Late Burdigalian (Miocene) age for pectinids (Mollusca-Bivalvia) from the Pirabas Formation (northern Brazil) derived from Sr-isotope (87Sr/86Sr) data

Abstract

The faunas of the highly fossiliferous Pirabas Formation belong to the southern part of the biogeographical unit known as "Neogene Tropical America". This unit developed prior to the closure of the Central American Seaway by the Isthmus of Panama. Until now, the age of the Pirabas Formation was inferred only from biostratigraphy. The Sr-isotope (87Sr/86Sr) values of pectinid shells from the Pirabas Formation show that most parts of this unit were deposited during the Late Burdigalian (about 16-17 Ma ). This result does not contradict biostratigraphic data and it constrains the age of the Pirabas Formation more tightly than do previous estimates of age, it for future, more precise biogeographical comparisons.