Jack Conklin, Clyde Moore
The Lower Cretaceous Cupido Limestone (late Neocomian to early Aptian) was deposited during the general Mesozoic transgression of a warm, clear-water, epeiric seaway over northeastern Mexico.
The development of the massive Cupido carbonate platform, with the Coahuila Peninsula acting as a nucleus, was primarily the result of the sudden proliferation of rudistid bivalves in the Early Cretaceous. Rudists, mostly requinids and caprinids, together with dendroid corals, red algae, and stromatoporoids constructed ecologic reefs in the higher energy zone as waves touched bottom along a shallow carbonate ramp formed by the underlying Taraises Formation. The reefs trapped bioclastic debris and baffled the wave energy to produce lower energy back-reef environments. The accumulation of carbonate material in the reef complex kept up with basinal subsidence and sea-level rise, and in approximately 9 m.y. formed a platform with a shelf margin of considerable submarine topographic relief
The vertical sequence of lithologies found at several localities indicate localized regression of the sea as the reef and its laterally coexisting environmental facies prograded over basinal carbonate muds.
Six laterally coexisting facies commonly are found in a vertical measured section. They are: (6) lagoon, restricted lagoon, and sabkha facies; (5) near-reef tidal flat facies; (4) near-reef shoal facies; (3) organic reef facies; (2) fore-reef slope talus facies; and (1) basinal facies.
AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas