Palynology through the early Wenlock Ireviken Event

  • Rhian Llewellyn

    Student thesis: Doctoral Thesis


    An early Sheinwoodian (Wenlock) chitinozoan assemblage is reported from a high-resolution investigation undertaken at Buttington Brick Pit, mid-Wales (positioned on the mid-shelf of the Welsh Basin in the early Wenlock). The lower Sheinwoodian strata from the locality are assigned herein to three local chitinozoan biozones: the margaritana chitinozoan Biozone, the bouniensis chitinozoan Biozone and the bella chitinozoan Biozone, which can all be correlated with the pre-established graptolite biostratigraphy of the section. The chitinozoan assemblage allows for, at least partial, stratigraphical correlation within the Welsh Basin and with other areas in Avalonia, Baltica, and peri-Gondwana. The ‘Interzone IV’ of Nestor (1994) is reported from the Welsh Basin for the first time. Chitinozoans are recovered throughout the section and show decreased diversity at levels within the riccartonensis graptolite Biozone.
    The lower part of the early Sheinwoodian positive carbon isotope excursion has been recognised previously from the section and a palaeoenvironmental investigation of the microphytoplankton assemblage herein has been undertaken from levels where carbon isotope data are available. The relative abundance of acritarchs (categorised by both genera and various informal morphotype groupings), prasinophytes, and sphaeromorphs within the microphytoplankton assemblage are considered to fluctuate with regard to proximity to shore, and are therefore considered diagnostic of sea-level change. The palaeoenvironmental signal from the microphytoplankton assemblage implies that a sea-level rise is associated with an interval of relatively low carbon isotope values that is superimposed upon the Sheinwoodian positive carbon isotope excursion, and recognised from multiple regions (e.g. Laurentia, Avelonia, and the Baltica).
    Date of AwardJul 2015
    Original languageEnglish
    Awarding Institution
    • University of Portsmouth
    SupervisorAnthony Butcher (Supervisor) & David Loydell (Supervisor)

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