The secret of the Kalahari sands - Nine tonnes of borehole cores tell the story of the sedimentary basin

The German-Namibian team, for the first time, has drilled a continuous core through the Kalahari deposits in the Namibian part of the Kalahari Basin. The scientists’ objective: understanding the geological setting of the groundwater system.

Geologist Dr. Roy Miller with drilling core Source: BGR

A huge sedimentary basin lies at the heart of the southern part of Africa – the Kalahari Basin. It stretches for more than 2,000 kilometres from South Africa to the Democratic Republic of Congo. The deposits in this basin were laid down over the course of many millions of years by rivers, inland lakes and aeolian sedimentation. These sediments now form different groundwater systems which are not easy to use. "It is very challenging to differentiate and classify the horizons in the aquifers and aquicludes," reports hydrogeologist Christoph Lohe from the German Federal Institute for Geosciences and Natural Resources (BGR). Although they appear homogenous at first sight, the sediments are far from uniform.

To gain a better understanding of the history of the Kalahari Basin, geologists from Germany and Namibia in 2015 cut a continuous core in the centre of a huge sedimentary fan, known as the Cubango Megafan, which comprises a former gigantic river delta in the north of Namibia. The core with a total length of 400 metres was then analysed in Hannover using the most up-to-date scientific methods. The results of the coring produced a small sensation for Dr. Roy Miller, the former director of the Namibian Geological Survey. "This core tells us a great story about the climatic and geological development in the north-western Kalahari from the Tertiary up until the present day," he says.

From its development, hydrogeologists can now draw conclusions about the available water resources underground. The borehole also provides important information on the hydraulic properties, and the water production capacity of specific sedimentary horizons.