Refining the chronology of Middle/Late Pleistocene fossil assemblages in the Argentine Pampas

Abstract

Middle and Late Pleistocene large and mega-mammal records of the Argentine Pampas, belonging to the Bonaerian and Lujanian Stages/Ages, have not yet been adequately dated by standard numerical radiometric methods. Reference timescales for Argentina and other South American fossil sites are mainly based on the mammalian faunal content (biostratigraphic units or biozones). We have recently dated three Middle and Late Pleistocene faunal sites located in the Buenos Aires Province using Electron Spin Resonance (ESR), U-series, Optically Stimulated Luminescence (OSL) and radiocarbon dating. The geographically distant sites (Salto de Piedra, Campo Spósito and Cascada de Paleolama) have yielded fossil assemblages representative of the Lujanian and Bonaerian Stages/Ages. Salto de Piedra, systematically excavated, records one of the most complete fossil sequences and our results indicate that it deposited between at least 127.4 ka (minimum age; Late Pleistocene, MIS 5) and 4.8–4.3 cal ka BP (Middle Holocene, MIS 1). Campo Spósito lower level (corresponding to ‘El Tala’ unit) was dated to >188 ka via ESR/U-series dating of teeth. Finally, Cascada de Paleolama Unit D, towards the base of the sequence, produced an age of 143 ± 20 ka (Late Pleistocene, MIS 5/6). The new dating results provide a crucial additional age control for the Bonaerian and Lujanian Stages/Ages, and allowed us to better identify and calibrate the limits of Equus neogeus, Megatherium americanum biozones, as well as to better constrain other index taxa that are used to construct local biostratigraphical frameworks. Our results indicate the need for a revision of the biozone schemes established for the Quaternary of Pampean region.