North-Eastern Niger: Sandstone Landscape of the Sahara

Abstract

The landform history of the sandstone scarpland, inselberg and plains landscape of the greater Djado region, part of the presently hyper-arid central Sahara, in north-eastern Niger, begins with all-encompassing Paleogene etchplanation under humid-tropical conditions, followed by the almost compete stripping of the original soil cover and silcrete induration of the uniform etchplain during the Oligocene. Still under very humid conditions, deep-reaching karstification then penetrates silcrete, contemporaneous ferricrete and, above all, the saprolitic sandstones, also creating numerous poljes. Gradually decreasing humidity up to the end of the Neogene, resulting in increasingly restricted etchplanation, leads to the formation of scarplands, inselbergs, intra-plateau basins, pediments, and still sandstone-karst-related scarpfoot depressions. During a final relapse to quite humid conditions, landslide fringes form along all heterolithic escarpments at the onset of the Pleistocene, later on merely subject to fluvial dissection in the context of at least three phases of Quaternary pluvial river aggradation and terrace formation. A thorough reshaping of most of the region under Quaterary arid conditions is effected by more than one phase of aeolian corrasion, as part of the largest wind-corrasion landscape on Earth.