Palaeozoic palaeogeography of Laurentia and its margins: a reassessment of palaeomagnetic data

Abstract

SUMMARY The recognition of wide-spread remagnetization events during the Palaeozoic has greatly added to the problems of reconstructing the Palaeozoic drift history of Laurentia and in recent years increasing emphasis has been placed on evaluating the relative reliability of palaeomagnetic data, in an attempt to overcome some of these difficulties. In the light of these developments a revised apparent polar wander (APW) path has been constructed following a rigorous evaluation of all published Palaeozoic palaeomagnetic data from Laurentia and its Palaeozoic margins (i.e. North America, northern Britain, Northern Ireland and Greenland). The use of data from the Laurentian margins, when corrected for the opening of the North Atlantic, has resulted in a revision of previously published Palaeozoic palaeogeographic reconstructions and these new palaeogeographic reconstructions for Laurentia are in good agreement with faunal and lithological data. A comparison of this new APW path with other APW paths from Avalonia and Baltica reveals a very close agreement between all three paths from mid-Silurian times onwards, indicating that the closure of the Iapetus ocean and the Tornquist sea was essentially complete by this time. Laurentia occupied equatorial latitudes from Cambrian to early Silurian times and its drift history was dominated by anti-clockwise rotation (up to 0.7°Ma−1) and low latitudinal drift rates (up to 3 cm yr−1). Late Silurian and early Devonian times were characterized by increased rates of anti-clockwise rotation (up to 1.3°Ma−1) and southerly directed latitudinal drift (rates up to 13 cm yr−1) of the continent, which place Laurentia in moderate southerly latitudes (30–40°S) by the early Devonian. These palaeolatitudes are comparable with those from Avalonia and Baltica for this time indicating that the amalgamation of Eurmerica had already taken place. By late Devonian time Laurentia had begun to drift north (rates up to 5 cm yr−1) towards equatorial latitudes by mid-Carboniferous time.