Magaliesberg - Geology

Geology

The Magaliesberg Range has a very long geological history. Its quartzites, shales, chert and dolomite were deposited as sediments in an inland basin on top of the 3 billion year old Archaean Basement Complex. This process of sedimentation lasted for about 300 million years. About 2 billion years ago a massive upwelling of molten magma resulted in what is now known as the Bushveld Igneous Complex. The enormous weight of this intrusion depressed the sediments that lay beneath and tilted the sediments along the edges so that the broken scarps faced outward and upward, and the gentler dip slopes inward. During the same period these sediments were fractured and igneous intrusions of dolerite filled the cracks. With the passage of time these intrusions eroded, especially on the dip slopes, forming deep kloofs or ravines providing excellent rock-climbing potential to modern man. This large dog-leg-shaped area is now termed the Transvaal Basin and includes the lofty escarpment of the Transvaal Drakensberg overlooking the Lowveld in the eastern part of the country. Massive outpourings of igneous material - volcanic lava - of the much younger Karoo Supergroup later covered the Transvaal Basin, but this was subsequently eroded so that it only remains along the Transvaal Basin's southern rim.