The palaeogeography of early Ordovician Iapetus terranes: an integration of faunal and palaeomagnetic constraints

New and existing fossil data from Ireland, Britain, Newfoundland and Scandinavia emphasize a significant degree of latitudinal variation in biogeographic patterns across the Ordovician Iapetus Ocean. Platform provinces together with marginal belts and island complexes can be recognised with increasing clarity on the basis of palaeontological information. Statistical analysis of the distribution patterns of about 70 early Ordovician brachiopod genera across some 25 sites, using both cladistic and phenetic methods, together with a critical analysis of their geological settings combined with current palaeogeographic and palaeomagnetic data, reaffirm the existence of the Celtic brachiopod province. During the early Ordovician, the majority of sites assigned to the Celtic province define a high-latitude, peri-Gondwanan belt shadowing the distribution of the low-latitude, circum-Laurentian Toquima-Table Head faunas. Rapidly changing Ordovician faunal signals across the Baltic province and Exploits Zone of central Newfoundland track the cross-latitude movement of these terranes from high temperate to near tropical belts during the period. New fossil information together with continuing statistical appraisal of an expanding database are providing more accurate and sophisticated models for the dynamics of the Iapetus ocean system.