Hostname: page-component-848d4c4894-xfwgj Total loading time: 0 Render date: 2024-06-28T07:11:10.024Z Has data issue: false hasContentIssue false
  • English
  • Français

Welsh Basin ‘contourites’ reinterpreted as fine-grained turbidites: the Grogal Sandstones

Published online by Cambridge University Press:  01 May 2009

R. D. A. Smith  and
J. M. Anketell
R. D. A. Smith
Affiliation:
KSPEL, Shell Research, Volmerlaan 6, 2288 GD Rijswijk, The Netherlands
J. M. Anketell
Affiliation:
Department of Geology, University of Manchester, Manchester, M13 9PL, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Since 1976 the Lower Silurian Grogal Sandstones of the Welsh Basin have been interpreted as contourites. Here we show that they are in fact fine-grained turbidites, frequently with pale-coloured oxidized top layers which enable distinction of individual event deposits. As reported previously, palaeocurrent directions derived from ripple cross-lamination are typically at a high angle, often close to perpendicular, to those measured from sole structures. The favoured explanation is that ripples migrated under transverse internal waves generated at an intrabasinal slope to the east. Evidence for the lateral confinement of the overlying Aberystwyth Grits by such a slope provides support for this explanation.

Type
Articles
Information
Geological Magazine , Volume 129 , Issue 5 , September 1992 , pp. 609 - 614
Copyright
Copyright © Cambridge University Press 1992

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

Anketell, J. M. & Lovell, J. P. B. 1976. Upper Llandoverian Grogal Sandstone and Aberystwyth Grits in the New Quay area, central Wales, A possible upwards transition from contourites to turbidites. Geological Journal 11, 101–8.Google Scholar
Bouma, A. H. 1972. Fossil contourites in Lower Niesenflysch, Switzerland. Journal of Sedimentary Petrology 42, 917.Google Scholar
Bouma, A. H. 1973. Contourites in Niesenflysch, Switzerland. Eclogae Geolicae Helveticae 66, 315.Google Scholar
Bouma, A. H. & Hollister, C. D. 1973. Deep ocean basin sedimentation. In Turbidites and Deep Water Sedimentation (eds Middleton, G. V. and Bouma, A. H.), pp. 79–118. SEPM Pacific Section, Los Angeles.Google Scholar
Cave, R. 1979. Sedimentary environments of the basinal Llandovery of mid-Wales. In Caledonides of the British Isles, Reviewed (eds Harris, A. L., Holland, C. H. and Leake, B. E.), pp. 517–26. Special Publication, Geological Society of London, no. 8.Google Scholar
Cope, J. W. & Bassett, M. G. 1987. Sediment sources and Palaeozoic history of the Bristol Channel area. Proceedings of the Geologists' Association 98, 315–30.Google Scholar
Craig, J. 1987. The structure of the Llangranog Lineament, West Wales: A Caledonian transpression Zone. Geological Journal 22, 167–81.Google Scholar
Gibbons, W. 1989. Basement-cover relationships around Aberdaron, Wales, UK: the fault reactivated north-western margin of the Welsh Basin. Geological Magazine 126, 363–72.Google Scholar
Heezen, B. C. & Hollister, C. D. 1971. The Face of the Deep. Oxford University Press, New York.Google Scholar
Hill, P. R. 1984. Facies and sequence analysis of Nova Scotian slope muds. In Fine-grained Sediments: Deep-Water Processes and Facies (eds Stow, D. A. V. and Piper, D. J. W.), pp. 311–18. Special Publication, Geological Society of London, no. 15.Google Scholar
Hollister, C. D. & Heezen, B. C. 1972. Geologic effects of ocean bottom currents: western north Atlantic. In Studies in Physical Oceanography, Vol. 2 (ed Gordon, A. L.), pp. 37–66. Gordon & Breach, New York.Google Scholar
Kelling, G. 1964. The turbidite concept in Britain. In Turbidites (eds Bouma, A. H. and Brouwer, A.), pp. 75–92. Elsevier.Google Scholar
Kneller, B. C. 1991. A foreland basin on the southern margin of Iapetus. Journal of the Geological Society 148, 207–10.Google Scholar
Kneller, B., Edwards, D., McCaffrey, W. & Moore, R. 1991. Oblique reflection of turbidity currents. Geology 14, 250–2.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.Google Scholar
McCann, T. & Pickering, K. P. 1989. Palaeocurrent evidence of a northern structural high to the Welsh Basin during the late Llandovery. Journal of the Geological Society 146, 211–12.Google Scholar
Pickering, K. T., Stow, D. A. V., Watson, M. & Hiscott, R. N. 1986. Deep-water facies, processes and models: a review and classification scheme for modern and ancient sediments. Earth Science Reviews 22, 75–174.CrossRefGoogle Scholar
Piciering, K. T., Hiscott, R. N. & Hein, F. J. 1990. Deep Marine Environments. Unwin Hyman, London.Google Scholar
Piper, D. J. W. 1978. Turbidite muds and silts on deepsea fans and abyssal plains. In Sedimentation in Submarine Canyons, Fans, and Trenches (eds Stanley, D. J. and Kelling, G.), pp. 163–76. Dowden, Hutchinson & Ross, Stroudsburg, Pennsylvania.Google Scholar
Piper, D. J. W. & Stow, D. A. V. 1991. Fine-grained turbidites. In Cycles and Events in Stratigraphy (eds Einsele, G. W. Ricken, and Seilacher, A.), pp. 360–76. Springer-Verlag, New York.Google Scholar
Shanmugam, G. & Moiola, R. J. 1982. Eustatic control of turbidites and winnowed turbidites. Geology 10, 231–5.2.0.CO;2>CrossRefGoogle Scholar
Smith, R. D. A. 1987 a. Structure and deformation history of the Central Wales Synclinorium, NE Dyfed: Evidence for a long-lived basement structure. Geological Journal 22, 183–98.Google Scholar
Smith, R. D. A. 1987 b. The griestoniensis Zone Turbidite System, Welsh Basin. In Marine Clastic Sedimentology (eds Leggett, J. K. and Zuffa, G. G.), pp. 89–107. Graham & Trotman, London.CrossRefGoogle Scholar
Smith, R. D. A. 1987 c. Early diagenetic phosphate cements in a turbidite basin. In Diagenesis of Sedimentary Sequences (ed. Marshall, J. M.), pp. 141–56. Special Publication, Geological Society of London, no. 36.Google Scholar
Smith, R. D. A. 1990. Discussion on palaeocurrent evidence for a northern structural high to the Welsh basin. Journal of the Geological Society 147, 886–7.Google Scholar
Smith, R. D. A. in press. Upper Llandovery trace fossil associations of Wales and the Welsh Borders. In Ecostratigraphy (ed. Boucot, A. J.). Cambridge University Press.Google Scholar
Smith, R. D. A., Waters, R. & Davies, J. 1991. Upper Ordovician and Lower Silurian Turbidite Systems in the Welsh Basin. International Sedimentological Congress, Nottingham, Field Trip Guide No. 20, 45 pp.Google Scholar
Stow, D. A. V. 1979. Distinguishing between fine-grained turbidites and contourites on the Nova Scotian deep water margin. Sedimentology 26, 371–87.Google Scholar
Stow, D. A. V. & Lovell, J. P. B. 1979. Contourites: their recognition in modern and ancient sediments. Earth Science Reviews 14, 251–91.Google Scholar
Stow, D. A. V. & Shanmugam, G. 1980. Sequence of structures in fine-grained turbidites: comparison of recent deep-sea and ancient flysch sediments. Sedimentary Geology 25, 23–42.CrossRefGoogle 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. and Piper, D. J. W.), pp. 611–46. Special Publication, Geological Society of London, no. 15.Google Scholar
Wood, A. & Smith, A. J. 1959. The sedimentation and sedimentary history of the Aberystwyth Grits (Upper Llandoverian). Quarterly Journal of the Geological Society of London 114, 163–90.Google Scholar
Woodcock, N. H., Awan, A., Johnson, T., Mackie, A. H. & Smith, R. D. A. 1988. Acadian tectonics of Wales during Avalonia/Laurentia convergence. Tectonics 7, 483–95.CrossRefGoogle Scholar
Wilson, D., Davies, J. R., Waters, R. A. & Zalasiewicz, J. A. 1992. A fault-controlled depositional model for the Aberystwyth Grits turbidite system. Geological Magazine 129, 595–607.Google Scholar