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《Journal of Chengdu University of Technology(Science & Technology Edition)》 2018-03
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Geochemical characteristics and palaeo-environmental implication of Middle Permian Maokou Formation in Wangcang region,Sichuan Basin,China

LI Qian;XU Shenglin;CHEN Hongde;LIN Liangbiao;YANG Shuai;YU Yu;SUN Fengrui;DONG Yixin;DENG Xiang;State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation,Chengdu University of Technology;College of Petroleum Engineering,China University of Petroleum;Key Laboratory of Shale Gas Evaluation and Exploitation of Sichuan Province;  
The palaeo-environment revealed by carbonate rocks of middle Permian Maokou Formation in Wangcang region is discussed on the basis of analysis of the geochemical characteristics.It showsthat theδ13 C andδ18 O of 32 samples are stable without any linear relationship.These parameters all meetδ18 O-6‰,Mn/Sr≤0.6,Fe/Sr3,MgO/CaO0.12,and are unlikely influenced by late diagenetic alteration,so they can be used as reliable targets for paleo-environmental analysis.The contents of terrigenous elements,Al_2O_3,TiO_2,are low and positively correlated,and the degree of REE differentiation is obviously weak.There is a strong positive correlation between ∑REE and∑(Al_2O_3+TiO_2).Vertically,∑(Al_2O_3 +TiO_2)and ∑REE have same variation tendency,but variation of the ancient water depth index Sr/Ba,1000×(Sr/Ca)has opposite trend. The characteristic ratios of MgO/CaO,Sr/Ba,1000×(Sr/Ca),U/Al,V/Al,Cr/Al,Co/Al,U/Th and V/(V+Ni)indicate that the terrigenous materials are insufficient during the depositional period and the REE content is mainly influenced by terrigenous supply.Analysis reveals that paleo-oceanic temperature is between 14.98~26.55℃,and the salinity of ancient seawater is in the range of 132.3~135.2.It conforms that the carbonate successions in the study area are deposited in an dysaerobicanaerobic environment,characteristic of relatively high sea level,small range of water depth variation,and three transgression and regression cycles.The trace element evolution curves and the corresponding lithofacies assemblage can be used as the basis of stratigraphic division.
【Fund】: 国家自然科学基金青年科学基金项目(41602107);; 成都理工大学中青年骨干教师培养计划项目(JXGG201537 JXGG201538)
【CateGory Index】: P588.245
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