Faunal Provinces in the Ordovician of North Atlantic Areas

Abstract

WILLIAMS¹ has recently pointed out a number of quantitatively significant relationships between Ordovician brachiopod faunas on both sides of the Atlantic. In the Early Ordovician and the early stages of the Middle Ordovician three brachiopod faunal provinces persisted in the area of the British Isles. The provinces occurred as belts in the NE–SW strike direction of the Caledonian geosyncline. Along the northern margin of the geosyncline, extending through NW Ireland and Scotland, there was a province with mainly North American faunal affinities (American Province). Williams suggests that the migration of the brachiopods in this province took place by a current transporting the brachiopod spat towards the NE. The central part of the geosyncline was occupied by anaerobic bottoms with graptolitic mud, devoid of significant brachiopod fauna. South of this belt there was a strip extending through SE Ireland and NW Wales (Anglesey), in which the Lower–Middle Ordovician brachiopod faunas are most closely related to stratigraphically equivalent faunas of the Baltic area (Baltic Province). Williams shows that these faunas probably spread with a current system flowing towards the SW. The same current system was responsible for the migration of the Anglo-Welsh fauna occupying the southern marginal area of the geosyncline.