This Chapter is included in the publication “The Sedimentary Basins of the United States and

Canada, 1st Edition” by Andrew D. Miall published by Elsevier Science in 2008.

Chapter 14

The Atlantic Margin Basins of North America

ANDREW D. MIALL, HUGH BALKWILL and JOCK McCRACKEN

ABSTRACT

The Atlantic margin of North America represents the classic “Atlantic-type” continental margin,

notably the margin off the east coast of the United States, which was the site of five deep

offshore stratigraphic test holes wells (the Continental Offshore Stratigraphic Test, or COST

series) drilled in 1976-1979 on the Georges Bank, the Baltimore Canyon Trough, and the

Southeast Georgia Embayment. Data from these holes were used in the development of what

have become standard backstripping methods and subsidence models for extensional

continental margins.

Development of the margin began with the initial rifting of Pangea in the Triassic. Sea-floor

spreading began in the central Atlantic Ocean during the early Middle Jurassic, and extended

northward past Newfoundland beginning in the Late Jurassic. Active sea-floor spreading

generated the Labrador Sea and Baffin Bay between the Cenomanian and the end of the

Oligocene.

The thickness of Jurassic-Recent sedimentary deposits on the continental margin locally reaches

25 km. Transects across the margin show a series of largely nonmarine rift basins, capped by a

breakup unconformity, above which is a seaward-thickening wedge of prograding shallow- to

deep-water marine deposits. Evaporites are widespread at the base of this section from the

Grand Banks to the Bahamas. Carbonates dominate the remaining deposits in the south,

notably in the Bahamas area, but as the North American continent drifted northwestward

through the Mesozoic, carbonate sedimentation gradually became less important in more

northerly parts of the continental margin. On Georges Bank, carbonate sedimentation ended in

the mid-Cretaceous, whereas on the Grand Banks it had essentially come to an end by the close

of the Jurassic. Shallow-marine and deltaic clastics comprise much the remaining succession

throughout the length of the Atlantic margin.

The continental margin developed by the processes of crustal thinning and crustal detachment.

Parts of the continental margin constitute an upper-plate margin, and parts a lower plate

margin. The Grand Banks area was affected by two distinct phases of rifting and flexural

subsidence as extension occurred in the central Atlantic, to the south, from Late Triassic to

Early Jurassic, and in the North Atlantic, to the northeast of the bank, from Late Jurassic to mid-

Cretaceous.

The discovery of major petroleum resources beneath the Grand Banks in 1979 led to extensive

seismic and offshore exploration work there, and additional oil and gas resources have been

discovered and developed. Gas reserves have been developed off Nova Scotia, and

undeveloped gas reserves are located on the Labrador shelf, but no commercial discoveries

have been made in the U.S. portion of the Atlantic margin.