Geology of the Darfur Megalake, Sudan: Implication for Groundwater Resources

The recent delineation of the boundaries of a vastly expanded paleo-lake (the Darfur Megalake) in the Darfur Region in western Sudan has renewed hopes for the presence of significant amounts of groundwater in this hyper-arid region of Sahara. A closed basin paleo-drainage system around the lake might have allowed for the collection of surface water during the Holocene wetter period. Subsequently, surface water infiltrated to recharge the Nubian Aquifer which is dominated by Mesozoic sandstone. However, the presence of surface and near-surface exposures of Precambrian rocks points to the lack of a thick Mesozoic sandstone section capable of holding any meaningful quantity of groundwater. In this work, we have integrated remote sensing, surface geology, and gravity data to show that the Darfur Megalake might have been underlain by a complex extensional structure represented by grabens and horsts of different orientations. For this, we have constructed a number of E-W trending geological cross-sections using digital elevation models (DEMs) extracted from the Shuttle Radar Topography Mission (SRTM) data and published geological maps. These cross-sections suggest possible presence of N- and NE-trending grabens that are filled with Mesozoic sedimentary rocks. Precambrian crystalline rocks and Paleozoic sedimentary rocks are exposed within horst structures bounding theses grabens. Known oasis in the region seems to align along grabenss boundaries. This geological interpretation is in good agreement with regional gravity data which show gravity lows extending in NE-direction and separated by gravity highs with steep gradients between the two anomalies. Additionally, gravity profiles constructed to coincide with the geological cross-sections show an intriguing correlation between the location of gravity lows and what appear to be drops in the stratigraphic section (lower depth to Precambrian basement). We argue that any future development plans for groundwater resources has to take into account structural complexity of the region.