Overberg Geoscientists Group
3570 Mya
Barberton Mountainland
The whole reason for the settlement of Barberton was, and is the mining of Gold. It was first discovered in 1881, but the main gold rush came in 1883. Barberton was named in 1884 after George Barber, who, with his brother, found one of the main the main outcrops of the Gold. Numerous other occurrences were found in the area and there are still 3 large mines active.
The major factor that makes the Barberton Geology unique is the degree of preservation of the rocks of this age. They date back some 3,500 ma (million years ago). Yet they are so well preserved, unlike most rocks of similar ages, that small and even microscale details are visible and interpreted.
This rock shows the debris that has fallen back to Earth after a huge meteorite strike. The energy of the impact vaporized the crust at the site and this debris cooled and fell back as small spherulites. The rock type is found throughout the area and at different ages, showing there was more than one giant impact. It has been estimated that the meteorite would have been 30 -45 km wide.
We can show that there was water – oceans – on the Earth at this time. These are pillow lavas, formed when lave erupts under the sea, just like what is happening today in places like Hawaii.
Structures identical to what we may see on beaches and sand dunes today can be found in the sandstones about 3,200ma. The first one shows sand that has been cascaded by currents over a sand bank.
Here we have something familiar to anyone who has walked on a beach; ripples in the sand, a beach formed 3,200ma. Tidal differences can be determined, showing that the Lunar month was only around 20 days as opposed to the present day 28 days. The Moon was much closer to the Earth.
Finally we have very clear, unmistakable evidence of very early life. These are called ‘Biomats’ and are layers of bacteria growing on sands in the intertidal zone. They formed Stromatolites in some areas, but also just laid down on the sand and pebbles.
Truly a unique geological environment. Made even more so by the fact that access is so easy. Drive along the Barberton Makonjwa Geotrail to see all of this and more.
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Further Reading:
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Barberton | The Barberton Makhonjwa Geotrail
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De Wit, M.J., Roering, C., Hart, R.J., Armstrong, R.A., de Ronde, C.E.J., Green, R.W.E., Tredoux, M., Peberdy, E., and Hart, R.A. (1992). Formation of an Archean continent: Nature, 357, 553-562
Heubeck, C. (2009) An early ecosystem of Archean tidal microbial mats (Moodies Group, South Africa, ca. 3.2 Ga): Geology, 37, p. 931–934.
Heubeck, C., and D.R. Lowe (1999). Sedimentary petrology and provenance of the Archean Moodies Group, Barberton Greenstone Belt, South Africa, in: Lowe, D.R., and Byerly, G.R., eds., Geologic Evolution of the Barberton Greenstone Belt, South Africa; Geological Society of America Special Paper 329, p. 259-286.
Heubeck, C., and D.R. Lowe (1994a). Depositional and Tectonic Setting of the Archean Moodies Group, Barberton Greenstone Belt, South Africa: Precambrian Research, 68, p. 257-290.
Hofmann, A. (2011). Archaean hydrothermal systems in the Barberton Greenstone belt and their significance as a habitat for early life. In: Golding, S. and Glikson, M. (Eds.), Earliest Life on Earth: Habitats, Environments and Methods of Detection. Springer-Verlag, p. 51-78.
Hofmann, A. and Bolhar, R. (2007). The origin of carbonaceous cherts in the Barberton greenstone belt and their significance for the study of early life in the mid-Archaean rocks: Astrobiology, 7, 355-388.
Lowe, D.R. (1994). Accretionary history of the Archean Barberton greenstone belt (3.55-3.22 Ga), southern Africa. Geology, 22, 1099-1102.
Lowe, D.R. (1999a). Geologic evolution of the Barberton greenstone belt and vicinity. In: Lowe, D.R. and Byerly, G.R. (eds.), Geologic Evolution of the Barberton Greenstone Belt, South Africa. Special Paper, Geological Society of America, 329, 287-312.
Lowe, D.R. (1999b). Shallow-water sedimentation of accretionary lapilli-bearing strata of the Msauli Chert: Evidence of explosive hydromagmatic komatiitic volcanism. In: Lowe, D.R. and Byerly, G.R. (eds.), Geologic Evolution of the Barberton Greenstone Belt, South Africa. Special Paper, Geological Society of America, 329, 213-232.
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D J Mourant July 2023