Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (4): 701-715.doi: 10.11743/ogg20190402

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Sedimentary environment of the Lower Cambrian Qiongzhusi Formation shale in the Upper Yangtze region

Zhao Jianhua1,2, Jin Zhijun3,4, Lin Changsong5, Liu Guangxiang3,4, Liu Keyu1,2, Liu Zhongbao3,4, Zhang Yuying1,2   

  1. 1. Key Laboratory of Deep Oil and Gas, China University of Petroleum(East China), Qingdao, Shandong 266580, China;
    2. College of Geosciences, China University of Petroleum(East China), Qingdao, Shandong 266580, China;
    3. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100083, China;
    4. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China;
    5. School of Ocean Sciences, China University of Geosciences(Beijing), Beijing 100083, China
  • Received:2018-10-08 Revised:2019-01-11 Online:2019-08-28 Published:2019-06-01

Abstract: The lower Cambrian shale shows a bright potential for shale gas exploration and is an important strategic successor play for oil and gas exploration in the Upper Yangtze region.The sedimentary environment of the Qiongzhusi Formation shale was comprehensively studied through outcrop observation, core description, thin section observation, SEM analysis, and geochemical analysis of major and trace elements.According to mineralogy, rock fabrics and sedimentary structures, five major- and 12 sub-lithofacies types were identified in the Qiongzhusi Formation shale, six typical sedimentary sequences developed in shallow-water shelf, deep-water shelf, and slope-basin sedimentary systems were summarized, and the corresponding sedimentary models were established.Under the paleoceanographic conditions of oxidation and relatively low productivity, phosphorus-dolomitic-argillaceous sedimentary sequences and sandy-argillaceous-calcareous sedimentary sequences were developed in shallow shelf facies with low TOC.In contrast, organic-rich argillaceous-phosphorus-dolomitic, siliceous-argillaceous, and argillaceous sedimentary sequences were developed in deep shelf and slope-basin facies with sediments deposited in oxygen-poor, anoxic oceans with relatively high productivity.The majority of sedimentary zones in deep shelf facies is favorable for the development of organic-rich shales in the interior of intracratonic rift along Ziyang-Changning trend within Sichuan Basin, central and northern Guizhou and western Hubei-Eastern Chongqing areas in southeastern Sichuan Basin.In addition, hydrothermal activities provide necessary materials and preservation conditions for the black shales of the Lower Cambrian Niutitang Formation in northwestern Guizhou, which in turn may generate organic-rich shales.

Key words: lithofacies type, sedimentary pattern, sedimentary sequence, sedimentary environment, shale, Lower Cambrian, Upper Yangtze region

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