Hostname: page-component-848d4c4894-x5gtn Total loading time: 0 Render date: 2024-06-09T14:47:50.344Z Has data issue: false hasContentIssue false
  • English
  • Français

Arenig sedimentation and basin tectonics in the Harlech Dome area (Dolgellau Basin), North Wales

Published online by Cambridge University Press:  01 May 2009

Traynor John-Joe
Traynor John-Joe
Affiliation:
Department of Earth Sciences, Downing Street, Cambridge CB2 3EQ, U.K.
Get access Rights & Permissions [Opens in a new window]

Abstract

Arenig (Ordovician) clastic sediments crop out in the Harlech Dome region (North Wales), and are placed in a single stratigraphic unit: the Allt Lwyd Formation. This unit records a marine transgression onto an erosion surface produced during late Tremadoc arc volcanicity. Four discrete petrofacies are denned, and reflect differing proportions of detritus derived from Tremadoc-type basic-intermediate igneous rocks, and the local sedimentary basement. Initial shallow marine siliciclastic sandstones and conglomerates are overlain by extensive deep water mud-rich units. These generally shallow up into a complex arc-apron deposit, with sediments derived from the eroding Tremadoc arc, as well as from similar, synchronous volcanics. Predominantly epiclastic sandstones and conglomerates were deposited in deltaic and tidal environments in an arc-apron complex, and capped by condensed mudstones and an ironstone, deposited as sea level rose across these systems. Sediments were ponded in north–south orientated troughs and derived from uplifted blocks. Facies and petrofacies distribution were controlled by syn-sedimentary north-south and northeast–southwest faults. The Allt Lwyd Formation was ponded in a fault-controlled basin (the Dolgellau Basin), one of a series of interconnected sub-basins flooded by the Arenig transgression. The sediments preserved reflect deposition during the transgression of a volcanic arc, prior to the extrusion of marginal basin-type volcanics.

Type
Articles
Information
Geological Magazine , Volume 127 , Issue 1 , January 1990 , pp. 13 - 30
Copyright
Copyright © Cambridge University Press 1990

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

Allen, J. R. L. 1980. Sand waves, a model of origin and internal structure. Sedimentary Geology 26, 281–328.CrossRefGoogle Scholar
Allen, P. M. & Jackson, A. H. 1985. Geology of the country around Harlech. Sheet Memoir 135 and part of 149. British Geological Survey. London: HMSO.Google Scholar
Beckly, A. J. 1987. Basin development in North Wales during the Arenig.Geological Journal 22, 19–30.CrossRefGoogle Scholar
Berne, S., Auffret, J.-P. & Walker, P. 1988. Internal structure of subtidal sandwaves revealed by high-resolution seismic reflection. Sedimentology 35, 5–20.CrossRefGoogle Scholar
Bevins, R. E., Kokelaar, B. P. & Dunkley, P. N. 1984. Petrology and geochemistry of lower to middle Ordovician igneous rocks in Wales: a volcanic arc to marginal basin transition. Proceedings of the Geologists' Association 95, (4), 337–47.CrossRefGoogle Scholar
Blair, T. C. 1987. Sedimentary processes, vertical stratification sequences, and geomorphology of the Roaring River alluvial fan, Rocky Mountain National Park, Colorado. Journal of Sedimentary Petrology 57, 1–18.Google Scholar
Branney, M. J. & Soper, N. J. 1988. Ordovician volcano-tectonics in the English Lake District. Journal of the Geological Society of London 145, 367–76.CrossRefGoogle Scholar
British Geological Survey, 1985. 1:25000. Parts of Sheets SH 65 and 66, Passes of Nant Ffrancon and Llanberis. London: HMSO.Google Scholar
British Geological Survey, 1986. 1:50000. Sheet 136, Bala. London, HMSO.Google Scholar
Brenchley, P. J. 1985. Storm influenced sandstone beds. Modern Geology 9, 369–96.Google Scholar
Campbell, S. D. G., Reedman, A. J. & Howells, M. F. 1985. Regional variations in cleavage and fold development in North Wales. Geological Journal 20, 43–52.CrossRefGoogle Scholar
Campbell, S. D. G., Howells, M. F., Smith, M. & ReedMan, A. J. 1988. A Caradoc failed-rift within the Ordovician marginal basin of Wales. Geological Magazine 125, 257–66.CrossRefGoogle Scholar
Chadwick, R. A. 1986. Extension tectonics in the Wessex Basin, southern England. Journal of the Geological Society of London 143, 465–88.CrossRefGoogle Scholar
Coleman, J. M., Prior, D. B. & Lindsay, J. F. 1983. Deltaic influences on shelf edge instability processes. Special Publication of the Society of Economic Paleontologists and Mineralogists no. 33, 121–37.Google Scholar
Cox, A. H. 1925. The geology of the Cadair Idris Range (Merioneth). Quarterly Journal of the Geological Society of London 81, 539–94.CrossRefGoogle Scholar
Cox, A. H. & Wells, A. K. 1921. The Lower Palaeozoic rocks of the Arthog-Dolgellau district (Merionethshire). Quarterly Journal of the Geological Society of London 76, 254–324.CrossRefGoogle Scholar
Cox, A. H. & Wells, A. K. 1927. The geology of the Dolgellau district, Merionethshire. Proceedings of the Geologists' Association 38, 265–318.CrossRefGoogle Scholar
Crimes, T. P. 1970. A facies analysis of the Arenig of Western Lleyn, North Wales. Proceedings of the Geologists' Association 81, 221–39.CrossRefGoogle Scholar
Dickinson, W. R. & Rich, E. I. 1972. Petrological intervals and petrofacies in the Great Valley Sequence, Sacremento Valley, California. Bulletin of the Geological Society of America 83, 3007–24.CrossRefGoogle Scholar
Dott, R. H. Jr, & Bourgeois, J. 1982. Hummocky stratification: significance of its variable bedding sequences. Bulletin of the Geological Society of America 93, 663–82.2.0.CO;2>CrossRefGoogle Scholar
Etheridge, F. G. & Westcott, W. A. 1984. Tectonic setting, recognition and hydrocarbon reservoir potential of fan-delta deposits. In Sedimentology of Gravels and Conglomerates (ed. Koster, E. H. & Steel, R. J.), pp. 217–35. Canadian Society of Petroleum Geologists, Memoir no. 10.Google Scholar
Fearnsides, W. G. 1905. On the geology of Arenig Fawr and Moel Llyfnant. Quarterly Journal of the Geological Society of London 61, 608–40.CrossRefGoogle Scholar
Fearnsides, W. G. & Davies, W. 1943. The geology of Deudraeth, the country between Traeth Mawr and Traeth Bach, Merioneth. Quarterly Journal of the Geological Society of London 99, 247–76.CrossRefGoogle Scholar
Fitches, W. R. & Campbell, S. D. G. 1987. Tectonic evolution of the Bala Lineament in the Welsh Basin. Geological Journal 22, 131–53.CrossRefGoogle Scholar
Fortey, R. A. 1984. Global earlier Ordovician transgressions and regressions and their biological implications. In Aspects of the Ordovician (ed. Bruton, D. L.), pp. 137–50. Oslo: Universitetsforlaget.Google Scholar
Fortey, R. A. & Owens, R. M. 1987. The Arenig Series in South Wales. Bulletin of the British Museum (Natural History), Geology 41, 69–307.Google Scholar
Frostick, L., Reid, I., Jarvis, J. & Eardley, H. 1988. Triassic sediments of the Inner Moray Firth, Scotland: early rift deposits. Journal of the Geological Society of London 145, 235–48.CrossRefGoogle Scholar
Gibbons, W. 1983. Stratigraphy, subduction and strike-slip faulting in the Mona Complex of North Wales – a review. Proceedings of the Geologists' Association 94, 147–63.CrossRefGoogle Scholar
Gibbs, A. D. 1984. Structural evolution of extensional basin margins. Journal of the Geological Society of London 141, 609–20.CrossRefGoogle Scholar
Harms, J. C., Southard, J. B. & Walker, R. G. 1982. Structures and sequences in clastic rocks. Society of Economic Paleontologists and Mineralogists, Short Course no. 10. Tulsa, Oklahoma.CrossRefGoogle Scholar
Hiscott, R. N. & James, N. P. 1985. Carbonate debris flows, Cow Head Group, Western Newfoundland. Journal of Sedimentary Petrology 55, 735–45.Google Scholar
Hoffman, H. J. 1975. ‘Bolopora’ not a bryozoan, but an Ordovician phosphatic, oncolitic accretion. Geological Magazine 112, 523–6.CrossRefGoogle Scholar
Hooke, R., Leb, . 1972. Geomorphic evidence for Late-Wisconsin and Holocene tectonic deformation, Death Valley, California. Bulletin of the Geological Society of America 83, 2073–98.CrossRefGoogle Scholar
Ingersoll, R. V., Bullard, T. F., Ford, R. L., Grimm, J. P., Pickle, J. D. & Sares, S. W. 1984. The effect of grain size on detrital modes: a test of the Gazzi-Dickinson point counting method. Journal of Sedi- mentary Petrology 54, (1), 103–16.Google Scholar
Institute Of Geological Sciences, 1972. 1:25000 Special Sheet, Parts of SH 53–55, 63–66, 74–76, Central Snowdonia. London: HMSO.Google Scholar
Institute Of Geological Sciences, 1982. 1:50000, Sheet 135, Harlech, and part of Sheet 149, Barmouth. London: HMSO.Google Scholar
Jennings, A. V. & Williams, G. J. 1891. Manod and the Moelwyns. Quarterly Journal of the Geological Society of London 47, 368–83.CrossRefGoogle Scholar
Jones, B. 1933. The geology of the Fairbourne-Llywngrwril District, Merioneth. Quarterly Journal of the Geological Society of London 89, 117–45.CrossRefGoogle Scholar
Kleinsplehn, K. L., Steel, R. J., Johannessen, E. & Netland, A. 1984. Conglomeratic fan delta sequences, late Carboniferous-early Permian, Western Spitz- bergen. In Sedimentology of Gravels and Conglomerates (ed. Koster, E. H. and Steel, R. J.), pp. 279–94. Canadian Society of Petroleum Geologists, Memoir no. 10.Google Scholar
Kokelaar, B. P. 1980. Tremadoc to Llanvirn volcanism on the south east side of the Harlech Dome (Rhobell Fawr), North Wales. In Caledonides of the British Isles – Reviewed (ed. Harris, A. L., Holland, C. H. and Leake, B. E.), pp. 591–6. Special Publication of the Geological Society of London no. 8.Google Scholar
Kokelaar, P. 1988. Tectonic controls of Ordovician arc and marginal basin volcanism in Wales. Journal of the Geological Society of London 145, 759–75.CrossRefGoogle Scholar
Kokelaar, B. P., Howells, M. F., Bevins, R. E., Roach, R. A. & Dunkley, P. N. 1984. The Ordovician marginal basin of Wales. In Marginal basin geology: volcanic and associated sedimentary and tectonic processes in modern and ancient marginal basins (ed. Kokelaar, B. P. and Howells, M. F.), pp. 245–69. Special Publication of the Geological Society of London no. 16.Google Scholar
Leeder, M. R. & Gawthorpe, R. L. 1987. Sedimentary models for tilt-block/half-graben basins. In Continental Extensional Tectonics (ed. Coward, M. P., Dewey, J. F. and Hancock, P. L.), pp. 139–52. Special Publication of the Geological Society of London no. 28.Google Scholar
Lewis, H. P. 1926. Bolopora undosa, gen. et sp.nov. Quarterly Journal of the Geological Society of London 82, 411–27.CrossRefGoogle Scholar
Lynas, B. D. T. 1973. The Cambrian and Ordovician rocks of the Migneint area, north Wales. Journal of the Geological Society of London 129, 481–503.CrossRefGoogle Scholar
McPherson, J. G., Shanmugam, G. & Moiola, R. J. 1987. Fan-deltas and braid deltas: varieties of coarse-grained deltas. Bulletin of the Geological Society of America 99, 331–40.2.0.CO;2>CrossRefGoogle Scholar
Mutti, E. 1985. Turbidite systems and their relations to depositional sequences. In The Provenance of Arenites (Zuffa, G. G.), pp. 65–93. NATO Advanced Science Institute.CrossRefGoogle Scholar
Mutti, E. & Normark, W. R. 1987. Comparing examples of modern and ancient turbidite systems: problems and concepts. In Marine Clastic Sedimentology: Concepts and Case Studies (ed. Leggett, J. K. and Zuffa, G. G.), pp. 1–38. London: Graham and Trotman.Google Scholar
Normark, W. R., Piper, D. J. W. & Hess, G. R. 1979. Distributary channels, sand lobes, and mesotopography of Navy submarine fan, California Borderland, with applications to ancient fan sediments. Sedimentology 26, 769–74.CrossRefGoogle Scholar
Pickering, K., Stow, D., Watson, M. & Hiscott, R. 1986. Deep water facies, processes and models: a review and classification scheme for modern and ancient sediments. Earth Science Reviews 23, 75–174.CrossRefGoogle Scholar
Rich, E. I., Ojakangas, R. W., Dickinson, W. R. & Swe, W. 1969. Sandstone petrology of the Great Valley Sequence, Sacremento Valley, California. Geological Society of America, Special Paper no. 121.Google Scholar
Ridgway, J. 1975. The stratigraphy of Ordovician rocks on the southern and eastern flanks of the Harlech Dome in Merionethshire. Geological Journal 10, 87–106.CrossRefGoogle Scholar
Ridgway, J. 1976. Ordovician palaeogeography of the southern and eastern flanks of the Harlech Dome, Merionethshire, North Wales. Geological Journal 10, 121–36.CrossRefGoogle Scholar
Shackleton, R. M. 1954. The structural evolution of North Wales. Liverpool and Manchester Geological Journal 1, 261–96.CrossRefGoogle Scholar
Shanmugam, G., Moiola, R. J. & Damuth, J. E. 1985. Eustatic control of submarine fan development. In Submarine Fans and Related Turbidite Systems (ed. Bouma, A. H., Normark, W. R. and Barnes, N. E.), pp. 23–8. New York: Springer-Verlag.CrossRefGoogle Scholar
Smith, M. 1987. The Tremadoc ‘Thrust’ Zone in southern central Snowdonia. Geological Journal 22, 119–29.CrossRefGoogle Scholar
Soper, N. J. & Hutton, D. H. W. 1984. Late Caledonian sinistral displacements in Britain: implications for a three plate model. Tectonics 3, 781–94.CrossRefGoogle Scholar
Stow, D. A. & 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. V. A., Howell, D. G. & Nelson, C. H. 1985. Sedimentary, tectonic, and sea-level controls. In Sub-marine Fans and Related Turbidite Systems (ed. Bouma, A. H., Normark, W. R. and Barnes, N. E.), pp. 15–22. New York: Springer-Verlag.CrossRefGoogle Scholar
Surlyk, F. 1984. Fan-delta to submarine conglomerates of the Volgian-Valanginian Wollaston Forland Group, east Greenland. In Sedimentology of Gravels and Conglomerates (ed. Koster, E. H. and Steel, R. J.), pp. 359–82. Canadian Society of Petroleum Geologists, Memoir no. 10.Google Scholar
Swift, D. J. P., Hudelson, P. M., Brenner, R. L. & Thompson, P. 1987. Shelf construction in a foreland basin: storm beds, sandbodies, and shelf-slope depositional sequences in the Upper Cretaceous Mesaverde Group, Book Cliffs, Utah. Sedimentology 34, 423–57.CrossRefGoogle Scholar
Traynor, J-J. 1988. The Arenig in south Wales: sedimentary and volcanic processes during the initiation of a marginal basin. Geological Journal 23, 275–92.CrossRefGoogle Scholar
Van Houten, F. B. & Purucher, M. E. 1984. Glauconitic peloids and chamositic ooids. Favourable factors, constraints, and problems. Earth Science Review 20, 211–43.CrossRefGoogle Scholar
Vos, R. G. 1981. Deltaic sedimentation in the Devonian of Western Libya. Sedimentary Geology 29, 67–88.CrossRefGoogle Scholar
Wells, A. K. 1925. The geology of the Rhobell Fawr district (Merioneth). Quarterly Journal of the Geological Society of London 81, 463–538.CrossRefGoogle Scholar
Whittington, H. B. 1966. Trilobites of the Henllan Ash, Arenig Series, Merioneth. Bulletin of the British Museum (Natural History), Geology 11, (10), 489–505.Google Scholar
Wilkinson, I. & Smith, M. 1988. Basement fractures in north Wales: their recognition and control on Caledonian deformation. Geologial Magazine 125, 301–6.CrossRefGoogle Scholar
Woodcock, N. H., Awan, M. A., Jonson, T. E., MacKie, A. H. & Smith, R. D. A. 1988. Acadian tectonics of Wales during Avalonia/Laurentia convergence. Tectonics 7, 483–95.CrossRefGoogle Scholar
Zalasiewicz, J. A. 1984. A re-examination of the type Arenig Series. Geological Journal 19, 105–24.CrossRefGoogle Scholar
Zuffa, G. G. 1987. Unravelling hinterland and offshore paleogeography from deep-water arenites. In Marine Clastic Sedimentology: Concepts and Case Studies (ed. Leggett, J. K. and Zuffa, G. G.), pp. 39–61. London: Graham and Trotman.CrossRefGoogle Scholar