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Abstract

The Cretaceous to Eocene sedimentary-volcanic sequence of the Disko Island area and southern Baffin Island indicates that the opening of Baffin Bay, which resulted when Greenland and North America drifted apart, involved the following historical sequence: (1) the presence of a land-locked rift valley filled with terrestrial deposits—Barremian to Turonian; (2) widening of the valley and occurrence of intermittent marine connections, plus the first volcanic activity—late Turonian to Danian; restricted bottom circulation with deposition of bituminous shales—Santonian through Danian; (3) deepening of the rift, opening of magma chambers, and effusion of basaltic lavas—Paleocene and Eocene (limited to Davis Strait area); (4) widening and deepening of the rift valley to the present BcfTin Bay and Davis Strait and deposition of a very thick, young sedimentary sequence in the deepest part of the graben. Baffin Bay shows no evidence of sea-floor spreading or of a mid-Baffin Bay ridge. In this respect, it appears similar to several other deep marine basins which are believed to be due to continental drift. Furthermore, the tectonic-depositional-volcanic histories of the Rhine Valley and East African rift systems closely parallel the first three stages of Baffin Bay's evolution. Rifting and continental drift apparently can occur independent of sea-floor spreading (which would be the last phase of the sequence). In Baffin Bay, the sedimentary units predate the volcanic deposits by about 50 m.y., which would not be the case if sea-floor spreading had created Baffin Bay; nor would the volcanic rocks be so limited in area. Sea-floor spreading in the Atlantic began only about 60 m.y. ago, long after the initial (Jurassic) phase of sedimentation.

Practical implications to the petroleum industry of considering rifting to be the primary cause of continental drift are that (1) the same sedimentary sequence is common to many coasts broken by drift—e.g., the oil provinces of western Africa; this sequence includes both source rocks and thick reservoir rocks; (2) the antithetically rotated fault blocks and crossfaults caused by rifting created suitable structural traps; (3) little danger of volatilization of hydrocarbons existed because volcanism started only at the end of the sequence; and (4) the central depression, representing the last stage of rift widening, was filled with thick clastic sediments without hydrocarbon source beds.

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