The Geology of Schoenmakerskop

This blog does not encompass the development of the geology of the area over the eons from Gondwana to the present. Instead this blog focuses upon the rocks and their features. The details have been extracted from an article entitled The Geology of Schoenmakerskop by Professor Peter Booth of NMU

Main picture: Rocks at Schoenmakerskop

The rocks

The rocks exposed at the shoreline at Schoenmakerskop are mainly pale grey coloured quartzites and dark grey to green black coloured shales. These rocks were originally deposits of sandstones and mudrocks that formed in offshore deposits similar to those occurring along the South African coast today.

This entire package of rocks was metamorphosed through increasing temperature and pressure during the compressional phase that formed the folds of the Cape Fold Belt mountains some 300 million years ago. During this phase the sandstones were transformed into quartzites and the muddy rocks into shales as well as other types called phyllites. The latter are characterised by a green micaceous mineral called chlorite.

Younger sediments only some 6 to 10 metres thick, on which Schoenmakerskop Village occurs, are found to lie on top of the folded strata of the Cape Folded Belt. These comprise mostly shelly sandstones, deposited some 10 million years ago during one of the periods when the sea was at a higher elevation than at present. These sediments along with sand dunes on top of them, are porous, allowing rainwater to seep through them and emerge as springs where they meet the hard quartzites and shales of the Cape Fold Belt mountains.

Other features

Some of the shales appear to have small holes in them. This is due either to preferential weathering out of original minerals in the shales, or to animal burrowing [bioturbation] which occurred at the time when the sediments were deposited, much like when we observe prawns burrowing in estuaries of modern rivers. These burrows were subsequently weathered out to produce the holes in the shale rock.

Quartz / calcite veins are a prominent feature in rocks at Schoenmakerskop. These are white, relatively thin tabular shaped “intrusions” into the shales and quartzites and are emplaced during the metamorphic period associated with the CFB. As a result, many of these veins have become incorporated into folds as the rocks are deformed and appear to be part of its original history.

The Geology of Schoenmakerskop by Professor Peter Booth NMU (Looking Back, Volume 57, November 2018)

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