811:(very fast) and geological sedimentation (slow). The time constant of photosynthesis cycles (day and night) is much faster than that of sedimentation (a slower process) and is hidden in the red bands. Sedimentation occurs on a much longer time scale, even if iron oxides were perhaps preferentially precipitated during the short period of daylight because this precipitation reaction is relatively fast. And finally, how to discern days and nights in very ancient sediments after more than 2 billion years.
682:, or such a sedimentation rate, is considerable when considered at the geological scale. In the absence of reliable references source, it has to be considered as a pure speculation and an unproven theory, or a geological fantasy. It is perhaps a joke or the results of a vandalism of the page. One could also argue that the rotation rate of the Earth on its axis was much slower 3-2 Ga than today. The cause of this cyclic sedimentation is enigmatic and deserves a robust explanation.
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and cities along the
Witwatersrand ridge, centered on Johannesburg (as in "the PWV area" = "Pretoria, Witwatersrand and Vereeninging"). But that is just its colloquial. The term "Witwatersrand" is a geographic/geological term, and the article should concentrate and explain that, especially the origin of the gold ores. I will attempt to rewrite the article with this in mind. It can always be changed back, or improved if my editing is considered inappropriate or misleading.
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I apologize, we both seem to be misreading each other's edits. Mine purely referenced the comma versus space in 40000 and yours referenced the duplicate "most". All I could see that was different was that you'd inserted a comma whereas there was none before, and I missed that there was a "most most".
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Cloud (1973) proposed that mesobanding was a result of self-poisoning by early cyanobacteria as the supply of reduced iron was periodically depleted. Mesobanding has also been interpreted as a secondary structure, not present in the sediments as originally laid down, but produced during compaction of
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File:Iron banding 01.jpg|thumb|right|300 px|An ashtray carved out of a soft form of banded ironstone from the
Barbeton Supergroup in South Africa. The red layers were laid down when Archaean photosynthesizing cyanobacteria produced oxygen that reacted with dissolved iron compounds in the water, to
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1. This fancy theory was initially added here with plenty other additions: Revision as of 14:08, 4 February 2014 Oggmus (As stated on the Talk page, I have completely rewritten this encyclopedic entry. If it does not find favor with the expert of merely curious readers, it can easily be undone, or
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I agree with the comments made in 2006, above, that an encyclopedic entry on the "Witwatersrand" should pay considerably more attention to the geography, geology and geological origins of this geological structure. It is true that the term "Witwatersrand" is also loosely used to refer to the towns
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2021-02-13: Correction of this fancy and erroneous explanation on the diurne cyclic character of sedimentation of the colored iron bands. No, the beige bands did not sediment during the night. It would imply a much too high sedimentation rate. This makes no sense. There is a confusion between two
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The red layers were laid down during the daylight hours when
Archaean photosynthesizing cyanobacteria produced oxygen that immediately reacted with the dissolved iron in the water, to form insoluble iron oxide (rust). The white layers are sediments that settled during the night when there was no
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because of the difference of solubility between Fe and Fe, this latter being about 100 times more soluble than the former one. The mechanism is correct, but not the ultra fast cyclic precipitation process and its short time scale claimed without any proof or argument.
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3. Unfortunately, this fancy theory was reintroduced during a merge operation: Revision as of 08:20, 25 September 2019 Klbrain (Merge from
Witwatersrand Basin following unopposed 2018 proposal; see Talk:Witwatersrand#Proposed merger with Witwatersrand Basin)
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No. I'd say this article should be redone to focus more on the physical geography, geology and important mining aspects while the urban and social geography stuff should go in the
Johannesburg article. Just my take, as Witwatersrand
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This revision has been uploaded, and can be checked for accuracy, and other mistakes. I hope it finds favor with the readers, be they experts in the field, or just looking for information. All my sources are recorded in the
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There seems to be a lot of overlap between the two articles. Either some way of differentiating them needs to be found or they should be merged. It seems that they both refer to the same area, but I could be mistaken.
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article was very low on geological facts. I have used some of what I have written here to re-write that article. The geology of the part (Witwatersrand) is inevitably very similar to that of the whole (Witwatersrand
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in the sediments. This could be related to fluctuations in concentration of oxygen dissolved into water and maybe also related to the activity of
Archaean photosynthesizing cyanobacteria producing this oxygen.
690:. What is the evidence to support a day/night cycle? How to determine that? Another explanation is that the Fe concentration in the water was fluctuating for another unknown reason, not the O
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Indeed, the considered time scale of day/night alternance is much too short, or the day/night frequency too high. A precipitation rate of several millimeters per day for Fe
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until about 2000 million years ago, when the rate of photosynthetic oxygen production began to exceed its rate of reaction with oxidizable materials (i.e. reducing agents).
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It's hard to see what benefit there is for two articles with lots of copy-pasting. Content should probably be consolidated here, with a redirect from the other article.
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It is clear that the red bands are richer in iron (III) oxides than the white (beige) bands and that there is an alternation related to the abundance of FeOOH or Fe
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microbanding would require a very high rate of deposition of 2 meters per year or 5 km/Ma. Estimates of deposition rate based on various models of deposition and
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estimates of the age of associated tuff beds suggest a deposition rate in typical BIFs of 19 to 270 m/Ma, which are consistent either with annual varves or
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Trendall, A.F.; Blockley, J.G. (2004). "Precambrian iron-formation". In
Eriksson, P.G.; Altermann, W.; Nelson, D.R.; Mueller, W.U.; Catuneanu, O. (eds.).
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Do we not like the idea of providing sources? I'm ok with it being fairly short as it's only a geological term, but back up your assertions, people!
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Morris, R.C.; Horwitz, R.C. (August 1983). "The origin of the iron-formation-rich
Hamersley Group of Western Australia — deposition on a platform".
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Cox, Grant M.; Halverson, Galen P.; Minarik, William G.; Le Heron, Daniel P.; Macdonald, Francis A.; Bellefroid, Eric J.; Straus, Justin V. (2013).
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that change the availability of reduced iron on time scales of decades. In the case of granular iron formations, the mesobands are attributed to
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which clearly rejects diurnal cycles as a sedimentation mechanism because of the much too high sedimentation rate (2 m/year).
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Is there any source for a maximum altitude of 1913 metres of the
Witwatersrand? I couldn't find any. Thanks in advance, --
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I don't think they should be merged either. The
Witwatersrand is a geological term, nothing to do with cities, or metros.
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of sediments in shallow water, in which wave action tended to segregate particles of different size and composition.
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form insoluble iron oxide (rust). The white layers are sediments that settled when there was no oxygen in the water.
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This article could do with a map of the mountain range. It is very hard to find a solid definition of its location
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the sediments. Another theory is that mesobands are primary structures resulting from pulses of activity along
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clearly makes problem and is highly dubious. Hereafter, a copy of this figure and its problematic caption.
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clearly distinct processes occurring at very different rates and time scales: chemical precipitation of
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on 25 September 2019. For the contribution history and old versions of the redirected page, please see
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on Knowledge. If you would like to participate, please visit the project page, where you can join
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Revision as of 18:51, 18 December 2018 204.136.15.5 (→Geological origin: Not a diurnal process)
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Do you think slimming down the "Geology of the Witwatersrand ridge" section of this article to a
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Margulis, L., Sagan, D. (1995). ’’What is Life?’’. p. 81-83. Weidenfeld and Nicolson, London.
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concentration. Thanks for a convincing explanation supported by strong evidence.
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would be advantageous, would it not? It would reduce
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498:summary-style level of detail
275:and see a list of open tasks.
42:Put new text under old text.
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564:merger - too much overlap.
383:gold and geology to me :-)
50:New to Knowledge? Welcome!
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1116:Encyclopedia of Geology
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