The Karoo Basin
… a mirror of 110 million years of
environmental change.
Dr Billy de Klerk
The Karoo Basin
focus on a few points:
1. It is the only sedimentary basin in the world that contains a continuous
record of terrestrial sediment accumulation over 110 million years.
2. It contains an uninterrupted accumulation of fossils of land animals and
plants that lived at that time.
3. These terrestrial fossils provide us with the wonderful evolutionary record
of both the mammals and the rise of dinosaurs.
4. MORE IMPORTANTLY – I believe that the bulk of the accumulated
natural gas, that is being targeted for exploration (Fracking), was driven off
at the end of the Karoo accumulation when the volcanic Drakensberg flood
basalts were erupted - 190 million years ago.
300 Ma
110 Ma
190 Ma
Karoo Supergroup
Stormberg Group
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Drakensberg Frm
Clarens Frm
Elliot Frm
Molteno Frm
190 Ma
Beaufort Group
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Cynognathus Zone
Lystrosaurus Zone
Dicynodon Zone
Cistecephalus Zone
Tropidostoma Zone
Pristrognathus Zone
Tapinocephalus Zone
Eodicynodon Zone
Ecca Group
Dwyka Group
300 Ma
Distribution of the rocks of
The Karoo Sequence
Karoo Supergroup
110 million years
Karoo Supergroup
10º
20º
30º
Dwyka Group times
300 Ma (Carboniferous)
Mesosaurus
Dwyka Glaciation
Glacial pavements
Glacial tillite
Ecca Group
280 Ma (Early Permian)
Beaufort Group
Sediments deposited by rivers
Beaufort Group
Karoo – 250 Ma
Middle Beaufort times
Cynodonts
Therapsids
(Mammal-like Reptiles)
Therocephalians
Gorgonopsians
Biarmosuchians
Dicynodonts
Dinocephalians
Therapsids
(Mammal-like Reptiles)
“The mammal-like reptiles of
South Africa may be safely
regarded as the most
important fossil animals ever
discovered, and their
importance lies chiefly in the
fact that there is little doubt
that among them we have the
ancestors of the mammals,
and the remote ancestors of
man.”
Dr Robert Broom (1932)
Van der Walt (in press)
Diictodon
A small dicynodont
Aulacephalodon
Dicynodonts
Trace fossil Dicynodont trackways
Carnivorous
Gorgonopsians
Cistecephalus Biozone - 253 Ma
Artist: Gerhard Marx
Chris Scotes (2002)
Stormberg Group
Drakensberg
Clarens
Elliot
Molteno
Barkly East
District
South African landscape - 200 Ma
Elliot & Clarens Formation
Prevailing winds
Climate - progressively more arid
Barkly Pass, Eastern Cape
There’s dinosaurs in them thar hills!
Clarens Formation
Elliot Formation (Red Beds)
Massospondylus
Elliot Formation – 210 Ma
About 6m long
Heterodontosaurus
117 mm
First Mammals
Megazostrodon & Moganucodon
Combined Elliot & Clarens Formation Landscape -200 Ma
Drakensberg
Volcanic eruptions
Drakensberg volcanics
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20 km
Nieu Bethesda
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Middelburg
Conclusions
1. The Drakensberg flood basalts were erupted over a period of at least
three million years.
2. Successive lava flows build up an accumulated thickness of no less than
1,4 km. Much of this basalt has been eroded away over the past 185
million years revealing the underlying Karoo sediments.
3. The volcanic eruptions were fed by magma that had to migrate and force
itself through the entire sedimentary succession of the Karoo Basin (c. 6
km thick). Today we see these conduits as topographic highs in the
Karoo landscape as dykes and sills – the koppies and flat-topped hills.
4. Liquid basaltic magma has a temperature of ~1200°C
5. Insulated and slow cooling magma would take a few hundred thousand
years to cool down and would therefore heat the containing sediments
considerably (hay-box effect).
6. As a consequence, the accumulated volatile natural gas, contained
within the adjacent sediments, would have been burned off or expelled.
Let us keep this wondrous treasure trove pristine!
Thank you.
Let us keep this wondrous treasure-trove pristine!
Thank you.
Reconstruction of Aulacephalodon
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Slides – Geology of the Karoo