DIAMICTITE

The rocks forming this ridge belong to the Government Subgroup of the Witwatersrand Supergroup and consist of a variety of rock types, shales and quartzites being the most abundant. The rock layers were originally horizontal but have been tilted to the vertical as a result of movement along the Rietfontein Fault which is located in the low ground to the north of this ridge. The outcrop is of sedimentary rock known as diamictite and is composed of fine silt particles containing dispersed coarser sand particles and pebbles. Sedimentary processes normally sort particles according to size, making this rock type rather uncommon. The diamicite at this locality is believed to have been deposited underwater by mudflows, possibly triggered by earthquakes. Diamictites similar to this occur only at two other levels within the Witwatersrand Supergroup: associated with the Main Reef and with the Kimberley Reef.
312 Highland Road, Kensington
Related Organisation: 
Geological Society of South Africa