Tuli’s stunning landscapes are quite unlike the rest of Botswana and resemble parts of Namibia or Arizona – but how were they formed?
We’ll take you on a quick whirl through the 3,500 million years of geological history behind the region’s unique scenery.
In a time long, long ago … there were two ancient sections of the earth’s crust, the Kaapvaal craton and the Zimbabwe craton, which collided in a shearing direction. The outer edges along with some of the crust exhumed and bound together through the ascending magma. Over a period of the next 700 million years the East/North East and West/South West fault lines resulted in the formation of a rift valley: the 700km Limpopo Belt. This depositional basin lead to the accumulation of sediment into the lower lying ground. Subsidence continued, further expanding the fault lines and dykes.
In the meantime, tectonic plate movement resulted in the formation of the supercontinent Gondwana. The Southern African portion of this supercontinent underwent a 100 million year ice age, with ice sheets several kilometres thick depositing the first layer of sediment (large metamorphic rocks) into the lower lying areas. The 1st sedimentary layer.
300 million years ago, Gondwana joined Laurasia to form the Pangea Supercontinent. As Pangea moved North, ice progressively melted leaving a vast inland sea, rivers drained mountains forming large swamp basins rich in prehistoric life and vegetation turning into peat and eventually coal. The 2nd sedimentary layer.
250–235 million years ago, the great Permian-Triassic extinction event resulted in 95% of all species becoming extinct over a period of 100,000 years, following a 10 degree Celsius increase of global temperatures caused by an enormous volcanic event in northern Pangea. This resulted in unprecedented global warming and changing weather patterns, changing the lush Southern African flood plains into scorched desert. The 3rd layer of sediment followed with the accumulation of sandstone which was initially deposited by wind, given the extreme desert-like conditions. As the climate changed, ephemeral streams and flood plains also deposited alluvia (silt, sand, clays and gravel) and it is within this layer of sediment that many dinosaur fossils have been found in the Tuli Basin.
Gondwana separated from Laurasia around 200 million years ago. At this time the landscape was flat and featureless. The breaking apart of Gondwana extended tectonic plates and created fissures in the Earth’s crust and huge volumes of basaltic lava were released, starting in the northern Tuli region where the existing fault lines in the Limpopo Belt (mentioned at the beginning and made more prominent with the weight of accumulated sediment) created a path for the magma. The welling up of this magma through long crack-like fissures elevated and folded sedimentary rock before cascading (rather than erupting) over the sandstone, the 4th layer. Below the surface magma formed dykes and sills whilst metamorphosing sedimentary strata.
Ever since, erosion has become the dominant force. Once the massive flows of basalt lavas had cooled they were immediately exposed to the erosive forces of the elements. Basaltic lavas were far from solid, being riddled with holes and tubes from hot gas bubbles. When the erosion broke through the basalt cap into the softer layers, erosion was fast. This erosion removed layers of sediment exposing the harder dykes and sill outcrops we see today that protect the softer layers beneath. There is much evidence of these sills in Tuli with abundant inslebergs (or outcrops) and dykes.
Tuli is a geologist’s paradise and its fabulous rock formations hold a real fascination for amateurs and experts alike. The Tuli landscape forms a spectacular backdrop which really enhances the safari experience.