Quaternary climate and landscape development in West Africa: evidence from satellite images

The landforms and drainage system of the humid forrested parts of West Africa have traditionally been associated with structural control by the Basement Complex rocks of the region. However, satellite observations from the NOAA AVHRR and LANDSAT Thematic Mapper sensors permit the identification of landscape lineations, parallel to each other and trending in the dominant wind direction, across large areas of West Africa, in both arid and humid regions and on a variety of rock types. Since those farther north, of similar direction and spacing, are known to represent the soils of fossil sand dunes, the present observations are interpreted as evidence of the extension of desert conditions well into the present humid zone at 7o\N during the Quaternary period. However, while the lineations in the north represent the soils of former dunes and interdunes respectively, no evidence of dune soils is observed in study areas in southern Nigeria. Here the lineations are interpreted in the light of existing data and observations of previous workers, as representing the remnants of a former dune land space, fossilised by concretionary laterites formed during previous arid and humid phases. The findings demand a revised approach to models of landscape development and of the magnitude of Quaternary climate change in West Africa.