High-resolution sedimentological and stratigraphic framework for the Pehuen Co Paleoichnological site, late Pleistocene, Buenos Aires, Argentina

Abstract

The Pehuen Co Paleoichnological site (Buenos Aires Province, Argentina) contains one of the more diverse and well-preserved mammal and bird fossil footprint assemblages from the Late Pleistocene. The purposes of this paper were a detailed paleoenvironmental assessment of the footprint-bearing unit (middle member of the Agua Blanca Sequence) and to date key stratigraphic surfaces to constraint the temporal development of the site. A total of twenty-two detailed sedimentological sections were measured and correlated and five sediment and fossil remain samples were dated by the Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) methods, respectively. The lower part of the local sequence represents dense to dilute alluvial deposits that were pedogenized. The middle part contains an alternance of sandy sheet-flood and lacustrine mudflat deposits with sand patches of eolian origin. Most of the fossil footprints with better preservation quality were recorded in the mudflats of a shallow lake sourced by unconfined fluvial currents. The participation of eolian deposits increases up section. Locally, a sandy plain of fluvial origin is developed at the top of the section. The new OSL ages along with a previous radiocarbon date led us to propose that sedimentation of footprint-bearing levels would have extended approximately between 28.5 and 12.0 ka. Reworked marine shell remains from the lowermost levels of site with fossil footprints gave considerably older analytical ages in the range of 97.6–62.5 ka, which is probably the maximum age for the middle member of the Agua Blanca Sequence. The “marine levels of Pehuen Co”, which are exposed at very low tides and contains in situ specimens of Ophiomorpha nodosa, are dated 7.0 ± 0.4 ka (OSL method). They reflect a Middle Holocene sea level rise in the area.