Baviaanskloof Geology

Baviaanskloof - ‘Valley of Baboons’ - is situated within what is referred to as the Cape folded belt, a geomorphic province which runs parallel to the coast from the west coast near Plettenberg Bay, to Port Elizabeth. The predominant rock type is sediment, which consists of compacted grains of sand and stones from ancient rivers and lakes that have petrified into rock. The specific rock is called the Cape Super Group, which consists of alternating layers of sandstone and shale that were deposited on the shores of a large inland sea between 300 and 400 million years ago.

Rock exposed to the Earth’s surface is subject to chemical attack by the atmosphere, a process called weathering. This leads to the disintegration of rock. Rocks may also be exposed to mechanical events that cause disintegration. The products of weathering and mechanical disintegration are transported away from the site of generation by flowing water, wind or ice, in a process called erosion. They will ultimately accumulate elsewhere as sediment. Sediment may ultimately become converted into sedimentary rocks during a process called lithification, which basically involves the cementation of the particles.

Flowing water separates material according to size. Large particles such as pebbles only move in rapidly flowing water. Sand moves in slower flowing water and silt in even slower flowing water, whereas mud (mainly made of clay minerals) requires hardly any flow to keep it dispersed in water. Sediments deposited by flowing water are therefore differentiated by size into gravel, sand, silt and mud. Lithification converts gravel into sedimentary rock called conglomerates (e.g. enons in Baviaanskloof), sand into sandstone, silt into siltstone/shale and mud into mudstone.

Sandstone is the red/orange stone that typically forms in layers, which is the main rock type in Baviaanskloof. It consists of deposited sediments that were transported there by ancient rivers or streams. Conglomerates (enons) were probably transported during times of fast flowing floods. Shales were probably deposited during a time of lakes. Specialists speculate that this happened during a time when Africa was still part of Gondwanaland.

The major valley formation of the area is due to the tectonic upheaval caused by the separation of the continents about 140 million years ago, after which extensive erosion further carved the valley to what it is today. The remaining rock is mainly erosion resistant quartzite sandstone and Enon conglomerates.

The dramatic altitude difference between valley and mountain top, combined with the fact that Baviaanskloof lies within the non-seasonal rainfall area of the Eastern Cape, makes it one the most diverse natural areas in the world.

Thank you Ronel Pieterse from Sedgefield for your beautiful photo contribution.

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