Drive to the Hantam National Botanical Garden south of the town of Nieuwoudtville on the Oorlogskloof Road, a gravel road, and a short distance past the Garden you can see the sign reading “glacial pavement”. Park here, walk about 200 m and look down at the rocks. Portions of the “pavement” at first glance resemble an old road with wagon wheel ruts. When one inspects the rocks more closely one can see that they are made of a light gray sandstone, and therefore the ruts are not the remains of a road. But the feature follows the contours of the ground surface in most locations where it is visible. The great grooves could not have been made by wagon wheels. What, then, made them?
The “wagon ruts” in the rocky “pavement” are grooves and gouges made in the sandstone by boulders and pebbles dragged along the bottom of a continental glacier of a vast size. This all took place approximately 300 million years ago during the Carboniferous period when South Africa was part of a supercontinent named Gondwanaland that included much of what we think of as South America and Australia and all of Antarctica. The “pavement” is part of the Dwyka Formation, and indeed the glacial period is alternately known as the Dwyka glaciation or Karoo glaciation. The Geological Society of South Africa has provided a plaque to inform visitors about what they are seeing. The site is on private property. When you enter and leave, please close the gate.
Other such glacial pavements from that same time in earth history can be found near Plooysburg, Herbert District, and the rock art at Driekopseiland, where Stone Age peoples carved images into the flat smooth pavement. They are all Grade II Provincial Heritage Sites and are on private property. At faraway Elandsvlei, elsewhere in the Karoo Basin, thick outcrops of a rock known as diamictite, a hardened and densely packed ancient “moraine” or glacial gravel deposit, stand out as stark reminders of the continental glacier that once covered the entire Karoo area. Outside South Africa Carboniferous glacial pavements are accessible near the town of Barreal, Argentina and at Hallett Cove, South Australia, and very, very few other locales. The Nieuwoudtville glacial pavement is worth getting excited about. To those who like to see unusual pieces of Earth history, such a glacial pavement, in such a convenient location, feels like discovering a part of the tomb of Amanishakheto, Warrior Queen of Nubia, and some overlooked treasures after it was assumed that the 19th century plunderer of Nubian tombs, Giuseppe Ferlini, had sold off or destroyed all of them when the Queen’s tomb was leveled!
South Africans know that there was more than one Ice Age, although many people the world over are unaware of any but the most recent one in the Northern Hemisphere. Geologists know of three ice ages. The first was the one that took place on all continents during the Neo-Proterozoic Era 1.0 billion years to 542 million years before the present day. The second, in the Southern Hemisphere, took place during the Carboniferous period (the Dwyka glaciation). The third was the most famous and most recent Wisconsinian ice age which began approximately 1.8 million years ago and ended about 11 thousand years before the present day. Confined to portions of the Northern Hemisphere, that most recent one left much more evidence behind. The further back in time an ice age came to a close, the more likely that glacial features like stray boulders carried by the ice, mounds of gravel or glacial pavements have been destroyed by normal plate tectonic movements like mountain building, or covered up by millions of years of normal soil deposition. The grooves, combined with the magnetic orientation of magnetic minerals in the Dwyka Formation, help geologists discern the direction of movement of the glacier and the central point of origin for the glacier.
Truly, South Africa’s roads lead to many pleasant surprises.
For Further Reading
Amanishaketo, Warrior Queen of Nubia. African Heritage web site
Crowell, John C. 1999. Pre-Mesozoic Ice Ages: Their Bearing on Understanding the Climate System. Memoir 192. The Geological Society of America. 106 pages.
Deynoux, M., J. M. G. Miller and E. W. Domack. 2004. Earth’s Glacial Record. Volume 5 of World and Regional Geology. Cambridge University Press, 204. 288 pages.
Fleminger, David. The Richtersveld Cultural and Botanical Landscape: Including Namaqualand. 2008. 30° South Publishers. 272 pages
Ngwao-Boswa Ya Kapa Bokone web site, Provincial Heritage Resources Authority of the Northern Cape Province