The continental shelf of eastern Canada extends from the Gulf of Maine to the head of Baffin Bay in the Northwest Territories, a distance of 3,500 mi (5,600 km). On the mainland the oldest outcrops are Proterozoic (Kenoran-Grenville), present on the Labrador coast and Baffin Island. The Atlantic Provinces occupy the northern part of the Appalachian System, a belt of folded and unfolded middle and lower Paleozoic sedimentary rocks subjected to the Taconic and Acadian orogenies. Late Paleozoic (Hercynian) faulting and folding along the Fundy geosyncline resulted in deposition of Mississippian continental and marine sediments in intermontane troughs, overlain by flat-lying late Pennsylvanian and Permian clastic sediments. Triassic rocks are restricted to a rift zone extendin from the Bay of Fundy to Chedabucto Bay. On the continental shelf and slope, the total rock section overlying a granitic or metamorphic basement, as calculated from seismic refraction, magnetics, and estimates from wells, reaches a maximum of more than 20,000 ft (6 km), consisting mainly of coastal-plain sediment, Jurassic to Tertiary in age. Triassic and late Paleozoic deposits may be represented in troughs on the inner shelf. In the central and southern part of the Gulf of St. Lawrence sediments reach a maximum thickness of 25,000 ft (7.6 km), probably Permian-Carboniferous to Triassic in age. In the Bay of Fundy, a thick Triassic and Carboniferous section is predicted from onshore geology and from seismic profiler.

The total thickness of sediments on the Labrador shelf, on the basis of magnetics and refraction data, is more than 20,000 ft (6 km) with compressional velocities consistent with the coastal-plain sediments on the south. On the Baffin shelf a total thickness of sediments of more than 30,000 ft (9 km) has been inferred from magnetics and from surface outcrops. Extrapolation from the south suggests the presence of rocks of Jurassic, Cretaceous, and Tertiary ages.

Seismic refraction profiles display five velocity layers which can be correlated roughly throughout most of the area south of lat. 56°N: Layer 1: 5,900-7,200 ft/sec (1.8-2.2 km/sec); Layer 2: 7,300-11,200 ft/sec (2.2-3.4 km/sec); Layer 3: 10,500-14,800 ft/sec (3.2-4.5 km/sec); Layer 4: 14,100-18,400 ft/sec (4.3-5.6 km/sec); Layer 5: 15,500-20,800 ft/sec (4.7-6.3 km/sec). An approximate correlation of the layers is made, respectively, with Tertiary, Upper Cretaceous, Lower Cretaceous-Triassic, Carboniferous-Permian, and "basement." The distribution of the deeper refraction layers suggests a fragmentation of the underlying basement in post-Carboniferous time.

Oil shows and seepages have been reported in each of the Atlantic provinces; the only commercial oil and gas production is from the Mississippian fluvio-lacustrine beds in the Stony Creek field of New Brunswick. Many of the offshore wells drilled since 1969 had shows of oil and gas, or reserves of oil and gas indicated from mechanical-log interpretation. On the Scotian shelf, one well, Mobil-Tetco Sable Island E-48, is an indicated gas and oil discovery from 17 separate zones in the Cretaceous. Shell Primrose N-50 flowed a total of 36 million cu ft/day natural gas from the three zones, and 300 bbl/day oil from another zone.