2014 Diary: Day 3 - Great Karoo

Our team continued in their journey across South Africa today entering the Western Cape and also making a symbolic stop in the Eastern Cape. The night was short for most, but all remained very eager to get on the road and learn some geology. Our overnight stop was at the Gariep Dam, near the source of the Orange River. This is the largest water reservoir in South Africa, capable of storing more than 5 billion litres of water and covering an aerial extent of more than 370 cubic kilometres. Water from the Gariep Dam is also released into the Vanderkloof dam. The latter has 4 hydroelectricity generators capable of producing up to 360 MW of electricity when needed (which is most of the time these days).

 The Gariep-Vanderkloof dam and hydroelectricity plant

Today, the geology was completely dominated by the Beaufort Group. From the Gariep Dam, to Fraserburg the team was treated to various mudrock and sandstones of the Adelaide Subgroup. An extra treat was the witnessing of a Karoo flash-flood that caught the team by surprise. In an instant, all dry river beds were awash with raging torrents that devoured roads and everything in its path. In another instant, it was all over and blue skies and sunshine prevailed. It is worth noting here that the present day Karoo is very much an arid landscape, however more than 200 million years ago, this was a lush and fertile land similar to the today’s tropical regions.

Flash flood in the central Karoo

The highlight of the day was a visit to Fraserburg and the Gansfontein Paleosurface. This represents a pool-like environment where various creatures gathered and left remarkably many trace fossils for the team to ponder over. This paleosurface is located in the Abrahamskraal Formation within the Beaufort Group, a unit that covers the infamous Permian-Triassic (PT) boundary. Infamous of course, because this period in geological history relates to a major extinction event that resulted in approximately 90 % of life to be erased! Question: What are the possible causes for this extinction? Luckily, the Paleosurface at Gansfontein provides a memoir of some of these creatures. This most notably includes a mammal-like reptile, or tetrapod, known as a Bradysaurus, part of the Pareiasaur group. This is also thought to be an ancient ancestor to the modern day tortoise. This is based on similar morphology of the skull and evidence of bony plates that could be precursors of the tortoise shell. This was a herbivore that reached up to 3 metres long and weighed more than half a ton! For more information about the Gansfontein Paleosurface, click here to download a short report and detailed description: 1986_deBeer

Bradysaurus tracks on the Gansfontein Paleosurface

Reconstruction of Bradysaurus (http://en.m.wikipedia.org/wiki/Bradysaurus)

There are many other spectacularly exposed sedimentary features and arthropod trace fossils on this Paleosurface. This makes is something that is most definitely worth visiting that next time you're anywhere near Fraserburg. To visit the paleosurface, simply go to the Fraserburg Museum and ask and a guide will accompany you and show you around! Tomorrow the team can look forward to a trip across the Cape Fold Belt and consider elements of continental building and structural geology.

View the days route here: Day 3