In Search of a Cordilleran Point Source to the McMurray Sub-Basin

Abstract

The sub-Cretaceous Unconformity (SCU) comprises a complex drainage pattern that controlled the delivery of sediments to the oilsands-hosting McMurray sub-basin. On its western margin, the McMurray sub-basin is constrained by Red Earth and Wainwright Highlands, and the Grosmont Ridge as well as others. Recent work has shown that the majority of sediments delivered to the McMurray sub-basin are derived from the southeastern United States and the Canada Shield. However, the highlands on the western flank of the sub-basin are periodically intersected by valleys that may have acted as sediment delivery conduits for Cordilleran sourced sediments. A combination of isopach mapping and petrographic analysis of 54 thin section from the southern end of the McMurray sub-basin (Twps. 50 to 70, Ranges 5 to 17 W4) are studied to identify if, and to what extent, Cordilleran sediments reached the McMurray sub-basin. Preliminary results demonstrate that the vast majority of sediments consist of detrital quartz, of which approximately 92% of grains are monocrystalline and 3% are polycrystalline. Some detrital quartz grains also have sillimanite, rutile, or vacoule inclusions, which reflects the granitic (sillimanite and rutile) or hydrothermal (vacuole) origin of the quatz. Moreover, the presence of detrital feldspar and polycrystalline quartz support a Canadian Shield and/or Appalachian provenance for the sediment. Evidence of a Cordilleran point source at the south-end of the McMurray sub-basin is not evident based on the mineralogy of the sediments. The mineralogical work presented herein confirms interpretations that McMurray Formation sediments are derived almost exclusively from the Canadian Shield and southeast United States, and that western highlands effectively blocked Cordilleran sediments from reaching the sub-basin. Moreover, the rivers that fed into the McMurray sub-basin from the west were likely small, and hence are unlikely to contain significant quantities of bitumen or other hydrocarbons.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016