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ORIGINAL RESEARCH article

Front. Earth Sci.
Sec. Economic Geology
Volume 12 - 2024 | doi: 10.3389/feart.2024.1384098

Geochemical characteristics and organic matter accumulation mechanism of the Permian Shanxi Formation transitional shale, Eastern Ordos Basin: Implications for paleo-weathering, provenance and tectonic setting

Provisionally accepted
Hongzhan Zhuang Hongzhan Zhuang 1Yuqiang Jiang Yuqiang Jiang 1*Xingtao Li Xingtao Li 2Chan Jiang Chan Jiang 3Shuxin Li Shuxin Li 2Zhanlei Wang Zhanlei Wang 1
  • 1 Southwest Petroleum University, Chengdu, Sichuan Province, China
  • 2 PetroChina Coalbed Methane Company, Beijing, China
  • 3 PetroChina Southwest Oil and Gasfield Company, Chengdu, Sichuan Province, China

The final, formatted version of the article will be published soon.

    The transitional shale of the Permian Shanxi Formation is an important source rock for shale gas, tight sandstone gas, and coalbed methane in the Ordos Basin. This study takes 3rd Sub-Member of Shanxi Formation as an example, and uses continuously collected shale core samples and matching geochemical data to restore the paleo-environmental conditions of its depositional period, clarify the formation mechanism of organic rich shale in different sedimentary environments under transitional facies background. According to different types of cross-plot patterns, paleo-weathering, provenance sources, and tectonic backgrounds were determined in this study. The results indicate that Shanxi organic-rich shale can be divided into two categories: estuarine shale in Unit 1 and lagoon shale in Units 2-4. The average TOC value of estuarine shale is significantly higher than that of lagoon shale, reaching 5.55%. Estuarine shale is mainly deposited in an suboxic-anoxic bottom water environments, with high surface seawater productivity, which is conducive to the formation and preservation of a large amount of organic matter. Lagoon shale is mainly composed of Type II2 and III kerogen, with a weakly oxic bottom water environment and low water surface paleo-productivity.The organic matter mainly comes from terrigenous plant debris, and its high sedimentation rate can effectively accumulate and preserve it. The chemical weathering indicators of Shanxi transitional shale are controlled by sedimentary recycling, hydrodynamic sorting, and diagenetic alteration, and the influence of changes in the source area is relatively small. The Shanxi transitional shale is mainly deposited on the active continental margin under collision background, and its source is mainly granodiorite from the Qinling orogenic belt.

    Keywords: Transitional shale, organic matter accumulation, Paleo-weathering, provenance, Tectonic setting, Ordos Basin

    Received: 08 Feb 2024; Accepted: 16 Dec 2024.

    Copyright: © 2024 Zhuang, Jiang, Li, Jiang, Li and Wang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Yuqiang Jiang, Southwest Petroleum University, Chengdu, 610500, Sichuan Province, China

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