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Geoscience ›› 2022, Vol. 36 ›› Issue (02): 729-741.DOI: 10.19657/j.geoscience.1000-8527.2021.197

• Oil and Gas Exploration • Previous Articles     Next Articles

Geochemistry of Carbonates Near the Cambrian Series 3-Furongian Boundary and Its Paleoenvironmental Constraints

BAI Xiangyu1,2(), MA Junwei3, XIA Qingping1,2, TAN Xianfeng4, LI Kaikai1,2()   

  1. 1. School of Energy Resources, China University of Geosciences, Beijing 100083, China
    2. Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Enrichment Mechanism, Ministry of Education, Beijing 100083, China
    3. Oil and Gas Resources Department, China Huayou Group Co., Ltd, Beijing 100101, China
    4. College of Petroleum and Natural Gas Engineering, Chongqing University of Science and Technology, Chongqing 401331, China
  • Received:2021-02-15 Revised:2021-05-15 Online:2022-04-10 Published:2022-06-01
  • Contact: LI Kaikai

Abstract:

The early Furongian mass extinction was likely related to paleoenvironmental changes, yet their relations remain unconstrained. Geochemical signals of shallow-water platform sediments are more sensitive to paleoenvironmental changes than deep-water sediments, which is conducive to understanding this issue. Carbonates in the Cambrian Series 3 Gushan Formation and the Furongian Changshan Formation in the Xiaweidian section of the Xishan (Beijing) were selected for element geochemical and isotopic analyses. The aim is to trace the paleoenvironmental evolution during the Kushanian-Changshanian transition, and to assess its effects on life evolution. The results reveal a major fluctuation in the paleoclimate and paleo-marine environment during the transition period. The sea-level lowstand at the end of Kushanian Stage was followed by rapid transgression in the early Changshanian Stage, during which seawater may have become significantly reducing. These changes, combining with the seawater temperature drop (to minimum) and salinity rise (to maximum), could explain the collapse of trilobite ecology and its subsequent extinction. During this period, the frequent alternation of dry-hot and warm-humid climate and the large-scale transgression may have facilitated the terrigenous detrital (and nutrients) input into the seawater, which promoted biological growth. The presence of deep reducing water is favorable for organic matter preservation, which eventually led to the Positive Carbon Isotope Excursion in the carbonates. We propose that strong correlation is unlikely between the Positive Carbon Isotope Excursion and the Middle to Late Changshanian sea-level drop.

Key words: element geochemistry, carbon isotopes, paleoenvironment, carbonates, Xiaweidian, Xishan, Beijing

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