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Early Neoproterozoic limestones from the Gwna Group, Anglesey

By Jana M. Horak and Jane A. Evans


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

Publisher: Cambridge University Press
Year: 2011
DOI identifier: 10.1017/S0016756810000464
OAI identifier:

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  1. (1920). 1:50,000 (& 1 inch to the mile) Geological Map of Anglesey. Geological Survey,
  2. (1992). 18O/16O and 13C/12C in Lower Palaeozoic articulate brachiopods: implications for the isotopic composition of sea water.
  3. (2004). 87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland.
  4. (2006). 87Sr/86Sr isotope composition of bottled mineral waters for environmental and forensic purposes.
  5. (1999). 87Sr/86Sr, δ13C and δ 18O evolution of of Phanerozoic seawater.
  6. (2009). A composite C-isotope profile for the Neoproterozoic Dalradian Supergroup of Scotland and Ireland.
  7. (1979). A new look at the Mona Complex (Anglesey, North Wales). doi
  8. (1985). A survey of white mica crystallinity and polytypes in pelitic rocks of Snowdonia and Llyˆn, North Wales. doi
  9. (2008). Assembly, configuration, and break-up history of Rodinia: a synthesis. Precambrian Research 160, doi
  10. (2008). Avalonia’s foundation?
  11. (2001). Chemostratigraphy of Neoproterozoic carbonates: implications for ‘blind dating’. doi
  12. (2000). Controls on Sr and C isotope compositions of Neoproterozoic Sr-rich limestones of East Greenland and North China.
  13. (1994). Criteria for the retention of original seawater 87Sr/86Sr in ancient shelf limestones.
  14. (1984). Crustal growth and late Precambrian–early Palaeozoic plate tectonic evolution of England and Wales.
  15. (2000). Dating the 840–544 Ma Neoproterozoic interval by isotopes of strontium, carbon and sulfur in seawater, and some interpretative models. doi
  16. Eozoon and other low organisms in Laurentian rocks at St.
  17. (2007). Evolution of the 87Sr/86Sr composition of Neoproterozoic seawater.
  18. (2000). Evolution of the Sr and C isotope composition of Cambrian oceans.
  19. (1992). Four-fold subdivision of the Late Precambrian magmatic record of the Avalon Zone Downloaded: 05
  20. (1996). Geology of the Brookville terrane,
  21. (1993). Geology of the country around Aberdaron, including Bardsey Island.
  22. (2005). Glendonites in Neoproterozoic low-latitude, interglacial sedimentary rocks, northwest Canada: Insights into the Cryogenian ocean and Precambrian cold-water carbonates.
  23. (2003). Late Neoproterozoic to Early Palaeozoic palaeogeography of Avalonia: some palaeomagnetic constraints from Nuneaton, central England.
  24. (1995). Mineral and isotope features related to resetting of Rb–Sr whole-rock isotope systems during low grade metamorphism.
  25. (2006). Mineral isograds and metamorphic zones of the Anglesey blueschist belt, UK: implications for the metamorphic development of a Neoproterozoic subduction–accretion complex.
  26. (1999). Modelling of the oxygen isotope evolution of seawater: implications for the climate interpretation of the δ18O of marine sediments.
  27. (1998). Neoproterozoic carbonate sequences of the Una Group, Irece Basin, Brazil: chemostratigraphy, age and correlations.
  28. (2000). Neoproterozoic chemostratigraphy and correlation of the Port Askaig glaciation, Dalradian Supergroup of Scotland. doi
  29. (1995). Neoproterozoic stromatolites from the Skates Hills Formation, Savory Basin, Western Australia, and a review of the distribution of Acaciella australica.
  30. (2001). Opening Iapetus: constraints from the Laurentian margin in Newfoundland. doi
  31. (1972). Origin of Sedimentary Rocks. Englewood Cliffs,
  32. (1979). Palaeontological evidence for the age of some supposedly Precambrian rocks in Anglesey, North Wales.
  33. (1984). Precambrian microfossils from the Longmyndian of Shropshire.
  34. (1994). Precambrian rocks in Anglesey, southwest Llyˆn and southeast Ireland. In A Revised Correlation of Precambrian Rocks
  35. (1973). Precambrian stromatolitic limestones from Northern Anglesey.
  36. (1988). Precise U–Pb dates from the Avalon terrane in Newfoundland. doi
  37. (1986). Precision K–Rb–Sr Isotopic Analysis – Application to Rb–Sr Chronology. doi
  38. (2004). Provenance and age constraints of the South Stack Group, Anglesey, UK: U– Pb SIMS detrital zircon data.
  39. (1995). Radiogenic Isotope Geology.
  40. (1984). Rb–Sr whole-rock ages δ 18O values and geochemical data for the Sarn Igneous Complex and the Parwyd gneisses of the Mona doi
  41. (1994). Recent trends in strontium isotope stratigraphy. doi
  42. (1994). Sr and C isotopes in Lower Cambrian carbonates from the Siberian craton: a paleoenvironmental record during the “Cambrian explosion”.
  43. (1989). Sr isotopic variations in Downloaded:
  44. (1995). Stable isotopic compositions of carbonates from the Mesoproterozoic Bangemall Group, northwestern Australia. doi
  45. (1972). Stromatolites and biostratigraphy of the Australian Precambrian and Cambrian.
  46. (1991). Strontium isotope variations of Neoproterozoic seawater: implications for crustal evolution. doi
  47. (2007). Terrane analysis along a Neoproterozoic active margin of Gondwana: insights from U–Pb zircon geochronology.
  48. (1987). The age of blueschist metamorphism in Anglesey, North Wales: evidence from 40Ar/39Ar mineral dates of the Penmynydd schists.
  49. (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
  50. (1919). The Geology of Anglesey.
  51. (1979). The Gwna Mélange, a late Precambrian olistostrome sequence,
  52. (1991). The lithostratigraphy, sedimentology and tectonic setting of the Monian Supergroup, western Anglesey, North Wales.
  53. (1928). The Precambrain Complex and associated rocks of S.W. Lleyn (Carnarvonshire). doi
  54. (1969). The Precambrian of North Wales.
  55. (1996). The Sr isotopic evolution of the oceans during the ‘Cambrian Explosion’.
  56. (1999). The Sr, C and O isotopic evolution of Neoproterozoic seawater.
  57. (1954). The structure and succession of Anglesey and the Lleyn peninsula.
  58. (1980). The structure of NE Islay.
  59. (1993). The Vendian record of Sr and C isotopic variations in seawater: implications for tectonics and paleoclimate.
  60. (1991). U–Pb zircon ages for the Late Precambrian igneous rocks in southern Britain.
  61. (2001). West African proximity of Avalon in the Latest Precambrian. doi
  62. (1999). Working towards a new stratigraphic calibration scheme for the Neoproterozoic–Cambrian. Eclogae Geologicae Helvetiae 92,

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