North Grand Banks Basin, offshore Newfoundland: a sedimentary epeiric basin west of the Murre-Mercury detachment fault

Abstract

The eastern Newfoundland offshore area is geologically the best known region of the northwestern Atlantic margin. Extensive geophysical coverage and about 140 exploratory and delineation wells have allowed structural and stratigraphic mapping of a Mesozoic rift basin network that includes the South Whale, Whale, Horseshoe, South Jeanne d'Arc, Carson-Bonnition, Jeanne d'Arc, Orphan and Flemish Pass Basins. A less explored basin, not yet targeted by the oil industry and accordingly less explored, has recently been discussed in the marine geoscience literature. Located on the Bonavista platform, west of the Jeanne d'Arc Basin bounding fault and defined here as the North Grand Banks Basin, this area has been described from refraction work correlated with deep seismic profiling (LITHOPROBE East) data as a possible Mesozoic rift basin with hydrocarbon potential, or as a Palaeozoic basin. Detected first by gravity measurements, but unconfirmed as a rift basin by reflection data, this basin is only 2 km deep and contains Palaeozoic and probably undeformed Mesozoic sedimentary infill. Its hydrocarbon potential is low. The Mesozoic sedimentary rocks, if present, are probably platform carbonates and clastics, formed during thermal subsidence episodes following the first two rifting stages that affected the Grand Banks of Newfoundland. The placement of the pre-rift unconformity within the sedimentary successions of the North Grand Banks Basin, and the precise nature of the rocks situated above the Avalon basement remain unresolved. A geodynamic model involving simple shear extension in the upper crust is used to explain the evolution of Newfoundland offshore sedimentary basins including the North Grand Banks. According to this model the basin is located on the upthrown side of the Murre-Mercury fault system that represents the upper crustal expression of a crustal penetrative detachment.