Field School 2017 Itinerary

The 2017 edition of the CGS field school is about to kick off and will have a special focus on the geodynamics of the early Earth. The participants will have an extensive trip covering much of the Barberton Greenstone Belt and the rocks of the Pongola Supergroup. One new aspect of the trip will focus on coastal geomorphology and Cenozoic geology. Below is the itinerary for 2017:

11th CGS Field School - Mapping the Gariep Belt

And so, finally we have completed another highly successful CGS Field School. This was arguably the most grueling and challenging field school yet. It all came to an end where our team set out to map in the Gariep fold and thrust belt. This of course represents a period spanning the existence of the Supercontinents' Rodinia and Gondwana. Read more about the Gariep Belt here.

Rocks

The team was split into three separate groups and allocated three different maps across the southern portion of the Gariep Belt. Each sheet was unique in its own right and required varying degrees of focus from the various groups. Throughout the mapping period the teams were exposed to several different rocks types characteristic of this region. Some of these include:

TL: Sheared 1,800 Ma Vioolsdrift (Richtersveld Suite) grano-diorite, note the development of spaced cleavage; TR: Magnetite-bearing quartzite of the Stinkfontein Group; ML: Kaigas diamictite with characteristic carbonate clasts; MR: Marble of the Hilda Subgroup; BL: Sheared Numees diamicitite; BR: Iron stone of the Jakkalsberg Member of the Numees.

Tectonics

For those who took the time to hike and closely examine the rocks, there was a continuous sense of dejavu. This was of course due to the continuous repetition of the Gariep sequence. This duplication allowed the team to really consider the tectonic history of this region. 

The tectonics characterises the period after Rodinia broke up, and in the process, formed the mighty Adamastor Ocean; and eventually the growth of Gondwana. This ocean could somewhat be synonymous to the present-day Atlantic, separating the Kalahari (KC) and Rio de la Plata (RC) Cratons. It was within the Adamastor Ocean where much of the Gariep rocks were deposited.

Imagination, and some walking is needed - But, after some time you may begin to exist in a strange space-time continuum bubble where you begin to visualise everything.

Tectonic inversion c. 555 Ma saw the RC and KC encroach, closing the Adamastor Ocean and eventually culminating with the RC accreting atop the KC during the formation of Gondwana. Several structural features were also seen characterising this event:

TL: Fault breccia within Numees diamictite; TR: Pseudotachylite development along the frontal thrust zone; BL: What was the Kaigas diamicitite, now highly deformed schist; BR: Mylonite developed along thrust zone.

Life

Another great thing about spending time in the Richtersveld is interacting with the local people, and clearing your troubled mind in vast and endless landscape.

Sometimes the roads are long and tough. Only for you to discover that this is only half the journey.

Sometimes you chose the easiest path home. Only to discover this means walking over isoclinally folded carbonates interlayered with thrust-bounded phyllite.

But, there's a story to be founded...

And history to be uncovered...

And, some crazy weather to Moer you

Come the third day of battle, look to the East!

And you'll find yourself sad to leave, because you've left a part of yourself behind...

11th CGS Field School - Cape Town

As the team prepares to head into the Richtersveld, there was some time to explore the Cape Peninsula:

The team on Signal Hill

Lots of fun in Cape Town

Lions Head

Testing the rock identification knowledge

11th CGS Field School - Southern Cape

As we approach the half-way mark of the 11th CGS Field School, we continued along the Cape Fold Belt to look at more structural elements. Here are some of the day's highlights:

Overview of the Enon Conglomerates, highlighting extensive weathering and uplift during the Cretaceous

Late fracture in the Enon Conglomerates

Getting a closer look at the Enon

Yasmeen's adopted children 

The Huisrivier Thrust Zone

Language lessons within the group

11th CGS Field School - The Karoo

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.

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.."

11th CGS Field School - Pongola

Following the recent excellent days in the Barberton Greenstone Belt, our team continued discussing early Earth dynamics when they visited the Pongola Supergroup. The rocks of Pongola form some of the earliest volcano-sedimentary units that formed atop some kind of stable continental platform that was likely undergoing a certain degree of extensional tectonic movement. 

The existence of ultramafic greenstone fragments within the c. 3105 Ma Pre-Pongola basement granitoids and the relationship with the overlying Pongola rocks makes this another important location to study the dynamics of the Archean. 

c. 3105 Ma Pre-Pongola basement rocks (with ant for scale)

The day began with the team passing the Commondale lavas (though I missed the turn); and then investigating the Pre-Pongola basement rocks. These granitoids form some of the earliest stable continental crust. Luckily, by now the team are really proficient at describing and characterising plutonic rocks and very quickly were able to classify these as "granitoids".

The weather changed rapidly resulting in us being constantly rained upon, however that didn't stop us from looking at the Pongola Nsuze and Mozaan Groups near the White Mfolozi River valler. We started with ultramafic and felsic lavas in the Nsuze and then quartzites, banded iron formation, and then gold-bearing conglomerates of the Mozaan.

These rocks display an exceptionally well-preserved range of magma compositions and chemically varied sedimentary rocks. The occurrence of stromatolites and banded iron formation speaks of the changes in the atmospheric conditions at this time too.

TL: Ultramafic lavas of the Nsuze Group; TR: Felsic pyroclastic lavas, with bombs of the Nsuze Group; BL: Banded iron formation of the Mozaan Group; BR: Denny Dalton conglomerates within the Mozaan Group.

We also had some time to look at the very classical Vryheid delta sequence. This forms part of the lower Karoo (Ecca Group) and displays excellent sedimentary features related to its deposition within a barrier-delta system. Fine coal seams related the extensive coal mining occurring in this region.

L: Deltaic sequence of the coal-bearing Vryheid Formation; R: Coal seam within the Vryheid Formation

How do I get down?!

Vryheid Formation, with outgoing  full and returning empty coal trains, looking south!

2700 Ma unconformity - Dwyka tillite and underlying striated Mozaan Quartzite

11th CGS Field School - Barberton

Firstly, I must apologise for the delayed update. For the last few days our group has been living on the banks of the Komati river deep within the southern Barberton mountains. This isolated region is definitely an ideal location for investigating the Barberton greenstone belt and discussing many important aspects of the early Earth, however is too deep for any mobile reception.

Anyway, I am happy to report that the team did have three (and today being the forth) excellent days exploring the Barberton greenstone belt and have clearly gained much from this experience.

The proper Barberton Mountainland welcome

Day one

The first day was spent along the Komati River with a section across the topmost units of the Onverwacht Group. The group had an opportunity of closely examining the contact relationships between the Mendon, Kromberg and Hooggenoeg Formations/Complexes. The contact between these units are clearly defined by the occurence of thick chert layers. The Buck Reef Chert, which separates the Kromberg and Hooggenoeg also has apparent algal biomats and early signs of life. During this time, we also began the complex debate regarding the dynamic functionality of the early Earth.

TL: Alteration of Hooggenoeg ultramafic rocks; TR: Plagioclase-varioles in Hooggenoeg pillow basalt; BL: The H6 conglomerate near the top of the Hooggenoeg Formation; BR: Magmatic breccia contact between the 3450 Ma Theespruit Pluton and the c. 3.5 Ga Sandspruit ultramafics

This debate was exasperated when the group came across the H6 within the Hooggenoeg, which includes sandstone and conglomerates. This apparent volcano-sedimentary sequence is surrounded by mafic and felsic interlayered volcanics and suggests the presence of kind of fluvial environment and potentially detrital input associated to tectonic-related mountain building processes.

The team examining highly altered ultramafic rocks in the Komati river

Sheep bridge across the Komati River, built in c. 1890

Pillow basalts in the Hooggenoeg Formation/Complex

Day two

During the second day, the group completed the Onverwacht Group, visiting the lowermost units. This included the Sand/Theespruit and Komati Formations. Of particular interest was the magmatic breccia contact between the c. 3510 Ma Theespruit Ultramafic rocks and the 3450 Ma Theespruit pluton. Here, the ultramafic rocks are also metamorphosed to upper amphibolite facies, quite a substantial PT increase from the overall greenschist grade. Having not completed a Thermocalc course, we briefly discussed the metamorphic implications of this and closely examined the occurence of garnet in the Theespruit ultramafic rocks.

Getting a close-up view of the Trondhjemite-ultramafic intrusive contact

We then entered the Tjakastad Schist Belt and looked at ductile deformational features, especially mineral lineations and rotated porphyroclasts within a felsic agglomerate unit on the outskirts of the belt. 

The team completed the second day with a section of the Moodies Group, near the Sheba Hills. Here we also looked at some of the later deformational structures and discussed their implication on gold mineralisation. Some of the team even managed to find sulphide mineralisation within the Moodies rocks.

TL: Magmatic breccia contact between the Theespruit Pluton and the Sandspruit ultramafics; TR: Felsic Agglomerate within the Theespruit Formation; BL: Olivine spinifex texture in the Komati Formation; BR: Moodies formation conglomerate

The team doing a road section along the Moodies

"Dangerous" river crossing - reflective vest is important in these conditions

After this day Tlou said: "...OMG this was such an amazing experience, I don't even know what to say, I have no words. At the CGS I have attended so many field trips, but this was clearly the best, OMG. I feel like my geology is coming back. Personally I would recommend that every young scientist attend this field school. It is worth it and I feel so sad to be leaving this place..."

Day three

On the third day, our team was given an opportunity of doing a geological mapping traverse through the Tjakastad Schist Belt. With this we began our mapping programme proper and got the team up to scratch with mapping techniques and then allowed them the opportunity of collecting data. While this is a highly complex region to begin with, the team did a wonderful job, inspite of the needing to identify and handle the various talc-carbonate schists, felsic agglomerates, pillow basalts and mylonites.

Measuring foliation on chlorite-bearing mylonite

With this introductory section complete (in Barberton nogal) the team should find mapping in the later Richtersveld mapping project a breeze.

TL: Beginning of the Tjakastad traverse on chlorite-bearing mylonites; TR: Rotated porphyroclast within a felsic agglomerate; BL: Sedimentary layering within the Hooggenoeg Formation; BR: The Theespruit Trondhjemite

We now start day four with a short film on the Barberton Greenstone Belt, a trip to visit the oldest of the TTG gneisses and finally an overview of the various geology with a trip across the Barberton Geotrail. Keep following us for the latest developments!

Climbing up an interlayered felsic unit

After this day Ma Connie said: "...I think this day really showed me that Barberton has lived up to it's expectations. At first I was so confused that I even saw the Bushveld Complex. But, overall it has been a thrilling experience, you know how it is: you read about these important rocks, but now to see it, OMG..."

Day four

Our film didn't quite go according to plan - turns out the Barberton greenstone belt film is 6 hours long. Instead, we decided to use this time with an overview along the Geotrail. The Geotrail provides excellent exposures across the entire greenstone belt. 

It begins on the c. 3.2 Ga Kaap Valley Tonalite and cuts across units of the Moodies, Fig Tree and ending with pillows within the Onverwacht. This provided the group with a great round up of the past few days.

TL: Moodies tidal sandstone; TR: Biomats within the Moodies, showing early signs of life; BL: Black chert within the Fig Tree; BR: Accretionary lapilli within the Fig Tree

We then also continued to investigate the oldest of the TTG gneisses in the region, namely, the c. 3450 Ma Steynsdorp Pluton.