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.

I Read Rocks - Part 1

A special series by Warren Miller

I read rocks! I am pretty average at it. If you were to compare my rock reading abilities to how fast a reader reads a book, I would say I read rocks the same as an average reader reads a book. The thing is – the point of reading (including rocks for this matter) is not to get to the last page of the book as fast as possible, but to rather enjoy the read. Take it step by step, enjoying the unfolding story and if necessary go back a few pages from time to time when things aren’t making sense.  

I have spent the past few years trying to understand a certain grouping of rocks that are rather old and severely deformed. These rocks I speak of outcrop near my home town of Port Elizabeth, along the striking coast between Sardinia Bay and Kini Bay (see below). 

Overview of the study area being investigated, highlighted in red

Similar aged rocks have also been studied in various other parts of the southern tip of Africa, including Damaraland, Cape Nollath, Cape Town, Oudtshroon and George. I have made a pretty picture to help you see the broader setting of southern African geology over the past 1000 – 200 Ma.

This is called a stratigraphic column. It is based on the principle of superposition: that is to say if a sequence of rocks are positioned below another sequence of rocks, the former sequence is older than the latter – assuming there has been no tectonic disruption or the tectonic disruption is resolvable. So look at my picture, enjoy it. I like to draw as I read. It makes the reading more fun.

Now back to my rocks. For months and months I hadn’t a clue what I was reading. Rocks were all over the place. I couldn’t piece the sentences together. It was a mess. It was like a riddle that kept banging against my head week in and week out. But luckily I have some friends who also enjoy reading rocks, of which some of them are a lot better than me. So I would bring them along and we would read together and discuss our interpretations over a big glass of black label beer often making very little progress. But after some time and a little help from another friend in Australia and a very hi-tech machine I was able to make some very interesting progress.

To be Continued…

Warren Miller is a Masters of Geology student at the Nelson Mandela Metropolitan University (NMMU), working within the Africa Earth Observatory Network (AEON) and Earth Stewardship Science Research Institute (ESSRI). He is currently finishing his thesis, looking into the structural dynamics effecting the rocks along the southeast coast of South Africa. Here, he will take us on a journey into the mind of Geologist, listening and observing carefully to the Earth’s Story as it unfolds layer, by layer. As you can see, this is a complex story!