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Silurian graptolite faunas of the Balbriggan Inlier, counties Dublin and Meath, and their evolutionary, stratigraphical and structural significance

1993; Zoological Society of London; Volume: 49; Issue: 4 Linguagem: Inglês

10.1144/pygs.49.4.283

2041-4811

Valentia Busty' Burns, R. B. Rickards,

Geology and Paleoclimatology Research

SUMMARY The Llandovery, Wenlock and Ludlow graptolites of the Leinster and Bellewstown terranes of the Balbriggan Inlier give a precise indication of their comparative stratigraphies. The earliest Silurian strata proven, north of the Lowther Lodge Fault that separates the Bellewstown (Northern) Terrane from the Leinster (Southern) Terrane, are referable to the riccartonensis Biozone (Wenlock). Comparisons are made between the Balbriggan and Skerries formations of the Leinster Terrane, the Silurian of the Bellewstown Terrane, and the Windermere Group (Silurian) of the English Lake District (Cumbria), the Howgill Fells (Cumbria) and parts of Yorkshire. Twenty graptolite species have been identified in the Bellewstown Terrane enabling unambiguous recognition of mid-Wenlock ( riccartonensis and rigidus biozones) to early Ludlow ( nilssoni Biozone). The Denhamstown Formation is shown to encompass the riccartonensis to lundgreni biozones, whilst the Clatterstown Formation and Kennetstown Formation can be referred respectively to the ludensis (Wenlock) and nilssoni (Ludlow) biozones. The faunas are of palaeobiological interest on several counts, but most strikingly because of the presence of Monograptus flemingii warreni subsp. nov. (here described); an evolutionary intermediate between Monograptus ex gr. riccartonensis and M. ex gr. flexilis; and the possible occurrence of Pristiograptus parvus, a species currently critical in global correlations.