GeoDigital Information's Regional Frontier Study in the northern Rocky Mountain basins is designed to enhance exploration efforts that are directed at Frontier and equivalent reservoirs. These reservoirs occur within a variety of sandstone depositional sequences at multiple stratigraphic horizons. GDI has created an extensive stratigraphic reference framework that documents the regional trends of these reservoir-potential intervals.

     This Regional Frontier study affords explorationists significant time savings in assimilating data and developing exploration strategies. The study area covers all of Utah, Wyoming exclusive of the northernmost part of the Denver Basin, most of Montana, southeastern Idaho, and part of northwestern Colorado.

     In this report, the Frontier and equivalent strata are subdivided into mappable, chronostratigraphic members, which are bounded by bentonite beds, disconformities, or unconformities. This chronostratigraphic methodology facilitated mapping of time-bounded lithofacies sequences and reconstruction of paleogeography through time. Physical correlations indicate there are regionally significant unconformities within the

Frontier Formation. In addition to the unconformities, the Frontier includes numerous disconformities. These most commonly occur at the tops of upward-coarsening sequences and record post-depositional erosion associated with transgression. In many instances, the amount of erosion associated with these disconformities was slight. In other cases, particularly in areas underlain by active basement structures, the amount of erosion was substantial. Reworking of sediment on these transgressive disconformities is responsible for the formation of some of the principle reservoir sandstones.

     The Frontier play consists of three principal reservoir sandstone types. The origins and distributions of these sandstone types are portrayed within the context of the complicated transgressive-regressive history of the Frontier. The analysis of the stratigraphic and sedimentologic characteristics in this report will assist exploration geologists in understanding the complex stratigraphic relationships, reservoir sandstone geometries, and hydrocarbon production within the Frontier play trend. The study discusses the potential for Frontier reservoirs throughout the northern Rocky Mountain region.