Highlights—The Bottom Drops Out in Mexico

Although potential central to understanding the evolution of both the southern part of North American Cordillera and the opening of the Gulf of Mexico, Early Cretaceous strata of Mexico have remained enigmatic. To better understand tectonic and stratigraphic evolution in this area, Sierra-Rojas and co-authors describe Lower Cretaceous strata of the Tentzo basin of southwestern Mexico. Integrating outcrop observations, petrography, and detrital-zircon geochronology, the study reveals a thick succession of red beds (conglomerate, sandstone, siltstone) overlain by carbonates, collectively interpreted to represent alluvial, lacustrine, fluvial, tidal, and marine environments. The thick succession, characterized by rapid accumulation (3.6 mm/yr), is interpreted to represent a backarc basin in an extensional setting on the paleo-western margin of Mexico, but that in time became part of the broad, stable platform facing the Gulf of Mexico. The results suggest that these basins in southwestern Mexico are more closely related to a Pacific volcanic arc, and are not related directly to the opening of the Gulf of Mexico, helping to constrain tectonodynamics.

The Lower Cretaceous Atzompa Formation in south-central Mexico: record of evolution from extensional backarc basin margin to carbonate platform by María I. Sierra-Rojas, Roberto S. Molina-Garza, and Timothy F. Lawton