COMPARING THE PERMIAN AND TRIASSIC CONODONT FAUNAS OF THE CACHE CREEK AND STIKINE TERRANES IN THE CANADIAN CORDILLERA: IMPLICATIONS FOR PALEOBIOGEOGRAPHY AND TECTONIC RECONSTRUCTION

The Canadian Cordillera is a composite of crustal terranes with various stratigraphic and tectonic histories. The relationships between these terranes, and their relative positions throughout the late Paleozoic and Mesozoic, are an ongoing field of research. In northern British Columbia and southern Yukon, the oceanic Cache Creek terrane is structurally juxtaposed with the island arc Stikine terrane. The fossil faunas recovered from these two terranes suggest that, although they are adjacent now, they have been widely separated in the past. For example, fusulinaceans from the Cache Creek terrane are exotic compared with their counterparts in North American rocks. Although it is clear that these two terranes were largely separate for much of their existence, estimates of how far they were separated, how far they have moved, and at what time they accreted to the North American margin, are still poorly constrained. The study of both new and archive collections of conodonts from the northern parts of both terranes provides the basis for assessing the variability between faunas of the two terranes. Cisuralian, Guadalupian, and Middle to Late Triassic conodont faunas can be recognised in both terranes, and initial comparisons of the faunas indicate that they were very different during the Permian but were almost identical during the Late Triassic. This implies that the Cache Creek terrane and the Stikine terrane were quite separate during the Permian, but became more proximal during the Triassic. An assessment of the effect that environmental tolerances of conodont species have on paleobiogeographical reconstructions is ongoing, and comparison with faunas from other terranes will be necessary to fully constrain the relationships between terranes in the Canadian Cordillera.