Trilobite faunas of the Duncannon Group: Caradoc stratigraphy, environments and palaeobiogeography of the Leinster terrane, Ireland

The Burrellian trilobite faunas of the Leinster terrane comprise at least 31 species from a spectrum of faunal associations. Strong faunal links with the Anglo-Welsh area confirm the likely close proximity of these parts of Avalonia during the mid Caradoc but together with existing magmatic and palaeomagnetic data, the Leinster faunas also indicate that the existing simple structural models of the relationship between these areas need to be reappraised. Of the 22 identifiable trilobite genera, eight are not known from equivalent or older horizons in the Anglo-Welsh area and indicate a significant link with Scoto-Appalachian faunas on the margins of Laurentia. This colonization by trilobites of Scoto-Appalachian origin may have been achieved by 'volcanic island hopping' across the shrinking Iapetus Ocean. The Leinster trilobites are therefore critical in documenting the breakdown of faunal provincialism and in fingerprinting the faunas and likely palaeogeographical setting of terranes now caught up in the Iapetus suture zone to the north. Eighteen species are described or discussed in detail including a new species of Ampyxina, A. hibernica sp. nov., a probable new species of Calyptaulax and revision of the M'Coy species Trinodus agnostiformis, Autoloxolichas laxatus, Flexicalymene forcipata and Remopleurides platyceps.