The Devonian clastic wedge and underlying strata of southwestern Canadian Arctic Archipelago: stratigraphic revisions

Abstract

The Devonian clastic wedge (DCW) and underlying carbonate platforms and basinal mudrocks of the study area are re-examined using legacy seismic data and XRF surveys of borehole chip samples. The Ordovician-Devonian basinal succession of Melville Island is consolidated under the name Ibbett Bay Group within the Northwest Territories, whereas equivalent strata in Nunavut are grouped into the Cape Phillips Formation. The Kitson Formation black shale is correlative with the upper Ibbett Bay Group. Six horizons with high TOC and high gamma response are traced in the Ordovician-Devonian, with the fourth (4a) approximating the Silurian/Devonian boundary; the upper two (4b, 5) are Emsian and Eifelian. In the direction of progradation, the base of Kitson Formation rises stratigraphically from gamma horizon 4a to 5. The upper Kitson represents basinal toes of westward prograding DCW clinoforms. The Blackley and Cape de Bray formations of Embry and Klovan (1976) are not traceable enough to warrant their formation rank. We revert to the original usage of Tozer and Thorsteinsson (1964) where these units are members within the Weatherall Formation. The distinctive seismic character of the Cape de Bray in western and central Melville Island warrants its recognition as a formal member; elsewhere it is informal as it cannot be consistently traced. The Blackey is treated as a formal member in an outcrop area of ⁓2000 km2 where it was defined; it is not recognized in the subsurface. Onset of the DCW is tentatively linked to flexural subsidence and crustal thickening caused by the Romanzof Orogeny in the hinterland.