--> Paleogeography and Facies Relations of the Middle Cretaceous Coahuila Carbonate Platform, Northeastern Mexico, by C. Lehmann, D. A. Osleger, and I. P. Montanez; #90986 (1994).

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Abstract: Paleogeography and Facies Relations of the Middle Cretaceous Coahuila Carbonate Platform, Northeastern Mexico

Christoph Lehmann, D. A. Osleger, I. P. Montanez

The paleogeography and facies relations of the middle Cretaceous (Albian) Coahuila carbonate platform in northeastern Mexico have been refined by decimeter-scale logging of 25 sections (totaling >10,000 m) spread out across the 60,000 sq km study area. The evaporites and carbonates under investigation (Acatita-Aurora-upper Tamaulipas Formations) are a well-constrained genetic unit, being bounded below (La Pena Formation) and above (Cuesta de Cura Formation) by deep-water shales and limestones representing globally correlated drowning events.

The Coahuila platform is composed of three major paleogeographic elements. (1) Mixed evaporites and carbonates (Acatita-upper Aurora formations) are centered on top of the basement core of the platform to the north-northwest. Intercalated beds of bioturbated dolomite and massive gypsum are interpreted to have been deposited in a restricted lagoon. Skeletal grainstones overlie the evaporitic facies and mark a return to normal marine conditions, perhaps related to incipient flooding associated with a global late Albian-early Cenomanian rise in sea level. (2) Massively-bedded grainstones and caprinid rudist packstones (Aurora Formation) exhibit progradational geometries and form a barrier shoal that protected and restricted the interior lagoon. Peritidal cycles overlie the massive grains ones and may have developed in the lee of the shoals; stacking patterns within the cycles appear to record several apparent changes in accommodation. (3) Homogeneous, massive lime mudstones and laminated calciturbidites (Upper Tamaulipas Formation) are significantly thinner than equivalent shallow-platform deposits and represent slow accumulation in deep-water settings. Some sections exhibit interbeds of contorted mudstone and intraclast wackestone that may represent slope deposition off the edge of a distally steepened ramp.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994