黔桂地区泥盆纪富有机质竹节石页岩:一个重要的潜在性页岩气勘探目的层
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1.中国地质大学地球科学与资源学院;2.广西地质调查院;3.巴基斯坦庞佳普大学

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广西重点研发计划项目资助(2021AB30011)


Organic-matter-rich tentaculitid shales of the Devonian in the region from the southern Guizhou to central Guangxi province of South China: An importantly potential target rock for shale-gas exploration
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1.School of Earth Sciences and Natural Resources,China University of Geosciences;2.Guangxi Geological Survey;3.University of the Punjab

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    摘要:

    泥盆纪是地球历史之中碳质页岩的全球性沉积作用一个特别显著的幕。在黔桂地区深水沉积主导的台间盆地相之中,从早泥盆世的埃姆斯期到晚泥盆世的弗拉斯期,集中发育一套总厚度超过600米的富有机质竹节石页岩,以下特征表明这些富有机质的竹节石页岩将成为重要的潜在性页岩气勘探目的层:1)页岩的总有机碳含量(TOC)值多为2%~4%,可以高达5%~6%;2)从早泥盆世的埃姆斯期至中泥盆世,有机碳多集中富集在三级海平面相对上升期沉积的、而且单层厚度常常超过百米的富有机质竹节石页岩主导的缺氧盆地相沉积之中,相对应的三级海平面下降期则为亏损有机碳的陆棚相沉积;3)在晚泥盆世弗拉斯期硅质岩主导的榴江组之中,有机碳多富集在三级海平面下降期的、单层厚度为30至40米的缺氧盆地相富有机质竹节石页岩之中,所对应的三级海平面上升期则为硅质岩主导的而且亏损有机碳的远洋盆地相沉积。暂时归为缺氧盆地相的富有机质竹节石页岩中的有机质堆积作用,主要受到以下三个因素之间的复杂的非线性相互作用所控制:生产率、保存作用和沉积作用速率;更为特别而且重要的是,基于高密度保存的竹节石化石(含量可以超过30%),研究区的泥盆纪富有机质竹节石页岩,除了这三个因素之外,浮游动物的“生物碳泵(The biological carbon pump)”作用过程,将是这些竹节石页岩富集有机质的另外一个重要机理。

    Abstract:

    The Devonian is a special geological time that was marked by an episode of Earth history noteworthy for the global deposition of organic-matter-rich shales. Within an inter-platform basin facies that is dominated by deep-water deposits in the region from the southern Guizhou to the central Guxngxi, a set of organic-matter-rich tentaculitid shales with the thickness of more than 600 meters was relatively concentrated and developed from the Emsian Age to the Frasnian Age of the Devonian. Following features not only characterize this set of organic-matter-rich tentaculitid shales but also demonstrate it is an importantly potential target rock for shale-gas exploration: 1) a relatively higher total organic carbon (TOC) value of more than 2% that can be up to 5% to 6%; 2) From the Amsian Age of the early Devonian to the middle Devonian, organic carbon content is typically enriched in massive organic-matter-rich tentaculitid shales with the monolayer thickness of more than 100 meters that is formed in the period of third-order relative sea-level rising, and depleted in the calcareous shales and muddy limestones of the shelf facies forming in the period of third-order relative sea-level falling; and 3) Within the Liujiang Formation that is dominated by silicalites of the Frasnian Age of the late Devonian, organic carbon content is typically enriched in massive organic-matter-rich tentaculitid shales with the monolayer thickness from 30 to 40 meters that is formed in the period of third-order relative sea-level falling, and depleted in silicalietes of the pelagic basin facies forming in the period of third-order relative sea-level rising. It can be certain that the accumulation of organic matter within organic-matter-rich tentaculitid shales in study area is controlled by complicated, nonlinear interactions among the three factors: productivity, preservation, and sedimentation rate. More particularly and importantly, the high-density preservation of tentaculitid fossils demonstrates that the accumulation of organic matter within organic-matter-rich tentaculitid shales in study area is genetically related to the biological carbon pump of zooplankton.

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  • 收稿日期:2023-11-05
  • 最后修改日期:2024-01-14
  • 录用日期:2024-01-16
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