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

190 Ma

110 Ma

Karoo SupergroupStormberg Group• Drakensberg Frm• Clarens Frm• Elliot Frm• Molteno Frm

Beaufort Group• Cynognathus Zone• Lystrosaurus Zone• Dicynodon Zone• Cistecephalus Zone• Tropidostoma Zone• Pristrognathus Zone• Tapinocephalus Zone• Eodicynodon Zone

Ecca Group

Dwyka Group 300 Ma

190 Ma

Distribution of the rocks of The Karoo Sequence

Karoo Supergroup

110 million years

10º 20º 30º

Kar

oo S

up

ergr

oup

Mesosaurus

Dwyka Group times

300 Ma (Carboniferous)

Dwyka Glaciation

Glacial tillite

Glacial pavements

Ecca Group

280 Ma (Early Permian)

Beaufort Group

Sediments deposited by rivers

Beaufort Group

Karoo – 250 Ma Middle Beaufort times

DinocephaliansDicynodonts

Cynodonts

Therocephalians

Gorgonopsians

Biarmosuchians

Therapsids(Mammal-like Reptiles)

Increasin

g “mammalness

”

advanced

primitiv

e

“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)

Therapsids

(Mammal-like Reptiles)

Van der Walt (in press)

Diictodon

A small dicynodont

Dicynodonts

Aulacephalodon

Trace fossil Dicynodont trackways

Carnivorous

Gorgonopsians

Artist: Gerhard Marx

Cistecephalus Biozone - 253 Ma

Chris Scotes (2002)

Barkly East District

Clarens

Elliot

Drakensberg

Stormberg Group

Molteno

South African landscape - 200 MaElliot & Clarens Formation

Climate - progressively more arid

Prevailing winds

Barkly Pass, Eastern CapeThere’s dinosaurs in them thar hills!

Elliot Formation (Red Beds)

Clarens Formation

Massospondylus

Elliot Formation – 210 Ma

About 6m long

117 mm

Heterodontosaurus

First MammalsMegazostrodon & Moganucodon

Combined Elliot & Clarens Formation Landscape -200 Ma

Drakensberg

Volcanic eruptions

Drakensberg volcanics

Nieu Bethesda •

• Middelburg

20 km

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