There are two unreconciled interpretations for the age and character of the boundary separating the Cambrian–Ordovician Potsdam and Beekmantown groups that underlie the Ottawa Embayment in eastern Ontario. These stratal groups consist of interior facies of the central Laurentian Platform. As exposed in the type section of the Nepean Formation (upper Potsdam Group), located in the City of Ottawa, the boundary was previously interpreted to be conformable and of Early Ordovician age. This intepretation was of enormous impact on subsequent regional geology compilations that showed a diachronous boundary across the platform interior. From recent subsurface analysis across eastern Ontario, the contact was interpreted to be disconformable, a sequence boundary separating Late Cambrian and Early Ordovician strata. This paper reexamines the type section. Lithologically, the group boundary should be repositioned downsection by ~1.5 m. The contact now lies coincident with a disconformity that has a paleorelief of < 10 cm. The proposed revision is geologically significant. Previous collections of Early Ordovician conodonts from the type section, used to define the age of what had been interpreted to be upper Potsdam strata, now fall entirely within the lower Beekmantown Group. Nepean (Potsdam) strata exposed in the type section remain undated. Regional correlation of the disconformity across the Laurentian platform suggests that Nepean strata at the type section are likely of Late Cambrian age. There now exists a regionally coherent separation of Cambrian and Ordovician sedimentation patterns in the Ottawa Embayment.

Reducing CO₂ emission from fossil fuels is crucial for the global aim of constraining greenhouse gas release into the atmosphere and the consequent adverse impact of the rising global temperature. One prominent approach for reducing the CO₂ influx concerns capturing and storing CO₂ in subterranean reservoirs. The properties of deep subsurface reservoirs that are appropriate for storing gasses require extensive scrutiny, including (i) the assessment of their reservoir characteristics, (ii) examinations of the nature of the caprock, and (iii) continuous monitoring of the movement of injected gas plumes. The sedimentary strata of Saskatchewan contains a number of reservoirs that are potentially good for Carbon Capture and Storage (CCS). The Late Ordovician Winnipeg Formation in Southern Saskatchewan constitutes a lower highly porous sandstone unit of the Black Island Member. Volumetric calculations of the Storage Space Capacity Potential of the sandstone indicate a subterraneous 974 km³ pore space. The porous sandstone unit is capped by a shale unit (Icebox Member). Thus, juxtaposition of these two lithologies makes the formation an excellent candidate for CCS.