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Structural Heritage and Salt Deposits Impact on the Sable Sub-basin Architecture

Abstract

The Central Scotian basin (Sable sub-basin) is a producing hydrocarbon region on the shelf, and remaining under-explored in the on the slope and the deep water. This passive margin results of a complex tectonic evolution since Proterozoic and the breakup of the Pangea at the end of Triassic. It follows the Central Atlantic opening with the rifting between Nova Scotia and Morocco. The Sable Sub-basin is a NE-SW rifted basin, bounded by the Mississauga Ridge to the North, the Shelburne Sub-basin to the SW and the Banquereau Synkinematic Wedge (BSW) to the NE. On the North, the shelf is disconnecting from the slope by the Alma and South Griffin Ridges. It is well known that the geological complexity of the study area is strongly impacted by the salt tectonic. Two salt layers could be distinguished: a basal autochthonous salt on top of which Jurassic series were faulted and tilted; an upper allochthonous salt layer, expelled from the North of the Sable sub-basin and creeping toward ocean driven by Cretaceous deltaic deposits loading. These two salt layers could be also connected and induced a Roho system active during Cretaceous. Based on the seismic lines interpretation and well data, three restored seismic cross-section has been done in the main tectonic domains: in the BSW, in the Sable Slope Canopy and in the Balvenie Roho System. It has been observed that tectonic architecture is mainly controlled by the salt tectonic and the structural heritage from rifting. The autochthonous salt basin is bounded to the south by the COB and its extension tends to decrease to the NE. Decreases in size of the salt basin coincides with changes in salt tectonic styles. The southwestern part shows a fishbones system with opposite tilted blocks of Jurassic and Cretaceous units. It formed a complex Roho system with autochthonous salt feeders and allocthonous salt tongues during Cretaceous times. In the central part, the autochtonous salt basin decrease and it is characterized by a deeply rooted growth fault system which induces vertical motion of salt (diapirs). In the northeastern part, the autochthonous salt doesn't exist oceanward. The salt creeps from the shelf part of the Sable sub-basin over the South Griffin Ridge and leads to the BSW formation during Jurassic times, where internal structure shows landward tilted blocks over a thin salt tonge. Contrasted evolution and structural style of each province has a direct impact on the hydrocarbon migration and entrapment.