Terrane history of the Canadian Cordillera: estimating amounts of latitudinal displacement and rotation of Wrangellia and Stikinia

Abstract

The Canadian Cordillera is largely a mosaic of terranes that are allochthonous relative to the autochthonous North American craton. Palaeobiogeographic data on pectinoid bivalves from various cratonal areas and from two western Canadian terranes, Wrangellia and Stikinia, are used to estimate the amounts of latitudinal displacement and rotation of these terranes that took place during and after Early Jurassic times. Distributional patterns of various species of the distinctive, very common bivalve Weyla, and a comparison of the positions of biogeographic boundaries between high-palaeolatitude, mixed and low-palaeolatitude faunas on the terranes and on the craton indicate that Wrangellia was displaced northward relative to the craton by at least several hundred and possibly more than 1000 km since Sinemurian and Pliensbachian times. For Stikinia such estimates are even higher and exceed 1000 km. Biogeographic patterns also suggest that Wrangellia experienced at best minor rotation since Sinemurian times, while rotation from a more or less east–west alignment to its present northwest–southeast position seems possible for Stikinia prior to the Pliensbachian. Palaeomagnetic interpretations, suggesting that during Sinemurian and Pliensbachian times Wrangellia and Stikinia were in much the same latitudinal position relative to the craton as they are now, are in sharp contrast to the results from faunal data. The presence of warm oceanic surface currents, oceanographic effects of elongated barriers, climatic change and differential latitudinal displacements due to rotation appear to be insufficient explanations for the discrepancy between the interpretation of palaeomagnetic and faunal evidence.