Abstract: Using Brining Cycles as a Guide to Hydrocarbon Exploration in the Wolfcampian Council Grove and Admire Groups (Permian), Alliance Basin, Nebraska

Steven M. Goolsby, Mathew D. Goolsby

Significant Paleozoic hydrocarbon resources have recently been identified in the Alliance basin of the Nebraska Panhandle. Several fields are now producing from the Wolfcampian Council Grove and Admire groups in this evolving play. The recognition of repetitive brining cycles in these stratigraphic units can aid in the exploration for productive hydrocarbon reservoirs. Each brining cycle represents a sedimentary sequence in which the Alliance basin fluctuated between restricted and open marine conditions with deposition controlled by variations in water salinity. The repetitiveness and symmetry of the brining cycles is strong evidence for glacioeustatic sea level changes during deposition of these sequences.

The base of an ideal carbonate cycle begins with a sharp irregular contact representing a flooding event over a subareal desiccation surface. Algal dolostones and thin, black, anoxic shales deposited under hypersaline conditions normally overly this surface. Open-marine carbonate shoaling cycles typically occur next in the sequence. A return to hypersaline conditions is then signaled by the advent of algal-laminated facies, and ultimately by subaqueous evaporite deposition. Thus, each onlap sequence is a symmetrical brining cycle created by deposition under successive subareal, hypersaline, open marine, hypersaline, and subareal conditions. Siliciclastic cycles develop where sand was blown into the area during subareal exposure and subsequently reworked by marine processes. Although s me production has been established in the algal-dominated hypersaline facies, superior pore systems are developed in facies deposited when wave energy was highest, or during the sea level highstands.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994