page_title: Cape Fold Belt
section_title: Appearance
hierarchical_section_title: Cape Fold Belt / Appearance
caption_attribution_description: English: A diagrammatic North-South geological cross section through the southern Cape, South Africa, at approximately the 21° 30' E showing the relationship between the Cape Fold Mountains and the Great Escarpment, and the geological structures that make up these geographical features, as well as the the position of the Great and Little Karoo in relation to the mountain ranges.
context_page_description: The Cape Fold Belt is a fold and thrust belt of late Paleozoic age, which affected the sequence of sedimentary rock layers of the Cape Supergroup in the southwestern corner of South Africa. It was originally continuous with the Ventana Mountains near Bahía Blanca in Argentina, the Pensacola Mountains, the Ellsworth Mountains and the Hunter-Bowen orogeny in eastern Australia. The rocks involved are generally sandstones and shales, with the shales persisting in the valley floors while the erosion resistant sandstones form the parallel ranges, the Cape Fold Mountains, which reach a maximum height of 2325 m at Seweweekspoortpiek.
  The Cape Fold Mountains form a series of parallel ranges that run along the south-western and southern coastlines of South Africa for 850 km from the Cederberg 200 km to the north of the Cape Peninsula, and then along the south coast as far as Port Elizabeth, 650 km to the east.
context_section_description: The mountains are not particularly ancient, despite their old-looking appearance. They are considered middle-aged in geologic terms. They were created when the Falkland Plateau collided with Southern Africa, when Pangaea, the supercontinent formed during the Cambrian-Ordovician periods (from 510 to about 330–350 million years ago),. Their stature, with heights varying from 1000m to 2300m, is mostly due to the weather-resistant rocks of quartzitic sandstone of the Peninsula Group (see above).
  They occur in long parallel ranges each not much more than 10 km wide, separated by equally long valleys with a maximum width of about 50 km (mostly only 15–30 km wide). Almost all of these ranges consist of hard erosion resistant Peninsula Group rocks. The valleys tend to be floored by Bokkeveld Group mudstones. A remarkable feature of these ranges is that the 1500 m high mountains (from base to crest) are cut through by very narrow, almost vertically walled defiles, not much more than 50–70 m wide at the bottom, through which rivers flow from the inland Great Escarpment to the sea. It is from within these narrow defiles, many of which can be traveled by road, that one is afforded a cross sectional view of the mountains, and can appreciate their intense folding and distortion (see the photographs on the top right above). Their origin is as follows:
  After the fold mountains had been formed they became buried under sediments derived from the massive Himalaya-sized Falkland Mountains to the south of the Cape Fold Belt. Sediments eroded from these mountains provided the bulk of the 6 km thick Beaufort sediments in the Karoo Basin, but they also covered the Cape Fold Belt, thereby protecting them from erosion. At the end of the Karoo Period about 180 million years ago, the subcontinent was covered by a thick layer of Drakensberg lavas, an event that was accompanied by upliftment or bulging of Southern Africa, ushering in an almost uninterrupted period, continuing to the present, of erosion removing many kilometers of surface rocks from the entire subcontinent. Rivers running off this bulging interior into the seas that were forming around South Africa as Gondwana was breaking up 150 million years ago, eventually encountered rocky ridges as the protective layer over the Cape Fold Belt eroded away, exposing their mountain tops. The rivers breached these ridges, after possibly being dammed back for a short period, creating a narrow passage through the low rocky barrier. Continued erosion exposed more and more of these quartzitic mountain ranges, but the rivers, now confined to narrow, fast flowing gorges, continued breaking through each barrier as the surrounding landscape eroded to lower and lower levels, particularly during the past 20 million years.
  These 150‑million-year-old rivers therefore cut the defile, starting by flowing over, and then through the gradually erupting Cape Fold Mountains, to form the spectacular "poorte" and "klowe" (plural of "poort" and "kloof", the Afrikaans for defile or chasm) that characterize these mountains today. The best known defiles are: Meiringspoort, Seweweekspoort, the Tradouw pass, Kogmanskloof, Garcia's pass, the Gourits River gorge (which does not have a road running through it), and Michell's Pass, which is, however, more V-shaped than the others, but impressive nevertheless. In addition several roads and highways crest the mountains over cols, or go through them via tunnels.
  A number of parallel faults still run roughly parallel with the coast, having formed during the Gondwana rifting when South America and the Falkland Plateau separated from Africa. Patagonia was to the west of Cape Town and the Falkland Islands were to the south during the Jurassic Period prior to separation. Most of these faults are inactive today, but on 29 September 1969 the towns of Ceres and Tulbagh, about 160 km north-east of Cape Town, were severely damaged by a major earthquake, originating from movement of the northern end of the Worcester Fault.
  Another major (inactive) fault runs for 300 km along the southern edge o
caption: A diagrammatic 400 km north-south cross-section through the southern portion of the country at approximately 21° 30' E (i.e. close to Calitzdorp in the Little Karoo), showing the relationship between the Cape Fold Mountains (and their geological structure) and the geology of the Little and Great Karoo, as well as the position of the Great Escarpment. The colour code for the geological layers is the same as those used in the diagram above. The heavy black line flanked by opposing arrows is the fault that runs for nearly 300 km along the southern edge of the Swartberg Mountains. The Swartberg Mountain range owes some of its great height to uplift along this fault. The subsurface structures are not to scale.
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