Table Mountain seen from Signal Hill, across the Cape Town city bowl. The portion of the mountain made up of Table Mountain Sandstone is indicated on the right.[1] It is this mountain that has given its name to the geological structure that occurs in the mountains throughout the Western CapeSchematic diagram of an approximate 100 km west-east (left to right) geological cross-section through the Cedarberg portion of the Cape Fold Belt (South Africa). 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 Table Mountain Sandstone (or Peninsula Formation 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 - see upper illustration).[2] The Upper Table Mountain Sandstone 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.[3] 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. Schematic geological west-east cross section through Cape Peninsula, based on a section through the Back Table just south of Table Mountain. Not to scale. On the Peninsula the basement layer consists in the main of Cape Granite. The Table Mountain Sandstone (in the same colour as in the diagram on the left) forms the steep escarpments that surround the approximately 5 km-wide central plateau. It consists of the layer below the "Pakhuis diamictite", of which there is only a trace at the highest point on Table Mountain at 1085 m above sea level. The lowermost formation of the Table Mountain Group is the "Graafwater Formation", which rests unconformally on the Cape Granite base, as opposed to the Malmesbury Formation base in most of the rest of the extent of Cape Supergroup in the Western Cape (see illustration above, on the left). Kirstenbosch Botanical Gardens, and all the major wines estates on the Peninsula are situated on the fertile (weathered) granite slopes on the east side of the mountain. The soils derived from Table Mountain Sandstone are very poor in nutrition.
Table Mountain Sandstone (TMS) is a group of rock formations within the Cape Supergroup sequence of rocks. Although the term "Table Mountain Sandstone" is still widely used in common parlance, the term TMS is no longer formally recognized; the correct name is the "Peninsula Formation Sandstone", which is part of the Table Mountain Group. The designation "Table Mountain Sandstone" will, however, in deference to the title, continue to be used in the rest of this article. The name is derived from the famous landmark in Cape Town, Table Mountain.
Table Mountain Sandstone is made up predominantly of quartzitic sandstone laid down between 510 (Cambrian Period) and 400 (Silurian Period) million years ago. It is the hardest, and most erosion resistant layer of the Cape Supergroup. It 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, despite being the oldest, and, therefore, lowermost of the Cape Supergroup sequence.[2] The folding of the sequence into the parallel mountain ranges of the Western Cape started about 330 million years ago, affecting the Cape Supergroup 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]
^Compton, J.S. (2004).The Rocks and Mountains of Cape Town. p. 24-26, 44-70. Double Storey Books, Cape Town. ISBN1-919930-70-1.
^ abNorman, N., Whitfield, G. (2006). "Geological Journeys. A Traveller’s Guide to South Africa’s Rocks and Landforms". pp. 208-212. Cape Town, Struik Publishers. ISBN1-77007-062-1.
^Cite error: The named reference whitfield was invoked but never defined (see the help page).
^McCarthy, T., Rubridge, B. (2005). The Story of Earth and Life. pp. 159–161, 182, 187–195, 202–207, 267–269, 302. Struik Publishers, Cape Town. ISBN1-77007-148-2
^Truswell, J.F. (1977). The Geological Evolution of South Africa. pp. 93-96, 114-159. Purnell, Cape Town. ISBN0-360-00290-0.
