The Magdalen Basin, in the Cabot Strait-Bay St. George area, was a major depocenter for Devonian-Carboniferous sediments in eastern Canada. Structure within the basin is complex and is characterized by northeast- and east-trending, mainly dextral strike-slip faults associated with the bend in the Appalachian orogenic belt known as the St. Lawrence Promontory. Under the Cabot Strait two linear grabens parallel the major fault trends and preserve up to 6 km of Devonian-Carboniferous sedimentary rocks, comprising mainly coarse-grained terrigenous clastics with a Lower Carboniferous transgressive episode recorded by marine carbonates, evaporites, and fine-grained clastics. Several unconformities within the sedimentary succession record deformation associated with movement alo g the regional strike-slip faults. Minor local unconformities are interpreted within the upper Horton (early Visean), upper Barachois (late Westphalian), and post-Pennsylvanian successions. A major unconformity cuts out most of the Namurian and Westphalian section in the study area and can be correlated on a regional scale.

Kinematic strain partitioning along the master Cabot fault led to the development of doubly vergent compressional structures within a wrench borderland. This was complicated by transpressive deformation at a restraining bend in the master fault, and by deformation associated with overstepped ends of splays of the regional fault system. The Magdalen Basin probably formed in an early phase of post-Acadian extension, and was later reactivated by regional strike-slip faults.

The presence of thick source and reservoir rocks, as well as diverse trapping possibilities and a favorable burial and maturation history, indicate that the Cabot Strait area has good potential for accumulating and preserving petroleum.