Late Cretaceous–Paleocene transition from calcareous platform to basinal deposition in western Chiapas, Mexico: Opening of the Chiapanecan embayment

ABSTRACT Tracing the evolution of the Cretaceous shelf margin of the southwestern Gulf of Mexico reveals a relatively stable area in northeastern Chiapas, Mexico, northern Guatemala and Belize, and the Yucatán Peninsula, where carbonate and evaporite platform conditions prevailed from the Aptian until at least the Paleocene. The area was flanked by zones of greater subsidence, where platform thickness reached several thousand meters and where foredeep depocenters were established due to collision of the Great Antilles arc with the passive margin of North America. Foredeep deposition initiated as early as the Maastrichtian in central Guatemala and in the Paleocene in Chiapas and south Petén, Guatemala. Northwestern Chiapas was characterized by a relatively deep basin and by southward retreat of the shelf break from the Albian to Maastrichtian. The retreat can be traced by the occurrence of periplatform slope facies. During the Santonian–early Campanian lowstand, the periplatform slope is thought to have become a bay, herein called the Chiapanecan embayment. Slope conditions reached the Tuxtla area (western Chiapas) in the Campanian, ultimately connecting Paleocene foreland basins with the Gulf of Mexico basin. Whereas the foredeep in Guatemala and Belize (Sepur and Toledo formations) was constrained by a backstop produced by the southernmost stable Yucatán platform (Lacandón Formation), the Tuxtla basin (Soyaló and Nanchital formations) was connected to the Gulf of Mexico, potentially allowing Paleocene bypass of sediment sourced in the colliding Great Antilles arc.