Unearthing the mysteries of the Sperrgebiet

The 29th Colloquium of African Geology (CAG29), which took place in Windhoek in September, provided a multitude of opportunities, such as offering a variety of field excursions and workshops. I was one of the fortunate few to have the privilege of embarking on an extraordinary journey to Tsau ǁKhaeb National Park, formerly known as Sperrgebiet (Prohibited Area). The park was established in 2008 with the aim of conserving the unique desert landscape and biodiversity of the area.

While the park is under protection, a significant portion of it remains inaccessible to travellers, or only with a guided tour, but our group of geologists had a chance to explore this wild landscape. The Sperrgebiet is part of the Namib Desert, one of the oldest deserts in the world. It covers the entire coastline of Namibia, extending into Angola to the north and South Africa to the south. The Sperrgebiet, an expanse of some 26 000 km², lies in the southern part of this vast area.

Upon entering the Sperrgebiet, one is not only confronted with the relentless force of the wind but also captivated by how it has significantly shaped its morphology and landscape for millions of years. The geology of the Sperrgebiet is characterised by ancient rocks and desert landforms. The deposition of these rocks occurred during different periods, from Precambian gneisses of the Namaqualand Metamorphic Complex (ca. 1200 million years) and metasedimentary and metavolcanic rocks of the Gariep Supergroup (ca. 600 million years) to the deposits of the Namib Group, the oldest of which are late Cretaceous (ca. 70 million years). But one of the prominent geological features of the Sperrgebiet is the Orange River Basin. The Orange River, which rises in the Lesotho highlands, drained this part of southern Africa for millions of years. During that time it transported an enormous sediment load downriver, depositing it partly along its banks as terraces, off the Orange River mouth in the Atlantic Ocean, and along the seashore, where it was transported and redistributed by ocean currents and winds. And contained within these sediments were diamonds, which accumulated in alluvial deposits, both onshore and offshore.

But have you ever wondered where and how these precious gems originated? It is widely accepted among geologists that the diamonds found in the Sperrgebiet come from Cretaceous diamondiferous kimberlites in the interior of South Africa, where graphite was converted to diamond under enormous pressures and temperatures deep within the earth. After being transported to the surface by volcanic processes, complex weathering and the action of streams and rivers, these diamonds embarked on a journey that ultimately deposited them on the western margin of the continent, as well as along the lower reaches of the Orange River. A combination of geological and atmospheric factors, including the interaction of river systems, coastal processes and wind regimes led to the accumulation of the diamonds in a variety of deposit types throughout the Sperrgebiet and off the Namibian and South African coast.

As soon as the first diamond was discovered near Lüderitz in 1908 by railway worker Zacharias Lewala, the Namibian diamond rush began. During its initial stages, diamonds were easily found and could be collected by hand in large quantities – especially on a full moon night, when they sparkled in the sand! The Sperrgebiet still retains remnants of the early diamond rush, notably gravel heaps, open-pit mining sites, mining equipment and infrastructure, the latter providing our group with shelter during our visit to this fascinating area. Apart from diamond recovery – now largely offshore – Namdeb Diamond Corporation is working to restore the damage caused during the past century by onshore mining, to revegetate spoil heaps and return the affected areas to as near their natural state as possible.

Beyond the allure of the diamond mining history, I soon discovered that the Sperrgebiet holds a hidden treasure trove of fossils, unlocking the mysteries of a bygone era. These fossils, preserved in ancient sedimentary layers, provide a glimpse into the prehistoric world that existed long before the evolution of homo sapiens. Palaeontologists have uncovered an array of fossils, which range from marine creatures to land-based mammals, shedding light on the evolution and biodiversity of this region. Marine reptiles, such as plesiosaurs and ichthyosaurs, lived in the southern Atlantic of those days, while shells of ancient ostrich eggs and fossilised termite hives are found onshore – indicating palaeoclimates which changed over time and at one stage must have been savannah-like.

As sedimentary layers accumulate slowly, the remains of plants and animals are gradually buried and, under suitable circumstances, preserved. Over millions of years, the immense pressure from the overlying sediments thus transforms the organic material into fossilised remains. Diamondbearing layers are often characterised by the dominance or occurrence of specific species of invertebrate fossils.

But apart from its treasures, the Sperrgebiet also has a remarkable landscape. One of its most notable features is the Bogenfels, some 80 km south of Lüderitz. This majestic natural rock arch formed over millions of years through wind and water erosion on this stormy coast and stands as a testament to nature's forces. The arch's massive structure of ca. 600-million-year-old sedimentary rock rises against the backdrop of the Atlantic Ocean, creating a dramatic contrast between land and sea. The surrounding cliffs and dunes add to the arch's grandeur, making it a picturesque setting for nature enthusiasts and photographers alike.

Last but not least, the Sperrgebiet is also known for its coastal dune fields with some of the highest sand dunes in the world. These dunes were formed by the interaction of wind, sand and the coastal environment over millions of years. With some reaching heights of over 200 metres, they make for a spectacular and ever-changing desert landscape. Aside from the Bogenfels Arch and coastal dune fields, the Sperrgebiet offers a range of other attractions that are worth exploring. From the ghost town of Kolmanskop, a once thriving diamond mining town swallowed by the desert, to the wild beauty of the Namib coastline, this region promises unique experiences waiting to be explored.

Victoria N Nakafingo