Abstract

In the Late Devonian through mid-Mississippian thick sequences of westerly and northerly derived chert-rich clastics inundated the northern part of the Canadian Cordilleran miogeocline. Coarse clastics (up to 2500 m) overlapped the western offshelf facies whereas shale covered the early Paleozoic carbonate platform on the east. The coarse clastics were deposited as submarine fan complexes. In central Yukon and British Columbia pebble to cobble conglomerate, sandstone and minor pebbly mudstone formed local massive submarine channel deposits up to 750 m thick. Except in northernmost Yukon fluvial equivalents of these deep marine sediments are unknown. In northern Yukon the clastic influx waned by Early Mississippian and the region was covered by transgressive shale. In southeast Yukon the basin had been filled or had shallowed by mid-Mississippian time and the clastics were succeeded by shallow marine quartz arenite.

Two geographically separate and fundamentally different tectonic regimes seem responsible for this clastic succession. In northern Yukon tectonism involved compression, uplift and granitic intrusion in Frasnian to Early Mississippian time, resulting in an upward shoaling and southward prograding clastic wedge. Compressional deformation migrated southward resulting in eventual folding of the clastics prior to the mid-Carboniferous.

In central Yukon and British Columbia a lack of compressional deformation, the presence of local volcanics of rift type and syn-sedimentary faults that may have partly controlled thickness and facies indicate block uplift of the outer miogeocline as a consequence of regional extension or strike- slip faulting.