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The Karoo Basin … a mirror of 110 million years of environmental change. Dr Billy de Klerk.

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Presentation on theme: "The Karoo Basin … a mirror of 110 million years of environmental change. Dr Billy de Klerk."— Presentation transcript:

1 The Karoo Basin … a mirror of 110 million years of environmental change. Dr Billy de Klerk

2 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 million years ago.

3 300 Ma 190 Ma 110 Ma

4 Karoo Supergroup Stormberg 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

5 Distribution of the rocks of The Karoo Sequence

6 Karoo Supergroup 110 million years

7 10º 20º 30º Karoo Supergroup

8 Mesosaurus Dwyka Group times 300 Ma (Carboniferous)

9 Dwyka Glaciation

10 Glacial tillite Glacial pavements

11 Ecca Group 280 Ma (Early Permian)

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13 Beaufort Group Sediments deposited by rivers

14 Beaufort Group

15 Karoo – 250 Ma Middle Beaufort times

16 Dinocephalians Dicynodonts Cynodonts Therocephalians Gorgonopsians Biarmosuchians Therapsids (Mammal-like Reptiles) Increasing “mammalness” advanced primitive

17 “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)

18 Van der Walt (in press)

19

20 Diictodon A small dicynodont

21 Dicynodonts Aulacephalodon

22 Trace fossil Dicynodont trackways

23 Carnivorous Gorgonopsians

24 Artist: Gerhard Marx Cistecephalus Biozone Ma

25 Chris Scotes (2002)

26 Barkly East District Clarens Elliot Drakensberg Stormberg Group Molteno

27 South African landscape Ma Elliot & Clarens Formation Climate - progressively more arid Prevailing winds

28 Barkly Pass, Eastern Cape There’s dinosaurs in them thar hills! Elliot Formation (Red Beds) Clarens Formation

29 Massospondylus Elliot Formation – 210 Ma About 6m long

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31 117 mm Heterodontosaurus

32 First Mammals Megazostrodon & Moganucodon

33 Combined Elliot & Clarens Formation Landscape -200 Ma

34 Drakensberg Volcanic eruptions

35 Drakensberg volcanics

36 Nieu Bethesda Middelburg 20 km

37 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.

38 Let us keep this wondrous treasure trove pristine! Thank you.

39 Let us keep this wondrous treasure-trove pristine! Thank you.

40

41 Reconstruction of Aulacephalodon


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