How the Gorge was Formed?

When you peer down over 300 m into the depths of Oribi Gorge you are looking back through well over 1,000 million years of Earth’s history. The Mzimkulwana River bed exposes marble deposits that formed when marine deposits that had been forced deep into the crust around 1,400 million years ago were engulfed by intruding magma at a depth of more than 10 km.

The coarse-grained Oribi Gorge Granitoids formed from these huge magma masses called ‘plutons’ that rose through the Earth’s crust about 1,000 million years ago. By 500 million years ago these rocks had been uplifted to the Earth’s surface, eroded and buried by thick river deposits (Natal Group sandstones).

These sandstones had also been eroded away in the Oribi Gorge area by about 350 million years ago when the area was covered by a shallow marine basin that extended across the country to the Cape. The prominent cliffs forming Oribi Gorge comprise the Msikaba Formation sandstones which accumulated as offshore sand bars on a stable continental shelf. During this period southern Africa was part of a supercontinent named Pangaea that broke up to form Gondwana, the supercontinent that included most of Africa, South America, Antarctica, Australia and India. During this period the southern African region was covered by the extensive Karoo Basin.

Plate tectonic processes caused the rifting of Gondwana after 180 million years ago forming the Indian Ocean and separating the continents as we know them today. At least 2,000 m of Karoo rocks were eroded off the Oribi Gorge area, leaving the resistant Msikaba Formation quartzitic sandstones exposed on the long-lived, ancient African land surface.

Rivers crossing this landscape responded to dramatic changes in sea-level and incised deep gorges through the sandstone, preferentially eroding linear zones of weakness along fracture zones.

Boulder beds exposed along the river valleys in the area trace the meandering and periodic incision of the river channels over the past 5 million years when the Oribi Gorge was scoured to its present form.

Article Supplied by NPC Cimpor
Approved by the Council for Geoscience

 

Explore the South Coast Tour 3