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Abstract

The present Atlantic passive margin of North America has been the site of recurrent plate activity over the course of geologic time. Different tectonic styles were superimposed over previously deformed basement rocks, so that today's margin is a collage of ancient converging, diverging, and strike slip plate boundaries. Tectonic suturing towards the middle and close of the Paleozoic Era produced a vast continental landmass extending from the Appalachians eastward through the Mauretanides and Hercynides (Arthaud and Matte, 1977; Ziegler, 1982).

As the Late Triassic land mass drifted north, perhaps over a field of hotspots (Morgan, 1980) or across a tensional stress field (Bedard, 1985), its crust was pulled apart along older fracture zones, sutures, and transforms. The landscape was marked by high-standing coastal ranges with synrift depositional basins that bordered a narrow band of salt flats, which were overlain by shallow, hypersaline waters derived from the Tethys Ocean to the east and/or from arctic Canada to the north (Fig. 1). Continued displacement along east-west trending transforms, coupled with extension along the proto-Atlantic axis, finally broke the narrow platform into multiple basins (e.g., Georges Bank and the Baltimore Canyon Trough) near the end of the Triassic and beginning of the Jurassic, thus bringing to a close the early rifting stage of the passive margins. Intermittent episodes of rifting and drifting followed into the Early Jurassic. Since the Middle Jurassic, however, the U.S. margin has been dominated by regional subsidence (drifting stage), so that today the record of Triassic-Liassic rifting is buried under a vast prism of postrift or drift sediment.

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