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现代地质 ›› 2025, Vol. 39 ›› Issue (04): 1129-1142.DOI: 10.19657/j.geoscience.1000-8527.2024.144

• 地球化学 • 上一篇    下一篇

鄂尔多斯盆地南缘直罗组顶部古沉积环境恢复:来自泥岩元素组成的证据

程先钰1,2(), 张天福1,2, 张云1,2, 何鹏1, 孙立新1,2, 马海林3, 鲁超4   

  1. 1.中国地质调查局天津地质调查中心,天津 300170
    2.中国地质调查局天津地质调查中心非化石能源矿产实验室,天津 300170
    3.内蒙古地质调查院,内蒙古 呼和浩特 010000
    4.核工业二○八大队,内蒙古 包头 014010
  • 出版日期:2025-08-10 发布日期:2025-08-27
  • 作者简介:程先钰,男,硕士,工程师,1991年出生,主要从事地质矿产调查与研究工作。Email:chengxianyu_601@163.com
  • 基金资助:
    中国地质调查局地质调查项目(DD20240035);中国地质调查局地质调查项目(DD20221727-3)

Restoration of Paleosedimentary Environment of the Top of Zhiluo Formation in the Southern Margin of Ordos Basin: Evidence from Geochemical Characteristics of Mudstone

CHENG Xianyu1,2(), ZHANG Tianfu1,2, ZHANG Yun1,2, HE Peng1, SUN Lixin1,2, MA Hailin3, LU Chao4   

  1. 1. Tianjin Center of Geological Survey, China Geological Survey, Tianjin 300170, China
    2. Laboratory of Non-Fossil Energy Minerals, Tianjin Center of Geological Survey, China Geological Survey, Tianjin 300170, China
    3. Inner Mongolia Institute of Geological Survey, Hohhot, Inner Mongolia 010000, China
    4. The 208th Geologic Party, China Nuclear Geology, China National Nuclear Corporation, Baotou, Inner Mongolia 014010, China
  • Published:2025-08-10 Online:2025-08-27

摘要:

鄂尔多斯盆地南部侏罗系泥岩地球化学证据记录了古沉积环境演化,中侏罗世古沉积环境演化是鄂尔多斯盆地铀元素沉积富集的基础。然而,有关鄂尔多斯东南部直罗组沉积环境的认识仍然薄弱,制约了砂岩型铀矿形成条件的深入理解。本文对黄陵店头地区中侏罗统直罗组及延安组顶部泥岩进行主、微量元素分析,然后根据泥岩典型地球化学参数的垂向变化对其古沉积环境进行了恢复。结果表明,B、相当B含量、Sr/Ba组合指示直罗组沉积水体为半咸水到微咸水环境;U/Th、V/(V+Ni)、V/Cr、Ni/Co组合指示直罗组及延安组顶部的古水体介质富氧;Fe2+/Fe3+指示延安组形成稳定的还原层,直罗组下段上亚段底部逐渐向弱还原环境过渡,上段为强氧化环境;古气候指标Sr、Sr/Cu、A12O3/MgO、FeO/MnO指示直罗组沉积期经历了半干旱逐渐向干旱环境转变;化学蚀变指数(CIA)、成分变异指数(ICV)反映直罗组上段相对于下段的化学风化程度有所减弱,表明鄂尔多斯盆地周缘构造活动性逐渐增强。物源输送的逐渐增多与直罗期古气候的转变,还原环境向氧化环境转换的古水体条件对本区铀元素富集成矿具有关键制约作用。

关键词: 鄂尔多斯盆地, 古环境, 延安组, 直罗组, 地球化学, 砂岩型铀矿

Abstract:

Geochemical evidence from Jurassic mudstones in the southern part of the Ordos Basin records the evolution of paleosedimentary environments, and the evolution of the Middle Jurassic paleoenvironment forms the basis for the sedimentary enrichment of uranium. However, understanding of the sedimentary environment of the Zhiluo Formation in the southeastern Ordos Basin remains insufficient, restricting in-depth understanding of the formation conditions of sandstone-type uranium deposits. This study conducts major and trace element analyses on mudstones from the Middle Jurassic Zhiluo Formation and the top of the Yan’an Formation in the Diantou area of Huangling County. Based on vertical variations in typical geochemical parameters of the mudstones, the paleosedimentary environment is reconstructed. Results show that: combinations of B, equivalent B content, and Sr/Ba indicate that the sedimentary water of the Zhiluo Formation was in a brackish to slightly saline environment; combinations of U/Th, V/(V+Ni), V/Cr, and Ni/Co indicate that the paleowater medium at the top of the Yan’an Formation and Zhiluo Formation was oxygen-rich; Fe2+/Fe3+ ratios indicate that the Yan’an Formation formed a stable reducing layer, with the bottom of the upper submember of the lower member of the Zhiluo Formation gradually transitioning to a weakly reducing environment, and the upper member of the Zhiluo Formation being a strongly oxidizing environment; paleoclimate indicators (Sr, Sr/Cu, Al2O3/MgO, FeO/MnO) reveal that the Zhiluo Formation sedimentary period experienced a transition from semi-arid to arid conditions; Chemical Index of Alteration (CIA) and Index of Compositional Variability (ICV) reflect weaker chemical weathering in the upper member of the Zhiluo Formation compared to the lower member, indicating intensified tectonic activity around the Ordos Basin. The gradual increase in provenance input, paleoclimate changes during the Zhiluo period, and the transition of the paleowater environment from reducing to oxidizing conditions played a key role in constraining uranium enrichment and mineralization in this area.

Key words: Ordos Basin, paleoenvironment, Yan’an Formation, Zhiluo Formation, geochemistry, sandstone-type uranium

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