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    • Keywords


      Late Miocene strata; Zebra layers; tilted side slope; anisotropy of magnetic susceptibility (AMS); palaeoenvironment; Linxia Basin.

    • Abstract


      Miocene strata in the Linxia Basin (Gansu, China) are usually interpreted as lacustrine sediments. However, the red–grey inter-beds known as ‘Zebra layers’ commonly tilt with respect to the terrain on the side slopes of the modern valley, which may be due to mantling palaeotopography (similar to aeolian loess). The anisotropy of magnetic susceptibility, which reflects the original arrangement of magnetic particles in sediments, was applied to investigate this phenomenon. The results showed that the tilting of the inter-beds in the side slope was due to mantle palaeotopography rather than soil creep, and that they were not deposited in a subaqueous environment. The grain sizes of sediments showed similar features as aeolian loess. We speculate that Miocene sediments were deposited by mantling the palaeotopography where aeolian materials accumulated. After deposition, flowing water submerged these strata, which caused the side slope to become gradually thinner from top to bottom and stirred the magnetic particles in these sediments. The grey colour of the Zebra layers may not be original, as it may be due to waterlogging and deoxidation after deposition; finally, when the iron oxides in these sediments were transformed or removed, their colours became grey. The formation of Zebra layers indicates that the Late Miocene palaeoenvironment of northwestern China was similar to that in which Quaternary aeolian loess was deposited.

    • Author Affiliations


      Xiuqing Nian1 2 3 Xiuming Liu4 5 6 Hui Guo2 7 Zhi Liu8 9 Bin Lu4 5 Fengqing Han1 3

      1. Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, People’s Republic of China.
      2. University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China.
      3. Qinghai Provincial Key Laboratory for Geology and Environment of Salt Lake, Xining 810008, People’s Republic of China.
      4. Institute of Geography, Fujian Normal University, Fujian 350007, People’s Republic of China.
      5. Key Laboratory for Subtropical Mountain Ecology, Ministry of Science and Technology and Fujian Province, College of Geographical Sciences, Fujian Normal University, Fujian 350007, People’s Republic of China.
      6. Department of Environment and Geography, Macquarie University, Sydney, NSW 2109, Australia.
      7. Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China.
      8. School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China.
      9. Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China.
    • Dates

  • Journal of Earth System Science | News

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