The Garoua Formation of the Upper Benue Trough (Cameroon), as a potential lateral extension of the Bima Formation (Nigeria): evidence from geomorphology, facies analysis, petrology and geochemistry

The Garoua Formation of the Upper Benue Trough in Northern Cameroon crops out as buttes or tabular hill cut by various deep valleys. They are similar to features widespread in the Upper Bima Member of Bima Formation in Nigeria. The numerous outcrops consist of East–West oriented sandstone (Hossere) hill. Angular to sub-angular quartz and potassic feldspars represent the main components. Feldspar is subject to diagenetic transformation into kaolinite. Clay mineral analysis of Garoua Formation reveals the abundance of kaolinite and smectite, along with illite and chlorite, which are scarce and occur in low proportions. The intergranular matrix consists of a mixture of microcrystalline quartz, clay and iron oxides. Diagenetic fluid circulation contributed to infill fractures of quartz grains and feldspar. The geochemical signature of wacke, arkose, litharenite and ferruginous sandstone of the Garoua Formation consists of more than 50 Wt % SiO 2 followed by Al 2 O 3 and Fe 2 O 3 making less than 20 Wt %. They occur as residual hills and must have been affected by Neogene tectonic movements in Africa. The Garoua Formation known as Cretaceous yielded little palynological residue with few fungal remains of the Rhizophagites type, little amorphous organic matter (AOM) and few translucent phytoclasts, insufficient for age dating at the current stage of the research. The Garoua Formation is tentatively interpreted as an extension of the Upper Bima Member known from the adjacent Nigeria territory, based on the geomorphological, lithostratigraphic, petrographic, mineralogical and geochemical similarities.