The major negative element of the North Slope has been called the Colville geosyncline, the Colville trough, the Colville foredeep, or the Colville basin, whereas the positive element coupled to the north has been universally called the Barrow arch. The name "Colville basin" is most consistent with the apparently compound nature of this foreland successor element. We also recommend that "Barrow inflection" be substituted for "Barrow arch" as the name for the positive element or structural hinge that formed between middle Cretaceous deposits in the basin and those along the continental margin. The term "inflection" aptly describes the weak reversals in regional dip that mark this feature, and constrains the sense of either active uplift or a preexisting high, which has evo ved with current usage of "arch".

The markedly asymmetric Colville basin consists of: deformed and thickened middle Cretaceous flyschoid deposits lying on earlier Cretaceous allochthons of the ancestral Brooks Range; a greater than 10-km thick belt of deposits that is incoherent on seismic records but is floored by poor reflectors, presumably of earliest Cretaceous and older age; and a foreland flank that slopes gently from within a kilometer of the surface at Point Barrow, about 200 km to the north. Seismic profiles show this flank to have been an abyssallike plain after Barrovia, the northern provenance of Ellesmerian deposition, had been replaced by the Arctic Ocean early in Cretaceous time. The flank was more than 1 km deep and stretched broadly southward from the new continental edge that now seems to be nearly 3 km north-northeast of Barrow. The plain was progressively loaded and depressed, first by the downlapped distal edge of the flysch prism in the south and then by the shelf of molassoid deposits that prograded from the Brookian orogen during the middle Cretaceous.

The Barrow inflection denotes reversals in regional dips from less than 2° to the south to approximately 1° to the north. The axes of reversals subparallel the present coastline between Barrow and the Arctic National Wildlife Refuge and plunge eastward at a rate of approximately 1 km/100 km. Inflections on successive stratigraphic horizons do not stack vertically as in parallel folds; dip reversals in the lowest Brookian strata, for example, occur several kilometers south of the inflection on the basement surface. The structure appears to have formed as the prograding middle Cretaceous deposits (Nanushuk Group) made the foundation for the present continental terrace; subsidence of the continental margin beneath that load reversed dips along the former north edge of the Colvi le basin. Minor and relatively passive upward bowing likely occurred along this hinge between the negative (depressed) elements. The Barrow positive feature clearly is an arch neither in the sense of a broad anticlinal fold nor in the sense of a high such as the Cincinnati arch. It had no north flank before the Late Cretaceous, and it could not have been an element of pre-Brookian (Ellesmerian) geology.

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