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The Zuloaga Formation at Sierra de Enfrente may be divided into 7 interbedded carbonate facies. In order of abundance, they are: pell-ooid grainstone-packstone, lime mudstone, pelletal packstone-grainstone, ooid grainstone, pelletal wackestone, skeletal wackestone, and algal boundstone.
Three measured sections located on an east-west trending, overturned anticline (Sierra de Enfrente) were described and sampled. The sections are oriented along depositional strike and are roughly 395 m (1,300 ft) thick. Approximately 20 shoaling-upward "cycles" that display an upsection trend from mudstone-wackestone lithofacies to packstone-grainstone-boundstone lithofacies are readily distinguished in each section. The cycles vary in thickness with thick cycles correlating well from section to section along depositional strike. Within any cycle, interpreted subenvironments may include, from base to top: subtidal, outer shoal, inner shoal, and inter-tidal-supratidal.
The Zuloaga Formation sediments were deposited on a broad carbonate ramp dipping southward off the emergent Coahuila peninsula. The study area is located between Zuloaga-equivalent, near-shore, siliciclastic deposits to the north and outer-ramp Zuloaga lime mudstone facies to the south. This intermediate position was ideally situated for the development of high-energy shoals. Time-equivalent shoal facies that rim the Gulf of Mexico are prolific hydrocarbon producers (Smackover Formation, USA; San Andres Formation, Mexico).
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