Southampton Island was located on the north margin of the Hudson Bay Basin, one of the largest Paleozoic sedimentary basins in North America. The Upper Ordovician sequence on the island includes the Bad Cache Rapids and Churchill River groups and the Red Head Rapids Formation; the latter contains three oil shale intervals in its lower part, which may have significant potential as hydrocarbon source rocks, but their precise biostratigraphic position remains unclear. Numerous conodont elements from 14 localities allow establishment of four interval zones throughout the Upper Ordovician on Southampton Island: the Belodina confluens and Pseudobelodina v. vulgaris zones in the Bad Cache Rapids Group, which are correlative to the upper Edenian – lowest Richmondian Stage; the Amorphognathus ordovicicus Zone from the uppermost Bad Cache Rapids Group to the top of Churchill River Group to the lower Richmondian Stage; and the Rhipidognathus symmetricus Zone in the Red Head Rapids Formation to the upper Richmondian Stage. The oil shale intervals in the lower Red Head Rapids Formation exposed at Cape Donavan, Sixteen Mile Brook, and Boas River on Southampton Island are correlated with the lower R. symmetricus Zone of the upper Richmondian Stage, not the Maysvillian–Richmondian Stage as previous interpreted. The “Boas River shale” and “Sixteen Mile Brook shale” biostratigraphically and lithostratigraphically equate to the Cape Donovan lower and middle oil shale intervals, respectively. The conodont data and continuous sections across the boundaries between the different lithostratigraphic units have proved the presence of Maysvillian strata on Southampton Island, rather than absence as previously interpreted.