Talk:Ellisras Basin

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The Ecca Group article does not list the three same formations:

"The Ecca Group, the second of the four groups in the Karoo Supergroup, is represented by the Wellington (alternatively assigned to the Dwuka Group), Swartrant (Vryheid Formation equivalent), and Grooteguluk Formations.[9][6]"

There could be good reasons for this, but, as this article names the formations of the group, then links to an article on the group, the two should be in agreement or the lack of agreement explained.

--68.107.134.74 (talk) 06:02, 4 January 2013 (UTC)[reply]

There are very good reasons for the apparent discrepancy.
This is related to how stratigraphic nomenclature is done. When a stratigraphic unit such as a formation is described and named, its description is referenced to a type locality. The unit name will be used over a larger geographic area, and when subsequent investigators encounter similar rocks at other sites, they attempt to correlate them to the type locality. If the correlation is close enough, the same name will be used (although disputes occur, correlations get revised, and names get changed). At some distance from the type locality, the rocks will be sufficiently different that a different name will be applied.
The above discussion focuses on the formation; a formation is a fairly narrowly defined type of unit. The "group" (like Ecca Group) and "supergroup" (like Karoo Supergroup) are higher levels of organization in stratigraphy; when these levels are used, the definitions are broader than for a formation and the name applies over a much larger geographic area. The Karoo Supergroup is recognized throughout sub-Saharan Africa. Its type locality (in this case, I think the term is "type area") is the Karoo Basin in southern Africa. groups within the Karoo also are widely recognized. The articles about the Karoo Supergroup and its constituent groups are currently narrowly focused on the Karoo Basin, which is analogous to creating an article about the English language and describing it only as the language of England. I did a wee bit of editing to Karoo Supergroup and the template there to acknowledge the existence of this unit outside of the Karoo Basin, but when I started reviewing the DYK I didn't intend to commit to rewriting all of the existing articles about the geology of Africa. ;-)
The figures on pages 213-216 of Catuneanu et al. show some correlations of the Karoo in different basins in Africa. Page 230 of that source shows the formations that are assigned to the Ecca Group in different basins, including the Ellisras Basin. Some of the names are different between the Karoo and Ellisras basins, but others are the same; that's to be expected given the distance. Also, Catuneanu and Mtimkulu do disagree as to whether the Wellington is part of the Dwyka Group or the Ecca Group. That kind of disagreement is fairly common in the field of stratigraphy, and may be due to the fact that Mtimkulu's work is more recent, so he probably had new information that wasn't available for the Catuneanu review. That particular discrepancy is a detail; both of them list the formations in the same sequence.
It is true that the Mtimkulu source is just a master's thesis. However, it is used in the article only to confirm and supplement information from secondary sources. (Because it is a long document and is focused on the geology of this basin, it pulls the information together in a fashion that sometimes is more readily understandable than the other sources.) Also, for technical subject matter, I generally consider a student thesis to be more reliable than a magazine or newspaper. --Orlady (talk) 21:50, 4 January 2013 (UTC)[reply]
" but, as this article names the formations of the group, then links to an article on the group, the two should be in agreement or the lack of agreement explained." In other words, the Ecca Group formations in the Ellisras Basin should be included in the Ecca Group article, especially if we already have a source for the formations; it confuses the reader that a wikilink takes them to the Group page, but the article does not cover the Ecca Group in the area of the Ellisras Basin. So why is it linked? An explanation or expansion is needed.
Catuneanu's article is from a peer-reviewed scientific journal, not from a "magazine or newspaper." He's a sequence stratigrapher, not a journalist.
I do agree the thesis may be more readily understandable, but theses are primary sources, and require secondary sources that support all findings in it; so it should not be a source for this article.
You did a good job with the stratigraphy background (above); thanks. (Not necessary, I'm okay with sed/strat, but it was thoughtful of you.)
--68.107.134.74 (talk) 04:09, 5 January 2013 (UTC)[reply]
My comment about magazines and newspapers was not directed at Catuneanu. Catuneanu is an excellent secondary source, and it is a major basis for this article. The article also cites "Mining Weekly", which is a trade publication of a sort that is often cited in articles about geologic topics. This article does not rely on "Mining Weekly" for information on basic geology of the basin, but articles like that typically contain a lot of geologic information, and I submit that a master's student will report this kind of content more reliably than a journalist.
The Catuneanu source dates from 2005 and the literature cited certainly dates from a couple of years earlier. There apparently has been a good bit of investigation in the basin in the years since (inluding the geophysical work that provides much of the basis for the half-graben geometry), so the 2009 thesis is likely to reflect newer information and thinking. Also, while Catuneanu discusses the Karoo stratigraphy all over Africa, the basin-specific focus of the thesis means that it expands upon some points that may be covered only superficially by Catuneanu. The items in the article that are sourced to the thesis are as follows: (1) It is one of two sources for the fact that there are few rock exposures in the basin, so stratigraphy in the basin has been investigated mainly by drilling. (2) The literature review in the thesis included word "diamictite" in describing the lithology of the Dwyka-equivalent units (not used in Catuneanu, but consistent with the info in Catuneanu). (3) The thesis describes the Wellington Fm. as a Dwyka-equivalent unit, apparently based on correlations in literature cited, so the article indicates that sources differ on the assignment of that unit. (4) It confirms the statement (from Faure et al.) that the Swartrant is mudstone, and adds that fact that it also includes some coal. (Note: I don't think any of us has seen the full Faure et al. paper -- rather, we've only read the abstract.) (5) It describes the Swartrant Fm. as a Vryheid Fm. equivalent. None of the article content is based on Mtimkulu's original scientific work. --Orlady (talk) 17:03, 5 January 2013 (UTC)[reply]

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