Talk:Chalk Formation
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I have added a section on the petroleum geology of the North sea chalk, I will expand this as time allows
A.Foum
The capitalization, i.e. "Upper Chalk" is deliberate. Please don't change it.
Dlloyd 09:11, 28 Jul 2004 (UTC)
http://www.bbm.me.uk/portsdown/PH_743_Chalk.htm says...
As described in stratigraphy, the Chalk of the Britain has been divided into 3 Provinces, the 'Northern', the 'Southern', and the 'Transitional'. These geographical classifications replace the old age-based units of 'Upper', 'Middle' and 'Lower' - which are, however, still used informally.
Now with the creation of the Southern England Chalk Formation page this can be a much more technical article about how Chalk is formed -- Any Geologists :) as I don't feel qualified to do this --Davelane 16:49, 1 Jan 2005 (UTC)
This article is close to Good Article level, if some one is prepared to propose and repair! GB 10:42, 4 July 2007 (UTC)
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- It is not. It is very confusing in its terminology and the division in paragraphs should be clearer too. Some points that need urgent attention:
- Is the Chalk a formation (as the title suggests) or a group (as appears from the text about its subdivisions) or even something else (somewhere it is called a series)? When describing a lithostratigraphic unit we should at least have the lithostratigraphic definitions clear.
- If you describe lithostratigraphy, an essential point is to name the units immediately above and below the one described. It could even go in a template. Yet it is lacking.
- It is said that the Chalk is "most prominently" found in England. That is an Anglocentric POV and should be removed, because chalk is also a lithology.
- It is not clear with which other formations the Chalk is correlated, for example in Northern France, the low countries or in Germany. Do they have the same lithology? What is different and why?
- The article lacks a good paleogeographic description.
- The Chalk is called an important reservoir unit. Yet, further in the text, it is called a seal. It cannot be both, so which is it?
- It should be made clear that there are two definitions of the word chalk: a lithology and a lithostratigraphic unit.
- Unfortunately, I have no literature here on the lithostratigraphy of England. I can guess that the Chalk is a group, since it is divided into formations. As for the rest I would say the article needs a thorough revision by an expert. Best regards all, Woodwalker (talk) 15:20, 31 May 2008 (UTC)
- It is not. It is very confusing in its terminology and the division in paragraphs should be clearer too. Some points that need urgent attention:
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- I have to agree with a lot of what Woodwalker says. The Chalk is problematic, it's generally defined lithostratigraphically and this rock type continues across the Cretaceous/Tertiary boundary into the overlying Danian so we can't even refer to it as Cretaceous. There is an agreed nomenclature used in the offshore areas and quite a lot of this has been included here, however, it dosen't fit in with the rest of the article, which describes it from an onshore exposure perspective.
- To answer two of Woodwalker's points,
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- it does act as both seal and reservoir due to variations in the distribution of the permeable allochthonous chalks. The Joanne oifield has a Tor chalk reservoir, the neighbouring Jade gas condensate field has a slightly older Hod chalk top seal.
- The article actually says that the chalk "appears" most prominently in England, for which I read "is exposed"; this just needs rewording to both clarify and include the equally dramatic exposures on the other side of the channel.
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- An overall correlation diagram showing how the onshore exposures in the UK, France, Belgium, Netherlands & Germany fit in with the sequences defined offshore would be extremely useful. Mikenorton (talk) 16:26, 31 May 2008 (UTC)
- Thanks for your fast reply Mike. Your first answer should be incorporated in the text, it clearifies the confusing reservoir/seal stuff. Your second answer: I know that at least in the low countries and Germany, the group/formation (?? I assume group but am not sure) has a different name. No surprise there, because the British Geologic Survey has no influence on lithostratigraphic names outside the UK... As far as I know (I am not sure about France) the name "Chalk" is therefore in a lithostratigraphic sense restricted to England. That its age is not only Cretaceous, is no problem and a common feature of larger lithostratigraphic units (that's why there is a difference between lithostratigraphy and chronostratigraphy I guess). To the point: I think this article should only refer to the Chalk unit in the UK, and mention its correlation with similar units in France and elsewhere. The article on chalk (the lithology) can then mention all exposures across the world. Woodwalker (talk) 18:54, 31 May 2008 (UTC)
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