Day one
The group actually began investigating the Karoo rocks near Vryheid and Denny Dalton, in the middle of our Pongola day. However, the Karoo proper began as we departed Pongola and drove west toward the Drakensburg mountains. We had some really interesting weather on this day, with extremely heavy rainfalls and massive electrical storms. These conditions resulted in major damages in several parts of northern South Africa. Fortunately, we were able to avoid the worst of these conditions and only had to endure getting soaked while looking at the Mozaan-Dwyka unconformity.
View of the Clarens sandstone landscape in the Golden Gate National Park
Anyway, our Karoo transect began with a brief introduction of the main Karoo Basin and then we promptly began overlooking the basaltic (dolerite) rocks making up the Drakensburg Mountains. From here we then entered the Stormberg Group, particularly spending some time looking at the mostly desert-dune deposits of the Clarens Formation. These magnificent sandstone cliffs are wonderfully exposed within the Golden Gate National Park.
Golden (gate) girls
Spot the dyke
Day two
We then spent most of the second day driving across the upper parts of the Beaufort Group, particularly discussing the Permo-Triassic boundary, which is exposed within the Tarkastad Subgroup. This boundary is especially important as it marks the extinction of the Dicynodonts in favour of Lystrosaurus.
The !Gariep Dam, currently below 50 % capacity
We also took some time visiting the largest dam in South Africa, i.e. the !Gariep Dam. The effects of the drought were clearly visible with the dam less than 50 % capacity. This is a scary reminder for us to become more water wise and efficient.
Through the Beaufort Group, the team also made a visit to the Karoo National Park to walk the famous Karoo fossil trail. The fossil trail provides a great overview of the various dinosaur fossils that were found in this region.
We then continued further south and intersected the lowermost group of the Karoo, the Ecca. Here we saw these mostly black mudrock and fine-grained sandstone highly folded and faulted due the effects of the c. 250 Ma Cape Orogeny.
On the Gariep dam wall, with our Japanese visitors
Day three
Our third day saw the group doing a transect from the escarpment, through the Cape Fold Belt mountains and into the underlying Pre-Cape Cango inlier. On the escarpment we began by looking at the geometry of the various dolerite (basaltic) dykes and sills. We also investigated the effect of the dolerite intrusion on the surrounding Beaufort sandstones. The dolerite intruded at a temperature of approximately 600-800 degrees and resulted in the formation of hornfels. These hornfels are also defined by the presence of andalusite.
L: "Dinosaur Egg/Onion-skin weathering" fracture-controlled preferential weathering of dolerite; R: Hornfels between dolerite sills
Taking out frustrations on that dyke
Through the Beaufort Group, the team also made a visit to the Karoo National Park to walk the famous Karoo fossil trail. The fossil trail provides a great overview of the various dinosaur fossils that were found in this region.
TL: Bradysaurus (Pareiasaur); TR: Dicynodont; BL: Bradysaurus head; BR: Diictodon
The team on the Karoo fossil trail
We then continued further south and intersected the lowermost group of the Karoo, the Ecca. Here we saw these mostly black mudrock and fine-grained sandstone highly folded and faulted due the effects of the c. 250 Ma Cape Orogeny.
T: (L-R) Ripon sandstone, White Hill shales, Collingham interbedded shale and tuff, Matjiesfontein chert bed; B: Swartberg Pass
We also discussed the merits and controls on the potential shale gas resources of the Karoo and discussed the various implications of harnessing (or attempting to harness) this gas from the Karoo.
The Whitehill Formation - all degassed
Ma Connie: "Forces were this big.."
No comments:
Post a Comment