--> Lithofacies Evolution of the Sierra de Chiapas Basin and the Chiapas Paleo Bay, Cretaceous to Eocene

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Lithofacies Evolution of the Sierra de Chiapas Basin and the Chiapas Paleo Bay, Cretaceous to Eocene

Abstract

Abstract

We re-evaluated previously mapped stratigraphic sections and paleobiologic information of the Sierra de Chiapas basin (Mexico), and produced new lithofacies maps for Late Cretaceous–Eocene time. The basin evolved from a middle Cretaceous passive margin carbonate mega-platform facing the Gulf of Mexico, to a mixed terrigenous-calcareous shelf in the latest Cretaceous. Northcentral and northeastern Chiapas remained relatively stable during this time and subsidence was relatively low. These areas were flanked by zones of greater subsidence in northwestern Chiapas and north-central Guatemala, where carbonate platforms reached a maximum thickness of 5000 m and where foredeeps were established in the latest Cretaceous. Northwest Chiapas was characterized by a relatively deep basin in which the shelf break retreated southward from the Aptian to the Paleocene, producing an embayment connecting the Sierra de Chiapas basin with the Gulf of Mexico basin. Here we introduce the name Chiapas Paleobay for this paleogeographic feature.

In the Paleocene, carbonate platform conditions were locally preserved in the southernmost cratonic part of Yucatan. South of Chiapas, a terrigenous foredeep was produced due to the collision of the Great Caribbean Arc with the south-facing passive margin of North America. The foredeep filled in the latest Paleocene allowing fluvial to shallow marine terrigenous and carbonaceous material to be deposited over a wide area in the Eocene, partially invading the pre-existing carbonate platform.

Detrital zircon geochronology and mineralogic characterization of Jurassic to Paleogene siliciclastic beds revealed a major shift in provenance, from relatively local sources in the Jurassic-Early Cretaceous, to the exposed Great Caribbean orogen in the Campanian-Maastrichtian. During this period, central Chiapas was still dominated by carbonate platform conditions separating the Chiapas Paleo Bay in the NW from the Sepur flysch in Guatemala. We found no evidence of sediment bypass between these two areas. This feature implies that ultramafic detritus present in Maastrichtian beds deposited in the Chiapas Paleo Bay was not sourced from ultramafic rocks now exposed in Guatemala. We conclude that Late Cretaceous delivery systems transported ultramafic detritus exposed in Cuicateco or Tehuantepec into the Chiapas Paleo Bay.