Day 4 - Confounding Contortions

By: Zamampondo and Leslee

After a relatively monotonous drive from Ermelo to East London the previous day, with the underlying stratigraphy comprising Beaufort Group sediments of the Karoo Supergroup. These deposits, though renowned for their luscious assemblages and variety of fossils from the Permian, make for unchanging scenery to the geologist’s eye.

Today, however, our group of mappers were treated to a continuously varied landscape as we travelled southwards from East London to Knysna and along the way passed down a major cascade of South African lithologies.

Catholic Church in King Williams Town - 1918

We hopped in our cars bright eyed and fluffly tailed, ready for a day of exploration. After exiting the Beaufort Group sediments of which we had become so fond, our journey took us down the stratigraphic column of South Africa and into the underlying Ecca Group shales and then briefly into the Dwyka tillites (both similarly of the Karoo Supergroup). Thereafter, we travelled down into the –dare we say significantly more exciting (~360-510 Ma) rocks of the Cape Supergroup, which is composed of the Table Mountain Group, Bokkeveld and Witterberg Groups. At this point our bored passengers were roused by the awe-inspiring folding to be seen in road cuttings and along steep banks along the way. Likewise, this portion of the trip took us through the world-renowned Tsitsikama Forest which several of our passengers had never yet had the chance to witness.

Along the way we were met by Warren Miller of Nelson Mandela University in Port Elizabeth. Warren, who has been researching the folding of the Cape Supergroup sediments in this region as a part of his master’s degree, explained to our group of young, intrepid mappers the history and nature of deformation and folding in this region and the complexity thereof.

Warren Miller explaining some Amazing Geology in Kini Bay

Warren spent countless days scoring over the highly inclined and deformed folds, felsic intrusions, veins and cleavage planes present along the beaches in his area of study – just slightly south of Port Elizabeth – trying to unravel the details and timing of various phases of the CFB’s deposition and deformation. Clues are to be found in the form of bedding-subparallel and bedding-oblique cleavage planes, felsic intrusions with cross-cutting relationships to the intruded rocks and the upending and contortion of the sequence. It is believed that the extreme degree of deformation seen along the southern limb of the Cape Fold Belt is the result of northward-verging subduction underneath the Kalahari Shield.

Work in this region and the raging debate regarding its’ history is ongoing and the interested reader is referred to recent literature regarding the Cape Fold Belt in this region.