Appendix A. Mineralogical and chemical data This appendix presents data on the clay mineral, non-clay known, beginning with his 1967 publication on 'The mineral and chemical composition of a small but varied significance of clay minerals in sediments'. More recently collection (N-- 105) of clay materials from the British he has documented and discussed trends and pattems of Isles. This collection was assembled and analyzed during clay mineral distribution on a global scale in Chapter 9 the writing of this report, such that the data have not been of his book 'Clays, muds and shales' (Weaver 1989), an published previously elsewhere. account which is remarkable in scope and coverage. Other Of course, there are many sources of mineralogical publications dealing with the stratigraphic distribution and chemical data on clay materials. In the British context of clay minerals include those of Chatzidimitriadis et al. these include several well-known publications which (1993) and Viczian (2002), which deal with argillaceous have attempted to compile and summarize data from rocks in Greece, and Hungary, respectively. No doubt many disparate sources (Perrin 1971; Ridgway 1982; there are others in existence not referenced here. Sellwood & Sladen 1981; Shaw 1981). The monograph All of these aforementioned publications deal primarily compiled by Perrin (1971) was published by the Mineral- with the clay mineralogy of argillaceous rocks as deter- ogical Society of Great Britain and Ireland, and is yet to mined on a clay-sized fraction (usually but not always be superseded in scope; although it should be noted that, <2 pm) that is physically separated from the bulk at the time of writing, the Mineralogical Society is in material. As pointed out by Shaw (1981) there are much the process of preparing a multi-author book review of less published data on the non-clay mineral composition the knowledge and progress in understanding of the clay (quartz, feldspars, carbonates and total amounts of clay mineralogy of the UK stratigraphic column, made since minerals etc.) of mudrocks, and certainly very few the publication of Perrin's 1971 monograph (Jeans & attempts to compile or summarise data in any strati- Merriman 2006). graphic sense. There have, however, been several The publication by Shaw (1981) is an overview of the attempts to determine the average mineralogical compo- mineralogy and petrology of the argillaceous rocks of sition of shale, as well as the more easily determined the UK. Shaw's discussion of the non-clay mineralogy of average chemical composition. Literature data on these these rocks was severely limited by lack of available data, aspects are discussed more fully in Chapter 3 section 6.4. but trends and patterns in the clay mineral assemblages, Additionally, a set of almost 100 whole rock mineralo- based on analyses of clay-sized fractions, throughout the gical analyses, mainly from North American shales, can UK stratigraphic column were presented and discussed. be found in the 'Argillaceous Rock Atlas', compiled by The paper by Sellwood & Slade (1981), which appeared O'Brien & Slatt (1990). in the same thematic volume of the Quarterly Journal of Engineering Geology, focused solely on the Mesozoic and Tertiary argillaceous units of the UK. Although A.1. Purpose and scope ten years had elapsed between the publication of these reviews and that of Perrin the latter works still drew The primary purpose of obtaining and presenting the new largely on Perrin's compendium and this remains the data in this appendix is to supplement previous data with most extensive and detailed compilation of clay mineral further analyses that, above all-else, are internally consis- data available in the UK to date. The British Geological tent. Where literature data from diverse and disparate Survey (BGS) did compile a limited UK mineralogical sources are concerned, amongst many other factors, meth- mudrock database in the late 1980s/early 1990's which ods and techniques change and vary with time, experi- included data from the NIREX (Nuclear Industry Radio- ence, and purpose. Lack of consistency is, therefore, a active Waste Executive) candidate sites for the disposal of perpetual and insoluble problem when data are compiled low-level radioactive waste, but this is no longer publicly and compared from different sources. The uncertainties available. The publication by Ridgway (1982) contains a attached to comparisons, and the conclusions that may be compilation of 85 whole-rock, major element, chemical drawn from such comparisons, are therefore larger and in analyses of clay materials from the UK. These chemical many cases unknown. Other problems arising from com- analyses may be directly compared with those in this paring data from different sources, often obtained using appendix. different analytical approaches have been discussed in Intemationally, Weaver's attempts to compile and ana- Chapter 8. lyze the trends in Phanerozoic clay mineral assemblages, The disadvantage of consistency is that the number based mainly on data from the United States, are also well of samples that can be compared is inevitably a much Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/4596174/9781862393837_backmatter.pdf by guest on 30 September 2021 450 APPENDIX A smaller number. In this appendix data are presented for A.2.1. Clay fraction analysis 105 samples. The samples range in age from Cambrian to Quaternary, and it must be stressed that such a small set of For clay mineral analyses, samples were dispersed in samples can not be considered as representative in a sta- de-ionised water, and a < 2 gm size fraction separated by tistical sense of any of the individual stratigraphic units timed sedimentation according to Stokes' Law. The clay from which they were collected. Thus it must be stressed was then deposited on a glass slide using the filter peel that the data are not presented as definitive analyses of transfer procedure and examined in a Siemens D5000 clay materials from particular stratigraphic units. They diffractometer in the air-dried state, after glycolation (by are simply presented as examples of analyses of particular vapour pressure method overnight) and after heating to clay materials. Samples from other localities, even the 300~ and 550~ for one hour. For each treatment the same locality, in the same stratigraphic unit will inevita- sample was scanned from 2-45~ in 0.02 ~ steps, count- bly be different in detail and in many instances may be ing for 1 second per step using Co-Ks radiation, selected wholly different. Nonetheless, certain trends and features by a diffracted beam monochromator. Clay minerals were in the new data are in general accord with prior knowl- identified by comparison of the response to the various edge, such as that summarized in the compilations of treatments and their effect on peak positions and intensi- Perrin (1971), Shaw (1981) and Sellwood & Slade (1981). ties as detailed in Hillier (2003). Clay minerals identified Some comments are therefore made to put these data into were quantified using a normalized (sum 100%) reference context. In addition, some new features are apparent that intensity ratio approach (Hillier 2003) based on factors have not been established previously and these are also obtained from calculated X-ray powder diffraction worthy of brief note. (XRPD) patterns. As mentioned above, this appendix also contains data on the 'whole-rock' or 'bulk' mineral composition of British argillaceous units. To our knowledge there are no A.2.2. Whole rock mineralogical analysis other compilations of such data in existence at this time. To complement the whole rock mineralogical data, whole Each bulk sample was disaggregated and reduced to a fine rock chemical analyses are also presented. These were powder (<2 mm) by hand, and/or using a hammer, obtained on a sub-sample of each specimen. For both depending on hardness. Then a carefully weighed mixture whole rock mineralogy and chemistry 'average' composi- of 2.4 g of each sample and 0.6 g of corundum was wet tions have been calculated for all data and these may be ground and spray dried to produce a random powder. The usefully compared with other attempts to compute the 20% corundum addition was used as an internal standard 'average' composition of shales, as detailed in Chapter 3, for quantitative phase analysis (QPA). XRPD patterns section 6.4. Average values have also been calculated for were recorded from 2-75~ in 0.02 ~ steps, counting for the various stratigraphic groupings into which the data are 2 seconds per step, using Co-Ks radiation selected by a divided. In most cases, the samples are too disparate in diffracted beam monochromator. QPA was performed nature for this to be truly meaningful, but in some cases using an internal standard reference intensity ratio (RIR) this is useful for comparative purposes. method. As detailed in Hillier (2003), a generalized esti- The samples were donated by various individuals listed mate of expanded uncertainty using a coverage factor of in the acknowledgments. Many come from construction 2, i.e. 95% confidence, is given by _+X~35, where X is the sites, but others were also obtained at outcrop, from min- concentration in wt%., e.g. 30 wt% + 3.3. eral exploitation pits, and previously assembled collec- tions. On the whole, most contributors donated samples A.2.3. Whole rock chemical analysis believed to be unaffected by weathering, but some sup- plied material noted as weathered. Because of the subjec- Whole rock chemical analysis was made by Mrs. tive nature of this judgement, as well as it inconsistent Sieglinde Still and Ms. Michele Heibel at the laboratories assessment, no remarks are recorded on the weathered of Watts Blake and Berne (WBB) Fuchs Laboratory, versus fresh state of the materials. However, the reader Ruppach-Goldhausen, Germany using X-ray fluores- may generally assume that the materials are not weath- cence spectroscopy (XRF).