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Early Neoproterozoic limestones from the Gwna Group, Anglesey

Published online by Cambridge University Press:  16 June 2010

JANA M. HORÁK  and
JANE A. EVANS
JANA M. HORÁK*
Affiliation:
Department of Geology, National Museum of Wales, Cardiff CF10 3NP, Wales, UK
JANE A. EVANS
Affiliation:
NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
*
*Author for correspondence: Jana.horak@museumwales.ac.uk
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Abstract

Limestone megaclasts up to hundreds of metres in size are present within the Gwna Group mélange, North Wales, UK. The mélange has been interpreted as part of a Peri-Gondwanan fore-arc accretionary complex although the age of deposition remains contentious, proposals ranging from Neoproterozoic to Early Ordovician. This paper uses strontium isotope chemostratigraphy to establish the age of the limestone blocks and thus provide a maximum age constraint on mélange formation. Results show that, although the carbonates are locally dolomitized, primary 87Sr/86Sr ratios can be identified and indicate deposition sometime between the late Tonian and earliest Cryogenian. This age is older than that suggested by stromatolites within the limestone and indicates that the limestone did not form as cap carbonate deposits.

Keywords

NeoproterozoiclimestoneAngleseychemostratigraphymélange
Type
Original Article
Information
Geological Magazine , Volume 148 , Issue 1 , January 2011 , pp. 78 - 88
Copyright
Copyright © Cambridge University Press 2010

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References

Asmerom, Y., Jacobsen, S. B., Knoll, A. H., Butterfield, N. J. & Swett, K. 1991. Strontium isotope variations of Neoproterozoic seawater: implications for crustal evolution. Geochimica et Cosmochimica Acta 55, 2883–94.Google Scholar
Barber, A. J. & Max, M. D. 1979. A new look at the Mona Complex (Anglesey, North Wales). Journal of the Geological Society, London 136, 407–32.Google Scholar
Beckinsale, R. D., Evans, J. A., Thorpe, R. S., Gibbons, W. & Harmon, R. S. 1984. Rb–Sr whole-rock ages δ18O values and geochemical data for the Sarn Igneous Complex and the Parwyd gneisses of the Mona Complex of Llŷn, N. Wales. Journal of the Geological Society, London 141, 701–9.Google Scholar
Birck, J. L. 1986. Precision K–Rb–Sr Isotopic Analysis – Application to Rb–Sr Chronology. Chemical Geology 56, 73–83.Google Scholar
Blatt, H., Middleton, G. & Murray, R. 1972. Origin of Sedimentary Rocks. Englewood Cliffs, New Jersey: Prentice-Hall, Inc., 634 pp.Google Scholar
Brasier, M. D. & Shields, G. 2000. Neoproterozoic chemostratigraphy and correlation of the Port Askaig glaciation, Dalradian Supergroup of Scotland. Journal of the Geological Society, London 157, 909–14.Google Scholar
Buick, R., Des Marais, D. J. & Knoll, A. H. 1995. Stable isotopic compositions of carbonates from the Mesoproterozoic Bangemall Group, northwestern Australia. Chemical Geology 123, 153–71.Google Scholar
Cawood, P. A., McCausland, P. J. A. & Dunning, G. R. 2001. Opening Iapetus: constraints from the Laurentian margin in Newfoundland. Geological Society of America Bulletin 113, 443–53.Google Scholar
Collins, A. & Buchan, C. 2004. Provenance and age constraints of the South Stack Group, Anglesey, UK: U–Pb SIMS detrital zircon data. Journal of the Geological Society, London 161, 743–6.Google Scholar
Dallmeyer, R. D. & Gibbons, W. 1987. The age of blueschist metamorphism in Anglesey, North Wales: evidence from 40Ar/39Ar mineral dates of the Penmynydd schists. Journal of the Geological Society, London 144, 843–50.Google Scholar
Denison, R. E., Koepnick, R. B., Fletcher, A., Howell, M. W. & Callaway, W. S. 1994. Criteria for the retention of original seawater 87Sr/86Sr in ancient shelf limestones. Chemical Geology (Isotope Geoscience Section) 112, 131–43.Google Scholar
Derry, L. A., Brasier, M. D., Corfield, R. M., Yu, R. A. & Yu, Z. A. 1994. Sr and C isotopes in Lower Cambrian carbonates from the Siberian craton: a paleoenvironmental record during the “Cambrian explosion”. Earth and Planetary Science Letters 128, 671–81.Google Scholar
Derry, L. A., Keto, L. S., Jacobsen, S. B., Knoll, A. H. & Swett, K. 1989. Sr isotopic variations in Upper Proterozoic carbonates from Svalbard and East Greenland. Geochimica et Cosmochimica Acta 53, 2331–9.Google Scholar
Dickin, A. P. 1995. Radiogenic Isotope Geology. Cambridge University Press, 452 pp.Google Scholar
Evans, J. A. 1995. Mineral and isotope features related to resetting of Rb–Sr whole-rock isotope systems during low grade metamorphism. In Low-Grade Metamorphism of Mafic Rocks (eds Schiffman, P. & Day, H. W.), pp. 157–69. Geological Society of America, Special Paper no. 296.Google Scholar
Fairchild, I. J. 1980. The structure of NE Islay. Scottish Journal of Geology 16, 189–97.Google Scholar
Fairchild, I. J., Spiro, B., Herrington, P. M. & Song, T. 2000. Controls on Sr and C isotope compositions of Neoproterozoic Sr-rich limestones of East Greenland and North China. In Carbonate Sedimentation and Diagenesis in the Evolving Precambrian World (eds Grotzinger, J. P. & James, N. P.), pp. 297–313. Society for Sedimentary Geology, Special Publication no. 67.Google Scholar
Gibbons, W. & Horák, J. M. 1996. The evolution of the Neoproterozoic subduction system: evidence from the British Isles. In Avalonian and related peri-Gondwanan terranes of the circum-North Atlantic (eds Nance, R. D. & Thompson, M. D.), pp. 269–80. Geological Society of America, Special Paper no. 304.Google Scholar
Gibbons, W. & McCarroll, D. 1993. Geology of the country around Aberdaron, including Bardsey Island. Memoir of the British Geological Survey, Sheet 133 (England and Wales).Google Scholar
Gibbons, W., Tietzsch-Tyler, D., Horák, J. M. & Murphy, F. C. 1994. Precambrian rocks in Anglesey, southwest Llŷn and southeast Ireland. In A Revised Correlation of Precambrian Rocks in The British Isles (eds Gibbons, W. & Harris, A. L.), pp. 75–84. Geological Society of London, Special Report no. 2.Google Scholar
Greenly, E. 1919. The Geology of Anglesey. Memoir of the Geological Survey of Great Britain no. 78, 980 pp.Google Scholar
Greenly, E. 1920. 1:50,000 (& 1 inch to the mile) Geological Map of Anglesey. Geological Survey, G.B., Special Sheet, no. 92 & 93 with parts of 94, 105 & 106.Google Scholar
Grey, K. 1995. Neoproterozoic stromatolites from the Skates Hills Formation, Savory Basin, Western Australia, and a review of the distribution of Acaciella australica. Australian Journal of Earth Sciences 42, 123–32.Google Scholar
Halverson, G. P., Dudás, F. O., Maloof, A. C. & Bowring, S. A. 2007. Evolution of the 87Sr/86Sr composition of Neoproterozoic seawater. Palaeogeography, Palaeoclimatology, Palaeoecology 256, 103–29.Google Scholar
Jacobsen, S. B. & Kaufman, A. J. 1999. The Sr, C and O isotopic evolution of Neoproterozoic seawater. Chemical Geology 161, 37–57.Google Scholar
James, N. P., Narbonne, G. M., Dalrymple, R. W. & Kyser, T. K. 2005. Glendonites in Neoproterozoic low-latitude, interglacial sedimentary rocks, northwest Canada: Insights into the Cryogenian ocean and Precambrian cold-water carbonates. Geology 33, 9–12.Google Scholar
Kaufman, A. J., Jacobsen, S. B. & Knoll, A. H. 1993. The Vendian record of Sr and C isotopic variations in seawater: implications for tectonics and paleoclimate. Earth and Planetary Science Letters 120, 409–30.Google Scholar
Kawai, T., Windley, B. F., Terabayashi, M., Yamamoto, H., Maruyama, S. & Isozaki, Y. 2006. Mineral isograds and metamorphic zones of the Anglesey blueschist belt, UK: implications for the metamorphic development of a Neoproterozoic subduction–accretion complex. Journal of Metamorphic Geology 24, 591–602.Google Scholar
Krogh, T. E., Strong, D. F., O'Brien, S. J. & Papezik, V. S. 1988. Precise U–Pb dates from the Avalon terrane in Newfoundland. Canadian Journal of Earth Science 25, 442–53.Google Scholar
Lécuyer, C. & Allemend, P. 1999. Modelling of the oxygen isotope evolution of seawater: implications for the climate interpretation of the δ18O of marine sediments. Geochimica et Cosmochimica Acta 63, 351–61.Google Scholar
Li, Z. X., Bogdanova, S. V., Collins, A. S., Davidson, A., De Waele, B., Ernst, R. E., Fitzsimons, I. C. W., Fuck, R. A., Ladkochub, D. P., Jacobs, J., Karlstrom, K. E., Lu, S., Natapov, L. M., Pease, V., Pisarevsky, S. A., Thrane, A. K. & Vernikovsky, V. 2008. Assembly, configuration, and break-up history of Rodinia: a synthesis. Precambrian Research 160, 179–210.Google Scholar
Matley, C. A. 1928. The Precambrain Complex and associated rocks of S.W. Lleyn (Carnarvonshire). Quarterly Journal of the Geological Society of London 84, 440–504.Google Scholar
Matthew, G. F. 1890. Eozoon and other low organisms in Laurentian rocks at St. John (Article 1). Bulletin of the Natural History Society, New Brunswick 2, 36–41.Google Scholar
McArthur, J. M. 1994. Recent trends in strontium isotope stratigraphy. Terra Nova 6, 331–58.Google Scholar
McCausland, P. J. A., Murphy, J. B., Hamilton, M. A., Pisarevsky, S. & O'Brien, S. J. 2008. Avalonia's foundation? Preliminary paleomagnetism and U–Pb zircon geochronology of the mid-neoproterozoic Burin Group, Newfoundland. Northeast GSA Meeting, Buffalo, NY, GSA Abstracts with Programs 40, 2.Google Scholar
McNamara, A. K., Mac Niocaill, C., Van der Pluijm, B. A. & Van der Voo, R. 2001. West African proximity of Avalon in the Latest Precambrian. Geological Society of America Bulletin 113, 1161–70.Google Scholar
Melezhik, V. A., Gorokhov, I. M., Kuznetsov, A. B. & Fallick, A. E. 2001. Chemostratigraphy of Neoproterozoic carbonates: implications for ‘blind dating’. Terra Nova 13, 1–11.Google Scholar
Merriman, R. J. & Roberts, B. 1985. A survey of white mica crystallinity and polytypes in pelitic rocks of Snowdonia and Llŷn, North Wales. Mineralogical Magazine 49, 345–56.Google Scholar
Misi, A. & Veizer, J. 1998. Neoproterozoic carbonate sequences of the Una Group, Irece Basin, Brazil: chemostratigraphy, age and correlations. Precambrian Research 89, 87–100.Google Scholar
Montañez, I. P., Osleger, D. A., Banner, J. L., Mack, L. & Musgrove, M. L. 2000. Evolution of the Sr and C isotope composition of Cambrian oceans. GSA Today 10, 1–7.Google Scholar
Montgomery, J., Evans, J. A. & Wildman, G. 2006. 87Sr/86Sr isotope composition of bottled mineral waters for environmental and forensic purposes. Applied Geochemistry 21, 1626–34.Google Scholar
Muir, M. D., Bliss, G. M., Grant, P. R. & Fisher, M. J. 1979. Palaeontological evidence for the age of some supposedly Precambrian rocks in Anglesey, North Wales. Journal of the Geological Society, London 136, 61–4.Google Scholar
Nicholas, C. J. 1996. The Sr isotopic evolution of the oceans during the ‘Cambrian Explosion’. Journal of the Geological Society, London 153, 243–54.Google Scholar
O'Brian, S. J., O'Driscoll, C. F., Tucker, R. D. & Dunning, G. R. 1992. Four-fold subdivision of the Late Precambrian magmatic record of the Avalon Zone type area (east Newfoundland): nature and significance. Geological Association of Canada – Mineralogical Association of Canada, Program with Abstracts 17, A85.Google Scholar
Peat, C. J. 1984. Precambrian microfossils from the Longmyndian of Shropshire. Proceedings of the Geologists’ Association 95, 17–22.Google Scholar
Phillips, E. R. 1991. The lithostratigraphy, sedimentology and tectonic setting of the Monian Supergroup, western Anglesey, North Wales. Journal of the Geological Society, London 148, 1079–90.Google Scholar
Prave, A. R., Fallick, A. E., Thomas, C. W. & Graham, C. M. 2009. A composite C-isotope profile for the Neoproterozoic Dalradian Supergroup of Scotland and Ireland. Journal of the Geological Society, London 166, 845–57.Google Scholar
Schuster, D. C. 1979. The Gwna Mélange, a late Precambrian olistostrome sequence, North Wales, United Kingdom. Abstract, AAPG 63, 523.Google Scholar
Shackleton, R. M. 1954. The structure and succession of Anglesey and the Lleyn peninsula. Advancement of Science 11, 106–8.Google Scholar
Shackleton, R. M. 1969. The Precambrian of North Wales. In The Precambrian and Lower Palaeozoic rocks of Wales (ed. Wood, A.), pp. 1–22. Cardiff: The University of Wales Press.Google Scholar
Shields, G. 1999. Working towards a new stratigraphic calibration scheme for the Neoproterozoic–Cambrian. Eclogae Geologicae Helvetiae 92, 221–33.Google Scholar
Strachan, R. A., Collins, A. S., Buchan, C., Nance, R. D., Murphy, J. B. & D'Lemos, R. B. 2007. Terrane analysis along a Neoproterozoic active margin of Gondwana: insights from U–Pb zircon geochronology. Journal of the Geological Society, London 164, 57–60.Google Scholar
Thomas, C. W., Graham, C. M., Ellam, R. M. & Fallick, A. E. 2004. 87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland. Journal of the Geological Society, London 161, 229–42.Google Scholar
Thorpe, R. S., Beckinsale, R. D., Patchet, P. J., 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, London 141, 521–36.Google Scholar
Tucker, R. D. & Pharaoh, T. C. 1991. U–Pb zircon ages for the Late Precambrian igneous rocks in southern Britain. Journal of the Geological Society, London 148, 435–45.Google Scholar
Veizer, J., Ala, D., Azmy, K., Bruckschen, P., Buhl, D., Bruhn, F., Carden, G., Diener, A., Ebneth, S., Godderis, Y., Jasper, T., Korte, C., Pawellek, F., Podlaha, O. & Stauss, H. 1999. 87Sr/86Sr, δ13C and δ18O evolution of of Phanerozoic seawater. Chemical Geology 161, 59–88.Google Scholar
Vizan, H., Carney, J. N., Turner, P., Ixer, R. A., Tomasso, M., Mullen, R. P. & Clarke, P. 2003. Late Neoproterozoic to Early Palaeozoic palaeogeography of Avalonia: some palaeomagnetic constraints from Nuneaton, central England. Geological Magazine 140, 685–705.Google Scholar
Wadleigh, M. A. & Veizer, J. 1992. 18O/16O and 13C/12C in Lower Palaeozoic articulate brachiopods: implications for the isotopic composition of sea water. Geochimica et Cosmoschimica Acta 56, 431–43.Google Scholar
Walter, M. R. 1972. Stromatolites and biostratigraphy of the Australian Precambrian and Cambrian. Special Papers in Paleontology 11, 268 pp., 34 pls.Google Scholar
Walter, M. R., Veevers, J. J., Calver, C. R., Gorgan, P. & Hill, A. C. 2000. Dating the 840–544 Ma Neoproterozoic interval by isotopes of strontium, carbon and sulfur in seawater, and some interpretative models. Precambrian Research 100, 371–433.Google Scholar
White, C. E. & Barr, S. M. 1996. Geology of the Brookville terrane, southern New Brunswick, Canada. In Avalonian and related peri-Gondwanan terranes of the Circum-North Atlantic (eds Nance, R. D. & Thompson, M. D.), pp. 95–108. Geological Society of America, Special Paper no. 304.Google Scholar
Wood, D. S. & Nicholls, G. D. 1973. Precambrian stromatolitic limestones from Northern Anglesey. Nature 241, 65.Google Scholar