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作 者:樊婷婷[1] 柳益群[2] 周鼎武[3] 车飞翔 杨皓凯 FAN TingTing;LIU YiQun;ZHOU DingWu;CHE FeiXiang;YANG HaoKai(College of Geology Environment,Xi’an University of Science and Technology,Xi’an 710054,China;Department of Geology,Northwest University,Xi’an 710069,China;College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao,Shandong 266510,China)
机构地区:[1]西安科技大学地质与环境学院,西安710054 [2]西北大学地质学系,西安710069 [3]山东科技大学地球科学与工程学院,山东青岛266510
出 处:《沉积学报》2023年第3期932-944,共13页Acta Sedimentologica Sinica
基 金:国家自然科学基金项目(41641018)。
摘 要:湖相油页岩中碳酸盐结核形成机制研究较为薄弱,因此以鄂尔多斯盆地南缘霸王庄延长组长7段油页岩中发育的巨型钙质结核为研究对象,通过野外观察、薄片鉴定和X射线衍射分析,结合结构构造、矿物组成、主微量元素以及碳、氧、锶、钕同位素特征,分析其形成条件和机理,其结果对研究与其伴生的优质泥质烃源岩的形成演化环境具有重要意义。研究认为:该结核矿物组成丰富,说明形成过程中发生了复杂的生物化学和化学沉积作用,结核中的滑石和文石矿物应为热液作用的产物;结核中方解石矿物主要有4种形态,其中钙质圆球粒应是蓝细菌鞘体矿化的产物。从结核边缘带到内、外环带及核部,主、微量元素含量差异较明显,表现出结核阶段性连续生长演化的特征。锶同位素值接近幔源锶同位素值,钕同位素值富集地幔特征,氧同位素值强烈负偏,以及高Sr、Ba含量均说明钙质结核形成时受到深部来源热液流体影响。此外结核中还发现在深湖热液环境中生存的鳕鱼的化石碎片和鱼粪化石。碳同位素值为-1.11‰~12.4‰,强烈正偏,表明碳酸盐结核的形成可能与产烷带微生物代谢活动引起的甲烷生成有关。灰岩结核成因指示该区长7油页岩生烃能力好,为优质烃源岩。The mechanism by which carbonate concretions develop in lacustrine oil shale continues to be relatively unclear.This study of the very large calcareous concretions in Chang 7 oil shale in the Yanchang Formation,southern Ordos Basin,included analysis of the conditions and mechanism by field investigation,thin section observations,Xray diffraction,features of isotopic geochemistry,major and trace elements,microfractures,mineral composition,structure,and texture from inner to outer zones of the concretions.The results add considerably to the study of the formation and evolutionary environment of the associated high-quality argillaceous source rocks.The study suggests that the mineral composition of the nodules is diverse,which indicates that complex biochemistry and chemical deposition took place during the formation process,and the talc and aragonite minerals in the nodules are the products of a hydrothermal process.Four main forms of calcite minerals are present in the nodules.Of these,calcareous spherules are produced by the mineralization of cyanobacterium sheaths.From the edge of the concretions to the inner and outer ring and the nucleus,the content of major and trace elements is clearly different,showing the characteristics of continuous growth and evolution of the concretions in stages.The various 87Sr/86Sr ratios are similar to those of mantlederived Sr isotopes;enrichment of a range of εNd(t) values is similar to mantle characteristics;δ18O is strongly negative;and Sr and Ba contents are high,all of which indicate that the formation of calcareous nodules is influenced by hydrothermal fluid from a deep source.In addition,fossilized fragments of cod that lived in a deep lake hydrothermal environment,and coprolites,were found in the nodules.The strongly positive bias of δ13C from-1.11‰ to 12.4‰ indicates that the formation of carbonate nodules may be related to methane generation caused by microbial metabolism in the alkane-producing zone.The origin of the calcareous nodules indicates that Chang 7 oil
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