摘要:
华北地区石盒子群的沉积环境长期以来一致存在较大的争议,大多数研究者认为该时期完全为陆相沉积,也有一些学者在该地层中发现了海相沉积物。本文着重对鲁西、河南等地区石盒子群的奎山砂岩进行岩石学、沉积学、地球化学等指标研究,在该砂岩中发现了冲洗交错层理,并在该砂岩中上部发现了海绿石的存在。通过详细分析奎山砂岩中海绿石的显微特征、元素地球化学特征,并进行比较研究发现,华北地区奎山砂岩中海绿石的化学成分、含量与国内外古代的海相、过渡相海绿石基本一致,推断其为滨浅海富氧环境的产物。华北地区奎山砂岩中发育的沉积构造和所含海绿石的元素地球化学特征,揭示了该时期曾发生过海侵,反映了石盒子群沉积期沉积环境的复杂性。华北地区石盒子群奎山砂岩中上部海相沉积环境的确定,可能改变华北盆地二叠纪以来单纯为陆相沉积的认识,这为精细研究华北地区中晚二叠世的盆地格局、充填演化及恢复古地理景观,提供了新的思路和重要依据。
Abstract:
Previous researcher mostly held that the North China Basin was turned into continental basin in the sedimentary period, and the sea water was all over after filling of the epicontinental sea basin during Late Carboniferous to Early Permian. In this paper, the sedimentology, petrology and geochemistry characteristics of Kuishan sandstone were studied, and the glauconite was discovered. Through quantitative analysis of microscopic characteristics and elements of glauconite, in combination with Kuishan sandstone sedimentary structure features, the authors consider that the chemical composition of glauconite in Upper Kuishan sandstone is similar to that of the other parts of the ancient and modern glauconite formed in marine facies or transitional facies environment, which were both formed in the oxygen enrichment of the offshore environment. The well-developed sedimentary structure and the element geochemical characteristics of the contained glauconite reveal that marine transgression happened in this period, and this reflects the complexity of the sedimentary environment during the sedimentation of the Shihezi Geoup. Therefore, the determination of marine sedimentary environment in Upper Kuishan sandstone of Shihezi Group might change the conclusion that the North China basin has been purely continental basin since Permian. The important value of this study is to identify the transgressive deposition in Upper Kuishan sandstone, which reveals that the important transgressive process happened in this period, and there might have existed a special kind of ancient oceans in the North China basin during Middle–Late Permian. The results obtained by the authors provide a new train of thought and important basis for further study of the pattern and evolution of the North China basin and the restoration of its ancient geographical landscape during Middle–Late Permian.
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