STRATIGRAPHY OF A MESOZOIC PLATFORM-BASIN MARGIN, SIERRA MOJADA, WESTERN COAHUILA, MEXICO

The stratigraphy of Sierra Mojada offers new insights into the evolution of carbonate platform systems that rimmed the ancestral Gulf of Mexico throughout the Early Cretaceous. Sierra Mojada is situated along the northeastern margin of the Coahuila Block and the northwestern trace of the San Marcos Fault Zone. The Coahuila Block is a regional uplift of Paleozoic to Triassic rocks. The San Marcos Fault originated during the Jurassic in response to the opening of the ancestral Gulf and serves as the boundary between the Coahuila Block and the Sabinas Basin. Close-spaced cores drilled for mineral exploration in the Sierra Mojada district allows the detailed stratigraphic analysis of the late Mesozoic platform margin. The paleogeography imposed by these regional elements governed depositional patterns and carbonate platform morphology throughout the Late Jurassic and Early Cretaceous. The Cupido carbonate system filled the Sabinas Basin with shallow water carbonates during the Barremian and Aptian. The Coahuila Block was exposed at this time. A major second order transgression during the Aptian marks the end of the Cupido platform and the beginning of the Aurora platform. During the Albian, carbonates were restricted to the topographically elevated Coahuila Block, with Sierra Mojada situated at the Coahuila Block margin. Sierra Mojada strata record the evolution of the most-proximal Cupido platform and subsequent inundation. A transect of the Aurora platform is preserved at Sierra Mojada and the Albian strata record the recovery of carbonates and progradation of the Aurora platform margin.