Short Paper: Palaeontological constraints on the definition and development of Irish Caledonide terranes

Abstract

The Irish Caledomde terranes occupied a variety of sites marginal to the cratons of Laurentia, Baltica and Gondwana. Palaeontological data provide age constraints on the timing of sedimentary linkage and the age of overlap sequences. The Northwestern terrane is characterized by the development of Toquima–Table Head faunas in the early Ordovician in contrast to the Celtic faunas of the Bellewstown and Rosslare terranes. During the middle Ordovician the Northwestern terrane and the Scottish equivalent of the Central terrane were occupied by the Scoto–Appalachian fauna. The Leinster terrane was dominated by Anglo-Welsh elements with varying proportions of the Scoto-Appalachian and Baltic faunas across the terrane. In the Iapetus suture zone in the east of Ireland the Grangegeeth terrane is characterized by a predominantly Scoto-Appalachian fauna.

A paleogeographical review of the peri-Gondwanan realm of the Appalachian orogen1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

“…Brachiopod and graptolite assemblages of similar age in Newfoundland and the Grangegeeth terrane in Ireland, specimens of Aulograptus cf. cucullus and Azygograptus, both of which occur in high paleolatitude settings (Harper and Parkes 1989;Williams et al 1995) confirm this affinity. Therefore, the Early Ordovicican fauna of Ganderia have Gondwanan affinities, suggesting that this terrane was then situated in a cool water region at relatively high latitudes along the margin of Gondwana.…”

“…Llanvirn -early Llandeilo conodonts, trilobites and brachipods in the Exploits subzone of Newfoundland (Dean 1971;Neuman 1984), Central and Grangegeeth terranes in Ireland (Harper and Parkes 1989; and Southern Uplands of Scotland (Owen and Clarkson 1992) have strong Laurentian affinities and record the transition into warmer water environments. The occurrence of the late Caradocian graptolite Geniculograptus typicalus (Williams 1993) in the Ganderian overlap sequence in central Newfoundland, confirms this warming trend as it is restricted to the eastern margin of Laurentia.…”

Trilobites from Kilbucho and Wallace’s Cast and the location of the Northern Belt of the Southern Uplands during the late Ordovician

“…Location of the faunas described herein within the context of the Northern Belt of the Southern Uplands (stippled) and the broader geological structure of the northern part of the British Isles (inset). Maps based on Leggett et al (1979) and Harper and Parkes (1989).…”

Late Ordovician (Sandbian) brachiopods from the Mweelrea Formation, South Mayo, western Ireland: stratigraphic and tectonic implications

“…Note the locality is west of Lough Bellawaum, not east as was erroneously printed in the Memoir (Locality 12 of Kinahan et al, 1876). (Harper and Parkes, 1989).…”

“…Around Laurentia and related terranes, the Scoto-Appalachian fauna is usually preceded by assemblages of the Toquima- Table Head province (Harper and Parkes, 1989;Harper et al, 1996); such an assemblage is characteristic of the older Uggool Member of the Mweelrea Formation (Williams, 1972;Harper and Parkes, 1989) and farther east in the Lough Shee Mudrocks (Harper et al, 1988).…”