Kerkenberg EarthCache
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Kerkenberg Earthcache
These big beautiful rocks (boulders) are sandstone, though not the same layer as Golden Gate. They’re slightly older, around 350 and 300 million years old. It is part of the Karoo rocks which occur over much of the interior of the country. Sandstone is a medium-grained sedimentary rock. It is pale yellow, grey or often red to brown. Composed of rounded grains of silica (quartz) that are all the same size, it is cemented together by silica, calcite or an iron mineral. Sandstones are often layered and can show colour variations between the layers.
There is an enormous amount of info available on these rocks, and because of this, it makes sense to concentrate on just a few little section of it all in this earthcache.
The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a period of about 120 million years.
(The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period, 298.9 Mya. The Early Jurassic starts 201.3 Mya)
Beautifully coloured bands appear in these rocks. The reddish-brown colours are derived from iron staining. As the rocks have been exposed, iron in them has dissolved and once it comes into contact with the air it precipitates out. This is why things rust!
Iron can form many minerals depending on the amount of oxygen and water present. The greyish could be several things, but a metallic element and most likely manganese.
Sandstone is a sedimentary rock that is highly resistant to weathering but the grains of sand in sandstone are usually particles of mineral, rock, or organic material that have been reduced to "sand" size by weathering and transported to their depositional site by the action of moving water, wind, or ice. Quartz is typically the most abundant type of sand grain present in sandstone.
Questions:
1) (Location requirement) Please take a photo of yourself, with any of the inscriptions on the rocks behind you. No need to have your face in the photo.
2) Facing the rock on which the Deborah inscription is, identify the different coloured bands. What, in your opinion, coloured these bands.
3) If one stands with the inscription written by Deborah on your right, you will see the very impressive almost triangular, grey, visibly weathered sandstone in front of you. How do you think this weathering occurs?
Reference:
https://en.m.wikipedia.org/wiki/Supergroup
https://commons.wikimedia.org/w/index.php?curid=36494470
Acknowledgment:
David Mourant
Grant Little
Image Credit: Ray Troll
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