Page 126 - Bulletin 11 2007

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quartzitic sandstone unit, the Peninsula Formation, up to 600 m thick, and which forms
the mountainous backbone of the South Peninsula.

 The Graafwater Formation rests unconformably on the granite and represents

fluvial, tidal and shallow-marine sediments that were deposited on a flat surface

above the granite about 475 million years ago. The granite would originally have
crystallised from liquid magma deep in the Earth’s crust and during the 65

million period prior to Graafwater Formation sedimentation, there was uplift,

mountain building and prolonged erosion that reduced the landscape to a vast
peneplain. (Cole, 2002).

 The younger Peninsula Formation that conformably overlies the Graafwater

Formation represents a thick fluvial sand deposit with infrequent marine
incursions similar to the present sandurs of Iceland. (Marren, 2002). Locally, the

youngest Peninsula Formation sediments are approximately 445 million years

old, but these were covered by at least 3 km of marine, terrestrial and glacial
sediments over a period of 165 million years. (Geological Society of South

Africa, 1994; Cole, 2002). This was followed by a period of uplift and mountain

building that finished about 170 million years ago. The burial and tectonism
(mountain building) of the Table Mountain Group sediments caused them to

become lithified with dissolution of felspathic minerals and precipitation of
quartz around existing quartz grains (quartz overgrowths) leading to the

formation of sandstone and quartzitic sandstone.

With the separation of Africa from the other continents, coinciding with the break-up of

Gondwanaland 170 million years ago, prolonged erosion took place, resulting in the
removal of all rocks and sediments above the Peninsula Formation, as well as those

linking Table Mountain with the inland mountains. During this break-up period,
extensive faults were developed, resulting in vertical displacement of the Table

Mountain Group strata. (Fig. 3.2; Geological Society of South Africa, 1994). For
example, the northwest-trending fault at Smitswinkel Bay throws down the Table