Timing of the Appalachian/Caledonian Orogen Contraction

Abstract

LOWER Palaeozoic faunal “provinces” in the northern hemisphere were controlled principally by the Appalachian/Caledonian orogen. Tuzo Wilson postulated a proto-Atlantic ocean closing during the Lower Palaeozoic so that the “American” and “European” landmasses collided during the Middle Palaeozoic¹. Dewey remarked that faunas were of great potential value for timing this contraction, which in his model finished during the Devonian². There is a differentiation of invertebrates into two or more markedly distinct faunas in the early Ordovician, which later merged³. This Wilson and Dewey related to closure along the length of the orogen.