The geology here is interesting and complex and as we aren’t geologists, we thought that we would concentrate on what one can observe and study fairly simply.
This is part of the Soutpansberg rocks. Most of them are about 1800 million years old and were laid down in a broad swathe running E/W.
It proved to be difficult to research Soutpansberg rocks, as the info that we found was complicated, but we were able to determine that the bottom parts are lavas; and that there are sandstones on top of the lavas that were deposited in an inland basin on top of the lavas, with rivers carrying sand from the north. These sediments were formed by the eroding of mountains further North and West.
Sandstone is a sedimentary rock composed of sand-size grains of mineral, rock, or organic material. It also contains a cementing material that binds the sand grains together and may contain a matrix of silt- or clay-size particles that occupy the spaces between the sand grains. Sandstones are made of sand grains that have been cemented together. Like sandpaper, sandstones usually have a rough, granular texture.
The formation of sandstone mainly involves two stages. First, a layer of sand accumulates as the result of sedimentation, either from water (as in a stream, lake, or sea) or from air (as in a desert). Sedimentation mostly occurs by the sand settling out from suspension and ceases rolling along the bottom of a body of water or ground surface. Then, once it has accumulated, the sand becomes sandstone when it is compacted by the pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains.
To qualify to log this earthcache, please answer the following questions and email us your answers.
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Facing the south side tunnel, observe the colours of the rock layers and explain in your own words why they would be the colour that they are?
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To the right of the south side tunnel, is a very distinct geological feature. What, in your opinion, formed that feature?
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Location question: Beyond the arch against the rock wall is something which most nature loving people would find disturbing. What is it?
Acknowledgement: David Mourant
Ref: www.pitt.edu/~cejones/GeoImages/5SedimentaryRocks
https://geology.com/rocks/sandstone
