Devonian

AbstractThe region described in this subchapter lies between the craton and the western edge of the carbonate platform built upon the Devonian continental shelf within one or two hundred kilometres of the continental margin. Sediments deposited west of the platform edge are described in the companion volume, “Geology of the Cordilleran Orogen in Canada” (Gabrielse and Yorath,1991). The depositional record described here starts with rocks deposited in Late Silurian time following a widespread regression accompanied by epeirogenic uplift, warping, and erosion. These rocks are the first of Kaskaskia sequence (Sloss, 1963). The record ends at the base of dark radioactive shales spanning the Devonian-Mississippian boundary and marking a major transgression. In the far north, this transgression is masked by a clastic wedge originating in the Ellesmerian Orogen of the Arctic Islands and northern Alaska.Within the region, Devonian sediments cover an area of 2 500 000 km2. Thickness varies greatly from place to place. The thickest carbonate packets occur at the margin of the platform; close to Selwyn Basin, for example, the “Bear Rock sequence”, one of the five divisions of the Devonian analyzed here, alone constitutes over 2000 m of carbonate strata. In contrast, some bathymetric basins, such as the one occupying the Mackenzie Valley region during the Givetian, were starved of sediment.