September 28. Karoo Supergroup

Map of the Karoo Supergroup in South Africa by
Oggmus, used under Creative Commons license.
Most of the Beaufort and Stormberg Groups are Triassic in age. 

The Karoo Supergroup is an extensive package of rocks in South Africa whose age extends from the Carboniferous into the Jurassic. As you probably recall, South Africa during most of that time was well inside the supercontinent of Gondwana and later Pangaea, distant from the sea, so it is no surprise that most of the rocks of the Karoo are non-marine, deposited in river systems, flood plains, lakes, deserts, and alluvial fans in uplands. The Karoo has some outstanding Triassic fossils.

Much of the late Triassic Stormberg group was deposited by a vast braided stream system that was home to abundant life by late Triassic time. Cycads and other gymnosperms including confers created diverse woodland habitats, from riparian along the rivers to marshes and meadows. The Molteno Formation in the Stormberg group is the primary coal producer in the eastern part of South Africa’s Cape Province – so we had clearly left the early Triassic coal gap behind.  

The coal-bearing sands of the Molteno Formation are overlain by younger red mudstones of the Eliot Formation, which spans the time from very late Triassic into the very early Jurassic, about 210 to 190 million years ago, with the Triassic-Jurassic boundary at 199 million years ago. The Eliot strata contain fossils of more than 40 species of dinosaurs, ranging from theropods like coelophysis which we mentioned a few days ago, to the multi-ton bipedal herbivore, plateosaurus.

The Stormberg group of the Karoo Supergroup also contains fossils of some of those almost-mammals that we discussed the other day, along with a remarkable array of fossil insects.

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Triassic Lystrosaurus  drawing by Dmitry Bogdanov,
used under Creative Commons license

Edwin Harris Colbert was born September 28, 1905, in Clarinda, Iowa. He was a vertebrate paleontologist who discovered and described the coelophysis dinosaurs in New Mexico, and his discovery of Lystrosaurus in Antarctica in 1969 contributed to the acceptance of the theory of continental drift. The dicynodont Lystrosaurus, a mammalian ancestor, was the most common terrestrial vertebrate of the early Triassic. It’s abundant in the early Triassic part of the Karoo sediments.

—Richard I. Gibson

Image sources:
Map of the Karoo Supergroup in South Africa by Oggmus, used under Creative Commons license. Most of the Beaufort and Stormberg Groups are Triassic in age. 

Triassic Lystrosaurus  drawing by Dmitry Bogdanov, used under Creative Commons license.