Late Paleozoic deep-water stratigraphic succession in central Youjiang basin: constraints on basin evolution
SHI Xiao-ying~ 1,2 , HOU Yu'an~ 1 , SHUAI Kai-ye~ 1 1.School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083,China 2.State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083,China
The Youjiang basin is situated on the SW margin of the Yangtze platform, southwest China, and is one of the important potential oil-gas basins in southern China. The depositional environment of Late Paleozoic sediments can be summarized as four major types: 1)shallow shelf, 2)platform margin to slope, 3)isolated carbonate platform, and 4)deep-water basin. In the above order, these depositional environments have a north to south spatial arrangement, thereby suggesting a marginal sea to oceanic basin framework. In the central parts of the basin, the Upper Paleozoic is characterized by chert, manganese claystone, and pillow basalt, a succession that is quite distinct from that at basin margins. Using the sequence stratigraphy and events recognized in the slope belt, a multi-folded stratigraphic system for the deep-water basin and its correlation has been set up. The study shows that in the deep-water areas, OIB alkaline basalt predominates, with tholeiite mainly concentrated in the SW part of the basin. Around Yunnan-Guangxi-Vietnam border areas, however, some of the basalts show a geochemistry that is transitional between OIB and MORB. Four magmatic episodes are recognized as follows:1)late Early to early Middle Devonian; 2)middle Late Devonian to Early Carboniferous; 3)middle Late Carboniferous to Early Permian; and 4)Late Permian to Early Triassic. Pillow basalt occurs in the last three episodes, of which the third one has largest thickness and most extensive occurrence. On the basis of our study we propose that the Youjiang basin originated as a small oceanic basin between the Yangtz and Indochina blocks. This small oceanic basin was an eastward branch of the eastern Paleotethys along Changning-Menglian belt, in southwest China. In a broader view, this constitutes a part of the archipelago in eastern Paleotethys. The stratigraphic architecture further suggests that the Youjiang basin evolved through five stages:1)shallow epeiric basin (late D_ 1 -early D_ 2 ); 2)rift basin (middle D_ 2 -D_ 3 ); 3)rapidly expanding oceanic basin (C_ 1 -P_ 2 ); 4)contracting oceanic basin (P_ 3 -early T_ 2 ); and , 5)remnant basin (middle T_ 2 -early T_ 3 ). Our study supports that, paleogeographically, the southwestern part of the basin may belong to the northern margin of the Indochina block, while the northern part may form southwestern margin of the Yangtz plate.
【Fund】： 国家自然科学基金资助项目(40272018);; 教育部优秀团队基金项目(IRT0546)
【CateGory Index】： P539.2
【CateGory Index】： P539.2