Microfacies analysis and paleoenvironmental dynamic of the Barremian-Albian interval in Sierra del Rosario, eastern Durango state, Mexico
The detailed microfacies analysis on a stratigraphic section located in eastern Durango contribute to the paleoenvironmental and paleogeographic understanding of the Cupido and Coahuila carbonate platforms in the southern part of the Coahuila basement block, a poorly investigated area. The stratigraphic section herein studied spans the Barremian-Albian interval and is composed of the upper Cupido, La Peña and Upper Tamaulipas formations. The recognition of this latter unit in the eastern part of the Durango state is a significant contribution to the stratigraphic scheme of the southern part of the Sierra del Rosario.
The studied interval of the Cupido Formation is represented by different microfacies associations: 1) peritidal and subtidal facies deposited in a shallow lagoon. In these facies, an important microbial contribution and high energy events are recognized; 2) sand bars facies accumulated on the platform margin. Interaction of these facies with sea level fluctuations caused different levels of restriction and periodic flooding in the platform interior; 3) platform margin and fore-reef facies. The microfacies associations of the La Peña Formation were deposited on the periplatform zone in an outer neritic to upper bathyal environment. The microfacies associations of the upper part of the La Peña Formation and those belonging to the Upper Tamaulipas Formation are typical of open marine and relatively deep-water conditions.
The microfacies have been divided according to their relation with the different phases of the Cupido Platform drowning. The definitive drowning phase began in the early Aptian when the sea level rose over the sand shoals on the platform margin. An increase in the crinoid content and a mixture of lagoonal and open marine biota are characteristics of the drowning phase at the end of the Cupido Formation deposition. The microfacies associations within the lower part of the La Peña Formation recorded the definitive drowning of the platform and an environmental stress that accentuated this event. Post-drowning facies in the upper part of the La Peña Formation and throughout the Upper Tamaulipas Formation are represented by pelagic facies deposited in an open marine environment with significant oxygen variations in the water-sediment interface. The sand shoals facies described in the Cupido Formation correspond to the western continuation of the Barremian-Aptian Cupido Platform margin.