The Niamey area lies on the south-western edge of the Iullemmeden Basin. The Continental terminal 3 (Ct3) formation, the subject of this study, represents the last infilling deposits of this basin. In order to determine the depositional environments of the Ct3 formation in the Niamey area, a methodological approach based on field data analysis followed by laboratory analyses was implemented. The main objective of this study is therefore to improve the knowledge of the sedimentary dynamics of Ct3 deposits in the Niamey area. Specifically, the aim of this study is to determine the Ct3 depositional environments. Sedimentological analysis enabled us to distinguish five (5) facies labelled F1, F2, F3, F4 and F5. These facies consist of alternating clayey sandstones and ferruginous lateritic oolitic sandstones with indurated levels, locally showing sandstones levels with unclear oblique bedding. The presence of casts of Gastropods, Lamellibranchs and Echinoderms indicates that the Ct3 deposits were emplaced in a shallow, lagoonal to lacustrine freshwater basin subject to fluvial inputs.

This study was carried out in the south-western part of Niger. The study area corresponds to the Niamey region, which straddles the south-eastern edge of the West African Craton and the south-western terminus of the Iullemmeden Basin. The general objective of this work is to determine the context in which the Ct3 deposits were emplaced in the Tondibia, «Rhodesia» and Kongou sectors. Specifically, the aim is to provide a petrographic description of the Ct3 deposits and to characterise the deformation that affected these deposits. The methodology used is based on the macroscopic and microscopic petrographic description of the samples taken and on structural measurements. Three sedimentological sections were taken from the three outcrops selected (Tondibia, Rhodesia and Kongou). The petrographic study of the Continental Terminal 3 (Ct3) deposits identified several facies whose sedimentological characteristics and number varied according to the sectors studied. The facies identified include: kaolinitic sandstones; ferruginous oolitic sandstones; sandstone clays; conglomeratic sandstones; clays intercalated with ferruginous oolitic sandstones; and iron oxide nodule conglomerates. Microscopic observations made it possible to identify several forms of oolitic concretions, namely: type α oolites (Oα), type γ oolites (Oγ), proto-oolites (PO), oolites of type γ (Oγ), oolites of type γ (Oγ), oolites of type γ (Oγ) and oolites of type γ (Oγ). proto-oliths (PO) and composite ooliths (OC). Tectonic analysis has revealed a NW-SE and NE-SW compressive phase of Oligo-Miocene age that affected the deposits of Terminal Continental 3 (Ct3).