鄂尔多斯盆地东缘石炭—二叠系页岩沉积相及微量元素地球化学研究

发布时间：2018-11-26 08:32

【摘要】：本论文以鄂尔多斯盆地东缘北部的哈尔乌素地区、中部的临县地区和南部的隰县地区为研究区,选取晚古生代石炭系太原组和二叠系山西组的煤系页岩为研究对象,结合前人的研究成果,以沉积学、地球物理学、岩石学、地球化学、煤田地质学为理论依据,结合露头、岩心、测井等地质资料开展研究层段沉积相和层序识别,并辅助以XRD和扫描电镜获取煤系页岩的岩石矿物组成,同时借助元素地球化学分析对沉积相进行定量分析。拟通过沉积层序格架的建立,分析沉积相的展布规律,查明煤系页岩沉积环境平面和垂向上的变化特征,指出层序格架内地化指标的变化规律。在前人研究的基础上,结合研究区的岩心、露头、测井等资料认为太原组为海相和海陆过渡相沉积,沉积相主要包括碳酸盐台地、障壁岛、泻湖、潮坪和三角洲相,山西组主要为三角洲相,细分为泛滥盆地,分流河道、分流间湾,泥炭沼泽等微相。对比发现中部和南部发育碳酸盐沉积,北部基本不发育,而北部三角洲相范围更广,持续时间较长。在此基础上建立了层序格架:垂向上划分为2个长期基准面旋回(LSC1、LSC2),长期基准面旋回的分界面为太原组和山西组的分界面,又进一步细分为4个中期旋回(MSC1~MSC4)。矿物组成是通过X射线衍射(XRD)实验和扫描电镜观察实现的。XRD实验结果显示:煤系页岩样品矿物组成主要为石英和粘土矿物,这也与扫描电镜观察结果相符。粘土矿物中高岭石、伊蒙混层矿物居多,表明沉积环境温暖潮湿。X射线荧光(X-ray fluorescence)是测定样品常微量元素的重要手段。通过微量元素来还原煤系页岩的沉积环境,分析其氧化还原条件、古气候、古盐度、古生产力变化。结果表明其形成于弱氧化-弱还原条件下,气候温暖潮湿,受海水作用较弱,整体生产力水平较高。煤系页岩样品稀土含量较高,稀土富集主要受控于物源,此外沉积速率、古气候、古盐度等也会影响稀土含量。在层序格架内,盐度与氧化还原条件的变化特征与中期基准面旋回变化相似,而古生产力(Baxs)和稀土总量(ΣREE)的变化趋势与中期基准面的变化相反。
[Abstract]:In this paper, the coal shale of Taiyuan formation of late Paleozoic and Shanxi formation of Permian is chosen as the research area, which is based on the Halwusu area in the north of the eastern margin of the Ordos Basin, the Linxian area in the middle part and the Xixian area in the south of the Ordos Basin. Based on the previous research results, based on sedimentology, geophysics, petrology, geochemistry and coalfield geology, combined with outcrop, core, logging and other geological data, the sedimentary facies and sequence of the studied interval are identified. The mineral composition of coal shale was obtained by XRD and SEM, and the sedimentary facies were quantitatively analyzed by element geochemistry analysis. Through the establishment of sedimentary sequence framework, this paper analyzes the distribution of sedimentary facies, finds out the variation characteristics of sedimentary environment plane and vertical direction of coal measures shale, and points out the variation law of the inland index of sequence framework. On the basis of previous studies, combined with the core, outcrop, logging and other data in the study area, it is considered that the Taiyuan formation is a marine and oceanic transitional facies, and the sedimentary facies mainly include carbonate platform, barrier island, lagoon, tidal flat and delta facies, and the sedimentary facies include carbonate platform, barrier island, lagoon, tidal flat and delta facies. Shanxi formation is mainly delta facies, subdivided into flood basin, distributary channel, distributary bay, peat swamp and other microfacies. It is found that carbonate deposits are developed in the middle and south of the region, but are not developed in the north, while the delta facies in the north is more extensive and lasts for a long time. On this basis, the sequence framework is established: vertically divided into two long-term base-level cycles (LSC1,LSC2), the interface of long-term base-level cycles is divided into the interfaces of Taiyuan formation and Shanxi formation, and further subdivided into four intermediate cycles (MSC1~MSC4). The mineral composition was observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results of XRD experiment show that the mineral composition of coal shale is mainly composed of quartz and clay minerals, which is also consistent with the observation of SEM. Kaolinite and immoniferous minerals are the majority of clay minerals, indicating that the sedimentary environment is warm and humid. X-ray fluorescence (X-ray fluorescence) is an important method for the determination of trace elements in samples. The depositional environment of coal shale was reduced by trace elements, and the changes of redox conditions, paleoclimate, paleosalinity and paleoproductivity were analyzed. The results show that it is formed under the condition of weak oxidation-weak reduction, the climate is warm and humid, the effect of seawater is weak, and the overall productivity level is higher. The content of rare earth in coal shale is high, the enrichment of rare earth is mainly controlled by the source, in addition, the deposition rate, paleoclimate and paleosalinity will also affect the content of rare earth. In the sequence framework, the variation characteristics of salinity and redox conditions are similar to those of the intermediate base-level cycle, but the trend of paleo-productivity (Baxs) and 危 REE is opposite to that of the intermediate base-level.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P534.4;P618.1

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