Shelf carbonate mounds of Desmoinesian (Pennsylvanian) age were developed in cyclic repetition along the southwestern flank of the Paradox basin. Optimum carbonate deposition occurred in an elongate northwest-southeast belt, approximately 50 miles wide and over 100 miles long, which contains about 35 Pennsylvanian oil and gas fields. Porosity occurs in three types of carbonate reservoirs: algal plate mounds, foraminiferal mounds or bioherms, and "leached oolite" banks. Most of the production is from limestone, but dolomite also is important as a reservoir rock.

Stratigraphic-facies mapping of the mound-bearing strata can be done on the basis of basin-wide, black, sapropelic shale marker beds, in conjunction with lithologic-petrographic analysis of rock types and associated faunal content. Shelf carbonate rocks occur in each main cycle of the Paradox Formation, grading basinward into evaporite and shoreward into sandy limestone and terrigenous clastic rocks.

The origin, distribution, and cyclic repetition of the carbonate-mound belts are thought to be related to periodic eustatic changes in sea-level associated with late Paleozoic glacial cycles of the Southern Hemisphere. The mounds probably developed along shallow-water mud banks or platforms which built basinward during the early clastic phase of each cycle. Completeness and duration of a cycle were major factors in determining the size attained by the mound complex.

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