Polyphasic tectonic history of the N70° DASA Graben (northern, Niger)

Abstract

Located in northern Niger, the N70° DASA graben is a trough discovered recently in the Tim Mersoï basin. In this study, a tectonic history of the DASA graben was presented based on the combined use of satellite imagery, field observations and measures, available literature and borehole data. These data were used to analyse the sedimentary facies and the tectonic deformations in the DASA graben, and derive their relative chronology. For this purpose, uplift and rift deformations and their interactions with sedimentation were characterized. Overall, the analyses suggest that the DASA graben was affected from the Carboniferous to the Cretaceous by three major tectonic phases: the first phase was an uplifting stage with extension during the Carboniferous to Permian; the second phase was a rifting stage. The mean extension was ~ N160° and dominantly produced ENE-WSW trending normal faults; and the third phase was a postrift stage. It was characterized by a ~ N130° compression. The structural and sedimentological features defined the DASA graben as a particular type of syn-sedimentary basin evolving from a transpressive tectonic regime during the period ranging from Carboniferous to Permian to an extensive tectonic regime during the period ranging from Triassic to Lower Cretaceous. Thus, the second period marked by an extensional regime would probably be related to the initial stage of the opening of the Atlantic Ocean. After this rifting period, the DASA graben was affected by a compressional phase related to the collision between Africa and Europe.