The Characteristics of Storm Deposits of the Lower Cambrian Qingxudong Formation in the Southeastern Margin of Yangtze Platform and Its Significance
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Chinese Academy of Geological Sciences,Chengdu Institute of Geology and Mineral Resources,Chengdu Institute of Geology and Mineral Resources,Chengdu Institute of Geology and Mineral Resources

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    Abstract:

    The Lower Cambrian Lungwangmiaoan Qingxudong Formation in the southeastern Yangtze area of South China mainly consists of shallow sea carbonate. Based on measurement of field outcrops and detailed petrographic observations of thin sections, a large amount of storm deposits was found to occur in different layers of the Qingxudong Formation, and a lot of storm induced sedimentary structures were found, such as sharp erosional base, coarse lag deposits, graded bedding, parallel bedding, hummocky cross-stratification (rare and questionable) and ripple bedding, and many types of storm deposit sequences. Due to scarcity of gravity flow deposits in deep section more close to the southeastern margin of the Yangtze platform, it can be inferred that the depositional model of Yangtze area during the early Cambrian Lungwangmiaoan should be carbonate ramp with a gentle gradient. Combined with the formation mechanism of storm deposits and the characteristics (especially the directional alignment of the coarse lag gravelsize intraclasts and the lack of typical hummocky crossstratification) of the storm deposits of the Qingxudong Formation, this study suggests that the storm deposits in the study area should be formed in intense winter storm, and the palaeogeographic position of South China should be located at midlatitudes during the early Cambrian Lungwangmiaoan. This conclusion comes up with queries to some famous palaeogeographic reconstruction results. What’s more, the largescale development of evaporates and carbonates at midlatitude areas favors the view that the Earth was in the period of hothouse during the Cambrian.

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ZHENG Binsong, MOU Chuanlong, LIANG Wei, CHEN Chao.2018. The Characteristics of Storm Deposits of the Lower Cambrian Qingxudong Formation in the Southeastern Margin of Yangtze Platform and Its Significance[J]. Acta Geologica Sinica,92(7):1524-1540

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History
  • Received:April 26,2017
  • Revised:June 01,2018
  • Adopted:November 24,2017
  • Online: July 13,2018
  • Published: