Synsedimentary Deformation Characterization of Niamey Sandstones in the Tondibia Area (Man Shield Northeastern Margin, Western Niger, Region of Niamey)

Niamey sandstones belong to a group of formations of Neoproterozoic-age, located on the Man shield northeastern margin. They sporadically outcrop along the Niger river valley. These geological formations, which occupy a central position in relation to the Taoudenni basin (further north) and the Voltas basin (further south), share similarities with the formations of the aforementioned basins. The research objective is to determine the synsedimentary deformation that has affected these Niamey sandstones in the Tondibia area. The methodological approach used focuses, firstly, on field measurements of synsedimentary deformation structures, and secondly, on projecting these measurements into the Win-Tenseur program in order to calculate stress tensors (s1, s2, s3). Synsedimentary deformations appear during the early stages of lithification, i.e. when the sediment is still loose and contains a high percentage of water. The analysis of these deformations is of great interest for the tectonic-sedimentary analysis of basin deposits. Deformation analysis reveals that the synsedimentary deformation phase affecting the Niamey sandstones is characterized by a NNW-SSE to NNE-SSW direction of elongation. This phase of deformation is marked in the field by normal faults with an average orientation of N80°. This extensive episode is concomitant with the extension of the Neoproterozoic Ocean (870 to 800 Ma).