Based on seismic analysis in conjunction with well control, 10 time-stratigraphic sequences and sub-sequences are mapped in Phanerozoic strata of the northern Williston basin. Seven additional time-unit subdivisions are distinguished in the upper-most Cretaceous. These sequences, sub-sequences, and units, and their unconformities, reveal that the northern Williston basin experienced three developmental episodes: initial subsidence during the time of deposition of the Sauk sequence (540–505 Ma); stability during the time of deposition of the Tippecanoe to Upper Colorado sequences (480–84 Ma); and deformation since the time of deposition of the Montana sequence (post-66 Ma). The seismic unconformities indicate nine subsidence events separated by five major erosional periods. All the major erosional cycles are consequences of periodic and incongruent uplift and tilting of the western and eastern flanks of the basin relative to its centre.

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