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

The Canadian Cordillera is largely a mosaic of terranes that are allochthon ous relative to the autochthonous North American craton. Palaeobiogeographi c data on pectinoid bivalves from various cratonal areas and from two weste rn Canadian terranes, Wrangellia and Stikinia, are used to estimate the amo unts of latitudinal displacement and rotation of these terranes that took p lace during and after Early Jurassic times. Distributional patterns of vari ous 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 indic ate that Wrangellia was displaced northward relative to the craton by at le ast several hundred and possibly more than 1000 km since Sinemurian and Pli ensbachian times. For Stikinia such estimates are even higher and exceed 10 00 km. Biogeographic patterns also suggest that Wrangellia experienced at b est minor rotation since Sinemurian times, while rotation from a more or le ss east-west alignment to its present northwest-southeast position seems po ssible for Stikinia prior to the Pliensbachian. Palaeomagnetic interpretati ons, suggesting that during Sinemurian and Pliensbachian times Wrangellia a nd Stikinia were in much the same latitudinal position relative to the crat on as they are now, are in sharp contrast to the results from faunal data. The presence of warm oceanic surface currents, oceanographic effects of elo ngated 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.