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《Geotectonica Et Metallogenia》 2008-02
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CENTER OF LATE TRIASSIC SUBSIDENCE AND DEPOCENTER FOR THE SOUTHERN ORDOS BASIN

CAO Hongxia1,LI Wenhou1,CHEN Quanhong2,XIAO Li1, WANG Lishe1,3,BU Jun1 and LIU Zhengwei4 (1.State Key Laboratory of Continental Dynamics of Ministry of Education, Northwest University, Xi'an 710069, Shaanxi, China; 2.CNOOC Research Center, Beijing 100027; 3.Xi'an Geological Survey Center, Xi'an 710054, Shaanxi,China; 4.No.1 Oil Producing Plant, Changqing Oil Field Company, Yan'an 716500, Shaanxi,China)  
From the angle of recovering palaeogeomorphology, according to the theory of impression way of remnant thickness and bucking thickness, the thickness of early Late Triassic paleo-formation is recovered and depocenter is confirmed. In terms of the average value of the grade moment method, the grades of same well location and stratigraphic position are averaged out,then projecting these data in a plane figure to obtain the plane isogram of grade mean value.The gathering area of fine-grained clastics of the lake basin reflexed the confluence of palaeocurrents and instructed the depocenters.The results indicate that the depocencer of the Ordos Basin in early Late Triassic lies in the Southwest Majiatan-Baibao-Yijun and Zhenyuan-Chongxin areas. The formation thickness of the basin changed greatly, which shows that in early Late Triassic the differential sagging is obvious and depocenter lies majorly in the range surrounding by Zhengning, Heshui, Jiyuan, Wuqi, Zhidan, Taibai, Huangling and Huanglong, stretching from northwest to southeast. From C10 to C7 of the Yanchang Formation lake strandlines extended along the northwest-southeast axis, and the area of the lake basin had been increasing until the depositional stage of C7 was over. The depocenter of the lake basin changed regularly and the area of the lake basin for every depositional stage changed obviously because of control of tectonic subsidence rate. Moreover, tectonic subsidence rate was biggest during the depositional stage of C7. The ranges of centers of subsidence and depocenters are different. Their migration and coincidence are of importance to the study of the abnormal high value of thermal evolution of source rocks.
【Fund】: 国家重点基础研究发展计划(973计划)项目(2003CB214602);; 长江学者和创新团队发展计划(IRT0559)联合资助.
【CateGory Index】: P512.2
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