The facies succession of shelf carbonates in the upper Yates and lower Tansill formations shows a complex progression of environmental conditions across the shelf through time. An interval approximately 50 m thick centered about the easily recognizable contact between the Yates and Tansill formations was studied in an outcrop belt 3.5 km wide and 11 km long parallel to, and 1 to 8.5 km shelfward of, the Capitan Limestone (Walnut Canyon, New Mexico). The stratigraphic interval includes three major outcrop-defined carbonate units; in ascending order, the Hairpin Dolomite (Yates Formation), Triplet Dolomite (Yates Formation), and Basal Tansill Dolomite (Fig. 1), which have been subdivided into eight fabric-specific facies (Neese and Schwartz, 1977).

The geological literature of the Guadalupian shelf is extensive; King (1948), Newell et al. (1953), and Hayes (1964) concentrated primarily on broad stratigraphic relationships, lithologic features, and biota of shelf sediments and their reef and basinal equivalents. More genetic sedimentologic considerations of the Guadalupian shelf strata and their environments have been presented by Dunham (1972), Smith (1974), Pray and Esteban (1977), Neese (1979), Sarg and Lehmann (1986), and Tye (1986). The focus of this study is on the facies relationships of the grainstone and packstone facies of Dunham (1972) and Smith (1974).