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    扬子板块北缘中元古代晚期地层年代学研究进展

    Geochronology of Upper Mesoproterozoic in the northern Yangtze Block: a review

    • 摘要: 中元古代晚期,地球在板块构造、生物演化和环境演变等方面发生了一系列重大事件,引起了地学界的广泛关注。扬子板块北缘出露了较为完整的中元古代晚期地层,为研究全球中元古代晚期重大事件提供了基础。近年来,围绕这套地层开展的综合地层学、古生物学和沉积地球化学等研究取得了一系列进展,但它们的沉积时代和年代地层格架仍未形成共识。文章总结了扬子板块北缘中元古代晚期神农架群、马槽园群(神农架地区)以及打鼓石群(大洪山地区)的地质年代学研究成果,梳理了其中与地层关系吻合的年龄数据,并讨论了与地层关系存在矛盾的年龄数据,在此基础上提出了初步的年代地层格架和区域对比方案:神农架群底界缺乏年龄约束,顶界年龄约为1.1 Ga;部分马槽园群对应于神农架群的上部,并可能延续到新元古代;打鼓石群中部对应于神农架群的上部,其“下部”的太阳寺组和韩家洼组沉积于新元古代早期,比上覆罗汉岭组年轻,说明打鼓石群局部发生了地层倒转。

       

      Abstract: In the late Mesoproterozoic period, a series of major plate tectonics, biological and environmental events occurred on the Earth, attracting more and more attention in the geosciences circle. Stratigraphic successions spanning this critical period are well developed and exposed in the northern part of Yangtze Block, laying the foundation for studying these late Mesoproterozoic major events. Although extensive stratigraphic, paleontological and geochemical studies have been carried out on these successions, their sedimentation period and geochronological frameworks are not well established. In this paper, we summarize the geochronological data of upper Mesoproterozoic in the northern part of Yangtze Block, discuss their consistency against the stratigraphic sequence, and propose a temporary geochronological framework and correlation scheme for these successions. The new framework shows that the Shennongjia Group lacks age constraints on its lower boundary and its deposition ended at ca 1.1 Ga; the lower part of Macaoyuan Group could be correlated to the upper part of Shennongjia Group and the deposition of its upper part may last till Neoproterozoic; the middle part of Dagushi Group is correlative with the upper part of Shennongjia Group, and the lower part of Dagushi Group including the Taiyangsi and Hanjiawa formations were deposited during the early Neoproterozoic, younger than the overlying Luohanling Formation, which indicates a reverse stratigraphic sequence within Dagushi Formation partially.

       

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