-   by Allan Fraser

Traveling through the rugged and expansive terrain of the northern Cape I stopped over at the glacial pavements at Barkley West. I found the glacial pavements fascinating – their smoothness is remarkable with crisscrossing striations across the polished surface. It is difficult to believe that ice sheets hundreds of meters in thickness covered this area at one time.

The pavements near Barkley West and other similar ones around the country were formed during the Carboniferous time period, 350 - 290 million years ago. At that time, southern Africa was still part of the supercontinent Gondwana, and was geographically positioned over the South Pole. A continental ice sheet covered the entire supercontinent (see figure 1). We know this because Carboniferous glacial deposits - tillite conglomerate and varved shales - occur throughout South America, southern Africa, India, Antarctica, Madagascar and Australia. These ice sheets were similar in size and scale to the present-day Antarctic ice sheets - hundreds of metres thick and thousands of square kilometres wide. The weight of this ice, pressing on the rocks below, produced the glaical striations. Similar striations occur at Amanzimtoti on the KwaZulu-Natal south coast and west of Vryheid, and on the top of "Table Mountain" in the Valley-of-a-Thousand-Hills", south of Pietermaritzburg ^(1.)

Figure 1: Gondwana in relation to the South Pole, 200 million years ago.
Courtesy: Greg Houseman - Click for website




Figures 2 & 3: The glacial pavements near Barkly West, Northern Cape

REFERENCES:

1. Email correspondence from Prof. Bruce Cairncross, Rand Afrikaans University