摘要
柳江盆地中石炭统本溪组底部发育一套铁质鲕粒粉砂岩地层,岩性特征明显,区域上厚度稳定。依据岩石薄片和扫描电镜的观察,铁质鲕粒直径一般0.1~1.0 mm,具有边界模糊的圈层结构,圈层数3~5层,内部包裹有细小的石英粉砂颗粒。根据能谱分析结果,鲕粒内部含有Fe、Si、Al、O、K、C、Ti等元素,不同部位含量不同。综合分析,主要矿物组分有褐铁矿、赤铁矿、石英和黏土矿物。通过微量元素的分析,认为本溪组沉积早期,该地区属于相对温暖、半湿润的气候,为半封闭的还原环境海湾,水体为半咸水。该地层沉积之前,地表长期处于风化剥蚀状态,风化残积的Fe元素比较富集,再次沉降接受沉积后,被径流带入海湾后,在有机碳的参与下,C与Fe_(2)O_(3)结合,形成菱铁矿(FeCO_(3)),菱铁矿围绕水体中悬浮的细小石英颗粒层层凝聚,随着颗粒的逐渐增大而沉淀到海底。菱铁矿不稳定,在成岩过程中分解成Fe_(3)O_(4),并进一步发生氧化作用,最终转化为褐铁矿[FeO(OH)·H_(2)O]。在后期异常干旱炎热的条件下,菱铁矿也极易氧化成赤铁矿,因此就出现了铁质鲕粒中褐铁矿和赤铁矿共存的局面。
A distinct layer of Ironic oolitic siltstone stratum is observed at the lower part of the Benxi Formation of the Middle Carboniferous in Liujiang Basin,exhibiting prominent lithological characteristics and consistent thickness within the region.According to the observation of rock thin sections and scanning electron microscopy,ironic oolites exhibit a diameter ranging from 0.1 to 1.0 mm,characterized by a ring structure with indistinct boundaries consisting of 3 to 5 layers enclosing fine quartz silt particles.According to the results of energy spectrum analysis,the oolite exhibits varying elemental compositions including Fe,Si,Al,O,K,C,and Ti in distinct regions.Through comprehensive analysis,it is determined that the predominant mineral constituents comprise limonite,hematite,quartz,and clay minerals.Through the analysis of trace elements,it is inferred that during the initial sedimentation of the Benxi Formation,the region was characterized by a relatively warm and semi-humid climate,a partially enclosed reducing environment bay,and brackish water conditions.After a prolonged period of weathering and erosion,the surface underwent deposition,resulting in a relatively enriched residual Fe element.Subsequently,through sedimentation and runoff processes,it was transported into the bay.The participation of organic carbon facilitated the formation of siderite(FeCO_(3))through its combination with Fe_(2)O_(3).This resulted in the gradual deposition of siderite layers around suspended small quartz particles in the water body,which eventually settled on the seabed as particle concentration increased.Siderite undergoes diagenesis,leading to its instability and subsequent decomposition into Fe_(3) O^(4).This process is further accompanied by oxidation,ultimately resulting in the transformation of siderite into limonite[FeO(OH)·H2 O].Additionally,under extremely arid and hot conditions during later stages,siderite readily oxidizes into hematite,thereby giving rise to the coexistence of limonite and hematite within irony ooids.
作者
刘书燕
孙浩元
胡烁
董常青
宋德邻
乔雨朋
邵先杰
LIU Shu-yan;SUN Hao-yuan;HU Shuo;DONG Chang-qing;SONG De-lin;QIAO Yu-peng;SHAO Xian-jie(Management Center of National Nature Reserve of Geological Relics in Liujiang Basin,Hebei Province,Qinhuangdao 066001,China;School of Vehicle and Energy,Department of Petroleum Engineering,Yanshan University,Qinhuangdao 066004,China;College of Petroleum&Gas Engineering,Liaoning Petrochemical University,Fushun 113001,China)
出处
《科学技术与工程》
北大核心
2024年第27期11547-11557,共11页
Science Technology and Engineering
基金
国家级自然保护区补助资金(冀林草发[2019]52号)
河北省林业和草原局批准项目(冀林草发[2019]41号)。
