Remote sensing evidence for a possible 10 kilometer in diameter impact structure in north-central Niger

Abstract

Remote sensing investigations of West Africa reveal a roughly 10 km in diameter, circular feature in north-central Niger. The circular feature is located within Early Devonian fluvio-marine sedimentary strata about 100 km to the north of a suite of igneous ring dikes located in the Aïr Massif. Whether the circular feature is related to the ring dikes, structural doming, or an impact crater can be evaluated from earlier geologic mapping (Black, 1967) and image analyses. Previous mapping indicates that the circular feature is defined by outcrops of Devonian Idekel sandstone and the Late Proterozoic, weakly-metamorphosed molasse of the Proche-Ténéré Formation. Absent in published lithologic descriptions of these sedimentary and metasedimentary rocks are diapiric evaporite deposits that could produce the observed circular morphologies. Lithologies that define the circular feature are confirmed by classification techniques using the ENVI software platform and band ratios/math from Landsat 8 and Sentinel 2A data. Spectral profile comparisons between the igneous intrusive rocks exposed in the Aïr Massif, outcrops of sedimentary rock that are proximal to the circular feature, and desert sand confirm that the sedimentary rocks mapped by Black (1967) define the circular feature. The shallow subsurface structure, revealed through Spaceborne Imaging Radar-C data, and 3-D modeling using Sentinel 1A data, is also not consistent with nearby ring dike structures. These data suggest that the circular feature did not likely form as a magmatic intrusion close to the time of sedimentary rock deposition. We propose that the circular feature formed from either a meteorite impact after deposition of the host sedimentary units or by some other, but less likely, geologic process. Confirmation of an impact explanation for the circular feature would require sample analysis and inspection for shock-metamorphosed materials.