Day 2 - Supercalifragilisticexpialidocious

Day 2

By: Mihlali, Jennifer and Matsie

Bright and early from Ermelo we headed down towards Vryheid to meet up with Nigel Hicks from the CGS Pietermaritzburg office. He would turn out to be a truly supercalifragilisticexpialidocious guide and we honestly think he would make a great lecturer (Just putting that out there). To the geology. The day was mainly about sedimentology and we started looking at the Vryheid Formation of the Karoo Supergroup. The impressive  railway cutting outcrop that Nigel showed us was deltaic in origin, showing planar bedding at the base indicative of the pro delta  and trough cross bedding near the top indicative of the delta- front. The Vryheid Formation is perhaps best known for coal; the seams occur in the distal delta plain, however, they were  not visible at this locality as the sediments had been eroded away.

We then got back on the road and made a quick stop along the way where we looked at an outcrop of the White Umfolozi Formation falling under the Pongola Supergroup. The outcrop was an exceptionally sheared and deformed quartzite, but the most interesting feature was the armored lapilli tuff. Nigel informed us that the lapilli tuff was formed during a volcanic eruption where the pyroclasts from the lapilli and the armour is the ash that covered the lapilli. The clear contact between these deposits and the overlying andesitic lava was thrown in for good measure at this exposure! Just for interest, the geology was first comprehensively described by P Matthews  in 1967 (The Pre-Karoo formations of the  White Umfolozi  inlier northern Natal) in the GSSA Transactions..

GOLD !!!! J J J

Denny Dalton Gold Mine No 22 : sorry to burst your bubble  but sadly the gold left in the area is not economically viable!  Back to the sedimentology. The gold is hosted by the conglomerates of the Singeni Formation still in the Pongola Supergroup, the conglomerate is known as the contact reef, existing as it does between the Agatha  and  Singeni  formations.

Midday and it was blazing hot and we were sweating like CRAZY! Nigel had one more stop to show us and oh what a stop it was. There was plenty to take in and again we gonna say that Nigel is supercalifragilisticexpialidocious as he took us across almost 3 billion years of geology in one human ‘step’!

According to the stratigraphy of South Africa the volcanics and quartzite of the Nsuza Group was deposited first and then followed the andesitc lava and siliclastics of the Mozaan Group;  these lithologies were affected by a clear normal fault. The tillites are not displaced at all (# current situation) so the fault pre-dated the Dwyka deposits.

We then saw the glacial striations showing a North to South flow directions, plus other the glacial features including well preserved rock flour ,a nail head indentation,  and an Eskia (conglowerate at front of the melting glacier) – now that was a new one for us guys! Can’t wait for tomorrow!

Snapshots - Day 2

Great news! The baton has been handed over, thus I have now much less work to do. From today our field school participants have held a mutiny to this blog and will start sharing their stories and what they've learnt during our trip. With that being said, I can now simply share some snapshots of the day!

Day 2 - AMAZING Geology

Nigel Hicks: Senior scientist and expert from the Pietermaritzburg regional office of the Council for Geoscience explaining the intricacies of Delta depositional environments. Note the expert drawing of the background Vryheid Shales trough cross beds - Ecca Group of the Karoo Supergroup.

Expert team work is important in these situations. 

Conglomerates of the Sinqeni Formation - 2.9 Ga Pongola Supergroup, with the notably erratic Mozaan Contact Reef, which was mined by the Denny Dalton family. Note the sulphides and uranium staining (yellow tinge).

The most AMAZING of all. Seems like the Dwyka does not only carry rocks, but also Baas Groenewald and Baas Mofokeng, who both exist ca. 390 Ma and 2900 Ma. Note the striations all over the quartzites.

RSA Geotour 2015: Day 1 - 2

The Council for Geoscience Field School provides an ideal opportunity for participants to experience just some of the special geological sites around South Africa! 

Overview of the Geological Tour around South Africa

Day 1

Here we go! We begin our journey at the head office of the Council for Geoscience in Silverton, Pretoria. Our start is located within the central region of the Transvaal Basin. These rocks were deposited ca. 2.7 – 2.1 Ga within an extensional basin located atop an Archean basement of granite-gneiss and Witwatersrand rocks. Five distinct and unconformably bounded sequences are recognised. These include various basal clastic and fluvial sediments deposited along with volcanic lavas, i.e. Protobasinal rocks and the Black Reef. This is overlain by the Chuniespoort, most notably, the Malmani dolomite and chert. Continued extensional subsidence in the Transvaal Basin created a deep marine environment and the deposition of uppermost Chuniespoort of banded iron formation, followed by an extensive marine regressive sequence. This latter depositional phase defines the Pretoria Group rocks.

Continuing east along the N4 highway, we arrive in Nelspruit and cross the ca. 3.2 Ga Kaap Valley Tonalite. This pluton is of special interest as it forms an example of the earliest continental crust on Earth. This is the result of partial melting of subducted hydrated oceanic crust, highlighting the existence of early Earth tectonic processes.

From Nelspruit we continue south along the R40 into the ca. 3.5 – 3.2 Ga Barberton Greenstone Belt. The Barberton Greenstone Belt is one of the most well preserved fragments of the early Earth and holds many secrets of early life and geodynamic evolution. There are three distinct lithological zones. From bottom to top, these are: The shallow marine Onverwacht Group of ultramafic-mafic volcanic rocks with minor felsic volcanics, tuff and lesser sediments. The shallow to deep marine turbidite, shale, mudstone, interbedded chert and banded iron formation of the Fig Tree Group. And, finally the topmost Moodies Group. The latter was deposited in a shallow marine to fluvial environmental setting and consists of conglomerate, feldspathic quartzite, shale and lesser banded iron formation and some volcanic rocks. Terrane assembly ca. 3.2 Ga, along the Saddleback-Inyoka fault system sutured these zones together and formed the general NE structural trend.

Our route then continues and straddles the Swazi border through vast indigenous forest until we finally reach the N17 and follow it to our overnight destination of Ermelo.

Day 2

We depart Ermelo nice and early (we hope) and continue east along the N2 toward Piet Retief. From here we head south toward Vryheid. Along the way we will encounter the Commondale Komatiites. The composition of these lavas implies a much higher melting point than what currently exists on Earth. This suggests that early Earth was much hotter, or perhaps had a sufficiently enough hydrous content. Further south, toward Paulpietersburg we cross the Pongola Basin and onto our final look at Archean granites. Heading further south and we enter the vast plains of the Karoo Supergroup.

The rocks of the Karoo Supergroup were deposited into numerous basins formed during tectonic processes defining the evolution of Gondwana; and a ca. 120 Ma geological record. For this trip, our interests lie with the Main Karoo Basin, which covers most of the country. Sedimentation of the Main Karoo Basin can be subdivided into five phases. These are: Glacial and the deposition of the Dwyka Group; Marine to coastal plains and the deposition of the Ecca Group; and fluvial to aeolian and the deposition of the Beaufort and Stormberg Groups. And finally, extensional tectonics and the outpouring of the Karoo Large Igneous Province.

As we head south we continue through the lower successions of the Ecca. This region is especially renowned for the vast coal deposits. Coal is the overwhelming fuel used for South Africa’s energy generation and is found largely within the Ecca; and also the Beaufort and Stormberg Groups. Depending on time, we will have numerous interesting sites to visit in the Karoo, including a Glacial Pavement developed on the ca. 2.9 Ga Mozaan Quartzites and several excellent stratigraphic unconformities and special fossil sites (ask me to tell you more about this while we’re in the field).

Heading even further south, we exit the Karoo Supergroup and enter the Natal Sector of the Namaqua-Natal Mobile Belt (NNMB). The NNMB is an orogenic suture that forms the basement underlying most of the Karoo. It represents the remnants of a collisional event defining the formation of Rodnia ca. 1250 – 950 Ma. The NNMB is exposed in two regions, namely, the Northern Cape and KZN. The Natal Sector comprises several distinct geological terrains that are thrust-bounded together. These are, from north to south; the Tugela greenschist ophiolite complex, Mzumbe upper-amphibolite facies granulites and Margate granulite facies rocks. A major feature of this region is the development of the Oribi Gorge Suite of granite and charnockite. These rocks are generally restricted to the Mzumbe and Margate terrains. We will encounter some of the granites as we head toward our overnight destination of Pietermartizburg.