Cape Fold Belt

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.[1] It was originally continuous with the Ventana Mountains near Bahía Blanca in Argentina, the Pensacola Mountains (East Antarctica), the Ellsworth Mountains (West Antarctica) and the Hunter-Bowen orogeny in eastern Australia. The rocks involved are generally sandstones and shales, with the shales (Bokkeveld Group) persisting in the valley floors while the erosion resistant sandstones (belonging to the Peninsula Formation) form the parallel ranges, the Cape Fold Mountains, which reach a maximum height of 2325 m at Seweweekspoortpiek (‘Seven Weeks Defile Peak’ in Afrikaans).

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 (see the two maps one above the other on the right).

Western Cape Topology
Map of the Western Cape, showing the main Cape Fold Mountain ranges. The Cape Fold belt is not part of the Great Escarpment shown in blue: the Roggeveld, Nuweveld and Sneeuberg "mountains". They are geographically and geologically distinct from the Cape Fold Mountains. The remaining named mountain ranges, to the south and southwest of the Escarpment, are all part of the Cape Fold Belt, which extends to the east as far as Port Elizabeth, about 150 km beyond the right-hand edge of the map.
The Escarpment and the Drakensberg
A map of South Africa showing the central plateau edged by the Great Escarpment and its relationship to the Cape Fold Mountains in the south. The portion of the Great Escarpment shown in red is known as the Drakensberg.

Geological origin

Earth's geolological timeline
A timeline of the earth's geological history, with an emphasis on events in Southern Africa. The yellow block labeled C indicates when the Cape Supergroup was deposited, in relation to the Karoo Supergroup, K, immediately after it. The W indicates when the Witwatersrand Supergroup was laid down, very much further in the past. The graph also indicates the period during which banded ironstone formations were formed on earth, indicative of an oxygen-free atmosphere. The earth's crust was wholly or partially molten during the Hadean Eon; the oldest rocks on earth are therefore less than 4000 million years old. One of the first microcontinents to form was the Kaapvaal Craton, which forms the foundation of the north-eastern part of the country. The assembly and break-up of Gondwana are, in terms of the earth's and South Africa's geological history, relatively recent events.
Swartberg, 2001
Klein Swartberg Range, seen from the Laingsburg area
SwartbergPICT3193
Folded rock formations of the Swartberg
Southern Gondwana
Southern Gondwana during the Cambrian-Ordovician Periods. Today's continents into which this Supercontinent eventually broke up, are indicated in brown. A rift developed about 510 million years ago, separating Southern Africa from the Falkland Plateau. Flooding of the rift formed the Agulhas Sea. The sediments which accumulated in this shallow sea consolidated to form the Cape Supergroup of rocks, which form the Cape Fold Belt today. This portion of Gondwana was probably located on the opposite side of the South Pole from Africa's present position,[2] but compass bearings are nevertheless given as if Africa was in its present position.
Formation of Cape Fold Mountains
A north-south cross-section through the Agulhas Sea (see above). The brown structures are continental plates, the thick black layer on the left is paleo-Pacific Oceanic plate, red indicates the upper mantle, and blue indicates flooded areas or ocean. The top illustration depicts the geology about 510 million years ago, with the sediments which would eventually form the Cape Supergroup settling in the Agulhas Sea. The middle illustration depicts the Falkland Plateau drifting northwards once again to close the Agulhas Sea, causing the Cape Supergroup to be rucked into a series of folds, running predominantly east-west. The lowest illustration shows how subduction of the paleo-Pacific Oceanic plate under the Falkland Plateau, during the Early Permian period, raised a massive range of mountains. These eventually eroded into the Karoo Sea, forming the Karoo Supergroup. Ultimately, the Falkland Mountains eroded almost completely away, but the Cape Fold Mountains had, by this time, become buried under the Karoo sediments. Being composed largely of quartzitic sandstone, they resisted subsequent erosion, when continental uplifting caused several kilometers of Southern Africa's surface to be planed away, and thus persist to this day as the Cape Fold Belt. The remnant of the Falkland Plateau broke away from Africa, and drifted south-westwards to its present position in the western South Atlantic Ocean, following the breakup of Gondwana about 150 million years ago.

The rocks were laid down as sediments in a rift valley that developed in southern Gondwana, just south of Southern Africa, during the Cambrian-Ordovician Periods (starting about 510 million years ago, and ending about 330-350 million years ago).[3][4][5] (See the yellow block labeled C on the Earth's geological timeline diagram on the right.) An 8-km-thick layer of sediment, known as the Cape Supergroup (see below), accumulated on the floor of this rift valley.[4] Closure of the rift valley, starting 330 million years ago, resulted from the development of a subduction zone along the southern margin of Gondwana, and the consequent drift of the Falkland Plateau back towards Africa, during the Carboniferous and early Permian periods. After closure of the rift valley, and rucking of the Cape Supergroup into a series of parallel folds, running mainly east-west (with a short section running north-south in the west, due to collision with eastward moving Patagonia), the continued subduction of the paleo-Pacific Plate beneath the Falkland Plateau and the resulting collision of the latter with Southern Africa, raised a mountain range of immense proportions to the south of the former rift valley. The folded Cape Supergroup formed the northern foothills of this towering mountain range.

The weight of the Falkland-Cape Supergroup mountains caused the continental crust of Southern Africa to sag, forming a retroarc foreland system, into which the Karoo Supergroup was deposited.[1][4][6] Eventually much of the Cape Supergroup became buried under these Karoo deposits, only to re-emerge as mountains when upliftment of the subcontinent, about 180 million years ago, and again 20 million years ago, started an episode of continuous erosion that was to remove many kilometers of surface deposits from Southern Africa.[4] Although the tops of the original Cape Fold Mountains were eroded away, they eroded much slower than the considerably softer Karoo deposits to the north. Thus the Cape Fold Belt "erupted" from the eroding African landscape to form the parallel ranges of mountains that run for 800 km along the southern and south-western Cape coastline today. In fact, they form the coastline, either sloping steeply directly into the sea, or are separated from it by a relatively narrow coastal plain.

The Falkland Mountain range had probably eroded into relative insignificance by the mid-Jurassic Period, and started drifting to the south-west soon after Gondwana began to break up 150 million years ago, leaving the Cape Fold Belt to edge the southern portion of the newly formed African continent. Even though the mountains are very old by Andean and Alpine standards, they remain steep and rugged due to their quartzitic sandstone geology (see below) making them very resistant to weathering. The famous Table Mountain forms part of the Cape Fold Belt, being made up of the local lowest (oldest) strata of the Cape Supergroup, composed predominantly of quartzitic sandstone which forms the impressive, almost vertical cliffs which characterize the mountain and the rest of the range which constitutes the backbone of the Cape Peninsula.[3][7]

The degree to which the original Cape Fold mountains (formed during the Carboniferous and early Permian Periods) have been eroded is attested to by the fact that the 1 km high Table Mountain on the Cape Peninsula is a syncline mountain, meaning that it formed part of the bottom of a valley when the Cape Supergroup was initially folded. The anticline, or highest elevation of the fold between Table Mountain and the Hottentots-Holland Mountains (1.2 to 1.6 km elevation), on the opposite side of the isthmus connecting the Peninsula to the Mainland, has been eroded away. The Malmesbury shale and granite basement on which this anticline mountain rested also formed an anticline; but being composed of much softer rocks, readily eroded into a 50 km wide flat plain, (now covered with dune sands) called the "Cape Flats".[3]

The Cape Fold Belt (i.e. the mountain ranges) extends from about Clanwilliam (approximately 200 km north of Cape Town), to about Port Elizabeth (approximately 650 km east of Cape Town). The Cape Supergroup sediments beyond these points are not folded into mountain ranges, but do, in places, form steep cliffs or gorges, where the surrounding sediments have been eroded away (see, for instance, Oribi Gorge in KwaZulu-Natal).[4][5]

The mountains, although only of moderate height, are majestic and dramatic. This is due in part to numerous geological factors; The ranges usually have few to no foothills and rise directly from valley floors. The bases of the mountains are usually at or near sea level.[8]

Cape Supergroup

The mountains of the Cape Fold Belt are composed of rocks belonging to the Cape Supergroup, which is more extensive than the Fold Belt. The Supergroup is divided into several distinct Groups.

The western and southern extents of the Supergroup have been folded into a series of longitudinal mountain ranges, by the collision of the Falkland Plateau into what would later become South Africa (see diagrams on the left). However, the entire suite in this region slopes downwards towards the north and east, so that the oldest rocks are exposed in the south and west, while the youngest members of the Supergroup are exposed in the north, where the entire Cape Supergroup dives beneath the Karoo rocks. Drilling in the Karoo has established that Cape Supergroup rocks are found below the surface up to approximately 150 km north of their northernmost exposure on the surface.[5]

The Cape Supergroup extends eastwards beyond the Fold Belt into the Eastern Cape and northern KwaZulu-Natal, where no folding took place.[5]

Klipheuwel and Natal Groups

The initial sedimentation into the rift valley which developed in southern Gondwana (see diagram at top left) was confined to the western and eastern ends of the rift. Rivers diverted into these early rifts deposited sand and gravel to form the Klipheuwel Group in the west, and the Natal Group in the east.[4][5] These formations contain no fossils. Today the Klipheuwel Group is exposed in several small patches near Lamberts Bay, Piketberg, and to the south-west of Paarl Rock.[9]

The Natal Group, which is similar to the Table Mountain Group (see below), is found in several elongated patches near the coast of the northern Eastern Cape and KwaZulu-Natal. It forms the impressive cliffs of Oribi Gorge, and can also be seen in a road cutting between Durban and Pietermaritzburg, particularly at the Marian Hill Toll Plaza.[4] Most of the group has been deeply eroded by numerous rivers creating the ragged plateaus and scarps of the Durban-Pietermaritzburg region.[5][10]

Table Mountain Group

With the widening and deepening of the rift valley, the entire southern portion of what was to become South Africa, as far as a line extending from Calvinia in the west to East London in the east, plus the KwaZulu-Natal coastline, became flooded,[5] leading to a seaway across the southern and eastern parts of the country, called the Agulhas Sea.[4] The sea floor consisted of the Klipheuwel Group in the west, the Natal Group in the east, and eroded pre-Cambrian rocks in between.[4]

Newlands Graafwater
A view of the eastern crags (or cliffs) of Table Mountain and Devils Peak as seen from Newlands Forest, above the University of Cape Town. The two layers of the Table Mountain Group which are represented on the Cape Peninsula, namely the Graafwater Formation and the Table Mountain Sandstone or Peninsula Formation, can readily be distinguished. The remaining layer, the Pakhuis Formation, occurs as a tiny remnant on the top of Table Mountain, not visible in the photograph. The granite basement on which the Table Mountain Group rests on the Cape Peninsula is obscured by the forest in the foreground.
Ou Kaapse weg
A view of the cutting at the second hairpin bend on Ou Kaapse Weg, as it winds on to the Silvermine Plateau. The transition between the lowermost layer of the Table Mountain Group on the Cape Peninsula - the Graafwater Formation - and the layer above it, the Table Mountain Sandstone or Peninsula Formation, can be clearly seen. The very abrupt transition between them suggests that the Aghulas Sea was initially (during the Graafwater period) an area of inland drainage, possibly below sea level (comparable to the Dead Sea in the Middle East today). When the rift extended into the ocean, the rift valley suddenly flooded to become a deep water passage similar to the Red Sea today. The photograph was taken at an elevation of 250 m.
Cederberg geology
Schematic diagram of an approximate 100 km west-east (left to right) geological cross-section through the Cederberg portion of the Cape Fold Belt. The rocky layers (in different colors) belong to the Cape Supergroup. Not to scale. The green layer is the Pakhuis diamictite formation which divides the Peninsula Formation Sandstone (or Table Mountain Sandstone) into a lower and upper portion. It is the lower (older) portion that is particularly hard and erosion resistant, and, therefore, forms most of the highest and most conspicuous peaks in the Western Cape, as well as the steepest cliffs of the Cape Fold Mountains (including Table Mountain).[11] The Upper Peninsula Formation, above the Pakhuis tillite layer, is considerably softer and more easily eroded than the lower Formation. In the Cederberg Mountains This formation has been sculpted by wind erosion into many fantastic shapes and caverns, for which these mountains have become famous.[12] The Graafwater Formation forms the lowermost layer of the Cape Supergroup in this region, but is, for simplicity, incorporated into the Table Mountain Sandstone Formation in this diagram.
Wolfbergarch-001
Wolfberg Arch in the relatively easily eroded Nardouw Formation (or Upper Peninsula Formation) rocks of the Cederberg.

The first sediments into the initially still shallow, possibly inland, sea were alternating layers of maroon-colored mudstones and buff-colored sandstones, each mostly between 10 and 30 cm thick.[3] The mudstone units commonly display ripple marks from the ebb and flow of tidal currents, as well as polygonal sand-filled mud cracks that indicate occasional exposure to desiccation.[3] This layer, known as the Graafwater Formation, reaches a maximum thickness of 400 m,[10] but on the Cape Peninsula it is only 60–70 m thick.[3] No fossils have been found in the Graafwater rocks, but shallow-water animal tracks have been found.[4][10] A particularly good example of these tracks can be viewed in the foyer of Geology Department of the University of Stellenbosch, where a slab of Graafwater rock from the Cederberg mountains has been built into the wall.[5]

The cutting for Chapman’s Peak Drive, on the Cape Peninsula, is carved into the Graafwater Formation which overlays the Cape Granite basement rock below the road. The Graafwater Formation can also be clearly seen in the cutting on the second hairpin bend as the Ou Kaapse Weg (road) goes up the slope from Westlake on to the Silvermine plateau. In the cutting one can also see the abrupt and obvious transition into the Peninsula Formation above it. Looking up the slope from below to the first hairpin bend, the granite basement on which the Graafwater formation rests is visible. And in the cutting at the first hairpin bend, the ocher-colored, gritty clay into which the granite weathers is clearly displayed.

With further subsidence of the rift valley floor, and possibly breaking through to the ocean, the sediments abruptly become more sandy, indicative of a sudden increase in the depth of the Agulhas Sea (see photograph on the right). A deposit, known as the Peninsula Formation (also often referred to as Table Mountain Sandstone), consisting of thickly layered quartzitic sandstone, with a maximum thickness of 2000 m, was laid down. These sandstones are very hard, and erosion resistant. They therefore form the bulk of mountains and steep cliffs and rugged crags of the Cape Fold Belt, including the upper 600 m of the 1 km high Table Mountain, below which Cape Town is situated. It contains no fossils.

The Peninsula formation can be traced from 300 km north of Cape Town (i.e. about 50 km north of Vanrhynsdorp on the West Coast), southwards to Cape Town and then eastwards to northern KwaZulu-Natal, a total distance of approximately 1800 km, roughly along the South African coastline.[9] Only the section between Clanwilliam (approximately 200 km north of Cape Town) and Port Elizabeth (approximately 650 km east of Cape Town) is folded into the Cape Fold Mountains.

During the laying down of the Peninsula Formation sediments, the western portion of the region was covered for a brief period of time by glaciers. The diamictite sediments that were laid down by these glaciers, or in glacial lakes, are known as the Pakhuis and Cederberg Formations.[4] A small patch of Pakhuis tillite occurs on the top of Table Mountain at Maclear's Beacon,[3] but most of the Pakhuis and Cederberg Formations are found as a thin layer (on average only about 60 m thick[5]) in the Peninsula Formation rocks of the more inland mountains to the west of a line between Swellendam and Calvinia.[5] These diamictite rocks are composed of finely ground mud, containing a jumble of faceted pebbles. They can easily be recognized at a distance as this formation readily erodes into fertile, gently sloping, green swaths in a landscape where this contrasts starkly with the bare rocky surfaces of the quartzites above and below.[5] In several locations the quartzites below the glacial horizon have been rucked into a series of folds. This is believed to have been caused by the movement of ice ploughing into the underlying unconsolidated sands.[5] A good example of this can be seen on a ridge of rocks near Maclear’s Beacon on Table Mountain, close to the edge of the plateau overlooking the Cape Town City Bowl and Table Bay.

The Pakhuis Formation is also well exposed on the road along Michell’s Pass just below the Tolhuis,[3] and especially on the Pakhuis Pass near Clanwilliam, from which the formation derives its name.[5]

The glaciers which formed the Pakhuis and Cederberg formations came from the north west, in the direction of the South Pole which was located in the neighborhood of Cameroon at the time.[10]

The Upper Peninsula Formation, above the Pakhuis and Cederberg Formations, consists of much softer sandstone than the Lower Peninsula Formation, and is often referred to as the Nardouw Formation.[5][12] In the Cederberg this formation has been eroded by the wind into a wide variety of "sculptures", caves, and other fascinating structures for which these mountains have become well-known.[12]

Bokkeveld Group

About 400 million years ago (in the early Devonian Period) there was further subsidence of the rift valley floor. This brought about the deposition of deeper-water, fine grained sediments of the Bokkeveld Group. This is in marked contrast to the predominantly sandy sediments of the Table Mountain Group. The Bokkeveld Group consists predominantly mudstones.[4]

After the Cape Supergroup had been folded into the Cape Fold Mountains, these soft mudstones readily washed away from the mountain tops, and only remain in the valleys. Here they form the fertile soils on which the vineyards and fruit orchards of the Western Cape flourish with the help of irrigation from the rivers that have their sources in the surrounding mountains.[4]

The Bokkeveld Group does not extend on to the Cape Peninsula or its isthmus (the Cape Flats). Here the Stellenbosch, Franschhoek, Paarl, Durbanville, Tulbagh and Constantia vineyards have been planted on the weathered Cape Granite and Malmesbury shale soils, which form the basement rocks on which the Cape Supergroup rocks in this region rest.

The Bokkeveld Group extends eastwards to Port Alfred (near Grahamstown), approximately 120 km beyond the eastern extent of the Cape Fold Belt.[9]

The bulk of the fossils found in the Cape Supergroup occur in the Bokkeveld mudstones. They include a variety of brachiopods, as well as trilobites, molluscs, echinoderms (including starfish, crinoids, and the extinct blastoids and cystoids), foraminifera and fish with jaws (placoderms).[4][5][10]

Witteberg Group

The upper layers of the Bokkeveld Group become increasingly more sandy, grading into the sandstone of the Witteberg Group, named for the range of mountains to the south of Matjiesfontein and Laingsburg in the southern Karoo. These rocks were laid down 370 - 330 million years ago in the silted up, and therefore shallow marine conditions of what remained of the Agulhas Sea.[4] The group contains fewer fossils than the Bokkeveld Group, but the assemblage that is preserved includes primitive fish, an extinct species of shark, brachiopods, bivalves, and a meter long sea scorpion. There are also plant fossils and numerous animal tracks.[4][5] The Witteberg Group is truncated by the overlying Dwyka sediments of glacial origin. The latter forms part of the Karoo Supergroup. Therefore, the Witteberg Group forms the uppermost layer of the Cape Supergroup. It tends to form the most inland outcrops of the Cape Supergroup, and can be traced eastwards as far as the Bokkeveld Group can be traced (i.e. to Port Alfred), about 120 km beyond the Cape Fold Belt.[5][9]

The Bokkeveld and Witteberg groups do not occur in the north-eastern Eastern Cape and KwaZulu-Natal, where the Cape Supergroup is represent only by the Natal Group and a trace of the Peninsula Formation (without the intervening Graafwater Formation).[9]

Formation of the Fold Mountains

Agulhas Bank NOAA ETOPO1
The Agulhas Bank is the broad, shallow part of the southern African continental shelf which extends up to 250 km (160 mi) south of Cape Agulhas before falling steeply to the abyssal plain. It represents the remains of the Falkland Plateau still attached to Southern Africa. The Agulhas Ridge (or Agulhas-Falkland Fracture Zone) which runs from the south-eastern edge of the Bank towards the south west for 1,200 kilometres (750 mi) across the South Atlantic, is the fault line along which the remainder of the Falkland Plateau moved to the southern tip of South America, a short while after Gondwana broke up, 110 million years ago.[4]

The Witteberg sediments were laid down in what remained of the Agulhas Sea - a shallow, much reduced expanse of water compared to its size during the Bokkeveld period.[5] Immediately following the Witteberg period (about 330 million years ago) much of Gondwana (particularly what was to become Africa and Antarctica, but also parts of South America and India) became covered in a kilometers thick layer of ice as the super-continent drifted over the South Pole.[4][5][11] The diamictite deposits left by these glaciers form the first layer of the Karoo Supergroup, called the Dwyka Group. During the glaciation period the Falkland Plateau started to move northwards into what was to become southern Africa, closing the depression that had been the Agulhas Sea, and rucking the Cape Supergroup sediments into folds running roughly parallel to what would ultimately become the south-western and southern coastlines of South Africa. This mountain building continued into the next phase of the Karoo sedimentation, which began about 260 million years ago, after the ice sheets had melted, leaving a large lake (the Karoo Sea) extending over much of South Africa. The resulting marine or lacustrine deposits form the Karoo's Ecca Group. During these Ecca times continued collision of the Falkland Plateau into Southern Africa, and subduction of oceanic crust under the plateau caused the formation of a range of mountains of Himalayan proportions to the south of South Africa.[4] The Cape Fold Mountains became fully formed during this period to become the northern foothills of this enormous mountain range. The folding that occurred during this period therefore involved not only the Cape Supergroup sediments, but also the southern portions of the Dwyka and Ecca Groups of the Karoo Supergroup.[4][5]

By the time Gondwana broke up about 150 million years ago, the Falkland Mountains had been all but eroded away, before drifting south-westwards to their present position off the coast of southern South America, close to Cape Horn, leaving behind only the submarine Agulhas Bank along the southern coastline of Africa. The Cape Fold Mountains possibly survived erosional obliteration, firstly because of the extremely hard rocks (the Peninsula Formation Sandstone) that form the backbone of the mountain chains, but also possibly because they had become buried under the Karoo deposits which originated in the Falkland Mountains. Thus traces of Karoo deposits can, for instance, be found in the Worcester-Robertson valley in the middle of the Fold Belt.[9][13]

Although the Dwyka and Ecca sediments adjoining the Cape Fold Mountains were subjected to the same compression forces that gave rise to the Cape Mountains, they do not form the same mountain ranges as do the Cape Fold Mountains. This is because they are composed of much softer rocks than the Peninsula Formation Sandstone, and were thus soon eroded into the flat plains of the "Lower Karoo", except where they were protected by hard, erosion resistant dolerite or turbidite caps, to form isolated mountains that stand out from the plain.[4][13]

Appearance

SW-NE geological cross section through South Africa
An approximate SW-NE geological cross section through South Africa, with the Cape Peninsula (with Table Mountain) on the far left, and north-eastern KwaZulu-Natal on the right. Diagrammatic and only roughly to scale to scale. The difference in both composition and structure of the Cape Fold Mountains and the Central Plateau surrounded by the Great Escarpment, in particular the Drakensberg, can clearly be seen.
NS cross section Southern Cape
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 upliftment along this fault line. The subsurface structures are not to scale.

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),.[3][4][5] 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.[4][14] Sediments eroded from these mountains provided the bulk of the 6 km thick Beaufort sediments in the Karoo Basin,[4] 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.[4] 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.[4]

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 in 1969 the towns of Ceres and Tulbagh, about 160 km north-east of Cape Town, were severely damaged by an earthquake, originating from movement of the northern end of the Worcester Fault.[4][5]

Another major (inactive) fault line runs for 300 km along the southern edge of the Swartberg Mountains. The Swartberg Mountains were uplifted along this fault, to such an extent that in the Oudtshoorn region the rocks that form the base of the Cape Supergroup are exposed. These are locally known as the "Cango Group", but are probably continuous with the "Malmesbury Group" that forms the base of Table Mountain on the Cape Peninsula, and similar outcrops in the Western Cape.[4] In the Little Karoo the outcrop is composed of limestone, into which an underground stream has carved the impressively extensive Cango Caves.[9][14][15][16]

The ranges

The following is a list of the largest individual ranges within the Cape Fold Belt include from west to east. (Translations in brackets; berg is Afrikaans for mountain; its plural is berge.)

  • Cederberg (Cedar) - Table Mountain Group
  • Olifants River Mountains (Elephant's) - Table Mountain Group
  • Piketberg (Picket) - Table Mountain Group
  • Winterhoek Mountains (Winter corner) - Table Mountain Group
  • Skurweberge (Rough or scaly) - Witteberg Group
  • Hex River Mountains (Witch river) - Table Mountain Group
  • Cape Peninsula and Table Mountain - Table Mountain Group
  • Du Toitskloof Mountains (Du Toit's canyon, from a French surname) - Table Mountain Group
  • Drakenstein Mountains (Dragon stone, the name of a country estate in the Netherlands) - Table Mountain Group
  • Simonsberg (Simon's) - Table Mountain Group
  • Hottentots-Holland Mountains (Hottentot, an old name for the Khoi aboriginal inhabitants) - Table Mountain Group
  • Kogelberg (Bullet, or cone-shaped) - Table Mountain Group
  • Stettynsberge (probably a surname) - Table Mountain Group
  • Langeberg (Long) - Table Mountain Group
  • Riviersonderend Mountains (River without end) - Table Mountain Group
  • Kleinrivier Mountains (Small river) - Table Mountain Group
  • Witteberge (White) Witteberg Group
  • Swartberge (Black) - Table Mountain Group
  • Outeniqua Mountains (aboriginal: place of honey) - Table Mountain Group
  • Langkloof Mountains (Long valley) - Table Mountain Group
  • Kouga Mountains (aboriginal) - Table Mountain Group
  • Tsitsikamma Mountains (aboriginal: place of much water) - Table Mountain Group
  • Baviaanskloof Mountains (Valley of baboons) - Table Mountain Group
  • Zuurberge (Sour, acid or acidic) - Witteberg Group

See also

References

  1. ^ a b Shone R.W. & Booth P.W.K. (2005). "The Cape Basin, South Africa: A review". Journal of African Earth Sciences. 43 (1–3): 196–210. doi:10.1016/j.jafrearsci.2005.07.013.
  2. ^ Jackson, A.A., Stone, P. (2008). "Bedrock Geology UK South". p. 6-7. Keyworth, Nottingham: British Geological Survey.
  3. ^ a b c d e f g h i Compton, J.S. (2004).The Rocks and Mountains of Cape Town. p. 24-26, 44-70. Double Storey Books, Cape Town.
  4. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab McCarthy, T., Rubridge, B. (2005). The Story of Earth and Life. pp. 159-161, 182, 187-199, 202-207, 247-248, 267-269, 302. Struik Publishers, Cape Town
  5. ^ a b c d e f g h i j k l m n o p q r s t u v Truswell, J.F. (1977). The Geological Evolution of South Africa. pp. 93-96, 114-159. Purnell, Cape Town.
  6. ^ Catuneanu O. (2004). "Retroarc foreland systems––evolution through time" (PDF). Journal of African Earth Sciences. 38 (3): 225–242. doi:10.1016/j.jafrearsci.2004.01.004.
  7. ^ Geology of the Cape Peninsula - Cape Fold Belt
  8. ^ The Cape Fold Belt
  9. ^ a b c d e f g Geological Map of South Africa, Lesotho and Swaziland. (1970). Council for Geoscience, Geological Survey of South Africa.
  10. ^ a b c d e Tankard, A.J., Jackson, M.P.A., Erikson, K.A., Hobday, D.K., Hunter, D.R., Minter, W.E.L. (1982) Crustal Evolution of Southern Africa: 3.8 Billion Years of Earth History. pp. 333-363. Springer-Verlag. New York.
  11. ^ a b Norman, N., Whitfield, G. (2006). “Geological Journeys. A Traveller’s Guide to South Africa’s Rocks and Landforms”. pp. 28, 208-212. Cape Town, Struik Publishers. ISBN 1-77007-062-1.
  12. ^ a b c Whitfield, Gavin (2015). "Stadsaal Caves. Cederberg Conservancy.". In: 50 Must-see geological sites in South Africa. Century City: Struik Nature. pp. 64–67. ISBN 978 1 92057 250 1.
  13. ^ a b Norman, Nick (2013). "N15/R62: Worcester to Zoar.". In: Geology off the beaten track. Exploring South Africa's hidden treasures. Century City: Struik Nature. pp. 67–71. ISBN 978 1 43170 082 0.
  14. ^ a b Norman, N., Whitfield, G. (2006). Geological Journeys. pp. 300-311. Struik Publishers, Cape Town.
  15. ^ Reader’s Digest Illustrated Guide to Southern Africa. (5th Ed. 1993). pp. 78-89. Reader’s Digest Association of South Africa Pty. Ltd., Cape Town.
  16. ^ Bulpin, T.V. (1992). Discovering Southern Africa. pp. 271-274, 301-314. Discovering Southern Africa Productions, Muizenberg.

Coordinates: 33°24′S 22°00′E / 33.4°S 22°E

Anysberg Nature Reserve

The Anysberg Nature Reserve of 62,500 ha is situated in the western Kleinkaroo region of the Western Cape province, South Africa. The central mountain is named after Anise, Pimpinella anisum, which is found here. The reserve was established in 1988 to conserve Succulent and Fynbos flora in the Cape Fold Belt, and to reintroduce game which formerly occurred here.

The nearest towns are Laingsburg and Ladismith, which are both about 55 km from the main reserve entrance.

Boland, Western Cape

The Boland (Afrikaans for "top country" or "land above") is a region of the Western Cape province of South Africa, situated to the northeast of Cape Town in the middle and upper courses of the Berg and Breede Rivers, around the Boland Mountains of the central Cape Fold Belt. It is sometimes also referred to as the Cape Winelands because it is the primary region for the making of Western Cape wine.

Byneskranskop

Byneskranskop is an archaeological site in present-day South Africa where the coastal plain meets the southern Cape Fold Belt. Neolithic human remains have been discovered in caves at the site. Carbon dating of the remains indicates the bodies date from 3,000 to 2,000 years BCE.Remains of tortoises at this site and a dig at Die Kelders, have been used to assess a correlation between tortoise size and human population, with a decrease in tortoise sizes as the human population grows.166,000 stone artefacts were recovered from the site during the first dig. These were dated as far back as 12,000 years BCE. Pottery sherds were limited to the period of 250 years BCE or later.

Drakenstein

The Drakenstein ("Dragonstone") Mountains are part of the Cape Fold Belt and are in the Western Cape province of South Africa; they were named in honour of Hendrik Adriaan van Rheede tot Drakenstein who visited the Cape as Commissioner-General in 1685; Drakenstein (modern spelling usually Drakestein) was the name of his estate in the Netherlands. They actually comprise two separate ranges, the Klein Drakenstein and Groot Drakenstein Mountains. The former located just to the east of Paarl being punctuated by the Huguenot Tunnel on the N1 highway and Du Toitskloof Pass (820 m (2,690 ft)) as the R101 route. The latter is much taller and is located south of Franschhoek and Stellenbosch, with Victoria Peak (1,590 m (5,220 ft)) as its highest point. It is traversed by no mountain passes, but contains the Hottentots-Holland Nature Reserve and also holds title of the wettest place in South Africa in the upper reaches of the Jonkershoek Valley, with over 2,000 millimetres (79 in) of precipitation per annum (precise measurement unverified).

Most vegetation is of the Cape Floristic Kingdom biome, and the primary rocks are of the Table Mountain Sandstone group of the Cape Supergroup. The region falls within the Mediterranean climatic zone, with cool, wet winters, with snow on the higher elevations and warm, dry summers.

Du Toits Peak

The Du Toitskloof Mountains (Dutoitsberge) are a range in the Cape Fold Belt in the Western Cape Province of South Africa. The highest point is Du Toits Peak (Dutoitspiek) (1,995 m or 6,545 ft) which is the highest seaward facing peak in the Cape Fold Belt ranges, i.e. the highest peak in the Western Cape within direct sight of the ocean.

Located between Paarl and Worcester in the south-west of South Africa, 70 kilometres (43 mi) to the north-east of the provincial capital of Cape Town, the mountains form a formidable barrier between Cape Town and the rest of Africa. The N1 highway, also called the Cape to Cairo Road crosses them at the Du Toitskloof Pass. The old route culminated at 820 metres (2,690 ft); however, the new Huguenot Tunnel, of 3.7 kilometres (2.3 mi) in length, cuts out the old mountain pass. Sometimes the Du Toitskloof Mountains together with the Wemmershoek Mountains and others are called the Klein Drakenstein, but it is more usually considered part of the greater Boland mountain range.

Structurally, the mountains form part of the Cape Syntaxis, a complex portion of the Cape Fold Belt where the north-south trending ranges meet the east-west trending ranges in a complex series of folds, thrusts and fault-lines. The range mostly consists of Table Mountain sandstone, an erosion-resistant quatzitic sandstone. Vegetation is almost exclusively montane fynbos of the Cape floristic region. The rest of the mountains are barren rocks and steep cliffs. Precipitation occurs primarily in the winter months as rain on the lower slopes and as snow higher up, usually above 1000m. Climate varies dramatically, with the surrounding valleys being up to 10°C (18°F) warmer than the mountains. The climate falls within the Mediterranean type.

The Limietberg Nature Reserve, known for its mountain fynbos, is located in the Du Toitskloof Mountains.

Gondwanide orogeny

The Gondwanide orogeny was a orogeny active in the Permian that affected parts of Gondwana that are by current geography now located in southern South America, South Africa, Antarctica, Australia and New Guinea. The zone of deformation in Argentina extends as a belt south and west of the cratonic nucleus of Río de la Plata–Pampia.

The deformation of the orogeny is visible in the Sierra de la Ventana mountains in Argentina and the Cape Fold Belt in South Africa. The Gondwanide orogeny might have been linked with the roughly contemporary San Rafael orogeny of western Argentina.The Gondwanide orogeny is the successor to the Neoproterozoic-Paleozoic Terra Australis orogeny in Gondwana.Following the Gondwanide orogeny southwestern Gondwana entered a period of extensional tectonics and crustal thinning leading to formation of various rift basins (e.g. Cuyo Basin) in the Triassic.

Groot Winterhoek

The Groot Winterhoek mountains are located in the Western Cape province of South Africa and are part of the Cape Fold Belt. They rise to a maximum height of 2077 m just north of the town of Tulbagh as Groot Winterhoek peak. The Groot Winterhoek Wilderness Area, operated by CapeNature, comprises a conservation area of 30,608 ha, and contains waterfalls, swimming holes, pristine rivers and mountain wilderness.

Hemicordylus

Hemicordylus, the false girdled lizards, is a genus comprising two lizard species endemic to the Cape Fold Belt of southern South Africa.

Hemicordylus capensis

The false girdled lizard (Hemicordylus capensis) is a lizard species endemic to the Cape Fold Belt of southern South Africa.

Hex River Mountains

The Hex River Mountains (Afrikaans: Hexrivierberge) make up the second highest mountain range in the Western Cape province of South Africa and are located 120 kilometres (75 miles) north-east of Cape Town. They form part of a large anticline in the Cape Fold Belt mountain system and form a north-east, south-west trending mountain system forming the core of the Cape Syntaxis between the towns of Worcester and De Doorns. They are mostly composed of Table Mountain sandstone and most peaks reach 2,000 metres (6,562 feet) in height or more. The highest mountain is Matroosberg at 2,249 metres (7,379 feet), making it the second tallest peak in the province after Seweweekspoort Peak in the Swartberg Mountain Range.

The vegetation is primarily montane fynbos and the mountains fall within the Cape's Mediterranean climate. The mountains provide some rudimentary snow-skiing opportunities in winter, with the Western Cape's heaviest snowfalls occurring in and around these ranges. The surrounding valleys support intensive deciduous fruit cultivation, mostly in the form of cherries and table grapes.

Block streams and terraces found in the near the summit of Matroosberg evidences past periglacial activity, which occurred likely during the Last Glacial Maximum.

Hottentots Holland Mountains

The Hottentots Holland Mountains are part of the Cape Fold Belt in the Western Cape, South Africa. The mountain range forms a barrier between the Cape Town metropolitan area and the southern Overberg coast.

The range is primarily composed of Table Mountain Sandstone, and forms a large range between the Cape Town outlying suburbs of Somerset West and Gordon's Bay to the west, and the large Elgin valley to the east. Sir Lowry's Pass is the only crossing, in the form of the N2 motorway. The Steenbras Dam, one of Cape Town's main supply dams, is located in the southern section of the range. This is due to the abundant rainfall experienced in the uplands, located in the Elgin Valley around the town of Grabouw on the eastern slopes.

At the start of the Great Trek in 1835 when migrants decided to leave the Cape Town area, or Cape Colony as it was then known, the first mountain range they crossed was this range. Cuts and wheel markings from their ox wagons can still be seen in rock formations in the vicinity of Sir Lowry's Pass on this mountain range. This route still serves as the primary route out of the Cape Town area for travellers heading up the east coast of South Africa.

The climate is typically Mediterranean, however it is generally much cooler and more verdant than other areas in the Western Cape, with annual precipitation exceeding 1500 mm and summertime maxima rarely exceeding 25 °C. Snow is not unusual on the higher peaks, like Verkykerkop, Somerset Sneeukop (Afrikaans: Snow Peak) at 1590 m high and The Triplets in the northern section of the range. This area and the other ranges to the south are considered the hub of the Cape floristic region with the most biodiversity in the entire fynbos biome. The surrounding lowlands have rich alluvial soils supporting viticulture and other deciduous fruit farms.

Kogelberg

The Kogelberg is a range of mountains along the False Bay coast in the Western Cape of South Africa. They form part of the Cape Fold Belt, starting south of the Elgin valley and forming a steep coastal range as far as Kleinmond.

The Kogelberg area has the steepest and highest drop directly into the ocean of any southern African coastal stretch.

Langeberg

The Langeberg Range is a mountain range in the Western Cape province of South Africa. Its highest peak is Keeromsberg at 2075m and 15 km NE of the town of Worcester.

Some of the highest peaks of the range are located just to the north of Swellendam, in a subrange known as the Clock Peaks whose highest point is 1710 m high Misty Point. Local lore states one can tell the time by means of the shadows cast by the seven summits of the Clock Peaks.

The name is Dutch and means "long mountain"

List of mountain ranges of South Africa

This is a list of mountain ranges of South Africa.

Overberg

Overberg is a region in South Africa to the east of Cape Town beyond the Hottentots-Holland mountains. It lies along the Western Cape Province's south coast between the Cape Peninsula and the region known as the Garden Route in the east. The boundaries of the Overberg are the Hottentots-Holland mountains in the West; the Riviersonderend Mountains, part of the Cape Fold Belt, in the North; the Atlantic and Indian Oceans in the South and the Breede River in the East.

The area has always been considered as the breadbasket of the Cape and is largely given to grain farming — mainly wheat. The wheat fields are a major breeding ground for South Africa's national bird, the blue crane. Another important food farmed in the Overberg is fruit with the Elgin Valley producing about 60 percent of the total annual apple crop of about 819,000 metric tonnes (2012 data).Nestled in the Overberg, one can find the Kogelberg Biosphere Reserve (recognised and registered with UNESCO) populated with a large diversity of flowering plants not found anywhere else in the fynbos biome.

The major towns are Hermanus, Caledon, Bredasdorp, Grabouw and Swellendam and the region includes Cape Agulhas, the southernmost point of Africa. The landscape is dominated by gently to moderately undulating hills enclosed by mountains and the ocean.

The name, derived from Over 't Berg, means "over the (Hottentots-Holland) mountain" and is a reference to the region's location relative to Cape Town.

Riviersonderend Mountains

The Riviersonderend Mountains are a mountain range in the Cape Fold Belt of the Western Cape province of South Africa. They run east to west from Riviersonderend to Villiersdorp, separating the Breede River Valley from the Overberg region. They are composed of Table Mountain Sandstone and attain a maximum height near McGregor and Riviersonderend as Pilaarkop (Afrikaans: Pillar Head (1654m)). The ranges are rich in fynbos flora and experience a typical Mediterranean climate.

The name stems from the Sonderend River, and was originally a literal translation of the Khoi-khoi name "Kannakamkanna" ("river without end") into Afrikaans.

Seweweekspoortpiek

Seweweekspoortpiek (Afrikaans for ‘Seven Weeks Defile Peak’) is a peak in the Western Cape, South Africa. It is the highest mountain in the Cape Fold Belt and the highest point in the Western Cape province. Along with its western neighbour, Du Toits Peak, it qualifies as an Ultra and these are the only two in the country.

It is located in the Klein Swartberg range, close to the Seweweekspoort mountain pass.

Simonsberg

Simonsberg (English: Simon's Mountain) is part of the Cape Fold Belt in the Western Cape province of South Africa. It is located between the towns of Stellenbosch, Paarl and Franschhoek, forming a prominent 1399 m high mountain, as it is detached from the other ranges in the winelands region. Simonsberg is named after Simon van der Stel, first governor of the Cape and founder and namesake of Stellenbosch and Simon's Town.

Swartberg

The Swartberg mountains (black mountain in Afrikaans) are a mountain range in the Western Cape province of South Africa. It is composed of two main mountain chains running roughly east–west along the northern edge of the semi-arid Little Karoo. To the north of the range lies the other large semi-arid area in South Africa, the Great Karoo. Most of the Swartberg Mountains are above 2000 m high, making them the tallest mountains in the Western Cape. It is also one of the longest, spanning some 230 km from south of Laingsburg in the west to between Willowmore and Uniondale in the east. Geologically, these mountains are part of the Cape Fold Belt.

Much of the Swartberg is part of a UNESCO World Heritage Site.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.