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Textural aspects of authigenic clay minerals formed during burial diagenesis of the sandstones (SEM images). (a,b) Mixture of pseudohexagonal plates of kaolinite (Kln) ( partially dissolved) and blocky crystals of dickite (Dc) in Carboniferous sandstones (a) and Jurassic sandstones (b), respectively. (c) Discontinuous coating of detrital quartz grains by Fe-rich chlorite spherules (Chl) and authigenic quartz overgrowths (Qtz) in Carboniferous sandstones. (d) Discontinuous coating of detrital albite grains by Fe-rich chlorite spherules (Chl) and authigenic albite overgrowths (Ab) in Jurassic sandstones.
Source publication
Tosudite, a regularly interstratified chlorite-smectite, crystallizes as an alteration mineral of several preexisting Al-bearing silicates (feldspars, kaolin minerals, chlorites) present in arkosic sandstones hosted in uranium deposits in Niger. X-ray diffraction patterns show a sharp superstructure at 29–29.6 Å for an air-dried state and a peak at...
Contexts in source publication
Context 1
... the kaolin sub-group; and (2) fine-grained Fe-rich chlorite. In the Carboniferous samples, kaolin minerals predominate over chlorite, whereas it is the opposite in the Jurassic samples. The crystal habits of the kaolin minerals range from a vermicular arrangement of pseudohexagonal plates typical of kaolinite to a blocky habit typical of dickite (Fig. 3a,b). According to XRD patterns, dickite is scarcer in the Jurassic formation than in the Carboniferous ones. Nevertheless, the relative intensities of d 20 2 , 1 31 reflections of kaolinite and d 132, 20 4 reflections of dickite demonstrate that kaolinite also predominates over dickite in both Jurassic and Carboniferous samples. In ...
Context 2
... of kaolinite Tosudite hosting U deposits in Niger over dickite in these sandstones is indicative of maximum burial depth which did not exceed 3-3.5 km ( Beaufort et al., 1998;Lanson et al., 2002). Fe-rich chlorite occurs essentially as a discontinuous coating on detrital quartz and feldspars, partially inhibiting overgrowths of quartz and albite (Fig. 3c, d). This mineral shows euhedral platy crystals that are oriented perpendicular to the framework grain surface arranged in either a rosette or spherule-like structure. Microprobe and XRD data of this chlorite are similar to those of Fe-rich chlorite commonly reported at low temperatures in siliciclastic reservoir sandstones (i.e. chlorite ...
Context 3
... main types of authigenic clay minerals were formed during the burial history of sandstones: (1) coarse-grained minerals of the kaolin sub-group; and (2) fine-grained Fe-rich chlorite. In the Carboniferous samples, kaolin minerals predominate over chlorite, whereas it is the opposite in the Jurassic samples. The crystal habits of the kaolin minerals range from a vermicular arrangement of pseudohexagonal plates typical of kaolinite to a blocky habit typical of dickite (Fig. 3a,b). According to XRD patterns, dickite is scarcer in the Jurassic formation than in the Carboniferous ones. Nevertheless, the relative inten- sities of d 20 2 , 1 31 reflections of kaolinite and d 132, 20 4 reflections of dickite demonstrate that kaolinite also predominates over dickite in both Jurassic and Carboniferous samples. In conditions of normal geothermal gradient, the predominance of kaolinite over dickite in these sandstones is indicative of maximum burial depth which did not exceed 3-3.5 km ( Beaufort et al., 1998;Lanson et al., ...
Context 4
... chlorite occurs essentially as a discontinuous coating on detrital quartz and feldspars, partially inhibiting overgrowths of quartz and albite (Fig. 3c, d). This mineral shows euhedral platy crystals that are oriented perpendicular to the framework grain surface arranged in either a rosette or spherule-like structure. Microprobe and XRD data of this chlorite are similar to those of Fe-rich chlorite commonly reported at low temperatures in siliciclastic reservoir sandstones (i.e. chlorite interstratified with small amounts of berthier- ine-like layers and Ib β = 90° polytype) (Beaufort et al, 2015 and references ...
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In this study, characteristics of Chang 8 tight sandstone pore structure and diagenesis are analyzed. A classification standard for sandstone diagenetic facies is established. Combined with the probabilistic neural network method, logging curves are used to predict the distribution of diagenetic facies. The following results are found: the Chang 8...
Citations
... Furon, 1942;Faure, 1954Faure, , 1966Faure et al., 1956 ;. References: Chudeau, 1908;Greigert et al., 1954;Faure et al., 1956 ;Greigert & Pougnet, 1967, p. 108;Bigotte & Obelianne, 1968;Valsardieu, 1971;Fabre et al., 1983;Moody & Sutcliffe, 1991;Kogbe, 1991;Wagani et al., 2011;Billon et al., 2016. Subgroups: Goufat, Wagadi, Lower Dabla. ...
... References: Fabre et al., 1983;Coquel et al., 1995;Wagani et al., 2011;Mamadou et al., 2016;Mamadou, 2016;Billon et al., 2016. ...
... References: Moody and Sutcliffe, 1991;Rauhut & López-Arbarello, 2009;Mudroch et al., 2011. References: Joulia, 1953;Abdoul Aziz, 1968;Bigotte & Obelianne, 1968;Valsardieu, 1971; Ministère des Mines et de l'Hydraulique, Direction des Mines et de la Géologie, 1977;Fabre et al., 1983;de Rouvre, 1985de Rouvre, , 1988Kogbe, 1991;Sidor et al., 2003;Tabor et al., 2011;Billon et al., 2016. ...
The current knowledge of the stratigraphy of Niger benefited greatly from the mining, hydrocarbon, hydrogeological, and paleontological sciences. Exploration by early explorers and studies of the aquifers initially sparked our understanding of the surface and shallow formations. Then, the discoveries in 1957 of important Uranium reserves and soon after in 1964 of the enormous Lower Cretaceous vertebrate site of Gadoufaoua stressed the need to undertake detailed stratigraphical investigations in the western Iullemmeden Basin. The geologist Hughes Faure then published his important, and still relevant, 1966 thesis on the surface geology of Eastern Niger. From that time onward, the Oil & Gas companies started paying attention to the most prospective areas in the Eastern Niger Basin. During the last decade, these same hydrocarbon companies finally allowed some geologists to share their knowledge of the sub-surface in relevant publications. It is from all these studies that the present Lexicon draws its content. It provides the historical background of all described geological units in Niger and summarizes each unit's lithological and paleontological knowledge in an easy-to-search format.
... Å that indicate as well a dioctahedral nature for tosudite. Billon et al. (2016) reported a similar octahedral occupancy value of tosudite in both underlying (Guezouman and Tarat) and overlying (Tchirezine) Sandstone Formations that host the uranium deposits in Niger. The chemical analyses of tosudite plotted in the Al (total) -Si -R 2+ ternary diagram confirm that the two end members in this mixed layer are sudoite (di-trioctahedral chlorite) and montmorillonite (dioctahedral smectite) i.e., spread between low charge and high charge end members (Fig. 8A, B, and 8C). ...
... Based on these results, the Teloua Formation seems to have been affected by a complex geological history that includes combinations of burial diagenesis, brittle deformation, and associated fluid flow events. This is consistent with the geological history of the Tim Mersoï Basin, where several studies demonstrate that the basin was impacted by diagenesis and circulation of hot fluids from the deeper part of the basin along the AIA fault (e.g., Pacquet, 1970;Pagel et al., 2005;Billon et al., 2016;Mamadou et al., 2016;Bohari et al., 2018;Billon and Patrier, 2019). ...
... The presence of tosudite in the Tim Mersoï Basin has been reported recently by Billon et al. (2016), and Billon and Patrier (2019) in the uranium-bearing Carboniferous formations of Guezouman, Tarat (below the Teloua Formation), and Upper Jurassic Formation of Tchirezrine (above the Teloua Formation). Chlorite/smectite mixed layer has also been mentioned in other previous studies in Arlit, Akouta, and Imouraren deposits, without identifying clearly tosudite (Pacquet, 1970;Forbes, 1988;Cavellec, 2006;Mamadou et al., 2016). ...
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 Mersoï 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 Mersoï 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.
