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Abstract

Vail's coastal onlap curves conventionally have been attributed to glacio-eustatic sea-level variations, but they show a better correlation with tectonic events. The tectonic and structural evolution of the Canadian Atlantic continental margin is recorded in the history of extensional subsidence of the Mesozoic basins underlying the Grand Banks and the Scotian Shelf. Large-scale unconformity-bounded sequences match the major basin-forming stages representing rift and postrift subsidence. Smaller scale local unconformities and regional limestone markers reflect adjustments to intermittent subsidence. This tectono-stratigraphic record, the timing and patterns of sea-floor spreading, and Vail's coastal onlap curves correspond closely, suggesting broad-scale tectonic linkage. Intermittent phases of accumulated tensional stresses that are associated with the rift episodes and subsequent rapid relaxation of these stresses may explain asymmetry in the relative onlap charts. Both the timing and nature of Vail's second-order and third-order cycles appear to be controlled by plate-tectonic evolution and the associated changes in the intraplate stress regimes of the central North Atlantic. The correspondence between Vail's cycles and the tectono-stratigraphic anomalies on the Grand Banks and offshore Nova Scotia suggests intraplate stress as the common cause.

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