Evaluation of the Olduvai subchron in the Orce ravine (SE Spain). Implications for Plio-Pleistocene mammal biostratigraphy and the age of Orce archeological sites

The Barranco de Orce (BO) section in the Baza basin (SE Spain) exposes several fossiliferous layers (O-1 to O-7) with Plio–Pleistocene micro- and macromammals. Biostratigraphic and magnetostratigraphic data from this and other sections in the basin have been extensively used to calibrate the Plio–Pleistocene chronology based on mammal biozonations. Because of its stratigraphic and geographic proximity, the BO section has also been used to date the paleontological and archeological sites of Barranco León, Fuentenueva-3 and Venta Micena. This study shows that the BO section crosses a mega-landslide that produces partial repetitions of the sedimentary sequence. The seven fossiliferous layers are actually the repetition of only two (O-6 and O-7) which are found in situ in the upper part of the ravine. New paleomagnetic results demonstrate the presence of Reverse magnetization throughout this section, contradicting the Normal event previously reported and assigned to the ‘Olduvai’ subchron (C2n). Published and new magnetostratigraphic data show that all archeological and paleontological sites in the Orce area are within a Reverse magnetochron, presumably C1r.2r (late Matuyama). The use of BO in the magnetobiostratigraphical calibration of the Pliocene/Pleistocene boundary for western Europe is not advised.