The North American segment of the Circum-Pacific east of the Aleutian Trench is distinguished from adjoining segments by the absence of an oceanic trench and the lack of recorded seismicity with focal depths exceeding 70 km. The continental margin seaward of the North American cordillera incorporates a series of irregularly distributed sedimentary basins of late Mesozoic and Cenozoic age. The structural development of these basins was determined by progressive, episodic subsidence accompanied by interbasin uplift.

The tectonic history, structural style, and distributions of the basins demonstrate the presence of a composite system of mobile vertical stress fields which has endured over the past 140 m.y. A superimposed horizontal stress field of uncertain duration is expressed tectonically by strike-slip faults and related structures. These data are incompatible with hypotheses of overriding lithospheric plates and their corollaries as currently proposed.

Basin development was initiated in late Mesozoic time, with the differentiation of the continental shelf into discrete basins of localized subsidence. Progressive deepening, migration, and reorientation of the basin axes, and local reversals of vertical movement combined to produce the present composite basins. Commonly structural relief of 20-30 km is developed on the steeper flanks and most basins contain sedimentary thicknesses in excess of 10 km. Internal structures, including basin-margin compressional features, reflect the dominant vertical stress system. Second-order drag folds are well developed in association with strike-slip fault systems.

The primary vertical tectonic forces which created these basins are still active, as evidenced by earthquake, geodetic, and geomorphic data.

A total of 21 billion bbl of oil and 37 trillion cu ft of gas has been discovered in seven of the 36 basins described. A practical understanding of the structural style and framework of these prime target areas is critical to the realization of the energy potential of the relatively untested basins of this province.

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