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!
