Site formation process and megamammal bone radiocarbon dates in Campo Laborde (Pampas of Argentina): Contribution towards a research methodology

Abstract

Dating bone collagen has been problematic in the Argentinean Pampas. Many bone samples do not have collagen or have poor preservation giving collagen of questionably quality, in many cases it is contaminated by humic substances. The combination of these factors has produced suspicious results, leading to the proposition of the Holocene survival in the region of the extinct Pleistocene megamammals such as the Megatherium Holocene ages from the Campo Laborde site. However, new dates from the same sample, purified from humates with XAD-2 resin, gave results of ~10,650 14C years BP. In this article, we apply different methodological procedures (chemical, geoarchaeological and taphonomic analysis) in order to reconstruct the formation at the Campo Laborde the site and identify the processes and agents that affected its chronology. The previously obtained Early Holocene ages of megafauna bones resulted from the interrelation of various factors as physical and chemical weathering, humification processes linked to pedogenesis, and diagenetic processes. In sum, they caused the degradation of collagen and the subsequent contamination by fulvic acids from the overlaying soil, which classic pretreatment techniques could not remove. We conclude that the obtained results do not support the Holocene survival of the megafauna in the Pampas.