun Department of Exploration, China National Offshore Oil Corporation, Beijing 100010, China  
SPENCE George School Earth & Ocean Sciences, University of Victoria, Victoria, V8p 5c2, Canada  
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Abstract:
      Triple mass-transport deposits (MTDs) with areas of 625, 494 and 902 km2, respectively, have been identified on the north slope of the Xisha Trough, northern South China Sea margin. Based on high-resolution seismic reflection data and multi-beam bathymetric data, the Quaternary MTDs are characterized by typical geometric shapes and internal structures. Results of slope analysis showed that they are developed in a steep slope ranging from 5° to 35°. The head wall scarps of the MTDs arrived to 50 km in length (from headwall to termination). Their inner structures include well developed basal shear surface, growth faults, stepping lateral scarps, erosion grooves, and frontal thrust deformation. From seismic images, the central deepwater channel system of the Xisha Trough has been filled by interbedded channel-levee deposits and thick MTDs. Therefore, we inferred that the MTDs in the deepwater channel system could be dominated by far-travelled slope failure deposits even though there are local collapses of the trough walls. And then, we drew the two-dimensional process model and threedimensional structure model diagram of the MTDs. Combined with the regional geological setting and previous studies, we discussed the trigger mechanisms of the triple MTDs.
中文摘要:
      调查发现,在南海北部西沙海槽北侧陆坡地区发育了三组块体搬运沉积体系(MTDs),其面积分别为625km2,494km2和902km2。根据对研究区周缘高分辨地震反射资料和多波束地形资料的解释,这些第四系MTDs具有典型的块体搬运表面形态特征和内部结构特征。该区地形坡度分析结果显示,MTDs分布于西沙海槽北侧陆坡的陡坡区,坡度范围为5°-35°,MTDs从后壁陡崖向下陆坡的搬运距离长达50km。内部结构单元主要包括了底部剪切面、生长断层、阶梯状陡崖、侵蚀沟槽和前端逆冲变形几个部分。文章通过主要地震剖面的精细解释发现,西沙海槽沉积地层为水道-堤坝沉积和较厚的MTDs事件型沉积互层构成。因此,尽管这三组MTDs为陆坡区的局部失稳现象,文章认为其仍然是控制西沙海槽水道沉积体系的主要因素。此外,通过对地形和地震资料的联合解释,给出了该研究区MTDs的二维发育过程模型和三维立体结构模型,结合区域地质背景和前人研究成果,探讨了该区MTDs的形成机理。
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