Chalk of the UK - Review of present practise and usage in BGS

At present many publications of BGS base their interpretation of the Chalk of England on the ‘traditional scheme’ [Fig.P900807/1] and, within the most recent output, on the various stages of the development of the new lithostratigraphical schemes.

As maps come up for revision the ‘traditional scheme’ is being replaced by the most appropriate ‘Southern’ or ‘Northern’ Province nomenclature (see Sections 3 and 4 respectively). Thus, for some years the scheme exemplified within Wood and Smith (1978) [Fig.P894998/7 and Fig.P895008/5] and later workers in Lincolnshire and Yorkshire has been used instead of the ‘traditional scheme’ of Jukes-Browne and Hill (1903, 1904) [Fig.P894998/6 and Fig.P895005/6]. South of the Wash through East Anglia and into southern England (with the exception of the most north-westerly outcrops that have used elements of the ‘northern province’ terminology) the ‘traditional scheme’ held sway until well into the 1990s. That ‘traditional’ nomenclature is being comprehensively replaced by the scheme developed on the Wincanton (297), Shaftsbury (313) [Fig.P900807/4] and Chichester (317/332) 1:50 000 scale sheets and later formalised in the paper by Bristow et al. (1997) [Fig.P894998/10, Fig.P900807/5 and Fig.P895005/10]. The most recent maps such as Winchester (299) in the Southern Province use nomenclature recommended in Rawson et al. (2001) [Fig.P894998/11, Fig.P900807/6 and Fig.P895005/11] which is a development of the earlier Bristow et al. (1997) paper.

It follows that there are a large number of lexicon entries, which require full descriptions so that both the ‘traditional scheme’ and the various iterations of the new terminology can be adequately understood. It is recommended that henceforth the new approved scheme be used for all England and Wales BGS maps and publications. There should be no need to vary terminology within the new framework, but it is envisaged that entirely new terms will only be required at member level (for which full lexicon entries will be required) as investigations proceed. In other circumstances the new group and formation terminology should be adhered to even if this means that amalgamations of strata (e.g. Lewes Nodular Chalk and Seaford Chalk formations, undifferentiated) are mapped to accommodate either the available field data or the type of map (e.g. full survey, revision, desk study). As time progresses the ‘traditional scheme’ entries will become redundant in terms of the new maps and reports published.

In Scotland the extremely condensed succession preserved beneath ‘Tertiary’ basalts, have been assigned, by the Survey, to a simple informal nomenclature: Morvern Greensand, Loch Aline Glass Sand and Silicified Limestone that has more in common with the Upper Cretaceous of Northern Ireland than England. Braley (1990) and Lowden et al., (1992) [Fig.P895010/6] introduced a number of formations within an “Inner Hebrides Group” to encompass all of the Cretaceous (implying an Albian age for the lowest beds) rocks of north-west Scotland. Emeleus (1997) in the Rum Memoir followed this nomenclature. The recently published GCR volume (Mortimore et al., 2001) [Fig.P895010/7] completely revised the terminology for the Scottish outcrops (formalising many existing terms but with the proviso that the dating of the sequence proposed by Braley was uncertain). As yet this scheme has not been tested by mapping. A digest of the terminology is added to the discussions in Section 5 (see Figure P895010).

The scheme for Northern Ireland has been well established following the work of Fletcher (1977) [Fig.P895013/6] with the two principal units being designated as the Hibernian Greensands Formation and overlying it, the Ulster White Limestone Formation. Each are divided into members. A brief outline of the Northern Ireland Upper Cretaceous succession is given below (Section 6). It is the recommendation of this report that it is now time to ‘up-grade’ the framework for Northern Ireland by raising the status of the presently defined formations to group and the present members to formation. Thus permitting other workers the greater latitude for the naming of stratal units at member and bed levels in detailed investigations.

A note on offshore nomenclature developed in response to hydrocarbon investigations since the early 1960s is included at the end of this report and in Figure P895014.

Appendices 1 and 2 give an appraisal of the terms used on BGS onshore geological maps available at the 1:50 000 and 1:63 360 scales. Appendix 3 gives the Lexicon style definitions for the redundant terminology used in older BGS publications and a listing of lithostratigraphical terms used in key papers from which the current terminology has been derived. Where possible cross-reference is made to redundant terms commonly used in the literature.