Magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion. This work, aims to show that, the magnetic susceptibility signature which exists in th...Magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion. This work, aims to show that, the magnetic susceptibility signature which exists in the cretaceous sediments of the Babouri-Figuil basin, resides mainly in the detrital constituents. Variations of amplitudes are observed, which can be useful for regional correlation.This amplitude variation results in the transgressive and regressive movements that give way to a fluctuation of detrital deposits because of erosion. Considering the sedimentological study, carried out, different microfacies have been identified in the basin, namely, fluvial facies and lake facies that sometimes contain fossils. The combination of detailed sedimentological analysis and sequence stratigraphy is based on the modeling of vertical and lateral variations within the basin. Finally, the interpretation of the magnetic susceptibility signal suggests that in the detrital domain, this signal is mainly controlled by environmental parameters such as the agitation of the water and the rate of sedimentation, as well as diagenesis.展开更多
Magmatism in the Cretaceous sedimentary basins of the Figuil and Léré regions constitutes one of the fundamental parameters in the reconstruction of the history of the Cretaceous sedimentary basins. The main...Magmatism in the Cretaceous sedimentary basins of the Figuil and Léré regions constitutes one of the fundamental parameters in the reconstruction of the history of the Cretaceous sedimentary basins. The main objective of this paper is to constrain the petrogenetic processes of hypovolcanic rocks and to determine their geodynamic context of emplacement. The petrographic study of mafic hypovolcanic and trachytic rocks was carried out under a polarizing microscope on thin sections. For the geochemical study, the major oxides and some trace elements were analyzed by ICP-AES. Trace and rare earth elements were analyzed by ICP-MS. The dolerites of the Cretaceous sedimentary basins are composed of dykes of amphibole bearing dolerites, biotite and pyroxene bearing dolerite, pyroxene bearing dolerites and trachytes. The dykes are in the order of 20 to 100 m wide by several kilometers long and oriented from N23<span style="white-space:normal;"><span style="white-space:normal;"><span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span></span></span>E to N90<span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>E. The textures of these rocks are sub-ophitic to intergranular for dolerites and trachytic for evolved rocks (trachytes). The geochemical study shows that the dolerites are basaltic in composition with alkaline to subalkaline character. The sampled dykes have an evolution dominated by fractional with the minor impact of the crustal assimilation characterized by low Rb/Y ratios for dolerites (0.36 - 0.97) and high values of Rb/Y for the Pan-African granitoid<span style="font-size:10.0pt;font-family:;" "="">s’</span><span style="font-size:10.0pt;font-family:;" "=""> samples (1.95 - 4.01).</span><span style="font-size:10.0pt;font-family:;" "=""> </span><span style="font-size:10.0pt;font-family:;" "="">The nature of doleritic and trachytic magma sources is supported by their (Tb/Yb)N > 1.9 (1.91 - 3.79) and Dy/Yb > 2 (2.32 - 3.50) ratios of most samples, which suggests melting in a garnet-bearing mantle. Concerning the geodynamic context of the studied rocks, doleritic samples are classified as within-plate tholeiite and volcanic arc basalt, and within-plate alkali basalts.</span>展开更多
The purpose of this work is to characterize the sediments of the Babouri-Figuil<span style="font-family:""><span style="font-family:Verdana;"> Basin from a diagenetic point of view...The purpose of this work is to characterize the sediments of the Babouri-Figuil<span style="font-family:""><span style="font-family:Verdana;"> Basin from a diagenetic point of view, the protolith context and weathering conditions, u</span><span><span style="font-family:Verdana;">sing major element geochemistry and mineralogy of the sedimentary rocks. Microscopic observations of diagenetic phenomena (on and around detrital grains of the basin), and the study of precipitation of the cement show that these sediments have undergone phenomena of compaction, dissolution, recrystallization and cementation. Cementation of quartz by silica is controlled by the rate of precipitation of silica, which is closely related to temperature than pressure. Thus, the sediments of the basin could be influenced by hydrothermalism during diagenesis, which would have inhibited their reservoir quality by generalized cementation phenomena. Geochemical features of the sediments show high contents in SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> (47.49 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">90.79 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Al</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (2.92 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">23.18 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Fe</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (0.2 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">6.22 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">) and alkali and alkaline earth metals (>3</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">). The chemical alteration index varies between 30.92</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"> and 95.08</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">. This variation in the CIA values reflects the variation in the proportion of feldspars and different clay minerals in these sediments. How</span></span><span style="font-family:""><span style="font-family:Verdana;">ever, the ICV calculation and the ICV versus CIA show compositional immature to mature sediments, with </span><span style="font-family:Verdana;">low to intense weathering character of these sediments. Petrographic and</span><span style="font-family:Verdana;"> geo</span><span style="font-family:Verdana;">chemical characteristics of sediments of the basin are compatible with the</span><span style="font-family:Verdana;"> composition of the granitic and gneissic surrounding bedrocks.</span></span>展开更多
The study area located between Figuil (Northern Cameroon) and Léré (Southwest Chad) belongs to the northern domain of the Pan-African Range of Central Africa (CPAC). The aim of this work is to highlight the ...The study area located between Figuil (Northern Cameroon) and Léré (Southwest Chad) belongs to the northern domain of the Pan-African Range of Central Africa (CPAC). The aim of this work is to highlight the petrogenesis of the hypovolcanic formations affecting the Pan-African base and the Cretaceous sedimentary basins of the study area as well as their geodynamic context. Hypovolcanic formations have a strong affinity with rocks of the continental tholeiitic series. The tholeiitic character with alkaline affinity constitutes the transition between alkaline and tholeiitic magmatisms. The low Rb/Sr ratios (0.24 - 1.24) constitute proof that the dolerites studied do not come from the partial fusion of Pan-African granitoids (Rb/Sr: 2.54 - 7.64) but rather from a mantle source as shown by the similar ratios of Zr/Hf (37.56 - 43.08), Nb/Ta (15.16 - 19.60) of dolerites from the Pan-African basement (DSP) and Zr/Hf (34.34 - 46.48), Nb/Ta (14.34 - 19.3) from dolerites from the Cretaceous sedimentary basins (DBSC). The enrichment in LREE relative to the HREE of the dolerites studied associated with the ratios (Tb/Yb)N (1.95 - 2.56), Dy/Yb (2.33 - 2.85) characterizes a mantle source of lherzolite with garnet.展开更多
文摘Magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion. This work, aims to show that, the magnetic susceptibility signature which exists in the cretaceous sediments of the Babouri-Figuil basin, resides mainly in the detrital constituents. Variations of amplitudes are observed, which can be useful for regional correlation.This amplitude variation results in the transgressive and regressive movements that give way to a fluctuation of detrital deposits because of erosion. Considering the sedimentological study, carried out, different microfacies have been identified in the basin, namely, fluvial facies and lake facies that sometimes contain fossils. The combination of detailed sedimentological analysis and sequence stratigraphy is based on the modeling of vertical and lateral variations within the basin. Finally, the interpretation of the magnetic susceptibility signal suggests that in the detrital domain, this signal is mainly controlled by environmental parameters such as the agitation of the water and the rate of sedimentation, as well as diagenesis.
文摘Magmatism in the Cretaceous sedimentary basins of the Figuil and Léré regions constitutes one of the fundamental parameters in the reconstruction of the history of the Cretaceous sedimentary basins. The main objective of this paper is to constrain the petrogenetic processes of hypovolcanic rocks and to determine their geodynamic context of emplacement. The petrographic study of mafic hypovolcanic and trachytic rocks was carried out under a polarizing microscope on thin sections. For the geochemical study, the major oxides and some trace elements were analyzed by ICP-AES. Trace and rare earth elements were analyzed by ICP-MS. The dolerites of the Cretaceous sedimentary basins are composed of dykes of amphibole bearing dolerites, biotite and pyroxene bearing dolerite, pyroxene bearing dolerites and trachytes. The dykes are in the order of 20 to 100 m wide by several kilometers long and oriented from N23<span style="white-space:normal;"><span style="white-space:normal;"><span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span></span></span>E to N90<span style="color:#4F4F4F;font-family:-apple-system, "font-size:16px;white-space:normal;background-color:#FFFFFF;">°</span>E. The textures of these rocks are sub-ophitic to intergranular for dolerites and trachytic for evolved rocks (trachytes). The geochemical study shows that the dolerites are basaltic in composition with alkaline to subalkaline character. The sampled dykes have an evolution dominated by fractional with the minor impact of the crustal assimilation characterized by low Rb/Y ratios for dolerites (0.36 - 0.97) and high values of Rb/Y for the Pan-African granitoid<span style="font-size:10.0pt;font-family:;" "="">s’</span><span style="font-size:10.0pt;font-family:;" "=""> samples (1.95 - 4.01).</span><span style="font-size:10.0pt;font-family:;" "=""> </span><span style="font-size:10.0pt;font-family:;" "="">The nature of doleritic and trachytic magma sources is supported by their (Tb/Yb)N > 1.9 (1.91 - 3.79) and Dy/Yb > 2 (2.32 - 3.50) ratios of most samples, which suggests melting in a garnet-bearing mantle. Concerning the geodynamic context of the studied rocks, doleritic samples are classified as within-plate tholeiite and volcanic arc basalt, and within-plate alkali basalts.</span>
文摘The purpose of this work is to characterize the sediments of the Babouri-Figuil<span style="font-family:""><span style="font-family:Verdana;"> Basin from a diagenetic point of view, the protolith context and weathering conditions, u</span><span><span style="font-family:Verdana;">sing major element geochemistry and mineralogy of the sedimentary rocks. Microscopic observations of diagenetic phenomena (on and around detrital grains of the basin), and the study of precipitation of the cement show that these sediments have undergone phenomena of compaction, dissolution, recrystallization and cementation. Cementation of quartz by silica is controlled by the rate of precipitation of silica, which is closely related to temperature than pressure. Thus, the sediments of the basin could be influenced by hydrothermalism during diagenesis, which would have inhibited their reservoir quality by generalized cementation phenomena. Geochemical features of the sediments show high contents in SiO</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;"> (47.49 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">90.79 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Al</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (2.92 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">23.18 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">), Fe</span><sub><span style="font-family:Verdana;">2</span></sub><span style="font-family:Verdana;">O</span><sub><span style="font-family:Verdana;">3</span></sub><span style="font-family:Verdana;"> (0.2 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:""><span style="font-family:Verdana;">6.22 wt</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">) and alkali and alkaline earth metals (>3</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;">). The chemical alteration index varies between 30.92</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"> and 95.08</span><span style="color:#4F4F4F;font-family:Verdana;">%</span><span style="font-family:Verdana;"></span><span style="font-family:Verdana;">. This variation in the CIA values reflects the variation in the proportion of feldspars and different clay minerals in these sediments. How</span></span><span style="font-family:""><span style="font-family:Verdana;">ever, the ICV calculation and the ICV versus CIA show compositional immature to mature sediments, with </span><span style="font-family:Verdana;">low to intense weathering character of these sediments. Petrographic and</span><span style="font-family:Verdana;"> geo</span><span style="font-family:Verdana;">chemical characteristics of sediments of the basin are compatible with the</span><span style="font-family:Verdana;"> composition of the granitic and gneissic surrounding bedrocks.</span></span>
文摘The study area located between Figuil (Northern Cameroon) and Léré (Southwest Chad) belongs to the northern domain of the Pan-African Range of Central Africa (CPAC). The aim of this work is to highlight the petrogenesis of the hypovolcanic formations affecting the Pan-African base and the Cretaceous sedimentary basins of the study area as well as their geodynamic context. Hypovolcanic formations have a strong affinity with rocks of the continental tholeiitic series. The tholeiitic character with alkaline affinity constitutes the transition between alkaline and tholeiitic magmatisms. The low Rb/Sr ratios (0.24 - 1.24) constitute proof that the dolerites studied do not come from the partial fusion of Pan-African granitoids (Rb/Sr: 2.54 - 7.64) but rather from a mantle source as shown by the similar ratios of Zr/Hf (37.56 - 43.08), Nb/Ta (15.16 - 19.60) of dolerites from the Pan-African basement (DSP) and Zr/Hf (34.34 - 46.48), Nb/Ta (14.34 - 19.3) from dolerites from the Cretaceous sedimentary basins (DBSC). The enrichment in LREE relative to the HREE of the dolerites studied associated with the ratios (Tb/Yb)N (1.95 - 2.56), Dy/Yb (2.33 - 2.85) characterizes a mantle source of lherzolite with garnet.
