PALEOGEOGRAPHY AND SEDIMENT SUPPLY ON THE SCOTIAN MARGIN IN THE UPPER CRETACEOUS AND CENOZOIC -- IMPLICATIONS FOR HYDROCARBON PROSPECTS

The Upper Cretaceous and Tertiary sediments of the Scotian Margin form a seaward-thickening wedge over 2 km thick at the shelf edge. Although only sub-economic gas reservoirs have been discovered in this interval on the shelf, greater economic potential exists in the area of thickest accumulation on the continental slope where extensive salt deformation has created attractive structures. Knowledge of sediment supply and loading on the slope in this interval will be crucial to understanding the history of hydrocarbon charge, salt mobility, and timing of structural trap formation.

A major uncertainty in models of slope hydrocarbon distribution is the occurrence of reservoir rocks, particularly the distribution of sands. A sequence stratigraphic interpretation of the Upper Cretaceous to Cenozoic interval on the shelf reveals the timing and distribution of major deltaic depositional lobes with respect to the shelf edge and canyon incisions. At various times, the paleo-shelf edge of some parts of the margin were sediment starved, while others had significant, probably deltaic, foresets building close to the paleo-shelf edge. Wells on the shelf reveal the presence of thick (up to 100 m) sandstone units within the topsets of these units, and it can be inferred that outboard of these locations, there is greater potential for reservoir sands on the slope. Through time, the major depositional lobes on the Scotian Margin alternated in position so that, depending upon the level examined, reservoir potential at a location can vary stratigraphically from good to poor. The occurrence of widespread, draping shales and chalks, usually associated with maximum flooding surfaces, may act as seals for reservoirs of this interval, and they also serve as important markers for regional correlation from shelf to slope.