ABSTRACT

The Jeanne d'Arc Basin off Newfoundland and the Kugmallit Trough in the southeastern Beaufort-MacKenzie Basin are two Canadian offshore basins where important hydrocarbon discoveries have been made. Thick successions of evaporite, carbonate and clastic rocks in the Jeanne d'Arc, and an exclusively clastic sequence in the Beaufort Sea, have been encountered in the wells drilled to date. The better known Jeanne d'Arc Basin was formed by extension along a deep crustal detachment during two successive Mesozoic rifting phases. The existence of this down-to-the-east 'Wernicke' detachment zone was first suggested by exploration data and later confirmed by deep seismic reflection profiles. A similar tectonic evolution is proposed for the Kugmallit Trough, an elongated northeast-southwest trench filled with Upper Cretaceous to Recent sediments. For this region, extension took place on a down-to-the-west crustal detachment and the rifting can be traced to mid-Miocene time.

In both basins, the rift-stage sediments are fragmented by two intersecting systems of extensional faults, one parallel and the other perpendicular to the basins' margins. As illustrated by several grids of modern three-dimensional seismic surveys, these faults are listric in any vertical section, and there is periodic growth associated with them. However, in plan view, they deviate significantly from the classical concave, "scoop" model of listric synsedimentary faults by being generally linear, sometimes convex and only rarely concave in shape. This implies that the faults are of tectonic, rather than depositional origin, even when they are formed in deltaic environments.

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