Foraminiferal biostratigraphy of the Pennsylvanian Cerro Prieto Formation, Amotape Mountains, NW Peru: Correlation with the Central Andean basin

Abstract

Carboniferous-Permian successions in the Amotape Mountains (NW Peru) are poorly dated due to the predominant siliciclastic intervals and the scarcity of fossils. The biostratigraphy of the formations is thus poorly constrained and, in general, limited to major systems or subsystems. The Cerro Prieto Formation was assigned to the Pennsylvanian or middle Pennsylvanian, but at the Caseta de la Antena section, the lower half of the formation contains carbonate horizons where diverse foraminiferal assemblages are recorded. Foraminifers allow to assign the base of the formation to the basal Bashkirian Stage, Morrowan Substage or Globivalvulina-Millerella Zone. This biostratigraphy can be extrapolated to the base of the Tarma Formation in central and south Peru, where this part of the latter formation remains undated. The upper limestone levels at Caseta de la Antena are assigned to the late Bashkirian, Atokan Substage or Eoschubertella-Pseudostaffella Zone. The upper half of the Cerro Prieto Formation, only composed of siliciclastics, might correspond to the uppermost late Bashkirian/lowermost Moscovian, or the mid-upper Atokan, due to fusulinids recorded at the top of the Tarma Formation. Foraminiferal assemblages are rather similar to those recorded from the lower part of the Copacabana Formation in Bolivia, although some differences occur, and apparently rather different from those in south Peru, a fact which suggests a slight biogeographic differentiation between the Amotape Mountains and the Central Andean Belt possibly related to its distinct geological setting.