The Karoo Supergroup Drakensberg Group Stormberg Group Beaufort Group Ecca Group Dwyka Group THEME 11: The Karoo Supergroup

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Bartholomew Haynes
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THEME 11: The Karoo Supergroup The Karoo Supergroup Drakensberg Group Stormberg Group Beaufort Group Ecca Group Dwyka Group The Cape Supergroup and Karoo Supergroup record 300 Ma of changing

1 THEME 11: The Karoo Supergroup The Karoo Supergroup Drakensberg Group Stormberg Group Beaufort Group Ecca Group Dwyka Group The Cape Supergroup and Karoo Supergroup record 300 Ma of changing environments and the life of a Supercontinent, during which time evolution was occurring Karoo strata were deposited in a foreland basin behind the Cape Fold Belt. Subduction under the southern continental margin of Gondwana continued, so thrusting and loading in the CFB continued, so the Karoo basin continued to deepen Very thick accumulation of sediments (up to 12km), which thins towards the north. Covers two thirds of SA MA (Late Carboniferous to Middle Jurassic) 1

Karoo Supergroup During the time of the Cape

Witteberg Group Fully glacial south polar

2 Karoo Supergroup During the time of the Cape Supergroup, South Africa had been drifting steadily towards the South Pole. Fully glacial conditions by the end of the Witteberg Group Fully glacial south polar conditions at start of Karoo. The Dwyka Group is tillite. Basin deepest in the South (where loading was greatest) Icebergs in South, glaciers in North 2

3 Northern side of Karoo Sea Southern side of the Karoo Sea Iceberg dropstones in southern Dwyka Gondwana drifted over the south pole and then continued, now drifting northwards..into warmer climates, so Dwyka glaciers melted. Karoo sea expanded. Deeper water. Ecca Group deposited in deltas along northern coast 3

4 Southern Africa s emergence from glacial conditions coincides with the evolution of Glossopteris flora (tree-like plants) Thick accumulations of dead vegetation became buried before it could be washed away.coal deposits of the Ecca. Extensive coal deposits in the Highveld (Witbank area) and Kwazulu Natal 4

Ecca deposits on the southern shore of the Karoo sea do not contain coal.

Turbitites instead Some of the earliest recorded reptile faunas (Mesosaurus) are

thrusting in the CFB, basin failed to deepen, so sediment from CFB filled the basin,

5 Ecca deposits on the southern shore of the Karoo sea do not contain coal. Only a very narrow coastal platform, so few swampy environments. Turbitites instead Some of the earliest recorded reptile faunas (Mesosaurus) are recorded from the southern Ecca Turbidites at Laingsburg Due to a reduction in the thrusting in the CFB, basin failed to deepen, so sediment from CFB filled the basin, and covered over northern shore Karoo sea shrank to a lake by 250 Ma (Permian). Much better environment for terrestrial flora and fauna 5

Transition from marine to terrestrial environments is

of the Beaufort Group The end of the Permian is marked

6 Transition from marine to terrestrial environments is the transition between the Ecca and Beaufort groups. Meandering rivers and floodplains. Earliest terrestrial reptiles Sandstones and mudstones of the Beaufort Group The end of the Permian is marked by a mass extinction event. 96% of species extinct at 251Ma. Change from meandering rivers to braided rivers (no vegetation). Katberg Fm. Dicynodont (mammal-like reptile) one of few survivors 6

7 Recolonisation of different plants marked by a return to meandering rivers. The Burgersdorp Fm. (uppermost Beaufort Group) Beaufort Group slightly uplifted and eroded prior to deposition of the Stormberg Group. Africa continuing to drift north, and steady aridification. Molteno, Elliot and Clarens Fm. Triassic to Early Jurassic Molteno Fm. Braided rivers Northwards drift of Gondwana into lower latitudes, global warming, interior position in Supercontinent, rainshadow of Cape mountains = aridity Elliot Formation is characterised by ephemeral river deposits. Dinosaurs and lungfish in temporary ponds. Elliot spans the end of the Triassic at 206 Ma. Another mass extinction event. Continued aridity led to desertification.the Clarens Fm. Extensive sand sea. Barchan and Transverse dunes 7

Karoo sedimentation ended at about 182 Ma,

Crack-like fissures fed by planar sheets of

Flows were 10-20 m thick, and covered most of

8 Karoo sedimentation ended at about 182 Ma, when a massive outpouring of basaltic lava erupted across the Clarens desert. The Drakensberg Group flood basalts Crack-like fissures fed by planar sheets of magma (dykes and sills). Flows were m thick, and covered most of southern Africa. 1600m of basalt accumulated Best preserved in Lesotho 3 million km 3 of lava 8

9 Second phase of volcanism restricted to Lebombo mountain area rhyolites and volcanic ash. 4800m of material accumulated Fissure eruptions occur under tension onset of break-up of Gondwana, triggered by mantle plume beneath Gondwana near southern Mozambique. 300 Ma of non-stop sedimentary accumulation ended. 9

PLATE TECTONICS THEORY

PLATE TECTONICS THEORY Continental drift Sea floor spreading CONTINENTAL DRIFT CONTINENTAL DRIFT 1. The fitness of continents and Continental Reconstruction Earth ~200 million years ago 1.1 Geometrical