Late Paleozoic Yuma Arch, Colorado and Nebraska: Implications for Oil Exploration in Pennsylvanian Carbonate Reservoirs

Abstract

The Yuma Arch is herein proposed as a major structural element forming the northeast margin of the Denver Basin. This previously little-recognized regional geological feature has significance in exploration for oil in this area of the basin. It was initially uplifted during the Paleozoic, but is largely masked by late Cretaceous - early Tertiary tectonic events. Limited pre-Cretaceous exploration drilling has not defined the precise location of the axis of the arch, but subsurface studies show that it occupies most of Yuma, Sedgwick and Phillips counties, Colorado, and Deuel County, Nebraska. The immediate west flank of the arch lies in parts of Washington and Logan counties, Colorado, and most significantly in Cheyenne County, Nebraska, where initial Paleozoic exploration has been focused around the discovery of Bird Oil Field in 1982, a small but unique, over-full, domal trap. Preservation of several cores from Pennsylvanian boreholes in Cheyenne County, Nebraska, facilitated study of cyclical Missourian-Virgilian carbonate reservoirs that provide significant future potential objectives for exploration on the underexplored arch. These cores also provided key biostratigraphic data that helped to clarify the correlation of classical Pennsylvanian strata. Studies of Paleozoic source rocks and migration pathways were conducted over the central and northeastern Denver Basin. These studies indicate that the immediate west flank and the crest of the Yuma Arch provide a significant regional catchment for oil in Paleozoic strata, and should be a target for future exploration. Processing and interpretation of aeromagnetic data provided a means to characterize the Precambrian crystalline core of the arch, and to define areas for seismic imaging of mobile basement block margins that appear to have initiated and sustained the growth of low-relief Paleozoic structural traps. This study reinforces the significant decoupling between pre-salt (Precambrian and Pennsylvanian) and post-salt (Cretaceous and Tertiary) geological processes in this area.