As central Africa entered the Phanerozoic, the current geologic eon in which multicellular plant and animal life is commonplace, sedimentary rocks were deposited in what may have been failed rift valleys. These rocks are mainly found in the Congo Basin, a structural tectonic feature that extends into neighboring Democratic Republic of Congo, formed within the Congo Craton. Because of thick layers of sediment atop the craton in central Africa, remoteness and sparse research from boreholes and seismic lines, the exact origins of many of these sedimentary units remains unclear. Geologists currently interpret many of the sedimentary sequences from the Late Permian into the Triassic as the remains of the Karoo rifting period. During the Karoo period, southern Gondwana rifted across a large area encompassing what is now southern South America and South Africa. The rift basin and surrounding regions were cloaked in thick layers of continental sediment and sedimentation accelerated when Gondwana drifted over the South Pole, causing massive glaciation of Africa in the Karoo Ice Age. Ultimately, the glaciers melted at the end of the Permian, creating a swampy delta environment. Rocks directly preserving this sequence are found in the Karoo Supergroup, one of the most extensive stratigraphic units in southern Africa.
