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Paleogeographic, paleoclimatic and sea-level implications of glauconite deposits in Egypt: A review
Journal of African Earth Sciences ( IF 2.2 ) Pub Date : 2020-11-01 , DOI: 10.1016/j.jafrearsci.2020.103944
Hassan Baioumy , Sherif Farouk , Khaled Al-Kahtany

Abstract Glauconite deposits are confined to the Western Desert in Egypt of four different sequences and ages from older to younger include, 1) Lower Cenomanian Bahariya Formation, 2) Lower-Middle Campanian Qusseir Formation, 3) Upper Campanian Duwi Formation, and 4) Lutetian-Bartonian Hamra Formation. Lower Cenomanian, Upper Campanian and Lutetian-Bartonian glauconites occur as pellets, while the Lower-Middle Campanian glauconite occurs as fine-grained particles of non-pelletal texture. Based on K2O contents, the Lower Cenomanian and Upper Campanian glauconites are classified as slightly evolved, while the Lower-Middle Campanian and Lutetian-Bartonian glauconite are categorized as evolved. Positive correlations between K2O and Fe2O3 in the Bahariya Formation, Qusseir Formation and Hamra Formation deposits suggest a layer lattice glauconitization mechanism for these deposits. On the other hand, the lack of correlation between Fe2O3 and K2O declines the layer lattice formational mechanism for the Duwi Formation glauconite. A neo-formation mechanism was suggested for this glauconite. Rare earth elements patterns are the same in the four deposits and resemble the shallow sweater pattern. The four glauconite deposits formed in shallow marine environments and might correspond to major eustatic transgressive and global warming events. Glauconite of the Bahariya Formation corresponds to the Early Cenomanian Tethys major transgression in Egypt and can be correlated to the Albian/Cenomanian global cycle boundary as well as the early Cenomanian “hot greenhouse”. The sequence boundary near the topmost part of the Qusseir Formation matches the global warming of the Middle Campanian Event (MCE). The upper Campanian glauconite of the Duwi Formation occurs as lowstand wedge and may correlate to the late Campanian climatic warm optimum. The stratigraphic position of the Hamra glauconite above the unconformity surface refers to transgressive phase that may match with latest Lutetian major sequence boundary (Lu4) and global warming event of the Middle Eocene Climatic Optimum (MECO). Paleogeographic maps show that the Western Desert of Egypt during Cenomanian and Lower Campanian covered by shallow marine setting, which match with the proposed setting for the glauconites in these ages. However, paleogeographic maps for the Upper Campanian and Middle Eocene were modified to fit with the suggested setting of glauconites of these epochs. The prevalence of shallow marine setting during these four ages interprets the restricted occurrences of glauconites at the Western Desert of Egypt during these epochs.

中文翻译:

埃及海绿石矿床的古地理、古气候和海平面影响:综述

摘要 海绿石矿床仅限于埃及西部沙漠,具有四个不同的层序和年龄,从旧到新包括:1) 下塞诺曼阶 Bahariya 组,2) 下中坎帕阶 Qusseir 组,3) 上坎帕阶 Duwi 组,以及 4) 卢特阶-巴托尼亚哈姆拉组。下森诺曼阶、上坎帕阶和卢特阶-巴顿阶海绿石以球团形式出现,而中下坎帕阶海绿石以非球团质地的细粒颗粒形式出现。根据 K2O 含量,下森诺曼阶和上坎帕阶海绿石被归类为轻度演化,而下中坎帕阶和卢特阶-巴顿阶海绿石被归类为演化。Bahariya 组中 K2O 和 Fe2O3 之间的正相关关系,Qusseir 组和 Hamra 组矿床表明这些矿床具有层状晶格海绿石化机制。另一方面,Fe2O3 和 K2O 之间缺乏相关性降低了 Duwi 组海绿石的层晶格形成机制。提出了这种海绿石的新形成机制。四种矿床中的稀土元素图案相同,类似于浅毛衣图案。这四种海绿石沉积物形成于浅海环境,可能对应于主要的海侵和全球变暖事件。Bahariya 组的海绿石对应于埃及的早 Cenomanian 特提斯海侵,可以与 Albian/Cenomanian 全球旋回边界以及早 Cenomanian “热温室”相关联。Qusseir 组顶部附近的层序边界与中坎帕尼亚事件 (MCE) 的全球变暖相匹配。Duwi 组的上坎帕阶海绿石以低位楔形出现,可能与晚坎帕阶气候温暖最优有关。不整合面以上哈姆拉海绿石的地层位置是指海侵相,可能与最新的卢特田主层序边界(Lu4)和始新世中始新世气候最优(MECO)的全球变暖事件相匹配。古地理地图显示,埃及西部沙漠在塞诺曼阶和下坎帕阶被浅海环境覆盖,这与这些时代海绿石的建议环境相匹配。然而,对上坎帕阶和中始新世的古地理地图进行了修改,以适应这些时代海绿石的建议设置。这四个时期浅海环境的盛行解释了这些时期埃及西部沙漠中海绿石的有限出现。
更新日期:2020-11-01
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