500-350 Mya
Table Mountain Group

The Cape Supergroup has been described as an “enormous pile of sand” (Compton, 2004). At over 7km thick this “pile of sand”, with intervals of mud was deposited between 510 and 340 million years ago.

Schematic stratigraphic profile of the Southern Cape geological column and rock units in the Kogelberg Biosphere reserve. The Witteberg Group referred to below, does not occur in this area..

The Cape Supergroup was deposited into a slowly opening rift that formed the Agulhas Sea, extending initially north-south down the southwest corner of Africa, then more extensively eastwards across the southern Cape) and from South America to Antarctica, within the Gondwana Supercontintent

The lowermost portion of this sequence is the Table Mountain Group (TMG) that comprises Table Mountain Sandstone (TMS), a thick section of quartz-rich rock formations within the TMG sequence of rocks. Although the term ‘Table Mountain Sandstone’ is no longer formally recognized, the correct names for the most extensive and common sandstone sequences within the TMG are the Peninsula Formation sandstone and the Nardouw sandstone, which are key components of the TMG.

These clean sandstone bodies lack any fossils and are believed to have been laid down on a seashore as braided streams and beaches in an environment lacking any land plants in a very cold climate, as evidenced by the glacial Pakhuis diamictite, immediately overlying it. Early marine brachiopods (types of shelly creatures) start to occur in the Cedarberg Formation which overlies these glacial rocks. This is believed to be evidence that development of life surges after major glacial periods, possibly due to an influx of fine mineral matter into the sea as a result of glacial actions..

The Peninsula Formation sequence forms the front face of Table Mountain and is also well represented in the Kogelberg Mountains along Clarence Drive (Figure 3) and Kogelberg Biosphere Reserve that abuts the Harold Porter Botanical Gardens (HPBG) at its northern end. Here spectacular cliffs and gorges rising above HPBG show sections of Peninsula, Pakhuis (indistinct) and Cedarberg Formations of the Cape Supergroup.

Cross section of Table Mountain Group stratigraphy. Cedarberg Formation shales weather negatively, while more resistant sandstone forms positive ridges. (Photo along Clarence Drive, near Pringle Bay).

Overlying this, the Bokkeveld Group is predominantly a sequence of finer grained mudstone (to later form shale) that was deposited in deeper water. The Bokkeveld Group contains a wide diversity of invertebrate fossils (no internal skeleton), particularly brachiopods as well as trilobites and molluscs (all with external shells) as well as early starfish.

The Bokkeveld rocks grade upwards into the Witteberg Group that was deposited in rivers, lakes and on shallow sea shores. Extinct species of shark have been identified as well as “sea scorpion” that leaves fossil tracks (trace fossil) in these sandy sediments.

The later compression (Plate Tectonics) causing folding, thrusting and deformation, of the TMG, during the Cape orogeny gave rise to the Cape Fold Belt, coast-parallel mountain ranges of the Western Cape and commenced about 280 million years ago, ending around 230 Ma. The Cape Orogeny event tectonically deformed the Cape Supergroup from about Clanwilliam, approximately 200 km north of Cape Town, to Port Elizabeth, approximately 650 km east of Cape Town.

These mountain building features are well displayed in various Cape Mountain Passes, such as Montagu, Seweweeks poort and Meiringspoort.

500-350 Mya Table Mountain Group

500-350 Mya
Table Mountain Group