| 下刚果盆地古近系Madingo组含磷泥岩元素地球化学特征及成因 |
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| 引用本文： | 季少聪,杨香华,朱红涛,康洪全.下刚果盆地古近系Madingo组含磷泥岩元素地球化学特征及成因[J].地质学报,2021,95(4):1128-1143. |
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| 作者姓名： | 季少聪 杨香华 朱红涛 康洪全 |
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| 作者单位： | 中国地质科学院岩溶地质研究所/自然资源部广西岩溶动力学重点实验室,广西桂林,541004;中国地质大学(武汉)资源学院,武汉,430074;中国海洋石油研究总院,北京,100027 |
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| 基金项目： | 本文为国家重点研发计划“古潜山和深部岩溶热储分布规律与成因机制”（编号2018YFC0604301）、中国地质调查局地调项目“贵州凯里- 都匀地区页岩气地质调查（岩溶所）”（编号DD20190723）、“南方重点地区1∶5万页岩气地质调查（岩溶所）”（编号DD20190562）和国家重大科技专项“西非- 南美海域重点区烃源岩识别与预测技术研究”（编号2017ZX05032- 001- 002）资助的成果。 |
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| 摘 要： | 下刚果盆地古近系Madingo组发育一套富有机质含磷泥岩,其上覆地层为Paloukou组粉砂质泥岩,下伏地层为Madingo组普通泥岩.应用薄片鉴定、扫描电镜、能谱分析及面扫描等室内技术手段,对含磷泥岩、普通泥岩及粉砂质泥岩样品进行了岩石学特征研究;在样品主量、微量及稀土元素测试的基础上,分析含磷泥岩、普通泥岩及粉砂质泥岩沉积时期古海洋水体的氧化还原条件;通过相关性分析、聚类分析等数理统计的方法,探讨研究区含磷泥岩沉积时期磷质来源及磷元素富集机制.研究结果表明:①含磷泥岩中微体古生物发育,以有孔虫为主,磷酸盐颗粒主要以胶状集合体形式存在;②含磷泥岩沉积时期为分层氧化海洋环境,含磷泥岩Ce负异常特征主要与磷酸盐矿物有关,携带Ce负异常特征的磷酸盐矿物形成于表层氧化水体并在底层水中沉淀,而底层水为贫氧-缺氧环境,U和V等氧化还原敏感元素富集;③海相沉积岩中磷质来源包括陆源、热液来源、生物来源、空源和宇宙源等几种类型,分析认为生物来源是研究区含磷泥岩中磷质的主要来源;④生物在含磷泥岩磷元素富集过程中起到间接作用,主要受生物量和氧化还原条件的影响.生物既是磷质来源,又改变介质的氧化还原条件,使磷元素从含磷有机化合物中释放出来并沉淀富集.
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| 关 键 词： | 下刚果盆地 Madingo组 含磷泥岩 成因 沉积学 |
| 收稿时间： | 2020/5/2 0:00:00 |
| 修稿时间： | 2020/7/8 0:00:00 |
Element geochemistry and genesis of phosphorus- containing mudstone of the Paleogene Madingo Formation in the Lower Congo Basin |
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| Ji Shaocong,Yang Xianghu,Zhu Hongtao,Kang Hongquan.Element geochemistry and genesis of phosphorus- containing mudstone of the Paleogene Madingo Formation in the Lower Congo Basin[J].Acta Geologica Sinica,2021,95(4):1128-1143. |
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| Authors: | Ji Shaocong Yang Xianghu Zhu Hongtao Kang Hongquan |
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| Institution: | 1) Institute of Karst Geology, CAGS/Key Laboratory of Karst Dynamics, MNR&GZAR, Guilin, Guangxi, 541004;2) Faculty of Earth Resources, China University of Geosciences, Wuhan, 430074; 3) CNOOC Research Institute, Beijing, 100027 |
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| Abstract: | The Paleogene Madingo Formation in the Lower Congo Basin developeda set of phosphorus- containing mudstone rich in organic matter. The overlying strata is silty mudstone of the Paloukou Formation, and the underlying strata is ordinary mudstone of the Madingo Formation. The petrological characteristics of phosphorus- containing mudstone, ordinary mudstone and silty mudstone are studied using thin sections, scanning electron microscope, energy spectrum and surface scanning. Redox conditions of paleo- ocean during the sedimentary period of the phosphorus- containing mudstone, ordinary mudstone and silty mudstone are analyzed based on the test of primary, trace and rare earth elements.The phosphorus source and the mechanism of phosphorus enrichment during the sedimentary period of the phosphorus- containing mudstoneare evaluated by mathematical statistical methods such as correlation analysis and cluster analysis.The results show that the microflora,mainly foraminifera,arewell developed in the phosphorus- containing mudstone. Phosphate particles mainly exist in the form of colloidal aggregates in phosphorus- containing mudstone. The water body was stratified and oxidized during the sedimentary period of the phosphorus- containing mudstone. Cerium anomaly of the phosphorus- containing mudstone was mainly related to phosphate minerals. The phosphate minerals with Cerium anomaly formed in the surface oxidation water and precipitated in the bottom water. The bottom water was hypoxic- anoxic, resulting in the enrichment of redox sensitive elements such as U and V.Phosphorus sources in the marine sedimentary rocks include terrestrial sources, hydrothermal sources, biological sources, air sources and cosmic sources.It is considered that the biological source is the main source of phosphorus in the phosphorus- containing mudstone in the study area. Organisms play an indirect role in the process of phosphorus enrichment in the phosphorus- containing mudstone, which is mainly affected by biomass and redox conditions.Biology is not only the source of phosphorus, but also changes the redox conditions of the medium to release and precipitate phosphorus from phosphorus- containing compounds. |
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| Keywords: | Lower Congo Basin Madingo Formation phosphorus- containing mudstone geochemistry sedimentology |
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