Abstract During the evolution of sedimentary basins, clay minerals may record changes in their mineralogy, chemistry, and texture as a response to diagenesis, fluid flows, and tectonic activities. Therefore, studying clay minerals in sedimentary rocks provides important information that may assist to decipher the basin history. The focus of the present study is the Teloua Sandstone Formation (Fm) which belongs to the Tim Mersoi Basin located in the NE of Niger republic (West Africa). The formation is cut by the major Arlit fault which is the largest tectonic structure impacting the Tim Mersoi Basin. The aim of the present work is to use the texture, mineralogy, and chemistry of clay minerals in the Teloua Fm as geochemical markers for burial diagenesis history and fluids flows (i.e., attributed mainly to the Arlit fault). Therefore, three drill holes (DH1, DH2, and DH3) were investigated as a function of their distance from the fault and samples have been collected all along the Teloua Fm (Upper Triassic-Lower Jurassic), at the unconformity surface with the underlaying Moradi Fm (Upper Permian), and at the top of the Moradi Formation. Petrographic observations demonstrate that the sediments of the Teloua Fm have undergone transformations induced by burial diagenesis, brittle deformation, and multiple stages of fluid flows. These transformations are marked by grain compaction, fragmentation, dissolution of detrital minerals, recrystallization of authigenic clay minerals, and modifications in the primary porosity. XRD and SEM results indicate no significant variation in the detrital mineralogy of the three drill holes; Teloua Fm samples are composed of quartz, feldspars (microcline and albite), micas (biotite and muscovite), minor heavy minerals such as hematite, anatase, phosphates (apatite and monazite), and zircon. The authigenic clay minerals observed in the three drill holes are rosette-like tosudite (i.e., a regular interstratified chlorite/smectite), saponite, montmorillonite, and kaolinite/smectite mixed layer. Regarding their vertical distribution, tosudite occurs throughout the Teloua Fm, whereas montmorillonite is mainly present at the top of the formation, and saponite is only observed at the unconformity between Teloua and Moradi formations. The Mg content of tosudite tends to decrease with increasing vertical distance from the basal unconformity and the lateral distance from the Arlit fault. This is interpreted as an evidence of Mg-rich fluid circulations related to the Arlit fault activity that penetrated the formation through the unconformity surface and fractures. This is also evidenced by the enrichment of dolomite at the unconformity when moving closer to the Arlit fault. In addition, the occurrence of both authigenic saponite (at the unconformity) and montmorillonite (upper part of the Teloua Fm) that post-dated tosudite is attributed to another stage of Mg-rich fluid circulation during late diagenesis. Furthermore, late downward circulation of meteoric fluids of low pH are evidenced by the partial alteration and replacement of montmorillonite by kaolinite/smectite mixed layer in the Teloua Fm (at shallow depth of the DH3). These results demonstrate the validity of clay minerals as reliable tools to provide information about fluid/rock interaction in complex geological and tectonic setting.

中文翻译：

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砂岩储层中断层相关流体流动的粘土矿物特征：来自尼日尔 Tim Mersoї 盆地 Teloua 组的案例研究

摘要 在沉积盆地演化过程中，粘土矿物可能会记录其矿物学、化学和质地的变化，作为对成岩作用、流体流动和构造活动的响应。因此，研究沉积岩中的粘土矿物提供了可能有助于破译盆地历史的重要信息。本研究的重点是位于尼日尔共和国（西非）东北部的 Tim Mersoi 盆地的 Teloua 砂岩组 (Fm)。该地层被主要的 Arlit 断层切断，Arlit 断层是影响 Tim Mersoi 盆地的最大构造结构。目前工作的目的是利用 Teloua Fm 粘土矿物的质地、矿物学和化学作为埋藏成岩历史和流体流动（即主要归因于 Arlit 断层）的地球化学标记。所以，研究了三个钻孔（DH1、DH2 和 DH3）作为它们与断层距离的函数，并在整个 Teloua Fm（上三叠统 - 下侏罗纪）的不整合面上收集了样品（下伏 Moradi Fm）（上二叠纪），并在莫拉迪组的顶部。岩石学观察表明，Teloua 组沉积物经历了埋藏成岩作用、脆性变形和多阶段流体流动引起的转变。这些转变的特点是颗粒压实、破碎、碎屑矿物溶解、自生粘土矿物的再结晶以及原生孔隙度的改变。XRD 和 SEM 结果表明三个钻孔的碎屑矿物学没有显着变化；Teloua Fm 样品由石英组成，长石（微斜长石和钠长石）、云母（黑云母和白云母）、少量重矿物，如赤铁矿、锐钛矿、磷酸盐（磷灰石和独居石）和锆石。在三个钻孔中观察到的自生粘土矿物为莲座状tosudite（即规则的绿泥石/蒙脱石层间）、皂石、蒙脱石和高岭石/蒙脱石混合层。从垂向分布看，托舒达岩分布于整个 Teloua 组，而蒙脱石主要存在于地层顶部，皂石仅在 Teloua 组和 Moradi 组之间的不整合面观察到。随着距基底不整合面的垂直距离和距 Arlit 断层的横向距离的增加，Tosuudite 的 Mg 含量趋于降低。这被解释为与 Arlit 断层活动相关的富镁流体循环的证据，这些循环通过不整合面和裂缝穿透地层。当靠近 Arlit 断层时，不整合面上的白云岩富集也证明了这一点。此外，晚成岩的自生皂石（在不整合面）和蒙脱石（Teloua Fm 的上部）的出现都归因于晚成岩过程中富镁流体循环的另一个阶段。此外，Teloua Fm（DH3 浅层）高岭石/蒙脱石混合层对蒙脱石的部分蚀变和替代证明了低pH 的大气流体晚期向下循环。