Hostname: page-component-cd9895bd7-7cvxr Total loading time: 0 Render date: 2024-12-25T07:41:41.864Z Has data issue: false hasContentIssue false
  • English
  • Français

A new Early Silurian turbidite system in Central Wales: insights into eustatic and tectonic controls on deposition in the southern Welsh Basin

Published online by Cambridge University Press:  10 September 2008

D. I. SCHOFIELD ,
J. R. DAVIES ,
R. A. WATERS ,
M. WILLIAMS  and
D. WILSON
D. I. SCHOFIELD*
Affiliation:
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottinghamshire, NG12 5GG, UK
J. R. DAVIES
Affiliation:
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottinghamshire, NG12 5GG, UK
R. A. WATERS
Affiliation:
Department of Geology, National Museum of Wales, Cathays Park, Cardiff, CF10 3NP, UK
M. WILLIAMS
Affiliation:
Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK
D. WILSON
Affiliation:
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottinghamshire, NG12 5GG, UK
*
†Author for correspondence: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

The newly recognized Nant Brianne turbidite system was a focus of laterally supplied coarse-grade sediment deposition that, along with the Caban–Ystrad Meurig system, punctuated late Hirnantian to early Telychian, mudstone-dominated slope apron deposition along the SE margin of the southern Welsh Basin. Geological mapping coupled with detailed biostratigraphy enable the depositional influence of sea-floor topography, an active Llyn Brianne Fault and eustatic sea-level changes to be tracked. The latter may represent ‘far field’ effects relating to the retreat and advance of contemporary Gondwanan ice sheets. Slope apron mudstone facies reveal a strong response to high order eustatic events; however, the response of contemporary, easterly sourced, coarse-grade turbidite systems was more complex, with some periods of increased sand and gravel input coinciding with times of rising global sea level. These anomalous relationships are explained by invoking a series of smaller-scale movements in marine base level. It was the interaction of these lower order events with the main eustatic cycles that appears to have been the primary control on sand and gravel input to the Welsh Basin. An early Telychian expansion of the Nant Brianne turbidite system records a marked increase in tectonically generated sediment at a time of palaeo-plate collision between Baltica/Avalonia and Laurentia before intra- and peri-basinal faulting led to its abandonment as a supply path to the basin centre.

Keywords

SilurianLlandoveryWalesturbidite
Type
Original Article
Information
Geological Magazine , Volume 146 , Issue 1 , January 2009 , pp. 121 - 132
Copyright
Copyright © Cambridge University Press 2008

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

Andrew, G. 1925. The Llandovery rocks of Garth (Breconshire). Quarterly Journal of the Geological Society of London 81, 389–406.Google Scholar
Ball, T. K., Davies, J. R., Waters, R. A. & Zalasiewicz, J. A. 1992. Geochemical discrimination of Silurian mudstones according to depositional process and provenance within the Southern Welsh Basin. Geological Magazine 129, 567–72.CrossRefGoogle Scholar
Baily, W. H. 1871. Palaeontological remarks. In Explanatory memoir to accompany sheets 49, 50 and part of 61 of the Maps of the Geological Survey of Ireland including the country around Downpatrick, and the shores of Dundrum Bay and Strangford Lough, County of Down (eds Traill, W. A. & Egan, F. W.), pp. 22–3. Dublin & London: Alexander Thom, 71 pp.Google Scholar
Barclay, W. J., Davies, J. R., Humpage, A. J., Waters, R. A., Wilby, P. R., Williams, M. & Wilson, D. 2005. Geology of the Brecon district – a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50000 Sheet 213 Brecon (England and Wales). Keyworth, Nottingham: British Geological Survey, 38 pp.Google Scholar
Barrande, J. 1850. Graptolites de Bohême. vi + 74 pp., 4 pls. Prague.Google Scholar
Bjerreskov, M. 1975. Llandoverian and Wenlockian graptolites from Bornholm. Fossils and Strata 8, 1–94.Google Scholar
Bouma, A. H. 1962. Sedimentology of some Flysch Deposits. Amsterdam: Elsevier, 168 pp.Google Scholar
Brenchley, P. J. 1988. Environmental changes close to the Ordovician–Silurian boundary. Bulletin of the British Museum of Natural History (Geology) 43, 377–85.Google Scholar
British Geological Survey. 2005. Builth Wells, England and Wales Sheet 196. Solid Geology. 1:50000. Keyworth, Nottingham: British Geological Survey.Google Scholar
British Geological Survey. 2006. Lampeter, England and Wales Sheet 195. Bedrock and Superficial Geology. 1:50000. Keyworth, Nottingham: British Geological Survey.Google Scholar
Butler, A. J., Woodcock, N. H. & Stewart, D. M. 1997. The Woolhope and Usk Basins: Silurian rift basins revealed by subsurface mapping of the southern Welsh Borderland. Journal of the Geological Society, London 154, 209–23.CrossRefGoogle Scholar
Cave, R. & Hains, B. A. 1986. Geology of the country between Aberystwyth and Machynlleth. Memoir of the British Geological Survey, Sheet 163 (England and Wales). Keyworth, Nottingham: British Geological Survey, 148 pp.Google Scholar
Chen, X. 1984. Silurian graptolites from southern Shaanxi and northern Sichuan with special reference to classification of Monograptidae. Palaeontologica Sinica, New Series B 166 (20), 1–102.Google Scholar
Cocks, L. R. M. & Fortey, R. A. 1982. Faunal evidence for oceanic separations in the Palaeozoic of Britain. Journal of the Geological Society, London 139, 467–80.Google Scholar
Cocks, L. R. M. & Torsvik, T. H. 2002. Earth geography from 500 to 400 million years ago: a faunal and palaeomagnetic review. Journal of the Geological Society, London 159, 631–44.CrossRefGoogle Scholar
Cocks, L. R. M., Woodcock, N. H., Rickards, R. B., Temple, J. T. & Lane, P. D. 1984. The Llandovery Series of the Type Area. Bulletin of the British Museum (Natural History) 38, 131–82.Google Scholar
Davies, J. R. & Waters, R. A. 1995. The Caban Conglomerate and Ystrad Meurig Grits Formation – nested channels and lobe switching on a mud-dominated latest Ashgill to Llandovery slope-apron, Welsh Basin, UK. In Atlas of Deep Water Environments: Architectural style in turbidite systems (eds Pickering, K. T., Hiscott, R. N., Kenyon, N. H., Lucci, F. Ricci & Smith, R. D. A.), pp. 184–93. London: Chapman and Hall.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 of the British Geological Survey, Sheets 178 and 179 (England and Wales). Keyworth, Nottingham: British Geological Survey, 267 pp.Google Scholar
Davies, J. R., Waters, R. A. & Copus, J. 1999. Facies and geometry of deep-water turbidite systems in the Lower Palaeozoic Welsh Basin. AAPG International Conference (Birmingham), Field Trip 2: 8–11 September. British Geological Survey Technical Report (WA/99/095).Google Scholar
Davies, J. R., Schofield, D. I., Sheppard, T. H., Waters, R. A., Williams, M. & Wilson, D. 2006. Geology of the Lampeter district –a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50000 Sheet 195 Lampeter (England and Wales). Keyworth, Nottingham: British Geological Survey, 34 pp.Google Scholar
Davies, K. A. 1933. The geology of the country between Abergwesyn (Breconshire) and Pumpsaint (Carmarthenshire). Quarterly Journal of the Geological Society of London 89, 172–201.Google Scholar
Elles, G. L. & Wood, E. M. R. 1906. A monograph of British graptolites. Edited by C. Lapworth. Part 5. Monograph of the Palaeontographical Society, London, lxxviii–xcvi, 181–216.Google Scholar
Elles, G. L. & Wood, E. M. R. 1907. A monograph of British graptolites. Edited by C. Lapworth. Part 6. Monograph of the Palaeontographical Society, London, xcvii–cxx, 217–72.Google Scholar
Fischer, A. G. & Bottjer, D. J. 1991. Orbital forcing and Sedimentary Sequences, Introduction. Journal of Sedimentary Petrology 61, 1063–9.Google Scholar
Gortani, M. 1923. Contribuzioni allo studio del Paleozoico Carnico. Partie VII. Faune a Graptoliti. Palaeontographica Italica 26, 1–56.Google Scholar
Harkness, R. 1851. Description of the graptolites found in the black shales of Dumfriesshire. Quarterly Journal of the Geological Society of London 7, 58–65.Google Scholar
Hein, F. J. & Walker, R. G. 1982. The Cambro-Ordovician Cap Enrage Formation, Quebec, Canada: conglomerate deposits of a braided submarine channel with terraces. Sedimentology 29, 309–29.CrossRefGoogle Scholar
Hutt, J. A. 1974. The Llandovery graptolites of the English Lake District. Part 1. Monograph of the Palaeontographical Society, London 128, 1–56.CrossRefGoogle Scholar
Hutt, J. A. 1975. The Llandovery graptolites of the English Lake District. Part 2. Monograph of the Palaeontographical Society, London 129, 57–137.CrossRefGoogle Scholar
James, D. M. D. 2005. Palaeotopography of the northern portion of the Telychian (Silurian) turbidite basin in central Wales. Geological Journal 40, 593–601.CrossRefGoogle Scholar
Johnson, M. E., Kaljo, D. & Rong, J.-Y. 1991. Silurian eustacy. In The Murchison Symposium; proceedings of an international conference on the Silurian System (eds Bassett, M. G., Lane, P. D. & Edwards, D.), pp. 145–63. Special Papers in Palaeontology no. 44.Google Scholar
Jones, O. T. 1922. Lead and Zinc. The mining district of north Cardiganshire and west Montgomeryshire. Memoirs of the Geological Survey, Special Reports on the Mineral Resources of Great Britain 20. London: HMSO, 207 pp.Google Scholar
Kelling, G. & Woollands, M. A. 1969. The stratigraphy and sedimentation of the Llandoverian rocks of the Rhayader district. In The Pre-Cambrian and Lower Palaeozoic rocks of Wales (ed. Wood, A.), pp. 255–81. Cardiff: University of Wales Press.Google Scholar
Kurck, C. 1882. Några nya Graptolitarter från Skåne. Geologiska Föreningens i Stockholm Förhandlingar 6, 294–304.Google Scholar
Lapworth, C. 1876. On Scottish Monograptidae. Geological Magazine (Decade 2) 3, 308–21, 350–69, 499–507, 544–52.Google Scholar
Lapworth, C. 1900. The Silurian sequence of Rhayader. Quarterly Journal of the Geological Society of London 56, 67–137.Google Scholar
Lowe, D. R. 1982. Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents. Journal of Sedimentary Petrology 52, 279–97.Google Scholar
Loydell, D. K. 1991. The biostratigraphy and formational relationships of the upper Aeronian and lower Telychian (Llandovery, Silurian) formations of western mid Wales. Geological Journal 26, 209–44.CrossRefGoogle Scholar
Loydell, D. K. 1993. Upper Aeronian and lower Telychian (Llandovery) graptolites from western mid-Wales. Part 2. Monograph of the Palaeontographical Society, London 147, 56–180.Google Scholar
Loydell, D. K. 1998. Early Silurian sea-level changes. Geological Magazine 135, 447–71.CrossRefGoogle Scholar
Mackie, A. H. 1993. The Ordovician and Llandovery strata in the Llanwrtyd Wells to Llyn Brianne area. In Geological excursions in Powys, Central Wales (eds Woodcock, N. H. & Bassett, M. G.), pp. 259–79. Cardiff: University of Wales Press, National Museum of Wales.Google Scholar
Mackie, A. H. & Smallwood, S. D. 1987. A revised stratigraphy of the Abergwesyn-Pumpsaint area. Geological Journal 22, 45–60.CrossRefGoogle Scholar
Manck, E. 1923. Untersilurische Graptolithenarten der Zone 10 des Obersilurs, ferner Diversograptus gen. nov. sowie einige neue Arten anderer Gattungen. Natur, Leipzig 14, 282–9.Google Scholar
M'Coy, F. 1850. On some new genera and species of the Silurian Radiata in the collection of the University of Cambridge. Annals and Magazine of Natural History (2) 6, 270–90.Google Scholar
Melchin, M. J., Cooper, R. A. & Sadler, P. M. 2004. The Silurian Period. In A Geologic Time Scale 2004 (eds Gradstein, F. M., Ogg, J. G. & Smith, A. G.), pp. 165–87. Cambridge: Cambridge University Press.Google Scholar
Mitchell, S. M., Beamish, G. W. J., Wood, M. V., Malecek, S. J., Armentrout, J., Damuth, J. E. & Olson, H. C. 1993. Palaeogene sequence stratigraphic framework of the Faeroe Basin. In Petroleum Geology of northwest Europe: Proceedings of the 4th Conference (ed. Parker, J. R.), pp. 1011–23. London: Geological Society.Google Scholar
Morton, A. C., Davies, J. R. & Waters, R. A. W. 1992. Heavy minerals as a guide to turbidite provenance in the Lower Palaeozoic Southern Welsh Basin: a pilot study. Geological Magazine 129, 573–80.Google Scholar
Page, A., Zalasiewicz, J., Willams, M. & Popov, L. E. 2007. Were transgressive black shales a negative feedback modulating glacioeustacy in the Early Palaeozoic Icehouse. In Deep time perspectives on climate change: marrying the signal from computer models and biological proxies (eds Williams, M., Haywood, A. M., Gregory, F. J. & Schmidt, D. N.), pp. 123–56. The Micropalaeontological Society. Bath: Geological Society Publishing House.CrossRefGoogle Scholar
Perner, J. 1897. Études sur les Graptolites de Bohême. IIième Partie. Monographie des Graptolites de L'Etage E, Section a, 1–25, pls 9–13. PragueGoogle Scholar
Pickering, K. T., Hiscott, R. N. & Hein, F. J. 1989. Deep marine environments: clastic sedimentation and tectonics. London: Unwin Heiman, 416 pp.Google Scholar
Přibyl, A. 1940. O českých zastupcích monograptid ů že skupiny Pristiograptus nudus. Rozpravy II. Třudy České Akademie 50 (16), 1–14.Google Scholar
Rickards, R. B. 1970. The Llandovery (Silurian) graptolites of the Howgill Fells (Northern England). Monograph of the Palaeontographical Society, London, 108 pp.Google Scholar
Ross, W. C., Halliwell, B. A., May, J. A., Watts, D. E. & Syvitski, J. P. M. 1994. Slope readjustment: A new model for the development of submarine fans and aprons. Geology 22, 511–14.Google Scholar
Schofield, D. I., Davies, J. R., Waters, R. A., Wilby, P. R., Williams, M. & Wilson, D. 2004. Geology of the Builth Wells district – a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50000 Sheet 196 Builth Wells (England and Wales). Keyworth, Nottingham: British Geological Survey, 34 pp.Google Scholar
Soper, N. J. & Hutton, D. H. W. 1984. Late Caledonian sinistral displacements in Britain: implications for three-plate collision model. Tectonics 3, 781–94.Google Scholar
Soper, N. J. & Woodcock, N. H. 2003. The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension? Geological Magazine 140, 627–47.Google Scholar
Stow, D. A. V. & Piper, D. J. W. 1984. Deep-water fine-grained sediments: facies models. In Fine-grained sediments: deep-water processes and facies (eds Stow, D. A. V. & Piper, D. J. W.), pp. 611–46. Geological Society of London, Special Publication no. 15.Google Scholar
Törnquist, S. L. 1883. Öfversigt öfver bergbygnaden inom Siljansområdets graptoliter. 1. Lunds Universitets Arsskrifter 26, 1–33.Google Scholar
Törnquist, S. L. 1892. Undersökningar öfver Siljansområdets graptoliter. Lunds Universitets Arsskrifter 28, 1–47.Google Scholar
Törnquist, S. L. 1899. Researches into the Monograptidae of the Scanian Rastrites Beds. Lunds Universitets Arsskrifter 35, 1–25.Google Scholar
Van Wagoner, J. C., Mitchum, R. M. Jr, Campion, K. M. & Rahmanian, V. D. 1990. Siliciclastic sequence stratigraphy in well logs, cores, and outcrops. Methods in Exploration, 7. Tulsa: American Association of Petroleum Geologists, 55 pp.Google Scholar
Woodcock, N. H. 1984. Early Palaeozoic sedimentation and tectonics in Wales. Proceedings of the Geologist's Association 95, 323–35.Google Scholar
Woodcock, N. H. & Gibbons, W. 1988. Is the Welsh Borderlands Fault system a terrane boundary? Journal of the Geoogical Society, London 145, 915–23.Google Scholar
Woodcock, N. H., Butler, A. J., Davies, J. R. & Waters, R. A. 1996. Sequence stratigraphical analysis of late Ordovician and early Silurian depositional systems in the Welsh Basin: a critical assessment. In Sequence stratigraphy in British geology (eds Hesselbo, S. P. & Parkinson, D. N.), pp. 197–208. Geological Society of London, Special Publication no. 103.Google Scholar
Woodcock, N. H., Soper, N. J. & Strachan, R. A. 2007. A Rheic cause for the Acadian deformation in Europe. Journal of the Geological Society, London 164, 1023–36.CrossRefGoogle Scholar
Zalasiewicz, J. A. 1996. Aeronian (Silurian: Llandovery) graptolites from central Wales. Geologica et Palaeontologica 30, 1–14.Google Scholar