Jurassic deep-water reservoirs at a transfer-transform offset: Modeling the mixed carbonate-siliciclastic Shelburne subbasin, southeastern Canadian margin

Abstract

The Mesozoic–Cenozoic Scotian Basin terminates southwestward at the Yarmouth transfer fault zone. That part of the basin, the western Shelburne subbasin, shows a different geological evolution from the main Scotian Basin. It is the most prospective part of the basin for oil, but it remains underexplored. This study investigates the role of the transfer fault zone in sediment dispersion and deep-water clastic reservoir location by using forward stratigraphic modeling. DionisosFlowTM software was used to simulate the distribution of Callovian–Tithonian (Jurassic) clastic and carbonate strata. Sensitivity to the uncertain parameters in the model was analyzed with CougarFlowTM software. The Yarmouth transfer fault zone created ramps and topographic lows in the basin, which influenced sediment distribution and also focused long-distance river supply at the Shelburne delta. In the Late Jurassic, humid climate led to high sediment discharge, resulting in clastic progradation even during times of rising sea levels and widespread carbonate accumulation. Away from the delta, modeling suggests that deeper initial bathymetry accounts for the observed stable shelf-edge reef growth better than a shallower ramp bathymetry. Sensitivity analysis indicates that clastic sediments from the Shelburne delta prograded into deep water, even if water discharge and sand diffusion coefficients were low. Where the upper slope was steep, it was bypassed by sandy sediment that accumulated in basin-floor fans, predicted by modeling and confirmed by seismic interpretation of a channel-levee system in small areas undisturbed by salt tectonics. Forward stratigraphic modeling is thus an important tool for understanding petroleum geology in such underexplored areas.