Hostname: page-component-8448b6f56d-dnltx Total loading time: 0 Render date: 2024-04-25T04:04:16.634Z Has data issue: false hasContentIssue false
  • English
  • Français

Clay mineral assemblages in British Lower Palaeozoic mudrocks

Published online by Cambridge University Press:  09 July 2018

R. J. Merriman
R. J. Merriman*
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
*
*E-mail: rjme@bgs.ac.uk
Get access Rights & Permissions [Opens in a new window]

Abstract

Lower Palaeozoic rocks crop out extensively in Wales, the Lake District of northern England and the Southern Uplands of Scotland; they also form the subcrop concealed beneath the English Midlands and East Anglia. These mainly marine sedimentary rocks were deposited in basins created during plate tectonic assembly of the various terranes that amalgamated to form the British Isles, 400-600 Ma ago. Final amalgamation occurred during the late Lower Devonian Acadian Orogeny when the basins were uplifted and deformed, producing belts of cleaved, low-grade metasediments, so-called slate belts, with a predominantly Caledonian (NE-SW) trend. The clay mineralogy of mudrock lithologies - including mudstone, shale and slate - found in these belts is reviewed. Using X-ray diffraction data from the <2 μm fractions of ~4500 mudrocks samples, clay mineral assemblages are summarized and discussed in terms of diagenetic and low-grade metamorphic reactions, and the metapelitic grade indicated by the Kübler index of illite crystallinity.

Two sequences of clay mineral assemblages, or regional assemblages, are recognized. Regional Assemblage A is characterized by a greater diversity of clay minerals in assemblages from all metapelitic grades. It includes K-rich, intermediate Na/K and Na-rich white micas, chlorite and minor amounts of pyrophyllite. Corrensite, rectorite and pyrophyllite are found in the clay assemblages of contact or hydrothermally altered mudstones. K-white micas are aluminous and phengite-poor, with b cell dimensions in the range 8.98-9.02 Å. Regional Assemblage B has fewer clay minerals in assemblages from a range of metapelitic grades. Phengite-rich K-mica is characteristic whereas Na- micas are rare, and absent in most assemblages; chlorite is present and minor corrensite occurs in mudrocks with mafic-rich detritus. Minor amounts of kaolinite are sporadically present, but dickite and nacrite are rare; pyrophyllite and rectorite are generally absent. The b cell dimensions of K-white mica in Regional Assemblage B are in the range 9.02-9.06 Å. The two regional assemblages are found in contrasting geotectonic settings. Regional Assemblage A is characteristic of the extensional basin settings of Wales, the northern Lake District and the Isle of Man. These basins have a history of early burial metamorphism associated with extension, and syn-burial or post-burial intrusive and extrusive volcanic activity. Intermediate Na/K mica probably developed from hydrothermal fluids generated around submarine volcanic centres. Deep diagenetic and low anchizonal clay mineral in these basins may develop a bedding-parallel microfabric. Chlorite-mica stacks also occur in the extensional basins and the stacking planes represent another type of bedding-parallel microfabric. Both types of microfabric are non-tectonic and developed by burial during the extensional phase of basin evolution. Regional Assemblage B is developed in the plate-convergent settings of the Southern Uplands and the southern Lake District. In the accretionary complex of the Southern Uplands the processes of burial diagenesis, metamorphism and tectonism were synchronous events. In both plate- convergent basins, low temperatures and tectonic fabric-formation had an important role in clay mineral reactions, whereas hydrothermal fluids played no part in clay genesis.

Keywords

clay mineralsmetapelitic gradeKübler indexNa/K-micasb cell dimensions
Type
Research Article
Information
Clay Minerals , Volume 41 , Issue 1 , March 2006 , pp. 473 - 512
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2006

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Ahn, J.H. & Peacor, D.R. (1986) Transmission and analytical electron microscopy of the smectite-to-illite transition. Clays and Clay Minerals, 34, 165–179.Google Scholar
Alt, J.C. & Teagle, D.A.H. (1998) Probing the TAG hydrothermal mound and stockwork: oxygen-isotope profiles from deep ocean drilling. Proceedings of the Ocean Drilling Program, Scientific Results, 158, 285–295.Google Scholar
Alt, J.C., Teagle, D.A.H., Brewer, T., Shanks, W.C. (III) & Halliday, A. (1998) Alteration and mineralization of an oceanic forearc and the ophiolite-ocean crust analogy. Journal of Geophysical Research, 103, 12,365–12,380.CrossRefGoogle Scholar
André, L. (1991) The concealed crystalline basement in Belgium and the 'Brabantia' microplate concept: constraints from the Caledonian magmatic and sedimentary rocks. Annales de la Société de Belgique, 114, 117–139.Google Scholar
rkai, P. (1991) Chlorite crystallinity: an empirical approach and correlation with illite crystallinity, coal rank and mineral facies as exemplified by Palaeozoic and Mesozoic rocks of northeast Hungary. Journal of Metamorphic Geology, 9, 723–734.Google Scholar
rkai, P. & Ghabrial, D.S. (1997) Chlorite crystallinity as an indicator of metamorphic grade of low-temperature meta-igneous rocks: a case study from the Bükk Mountains, northeast Hungary. Clay Minerals, 32, 205–222.Google Scholar
rkai, P., Merriman, R.J., Roberts, B., Peacor, D.R. & Toth, M. (1996) Crystallinity, crystallite size and lattice strain of illite-muscovite and chlorite: comparison of XRD and TEM data for diagenetic and epizonal pelites. European Journal of Mineralogy, 8, 1119–1137.Google Scholar
Awan, M.A. & Woodcock, N.H. (1991) A white mica crystallinity study of the Berwyn Hills, North Wales. Journal of Metamorphic Geology, 9, 765–773.CrossRefGoogle Scholar
Austin, G.S., Glass, H.D. & Hughes, R.E. (1989) Resolution of the polytype structure of some illitic clay minerals that appear to be 1Md. Clays and Clay Minerals, 37, 128–134.Google Scholar
Barnes, R.P. (in press) The Geology of the Kirkcowan-Wigtown district – . concise account of the geology. Memoir of the British Geological Survey, Sheets 4E, 4W and part of 2 (Scotland). British Geological Survey, Keyworth, Nottingham, UK.Google Scholar
Batchelor, R.A. & Weir, J.A. (1988) Metabentonite geochemistry: magmatic cycles and graptolite extinctions at Dob's Linn, southern Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences, 79, 19–41.Google Scholar
Bevins, R.E. & Merriman, R.J. (1988) Co-existing prehnite-actinolite and prehnite-pumpellyite facies assemblages in the Tal y Fan Metabasite Intrusion, North Wales: Implications for Caledonian metamorphism. Journal of Metamorphic Geology, 6, 17–39.Google Scholar
Boles, J.R. & Franks, S.G. (1979) Clay diagenesis in Wilcox sandstones of southwest Texas: implications of smectite diagenesis on sandstone cementation. Journal of Sedimentary Petrology, 49, 55–70.Google Scholar
Bottrell, S.H., Greenwood, P.B., Yardley, B.W.D., Shepherd, T.J. & Spiro, B. (1990) Metamorphic and post-metamorphic fluid flow in the low-grade rocks of the Harlech Dome, north Wales. Journal of Metamorphic Geology, 8, 131–143.CrossRefGoogle Scholar
Brearley, A.J. (1988) Chloritoid from low grade pelitic rocks in North Wales. Mineralogical Magazine, 52, 394–396.Google Scholar
Bridge, D.M., Carney, J.N., Lawley, R.S. & Rushton, A.W.A. (1998) Geology of the country around Coventry and Nuneaton. Memoir of the British Geological Survey, Sheet 169 (England and Wales). The Stationary Office, London, for the British Geological Survey.Google Scholar
British Geological Survey (1985) Bangor. Sheet 106. Solid Geology. 1:50,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1992a) Kirkcowan, Scotland. Sheet 4W. Solid Geology. 1:50,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1992b) Wigtown, Scotland. Sheet 4E. Solid Geology. 1:50,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1993a) The Rhins of Galloway, Scotland. Sheets 1 and 3 with parts of 7 and 4W. Solid Geology. 1:50,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1993b) Rhayader, England and Wales. Sheet 179. Solid Geology. l:50,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1993c) Llanilar, England and Wales. Sheet 178. Solid with Drift Geology. 1:50,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1993d) Kirkcudbright, Scotland. Sheet 5W. Solid Geology. 1:50,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1994) Geological Map of Wales. Solid Geology. 1:250,000 1st edition. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1996) Tectonic Map of Britain, Ireland and adjacent areas. (Pharaoh, T.C., Morris, J.H., Long, C.B. & Ryan, P.D., compilers). 1:1500,000. Keyworth, Nottingham, UK.Google Scholar
British Geological Survey (1997) New Galloway, Scotland. Sheet 9W. Solid Geology. 1:50,000. Keyworth, Nottingham, UK.Google Scholar
Buatier, M.D., Travé A., Labaume, P. & Potdevin, J.L. (1997) Dickite related to fluid-sediment interaction and deformation in Pyrenean thrust-fault zones. European Journal of Mineralogy, 9, 857–888.Google Scholar
Bucher, L. & Frey, M. (1994) Petrogenesis of Metamorphic Rocks. 6th edition. Springer-Verlag. Berlin, Heidelberg, Germany.Google Scholar
Burst, J.F. (1959) Post diagenetic clay mineral-environmental relationships in the Gulf Coast Eocene in clays and clay minerals. Clays and Clay Minerals, 6, 327–341.Google Scholar
Carney, J.N.C. (1999) Revisiting the Charnian Supergroup: new advances in understanding old rocks. Geology Today, 15, 221–229.Google Scholar
Carney, J.N.C., Glover, B.W. & Pharaoh, T.C. (1992) Pre-conference field excursion: Midlands. British Geological Survey Technical Report, WA/92/72.Google Scholar
Carr, A.D. (1998) A vitrinite reflectance kinetic model incorporating overpressure retardation. Marine & Petroleum Geology, 16, 355–377.Google Scholar
Cave, R. (1965) The Nod Glas sediments of Caradoc age in North Wales. Geological Journal, 4, 279–298.Google Scholar
Cooper, A.H., Fortey, N.J., Hughes, R.A., Molyneux, S.G., Ruston, A.W.A. & Stone, P. (2004) The Skiddaw Group of the English Lake District. Memoir of the British Geological Survey. British Geological Survey, Keyworth, Nottingham, UK.Google Scholar
Crockett, R.N. (1975) Slate. Mineral Dossier No. 12. Mineral Resources Consultative Committee, Institute of Geological Sciences. The Stationery Office.Google Scholar
Davies, J.R., Fletcher, C.J.N., Waters, R.A. Wilson, D., Woodhall, D.G. & Zalasiewicz, J.A. (1997) Geology of the country around Llanilar and Rhayader. Memoir for 1:50,000 Geological Sheets 178 &179 (England & Wales). The Stationery Office, London, for British Geological Survey.Google Scholar
Davies, J.R., Wilson, D. & Williamson, I.T. (2004) Geology of the country around Flint. Memoir of the British Geological Survey, Sheet 108 (England and Wales). HMSO, London.Google Scholar
Dong, H. & Peacor, D. R. (1996) TEM observations of coherent stacking relations in smectite, I-S and illite of shales: Evidence for MacEwan crystallites and dominance of 2M1 polytypism. Clays and Clay Minerals, 44, 257–275.CrossRefGoogle Scholar
Dong, H., Hall, C.M., Halliday, A.N., Peacor, D.R., Merriman, R.J. & Roberts, B. (1997) 40Ar/39Ar dating of Late Caledonian (Acadian) metamorphism and cooling of K-bentonites and slates from the Welsh Basin, U.K. Earth & Planetary Science Letters, 150, 337–351.Google Scholar
Dong, H., Peacor, D.R., Merriman, R.J. & Kemp, S.J. (2002) Brinrobertsite: a new R1 interstratified pyrophyllite/smectite-like clay mineral: characterization and geological origin. Mineralogical Magazine, 66, 605–617.Google Scholar
Drief, A. & Nieto, F. (2000) Chemical composition of smectites formed in clastic sediments. Implications for the smectite-illite transformation. Clay Minerals, 35, 665–678.Google Scholar
Eberl, D.D. (1984) Clay mineral formation and transformation in rocks and soils. Philosophical Transactions of the Royal Society of London, A 311, 241–257.Google Scholar
Ehrenberg, S.N., Aagaard, P., Wilson, M.J., Fraser, A.R. & Duthie, D.M.L. (1993) Depth-dependent transformation of kaolinite to dickite in sandstones of the Norwegian continental shelf. Clay Minerals, 28, 325–352.Google Scholar
Essene, E.J. & Peacor, D.R. (1995) Clay mineral thermometry – A critical perspective. Clays and Clay Minerals, 43, 540–553.Google Scholar
Essene, E.J. & Peacor, D.R. (1997) Illite and smectite: metastable, stable, or unstable? Further discussion and a correction. Clays and Clay Minerals, 45, 116–122.Google Scholar
Floyd, J.D. (1996) Lithostratigraphy of the Ordovician rocks in the Southern Uplands: Crawford Group, Moffat Shale Group, Leadhills Supergroup. Transactions of the Royal Society of Edinburgh: Earth Sciences, 86, 153–165.Google Scholar
Fortey, N.J. (1989) Low grade metamorphism in the Lower Ordovician Skiddaw Group of the Lake District, England. Proceedings of the Yorkshire Geological Society, 47, 325–337.Google Scholar
Fortey, N.J., Roberts, B. & Hirons, S.R. (1993) Relationship between metamorphism and structure in the Skiddaw Group, English Lake District. Geological Magazine, 130, 631–638.Google Scholar
Frey, M. (1969) A mixed-layer paragonite/phengite of low-grade metamorphic origin. Contributions to Mineralogy and Petrology, 14, 63–65.Google Scholar
Frey, M. (1970) The step from diagenesis to metamorphism in pelitic rocks during Alpine orogenesis. Sedimentology, 15, 261–279.CrossRefGoogle Scholar
Frey, M. (1987a) The reaction-isograd kaolinite + quartz = pyrophyllite + H2O, Helvetic Alps, Switzerland. Schweizerische Mineralogische und Petrographische Mitteilungen, 67, 1–11.Google Scholar
Frey, M. (1987b) Very low-grade metamorphism of clastic sedimentary rocks. Pp. 9–58 in: Low Temperature Metamorphism (Frey, M., editor). Blackie and Son Ltd., Glasgow, UK.Google Scholar
Gibbons, W. & Horak, J. (1990) Contrasting metamorphic terranes in northwest Wales. Pp. 315–327 in: The Cadomian Orogeny (D'Lomas, P.S., Strachan, R.A. & Topley, C.G., editors). Special Publication, 51. Geological Society, London.Google Scholar
Guggenheim, S., Bain, D.C., Bergaya, F., Brigatti, M.F., Drits, A., Eberl, D.D., Formoso, M.L.L., Galán, E., Merriman, R.J., Peacor, D.R., Stanjek, H. & Watanabe, T. (2002) Report of the AIPEA nomenclature committee for 2001: Order, disorder and crystallinity in phyllosilicates and the use of the 'Crystallinity Index'. Clay Minerals, 37, 389–393.Google Scholar
Guidotti, C.V. & Sassi, F.P. (1986) Classification and correlation of metamorphic facies series by means of muscovite b data from low-grade metapelites. Neues Jahrbuch fur Mineralogie Abhandlungen, 153, 363–380.Google Scholar
Guidotti, C.V. & Sassi, F.P. & Blencoe, J.G. (1989) Compositional controls on the a and b cell dimensions of 2M1 muscovite. European Journal of Mineralogy, 1, 71–84.Google Scholar
Hillier, S. (1993) Origin, diagenesis, and mineralogy of chlorite minerals in Devonian lacustrine mudrocks, Orcadian Basin, Scotland. Clays and Clay Minerals, 41, 240–259.Google Scholar
Hirons, S.R. & Roberts, B. (1999) Metamorphic survey of the 1:50 000 Kendal and Kirkby Lonsdale geological sheets 39 and 49. British Geological Survey Technical Report WA/99/51, 27 pp., 2 figs.Google Scholar
Hirons, S.R., Roberts, B. & Merriman, R.J. (1997) Metamorphism of of the Lower Palaeozoic rocks of the Carrick-Loch Doon region, southern Scotland. British Geological Survey Technical Report WG/97/ 25. 8 pp., 2 figs.Google Scholar
Honnorez, J.J., Alt, J.C. & Humphris, S.E. (1998) Vivisection and autopsy of active and fossil hydrothermal alterations of basalt beneath and within the TAG hydrothermal mound. Proceedings of the Ocean Drilling Program, Scientific Results, 158, 231–254.Google Scholar
Howells, M.F., Reedman, A.J. & Campbell, S.D.G. (1991) Ordovician (Caradoc) marginal basin volcanism in Snowdonia (North-West Wales). HMSO for the British Geological Survey, London.Google Scholar
Hower, J., Eslinger, E.V., Hower, M.E. & Perry, E.A. (1976) Mechanism of burial metamorphism of argillaceous sediments: Mineralogical and chemical evidence. Geological Society of America Bulletin, 87, 725–737.Google Scholar
Huff, W.D., Whiteman, J.A. & Curtis, C.D. (1988) Investigation of a K-bentonite by X-ray powder diffraction and analytical transmission electron microscopy. Clays and Clay Minerals, 36, 83–93.Google Scholar
Hughes, R.A., Cooper, A. H. & Stone, P. (1993) Relationship between metamorphism and structure in the Skiddaw Group, English Lake District. Geological Magazine, 130, 621–629.Google Scholar
Hunziker, J.C., Frey, M., Clauer, N., Dallmeyer, R.D., Friedrichsen, H., Flehmig, W., Hochstrasser, K., Roggwiler, P. & Schwander, H. (1986) The evolution from illite to muscovite: Mineralogical and isotopic data from the Glarus Alps, Switzerland. Contributions to Mineralogy and Petrology, 92, 157–180.Google Scholar
Jiang, W.-T. & Peacor, D.R. (1993) Formation and modification of metastable intermediate sodium potassium mica, paragonite and muscovite in hydrothermally altered metabasites from northern Wales. American Mineralogist, 78, 782–793.Google Scholar
Jiang, W.-T. & Peacor, D.R. (1994) Prograde transitions of corrensite and chlorite in low-grade mudrocks from the Gaspe Peninsula, Quebec. Clays and Clay Minerals, 42, 497–517.Google Scholar
Jiang, W.-T., Peacor, D.R., Merriman, R.J. & Roberts, B. (1990) Transmission and analytical electron microscopic study of mixed-layer illite/smectite formed as an apparent replacement product of diagenetic illite. Clays and Clay Minerals, 38, 449–468.Google Scholar
Johnson, E.W., Soper, N.J. & Burgess, I.C. (2001) Geology of the country around Ulverston. Memoir for 1:50,000 Geological Sheets 48 (England & Wales). The Stationery Office, London, for the British Geological Survey.Google Scholar
Kemp, A.E.S., Oliver, G.J.H. & Baldwin, J.R. (1985) Low-grade metamorphism and accretion tectonics: Southern Uplands terrain, Scotland. Mineralogical Magazine, 49, 335–344.Google Scholar
Kemp, S.J. & Merriman, R.J. (1995) White mica (illite) crystallinity of Charnian rocks from the Loughborough district, 1:50k sheet 141. British Geological Survey Internal Report, WG/95/7, 7 pp.Google Scholar
Kemp, S.J. & Merriman, R.J. (2002) Metamorphism of the Lower Palaeozoic rocks of the Builth Wells district, Wales, 1:50k sheet 196. British Geological Survey Internal Report, IR/02/025, 14 pp.Google Scholar
King, L.M. (1994) Subsidence analysis of Eastern Avalonian sequences: implications for Iapetus closure. Journal of the Geological Society, London, 151, 647–657.Google Scholar
Kisch, H.J. (1983) Mineralogy and petrology of burial diagenesis (burial metamorphism) and incipient metamorphism in clastic rocks. Pp. 289–493 and 513–541 (Appendix B –literature published since 1976) in: Diagenesis in Sediments and Sedimentary Rocks, 2 (Larsen, G. & G.V Chilingar, editors) Elsevier, Amsterdam,Google Scholar
Kisch, H.J. (1990) Calibration of the anchizone: a critical comparison of illite 'crystallinity' scales used for definition. Journal of Metamorphic Geology, 8, 31–46.Google Scholar
Kisch, H.J. (1991a) Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings and interlaboratory standards. Journal of Metamorphic Geology, 6, 665–670.Google Scholar
Kisch, H.J. (1991b) Development of slaty cleavage and degree of very low-grade metamorphism. Journal of Metamorphic Geology, 6, 735–750.Google Scholar
Kneller, B.C. (1991) A foreland basin on the southern margin of Iapetus. Journal of the Geological Society, London, 148, 207–210.Google Scholar
Kneller, B.C., King, L.M. & Bell, A.M. (1993) Foreland basin development and tectonics on the northwest margin of eastern Avalonia. Geological Magazine, 130, 691–697.CrossRefGoogle Scholar
Knipe, R.J. (1981) The interaction of deformation and metamorphism in slates. Tectonophysics, 78, 249–272.CrossRefGoogle Scholar
Kübler, B. (1964) Les argiles, indicateurs de métamor-phisme. Reviewe Instituté de la Francais de Pétrole, 19, 1093–1112.Google Scholar
Kübler, B. (1967a) La cristallinité de l'illite et les zones tout á fait supérieures du métamorphisme. Pp. 105–121 in: Étages tectoniques. Colloque de NeuchaÃtel 1966, À la Baconnière, NeuchaÃtel, Switzerland.Google Scholar
Kübler, B. (1967b) Anchimetamorphisme et schistosité. Bulletin de la Centre de Recherche, Pau-SNPA, 1, 259–278.Google Scholar
Kübler, B. (1968) Evaluation quantitative du méta-morphism par la cristallinité de l'illite. Bulletin de la Centre de Recherche, Pau-SNPA, 2, 385–397.Google Scholar
Lee, M.K. (1986) A new gravity survey of the Lake District and three-dimensional model of the granite batholith. Journal of the Geological Society, London, 143, 425–436.Google Scholar
Lee, M.K., Pharoah, T.C., Williamson, J.P., Green, C.A. & De Vos, W. (1991) A new look at Belgian aeromagnetic and gravity data through image-based display and integrated modelling techniques. Geological Magazine, 130, 583–591.Google Scholar
Leggett, J.K., McKerrow, W.S. & Eales, M.H. (1979) The Southern Uplands of Scotland: A Lower Palaeozoic accretionary prism. Journal of the Geological Society, London, 136, 755–770.Google Scholar
Li, G., Peacor, D.R., Merriman, R.J. & Roberts, B. (1994a) The diagenetic to low grade metamorphic evolution of matrix white micas in the system muscovite-paragonite in a mudrock from Central Wales, U.K. Clays and Clay Minerals, 42, 369–381.CrossRefGoogle Scholar
Li, G., Peacor, D.R., Merriman, R.J., Roberts, B. & Van der Pluijm, B.A. (1994b) TEM and AEM constraints on the origin and significance of chlorite-mica stacks in slates: an example from Central Wales, UK. Journal of Structural Geology, 16, 1139–1157.Google Scholar
Lintern, B.C. & Floyd, J.D. (2000) The Kirkcudbright-Dalbeattie district – . concise account of the geology. Memoir of the British Geological Survey, Sheets 5W, 5E and part of 6W (Scotland). British Geological Survey, Keyworth, Nottingham, UK.Google Scholar
Livi, K.J.T., Veblen, D.R., Ferry, J.M. & Frey, M. (1997) Evolution of 2:1 layered silicates in low-grade metamorphosed Liassic shales of Central Switzerland. Journal of Metamorphic Geology, 15, 323–344.Google Scholar
Masuda, H., O'Neil, J.R., Jiang, W.-T. & Peacor, D.R. (1996) Relations between interlayer composition of authigenic smectite, mineral assemblages, I/S reaction rate and fluid composition in silicic ash of the Nankai Trough. Clays and Clay Minerals, 44, 460–469.Google Scholar
McKerrow, W.S. (1988) The development of the Iapetus Ocean from the Arenig to the Wenlock. Pp. 405–412 in: The Caledonian-Appalachian Orogen (Harris, A.L. & Fettes, D.J., editors). Special Publication, 38, Geological Society, London.Google Scholar
McKerrow, W.S., Leggett, J.K. & Eales, M.H. (1977) Imbricate thrust model of the Southern Uplands of Scotland. Nature, 267, 237–239.Google Scholar
McMillan, A.A. (2001) Geology of the New Galloway and Thornhill district. Memoir of the British Geological Survey, Sheets 9W and 9E (Scotland). British Geological Survey, Keyworth, Nottingham, UK.Google Scholar
Merriman, R.J. (2002) Contrasting clay mineral assemblages in British Lower Palaeozoic slate belts: the influence of geotectonic setting. Clay Minerals, 37, 207–219.CrossRefGoogle Scholar
Merriman, R.J. (2005a) Clay minerals and sedimentary basin history. European Journal of Mineralogy, 17, 7–20.Google Scholar
Merriman, R.J. (2005b) From mud to roofing slate: How Wales's best-known building stone was formed. Pp. 14–17 in: Stone in Wales: Materials, Heritage and Conservation (Coulson, M.R., editor). Cadw, Cardiff, UK.Google Scholar
Merriman, R.J. & Frey, M. (1999) Patterns of very low-grade metamorphism in metapelitic rocks. Pp. 61–107 in: Low-Grade Metamorphism (Frey, M. & Robinson, D., editors). Blackwell Science, Oxford, UK.Google Scholar
Merriman, R.J. & Kemp, S.J. (1996) Clay minerals and sedimentary basin maturity. Mineralogical Society Bulletin, 111, 7–8.Google Scholar
Merriman, R.J. & Kemp, S.J. (1997) Metamorphism of the Charnian Supergroup in the Loughborough district, 1:50K sheet 141. British Geological Survey Technical Report, WG/97/7, 10 pp, 2 figs.Google Scholar
Merriman, R.J. & Peacor, D.R. (1999) Very low-grade metapelites; mineralogy, microtextures and measuring reaction progress. Pp. 10–60 in: Low-Grade Metamorphism (Frey, M. & Robinson, D., editors). Blackwell Science, Oxford, UK.Google Scholar
Merriman, R.J. & Roberts, B. (1985) A survey of white mica crystallinity and polytypes in mudrocks of Snowdonia and Llyà n, N. Wales. Mineralogical Magazine, 49, 305–319.Google Scholar
Merriman, R.J. & Roberts, B. (1990) Metabentonites in the Moffat Shale Group, Southern Uplands of Scotland: Geochemical evidence of ensialic marginal basin volcanism. Geological Magazine, 127, 259–271.Google Scholar
Merriman, R.J. & Roberts, B. (1992) Low grade metamorphism of Lower Palaeozoic strata on the Rhins of Galloway, SW Scotland, 1:50K Sheet 15W. British Geological Survey Technical Report WG/92/40, 9 pp, 3 figs.Google Scholar
Merriman, R.J. & Roberts, B. (2001) Low-grade metamorphism in the Scottish Southern Uplands terrane: deciphering the patterns of accretionary burial, shearing and cryptic aureoles. Transactions of the Royal Society of Edinburgh: Earth Sciences, 91, 521–537.Google Scholar
Merriman, R.J., Roberts, B. & Peacor, D.R. (1990) A transmission electron microscope study of white mica crystallite size distribution in a mudstone to slate transitional sequence, North Wales, U.K. Contributions to Mineralogy and Petrology, 106, 27–40.Google Scholar
Merriman, R.J., Roberts, B. & Hirons, S.R. (1992) Regional low grade metamorphism in the central part of the Lower Palaeozoic Welsh Basin: an account of the Llanilar and Rhayader Districts, BGS 1:50K sheets 178 & 179. British Geological Survey Technical Report, WG/92/16.Google Scholar
Merriman, R.J., Pharaoh, T.C., Woodcock, N.H. & Daly, P. (1993) The metamorphic history of the concealed Caledonides of eastern England and their foreland. Geological Magazine, 130, 613–620.CrossRefGoogle Scholar
Merriman, R.J., Rex, D.C., Soper, N.J. & Peacor, D.R. (1995a) The age of Acadian cleavage in northern England, U.K: K-Ar and TEM analysis of a Silurian metabentonite. Proceedings of the Yorkshire Geological Society, 50, 255–265.Google Scholar
Merriman, R.J., Roberts, B., Peacor, D.R. & Hirons, S.R. (1995b) Strain-related differences in the crystal growth of white mica and chlorite: a TEM and XRD study of the development of metapelite microfabrics in the Southern Uplands thrust terrane, Scotland. Journal of Metamorphic Geology, 13, 559–576.Google Scholar
Millward, D., Johnson, E.W., Beddoe-Stephens, B., Young, B., Kneller, B.C., Lee, M.K. & Fortey, F.J. (2000) Geology of the Ambleside district. Memoir for 1:50,000 Geological Sheets 38 (England & Wales). The Stationery Office, London, for the British Geological Survey.Google Scholar
Milodowski, A.E. & Zalasiewicz, J.A. (1991) The origin, depositional and prograde evolution of chlorite-mica stacks in Llandovery sediments of the central Wales Basin. Geological Magazine, 128, 263–278.Google Scholar
Molyneux, S.G. (1979) New evidence for the age of the Manx Group, Isle of Man. Pp. 415–422 in: The Caledonides of the British Isles – reviewed. (Harris, A.J., Holland, C.H. & Leake, B.E., editors). Special Publication 8, Geological Society, London.Google Scholar
Moore, D.M. & Reynolds, R.C. (1997) X-ray Diffraction and the Identification and Analysis of Clay Minerals. 2nd edition. Oxford University Press, New York.Google Scholar
Morse, J.S. & Casey, W.H. (1988) Ostwald processes and mineral paragenesis in sediments. American Journal of Science, 288, 537–560.Google Scholar
Neuhoff, P.S., Watt, W.S., Bird, D.K. & Pedersen, A.K. (1997) Timing and structural relations of regional zeolite zones in basalts of the East Greenland continental margin. Geology, 25, 803–806.Google Scholar
North, F.J. (1946) The Slates of Wales. National Museum of Wales, Cardiff, UK.Google Scholar
Offler, R., McKnight, S. & Morand, V. (1998) Tectonothermal history of the western Lachlan Fold Belt, Australia: insights from white micas. Journal of Metamorphic Geology, 16, 531–540.Google Scholar
Oliver, G.J.H., Smellie, J.L., Thomas, L.J., Casey, D.M., Kemp, A.E.S., Evans, L.J., Balwin, J.R. & Hepworth, B.C. (1984) Early Palaeozoic metamorphic history of the Midland Valley, the Southern Uplands–Longford-Down massif and the Lake District, British Isles. Transactions of the Royal Society of Edinburgh, Earth Sciences, 75, 259–273.Google Scholar
Ostwald, W.Z. (1897) Studien uber die Bildung und Umwandlung fester Kö rper. 1. Abhandlung: Bersstattigung und Begrundlung. Zeit. Physik Chemie, 22, 289–330.Google Scholar
Peacor, D.R. (1992) Diagenesis and low-grade metamorphism of shales and slates. Pp. 335–380 in: Minerals and Reactions at the Atomic Scale: Transmission Electron Microscopy (Buseck, P.R., editor). Reviews in Mineralogy, 27. Mineralogical Society of America, Washington, D.C.Google Scholar
Petterson, M.G., Beddoe-Stephens, B., Millward, D. & Johnson, E.W. (1992) A pre-caldera plateau-andesite field in the Borrowdale Volcanic Group of the English Lake District. Journal of the Geological Society, London, 149, 889–906.Google Scholar
Pharaoh, T.C., Merriman, R.J., Webb, P.C. & Beckinsale, R.D. (1987) The concealed Caledonides of eastern England: preliminary results of a multi-disciplinary study. Proceedings of the Yorkshire Geological Society, 46, 355–369.Google Scholar
Pharaoh, T.C., Merriman, R.J., Evans, J.A., Brewer, T.S., Webb, P.C. & Smith, N.J.P. (1991) Early Palaeozoic arc-related volcanism in the concealed Caledonides of southern Britain. Annales de la Société de Belgique, 114, 63–91.Google Scholar
Pharaoh, T.C., Molyneux, S.G., Merriman, R.J. Lee, M.K. & Verniers, J. (1993) The Caledonides of the Anglo-Brabant Massif reviewed. Geological Magazine, 130, 561–562.Google Scholar
Pharaoh, T.C., England, R.W., Verniers, J. Çelaz´niewicz, A. (1997) Introduction: geological and Zgeophysical studies in the Trans-European Suture Zone. Geological Magazine, 134, 585–590.Google Scholar
Phillips, E.R., Barnes, R.P., Boland, M.P., Fortey, N.J. & McMillan, A.A. (1995) The Moniaive Shear Zone: a major zone of sinistral strike-slip deformation in the Southern Uplands of Scotland. Scottish Journal of Geology, 31, 139–149.Google Scholar
Power, G.M. & Barnes, R.P. (1999) Relationships between metamorphism and structure on the northern side edge of eastern Avalonia in the Manx Group, Isle of Man. Pp. 289–305 in: In Sight of the Suture: the Palaeozoic geology of the Isle of Man in its Iapetus Ocean context (Woodcock, N.H., Quirk, D.G., Fitches, W.R. & R.P Barnes, editors). Special Publications 160, Geological Society, London.Google Scholar
Reedman, A.J., Leveridge, B.E. & Evans, R.B. (1984) The Arfon Group ('Arvonian') of North Wales. Proceedings of the Geologists' Association, 95, 313–321.Google Scholar
Reynolds, R.C. & Reynolds, R.C. (1996) Description of Newmod-for-Windows. The Calculation of One-dimensional X-ray Diffraction Patterns of Mixed-Layered Clay Minerals. R.C. Reynolds, Jr., 8 Brook Drive, Hanover, NH, USA.Google Scholar
Roberts, B. & Merriman, R.J. (1985) The distinction between Caledonian burial and regional metamorphism in metapelites from North Wales: an analysis of isocryst patterns. Journal of the Geological Society of London, 142, 615–624.Google Scholar
Roberts, B. & Merriman, R.J. (1990) Cambrian and Ordovician metabentonites and their relevance to the origins of associated mudrocks in the northern sector of the Lower Palaeozoic Welsh marginal basin. Geological Magazine, 127, 31–43.Google Scholar
Roberts, B., Evans, J.A., Merriman, R.J. & Smith, M. (1989) Discussion on: 'Bevins, R.E. & Robinson, D. 1988. Low grade metamorphism of the Welsh Basin Lower Palaeozoic succession: an example of dia-stathermal metamorphism?'' Journal of the Geological Society, London, 146, 885–90.Google Scholar
Roberts, B., Morrison, C. & Hirons, S. (1990) Low grade metamorphism of the Manx Group, Isle of Man: a comparative study of white mica 'crystallinity' techniques. Journal of the Geological Society, London, 147, 271–277.Google Scholar
Roberts, B., Merriman, R.J. & Pratt, W. (1991) The relative influences of strain, lithology and stratigraphical depth on white mica (illite) crystallinity in mudrocks from the district centred on the Corris Slate Belt, Gwynedd-Powys. Geological Magazine, 128, 633–645.Google Scholar
Roberts, B., Merriman, R.J., Hirons, S.R., Fletcher, C.J.N. & Wilson, D. (1996) Synchronous very low grade metamorphism, contraction and inversion in the central part of the Welsh Lower Palaeozoic Basin. Journal of the Geological Society, London, 153, 277–286.Google Scholar
Robinson, D. (1987) Transition from diagenesis to metamorphism in extensional and collisional settings. Geology, 15, 866–869.Google Scholar
Robinson, D. & Bevins, R.E. (1986) Incipient metamorphism in the Lower Palaeozoic marginal basin of Wales. Journal of Metamorphic Geology, 4, 101–113.Google Scholar
Romano, M. & Spears, D.A. (1991) Bentonites from the Horton Formation (Upper Silurian) of Ribblesdale, Yorkshire. Proceedings of the Yorkshire Geological Society, 48, 277–285.Google Scholar
Ruiz Cruz, M.D. & Andreo, B. (1996) Genesis and transformation of dickite in Permo-Triassic sediments (Betic Cordilleras, Spain). Clay Minerals, 31, 133–152.Google Scholar
Rushton, A.W.A. & Fortey, R.A. (1992) Tremadoc. P. 24 in: Atlas of Palaeogeography and Lithofacies (Cope, J.C.W., Ingham, J.K. & Rawson, P.F., editors). Memoir No. 13, Geological Society of London.Google Scholar
Schmidt, D. & Livi, K.J.T. (1999) HRTEM and SAED investigations of polytypism, stacking disorder, crystal growth, and vacancies in chlorite from subgreenschist facies outcrops. American Mineralogist, 84, 160–170.Google Scholar
Schmidt, S.Th. & Robinson, D. (1997) Metamorphic grade and porosity/permeability controls on mafic phyllosilicate distributions in a regional zeolite to greenschist facies transition of the North Shore Volcanic Group, Minnesota. Geological Society of America Bulletin, 109, 683–697.Google Scholar
Sherlock, S.C., Kelley, S.P., Zalasiewicz, J., Schofield, D., Evans, J., Merriman, R.J. & Kemp, S.J. (2003) Precise dating of low-temperature deformation: strain-fringe analysis by 40Ar-39Ar laser microprobe. Geology, 31, 219–222.Google Scholar
Smith, N.J.P. & Rushton, A.W.A. (1993) Cambrian and Ordovician stratigraphy related to structure and seismic profiles in the western part of the English Midlands. Geological Magazine, 130, 665–671.Google Scholar
Soper, N.J. & Dunning, F.G. (2005) Structure and sequence of the Ingleton Group, basement to the central Pennines of northern England. Proceedings of the Yorkshire Geological Society, 55, 241–261.Google Scholar
Soper, N.J. & Woodcock, N.H. (2003) The lost Old Red Standstone of England and Wales: a record of post-Iapetan flexure of Early Devonian transtension? Geological Magazine, 140, 627–647.Google Scholar
Soper, N.J., Webb, B.C. & Woodcock, N.J. (1987) Late Caledonian (Acadian) transpression in north West England: timings, geometry and geotectonic significance. Proceedings of the Yorkshire Geological Society, 46, 175–192.Google Scholar
Sorby, H.C. (1853) On the origin of slaty cleavage. New Philosophical Journal (Edinburgh), 55, 137–148.Google Scholar
Sorby, H.C. (1908) On the application of quantitative methods to the study of the structure and history of rocks. Quarterly Journal of the Geological Society of London, 64, 171–233.Google Scholar
Środoń, J. (1999) Nature of mixed-layer clays and mechanisms of their formation and alteration. Annual Reviews of Earth and Planetary Science, 27, 19–53.Google Scholar
Stone, P. (1995) The Geology of the Rhins of Galloway district. Memoir of the British Geological Survey, Sheets 1and 3 (Scotland). British Geological Survey, Keyworth, Nottingham.Google Scholar
Stone, P. & Merriman, R.J. (2004) Basin thermal history favours an accretionary origin for the Southern Uplands terrane, Scottish Caledonides. Journal of the Geological Society, London, 161, 829–836.Google Scholar
Stone, P., Cooper, A.H. & Evans, J.A. (1999) The Skiddaw Group (English Lake District) reviewed: early Palaeozoic sedimentation and tectonism at the northern margin of Avalonia. Pp. 325–336 in: In Sight of the Suture: the Geology of the Isle of Man in its Iapetus Ocean Context (Woodcock, N.H., Fitches, W.R., Quirk, D.G. & Barnes, R.P., editors). Special Publication 160, Geological Society, London.Google Scholar
Thomas, L.J. (1986) Low Grade Metamorphism of the Lake District, England. Unpublished PhD thesis, University of St. Andrews, UK.Google Scholar
Thorpe, R.S., Beckinsale, R.D., Patchett, P.D., Piper, J.D.A., Davies, G.R. & Evans, J.A. (1984) Crustal growth and late Precambrian-early Palaeozoic plate tectonic evolution of England and Wales. Journal of the Geological Society of London, 141, 521–536.Google Scholar
Underwood, M.B., Laughland, M.M. & Kang, S.M. (1993) A comparison among organic and inorganic indicators of diagenesis and low-temperature metamorphism, Tertiary Shimanto Belt, Shikoku, Japan. Pp. 45–61 in: Thermal Evolution of the Tertiary Shimanto Belt, Southwest Japan: An example of Ridge-trench Interaction (Underwood, M.B., editor). Special Paper 273, Geological Society of America, Boulder, Colorado.Google Scholar
van de Pluijm, B.A., Ho, N.-C., Peacor, D.R. & Merriman, R.J. (1998) Contradictions of slate formation resolved? Nature, 392, 348.Google Scholar
Velde, B. (1968) The effects of chemical reduction on the stability of pyrophyllite and kaolinite in pelitic rocks. Journal of Sedimentary Petrology, 38, 13–16.Google Scholar
Warr, L.N. & Nieto, F. (1998) Crystallite thickness and defect density of phyllosilicates in low-temperature metamorphic pelites: a TEM and XRD study of clay-mineral crystallinity-index standards. The Canadian Mineralogist, 36, 1453–1474.Google Scholar
Warr, L.N. & Rice, A.H.N. (1994) Interlaboratory standardization and calibration of clay mineral crystallinity and crystallite size data. Journal of Metamorphic Geology, 12, 141–152.Google Scholar
Weaver, C.E. (1959) The clay petrology of sediments. Pp. 15–187 in: Proceedings of the 6th National Conference, Clays and Clay Minerals.Google Scholar
Weaver, C.E. (1960) Possible uses of clay minerals in search for oil. Bulletin of the American Association of Petroleum Geologists, 44, 1505–1518.Google Scholar
Woodcock, N.H. (1984) Early Palaeozoic sedimentation and tectonics in Wales. Proceedings of the Geologists Association, 95, 323–335.Google Scholar
Woodcock, N.H. (1990) Sequence stratigraphy of the Palaeozoic Welsh Basin. Journal of the Geological Society London 147, 537–547.Google Scholar
Woodcock, N.H. & Pharaoh, T.C. (1993) Silurian facies beneath East Anglia. Geological Magazine, 130, 681–690.Google Scholar
Woodcock, N.H., Quirk, D.G., Fitches, W.R. & Barnes, R.P. (1999) In sight of the Suture: the early Palaeozoic history of the Isle of Man. Pp. 1–10 in: In Sight of the Suture: the Palaeozoic Geology of the Isle of Man in its Iapetus Ocean Context (Woodcock, N.H., Quirk, D.G., Fitches, W.R. & R.P Barnes, editors). Special Publications 160, Geological Society, London.Google Scholar
Woodland, B.G. (1985) Relationship of concretions and chlorite-muscovite porphyroblasts to the development of domainal cleavage in low-grade metamorphic deformed rocks from north-central Wales, Great Britain. Journal of Structural Geology, 7, 205–215.Google Scholar