Talk:Witwatersrand

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Merge with Greater Johannesburg Metropolitan Area[edit]

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. 168.209.98.35 14:07, 28 January 2006 (UTC)[reply]

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 means gold and geology to me :-) Vsmith 14:24, 28 January 2006 (UTC)[reply]

I don't think they should be merged either. The Witwatersrand is a geological term, nothing to do with cities, or metros. Joziboy 3 April 2006, 19:48 (UTC)

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!

Map of the witwatersrand mountain range[edit]

This article could do with a map of the mountain range. It is very hard to find a solid definition of its location Park3r (talk) 14:02, 5 July 2013 (UTC)[reply]

More geology and geological origins needed[edit]

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 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. Oggmus (talk) 06:04, 3 February 2014 (UTC)[reply]


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 references.Oggmus (talk) 13:12, 4 February 2014 (UTC)[reply]


Use of some of this article's material in the Witwatersrand Basin article[edit]

The Witwatersrand Basin 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 Basin).Oggmus (talk) 14:47, 7 February 2014 (UTC)[reply]

@Oggmus: Do you think slimming down the "Geology of the Witwatersrand ridge" section of this article to a summary-style level of detail would be advantageous, would it not? It would reduce the appearance this article has of being a redundent WP:CONTENTFORK of the Basin article. Batternut (talk) 11:32, 14 November 2017 (UTC)[reply]

Maximum altitude[edit]

Is there any source for a maximum altitude of 1913 metres of the Witwatersrand? I couldn't find any. Thanks in advance, --Vanellus (talk) 14:13, 25 February 2017 (UTC)[reply]

Proposed merger with Witwatersrand Basin[edit]

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. Park3r (talk) 13:24, 4 April 2018 (UTC)[reply]

  checkY Merger complete. Klbrain (talk) 06:20, 25 September 2019 (UTC)[reply]

Geological origin[edit]

A theory developed in the figure depicting an ashtray carved out of a soft form of banded ironstone clearly makes problem and is highly dubious. Hereafter, a copy of this figure and its problematic caption.

An ashtray carved out of a soft form of banded ironstone. Note the alternating red and white layers that make up this rock. 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 oxygen in the water[dubious – discuss][citation needed]. The earth's atmosphere was oxygen-free 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).[1]

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 Fe2O3 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.

The precipitation of Fe2O3 is due to the oxidation of Fe2+ by O2 because of the difference of solubility between Fe3+ and Fe2+, 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.

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 Fe2O3, 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. "Strong claim requires strong evidence" as often repeated by Carl Sagan. What is the evidence to support a day/night cycle? How to determine that? Another explanation is that the Fe2+ concentration in the water was fluctuating for another unknown reason, not the O2 concentration. Thanks for a convincing explanation supported by strong evidence. Shinkolobwe (talk) 22:02, 12 February 2021 (UTC)[reply]

When looking at the page Banded iron formation (BIF) and the reference 13 of Cox et al. (2013) there,[2] I could not find any theory supporting a fast day/night precipitation cycle. Shinkolobwe (talk) 22:33, 12 February 2021 (UTC)[reply]

Page history: a fancy zombie never dies (Shinkolobwe (talk) 15:10, 13 February 2021 (UTC))[reply]

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 improved.) Shinkolobwe (talk) 23:27, 12 February 2021 (UTC)[reply]

2. After 4 years, someone (IP) already corrected this fancy theory:

Revision as of 18:51, 18 December 2018 204.136.15.5 (→‎Geological origin: Not a diurnal process)

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 form insoluble iron oxide (rust). The white layers are sediments that settled when there was no oxygen in the water.[1] Shinkolobwe (talk) 22:55, 12 February 2021 (UTC)[reply]

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)

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 clearly distinct processes occurring at very different rates and time scales: chemical precipitation of Fe
2O
3 (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. Shinkolobwe (talk) 13:20, 13 February 2021 (UTC)[reply]

Explanation of the microbanding (Shinkolobwe (talk) 16:15, 13 February 2021 (UTC))[reply]

See the main article: Banded iron formation#Formation processes which clearly rejects diurnal cycles as a sedimentation mechanism because of the much too high sedimentation rate (2 m/year).

The microbands within chert layers are most likely varves produced by annual variations in oxygen production. Diurnal 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 SHRIMP 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 rhythmites produced by tidal cycles.[3]

Cloud (1973) proposed that mesobanding was a result of self-poisoning by early cyanobacteria as the supply of reduced iron was periodically depleted.[4][5] Mesobanding has also been interpreted as a secondary structure, not present in the sediments as originally laid down, but produced during compaction of the sediments.[3] Another theory is that mesobands are primary structures resulting from pulses of activity along mid-ocean ridges that change the availability of reduced iron on time scales of decades.[6] In the case of granular iron formations, the mesobands are attributed to winnowing of sediments in shallow water, in which wave action tended to segregate particles of different size and composition.[3][7]

References[edit]

  1. ^ a b Margulis, L., Sagan, D. (1995). ’’What is Life?’’. p. 81-83. Weidenfeld and Nicolson, London. Cite error: The named reference "Margulis" was defined multiple times with different content (see the help page).
  2. ^ Cox, Grant M.; Halverson, Galen P.; Minarik, William G.; Le Heron, Daniel P.; Macdonald, Francis A.; Bellefroid, Eric J.; Straus, Justin V. (2013). "Neoproterozoic iron formation: An evaluation of its temporal, environmental and tectonic significance" (PDF). Chemical Geology. 362: 232–249. Bibcode:2013ChGeo.362..232C. doi:10.1016/j.chemgeo.2013.08.002. Retrieved 23 June 2020.
  3. ^ a b c 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.). Evolution of the Hydrosphere and Atmosphere. Developments in Precambrian Geology. Developments in Precambrian Geology. Vol. 12. pp. 359–511. doi:10.1016/S0166-2635(04)80007-0. ISBN 9780444515063.
  4. ^ Cloud, P. (1973). "Paleoecological Significance of the Banded Iron-Formation". Economic Geology. 68 (7): 1135–1143. doi:10.2113/gsecongeo.68.7.1135.
  5. ^ Holland, Heinrich D (19 May 2006). "The oxygenation of the atmosphere and oceans". Philosophical Transactions of the Royal Society B: Biological Sciences. 361 (1470): 903–915. doi:10.1098/rstb.2006.1838. PMC 1578726. PMID 16754606.
  6. ^ Morris, R.C.; Horwitz, R.C. (August 1983). "The origin of the iron-formation-rich Hamersley Group of Western Australia — deposition on a platform". Precambrian Research. 21 (3–4): 273–297. doi:10.1016/0301-9268(83)90044-X.
  7. ^ Trendall, A. (2005). "Banded iron formations". Encyclopedia of Geology. Elsevier. pp. 37–42.

Misreading our edits.[edit]

@Arjayay: 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". I've tried to sort out both errors. Avi8tor (talk) 08:24, 4 May 2022 (UTC)[reply]

Hi Avi8tor no worries, and thanks for the apology - Arjayay (talk) 10:25, 4 May 2022 (UTC)[reply]
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