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<p>The shale gas exploration of marine-continental transitional facies has gained great attention in China, which is viewed as another breakthrough following the marine shale gas prior to continental shale gas. The Upper Paleozoic marine-continental transitional shales have high TOC abundance with large total thickness in the eastern Ordos Basin, progressively becoming a favorable area for exploration of transitional shale gas. Nevertheless, compared with the relatively homogeneous marine shales, the marine-continental transitional shales demonstrated strong anisotropy in the aspects of thickness, lithology and organic matter (OM). Thus, in this paper, based on the trace element and rock-eval data, we investigated the sedimentary facies, provenance, paleoclimate, paleobathymetry, and redox condition, as well as their controls on the enrichment of organic matter in the Shenfu Block, eastern Ordos Basin. The results of trace element experiments indicate that the paleoenvironment of the Ordos Basin underwent a transition from a marine to a continental environment, evolving from the Benxi Formation of the Carboniferous system to the Upper Shihezi Formation of the Permian system. The provenance area is characterised by the presence of high iron and high magnesium feldspar, with a medium degree of weathering. The paleoclimate experienced alternating periods of dry heat, relatively warm wet conditions, and dry heat. The paleowater depth decreased along the sedimentary profile. With regard to the redox environment index, the Taiyuan Formation is the stratum exhibiting the highest degree of reduction. The detection criteria for biomarkers were found to be consistent with the inorganic geochemical characteristics. The relationship between various trace elements and TOC indicates that redox conditions are the primary factors influencing the accumulation of organic matter in transitional shale. Organic matter is more abundant in warm and humid marine and terrestrial environments than in deep water and anoxic conditions. The characteristics of trace elements can be inferred to suggest that the Benxi Formation and Taiyuan Formation have greater potential for exploration and development.</p>

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Impact of Sedimentary Environmental Evolution on Organic Matter Enrichment in Upper Paleozoic Marine-Continental Transitional Shales in the Shenfu Block, Eastern Ordos Basin, China: Evidence from Geochemistry

  • 期刊论文

  • 发表日期：

    2026年4月8日

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  • Yanchao Zhang,
  • Xiangdong Yin,
  • Shu Jiang,
  • Litao Ma,
  • Jiaming Li

摘要

The shale gas exploration of marine-continental transitional facies has gained great attention in China, which is viewed as another breakthrough following the marine shale gas prior to continental shale gas. The Upper Paleozoic marine-continental transitional shales have high TOC abundance with large total thickness in the eastern Ordos Basin, progressively becoming a favorable area for exploration of transitional shale gas. Nevertheless, compared with the relatively homogeneous marine shales, the marine-continental transitional shales demonstrated strong anisotropy in the aspects of thickness, lithology and organic matter (OM). Thus, in this paper, based on the trace element and rock-eval data, we investigated the sedimentary facies, provenance, paleoclimate, paleobathymetry, and redox condition, as well as their controls on the enrichment of organic matter in the Shenfu Block, eastern Ordos Basin. The results of trace element experiments indicate that the paleoenvironment of the Ordos Basin underwent a transition from a marine to a continental environment, evolving from the Benxi Formation of the Carboniferous system to the Upper Shihezi Formation of the Permian system. The provenance area is characterised by the presence of high iron and high magnesium feldspar, with a medium degree of weathering. The paleoclimate experienced alternating periods of dry heat, relatively warm wet conditions, and dry heat. The paleowater depth decreased along the sedimentary profile. With regard to the redox environment index, the Taiyuan Formation is the stratum exhibiting the highest degree of reduction. The detection criteria for biomarkers were found to be consistent with the inorganic geochemical characteristics. The relationship between various trace elements and TOC indicates that redox conditions are the primary factors influencing the accumulation of organic matter in transitional shale. Organic matter is more abundant in warm and humid marine and terrestrial environments than in deep water and anoxic conditions. The characteristics of trace elements can be inferred to suggest that the Benxi Formation and Taiyuan Formation have greater potential for exploration and development.