Sahara as a continent-wide Mars analogue

Sahara has experienced during its long geological history a large number of climatic changes from humid conditions (with savanna-type environments) to dry conditions (with hot desert enviroments). Therefore since the late... [ view full abstract ]

Sahara has experienced during its long geological history a large number of climatic changes from humid conditions (with savanna-type environments) to dry conditions (with hot desert enviroments). Therefore since the late Miocene Sahara alternated periods with rivers, lakes, deltas swamps with periods with a strong aeolian activity and the formation of deflation surface and sand seas.The Sahara is also dominated by a cratonic landscape with a marginal mountain chain (the Atlas) and volcanic centres (Hoggar, Tibesti). The landscape is therefore broad with swells and domes resembling the Martian topography. Wind processes have reworked, during the dry periods, the fluvial deposits that formed during humid period. The aeolian erosion has been extremely efficient leaving some remains of the fluvial deposits as meander belts or exhumed (inverted) channels. Deltaic deposits are strongly eroded and large inland lakes and swamp eroded and a few remains are mostly buried below dunes and sand seas. The leftover of the fluvial deposits is basically the coarse-grained component because the finer sediment has been removed by the wind. Sand to silt material accumulated (mostly by saltation) in the sand sheets and seas. The finer portion (able to enter the wind as suspended material) can be trapped in the large- scale atmospheric circulation. The consequence is that it enters the large-scale atmospheric circulation and has been redistributed in Sahara and in other adjacent continents (mostly Europe and South America) and oceans. The results of these climatic changes are fluvial systems and lacustrine deposits interrelated with deflation surfaces and sand accumulations. This situation is similar to Mars where fluvial deposits and morphologies abound but are largely eroded. When deposits are present are basically coarse-grained (e.g. the meandering channels of the Eberswalde deltaic plain) because the long lasting eolian. This has removed the finer portion of the sediment and accumulated the sand to silt grade portion in sand seas and sheets and the fines in a sort of draping dust. This picture perfectly matches the Martian evolution where the planet experienced a Noachian climatic optimum with the formation of a number of water-related environments. Then, during the Hesperian probably an alternation of dry and wet periods alternated. These climatic changes declined leaving a planet-wide dry, desert-like, environment. Sahara is a good continent-wide analogue because id probably the oldest desert environments and the deflation activity has been persistent and widespread.