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

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. Fil: Martinez, Sergio. Universidad de la República; Uruguay Fil: Feijó Ramos, María Inês. Museo Paraense Emilio Goeldi; Brasil Fil: McArthur, John M.. University College London; Estados Unidos Fil: del Río, Claudia Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Thirlwall, Matthew F.. Royal Holloway University Of London; Reino Unido