Fluid inclusion homogenization temperatures (Th) of dolomite cements from the Manetoe Dolomite exhibit a close correspondence to their delta(18)O values if these dolomites precipitated from residual Devonian seawater brines (delta(18)O -2.0 to +5.0 per mil) at shallow depths. Pressure corrections, which must be applied to these temperatures if dolomite cementation occurred during deeper Late Cretaceous to Tertiary burial, and the lower delta(18)O values of subsurface fluids during this time period result in non-correspondence between the corrected fluid inclusion paleotemperatures and those calculated directly from the delta(18)O values of dolomite cements. Solid pyrobitumen in the centres of vugs lined with dolomite cement attests to the former presence of oil. Burial maturation models, based upon comparisons with vitrinite reflectance data, indicate that oil maturation and migration into Manetoe Dolomite reservoirs occurred during Carboniferous time. These data comparisons, models and observations all indicate that emplacement of the Manetoe Dolomite occurred during Late Devonian to Carboniferous time rather than during Late Cretaceous to Tertiary time. The close geographic and stratigraphic relationship between the Manetoe and Presqu＇ile dolomites, and their geochemical similarities implies that the Presqu＇ile Dolomite also formed in Late Devonian to Carboniferous time. Lateral facies equivalence between basal Besa River shales and upper Nahanni beds in the subsurface south of 61 degrees N latitude facilitated efficient migration of hydrocarbons into Manetoe reservoirs in places where Manetoe Dolomite is in direct contact with Besa River shale. Farther north where the Nahanni-Besa River contact is planar and isochronous, lateral migration of hyydrocarbons into Manetoe reservoirs was not possible.