Oil & Gas Geology ›› 2018, Vol. 39 ›› Issue (4): 749-758.doi: 10.11743/ogg20180412

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Milankovitch cycles in the Silurian Kepingtage Formation in Shuntuoguole area,Tarim Basin

Jia Dongli1, Tian Jingchun1, Lin Xiaobing1, Yang Guohua2, Feng Wenxin2, Zhang Xiang1, Tang Yan3, Yang Chenyu4   

  1. 1. Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China;
    2. Zhengzhou Industry and Trade Schools, Zhengzhou, Henan 450007, China;
    3. The Third Academy of Engineering of Surveying and Mapping, Chengdu, Sichuan 610500, China;
    4. Geochemistry Exploration Brigade of Sichuan Bureau of Exploration and Development of Geology and Minerals Resources, Deyang, Sichuan 618000, China
  • Received:2017-12-15 Revised:2018-05-09 Online:2018-08-28 Published:2018-07-23

Abstract: The Silurian Kepingtage Formation in the Tarim Basin is mainly deposited in the tidal flat environment during a relatively stable period of tectonic activity.It is one of the typical marine clastic sequences in the basin.And it is composed of frequently alternating and superimposing medium-fine sandstone and mudstone,and can be obviously divided into three intervals.According to previous research results,the Kepingtage Formation can be approximately correlated with the Telychian,Aeronian and Rhuddanian Stage of the International Stratigraphic Chart,and its deposition period should be within 8.1-12.7 Ma.However,its Milankovitch high-frequency stratigraphic cycle framework is rarely discussed.Ta-king the Gamma-Ray logs of Well Shun-9 as proxies and using spectral analysis method for computation,we found that the Kepingtage Formation in Well Shun-9 recorded the complete Milankovitch cycle.The astronomical cycle significantly controls the cycle thickness,with the cycle thickness of 16.73 m corresponding to the long eccentricity of 405 ka,the cycle thickness of 5.24 m and 3.92 m corresponding to the short eccentricity of 125 ka and 95 ka respectively,and the cycle thickness of 1.59 m and 1.26 m corresponding to the obliquity of 38.1 ka and 31.1 ka respectively.The average sedimentary rate was estimated as 4.15 cm/ka and the depositing time as 10.4 Ma.And a "floating" astronomical time scale was established for the Kepingtage Formation in Well Shun-9 based on Empirical Mode Decomposition(EMD).The Kepingtage Formation was found to have 83 cycles with short eccentricity of 125 ka and 334 cycles with obliquity of 38.1 ka.Finally,we analyzed the superposition differences and their causes of each high-frequency cycle by using the Fischer plots and a standard model for fifth-order cycle division under the control of the short eccentricity of 125 ka.This result provides a new method that is unified and unbiased for high-frequency cycle division of marine clastic strata in this basin and similar basins.

Key words: Milankovitch cycle, spectral analysis, EMD, astronomical time scale, Kepingtage Formation, Tarim Basin

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