Loponte, D.; Carbonera, M.; Schneider, F.; Galarce Machado, N.; Bertoncello, A.; Telles Szczygel, M.; Acosta, A.; Mazza, B.; Sheila, A.; Capparelli, I.

This study presents new analyses of the archaeological record recovered at the Guarani site of Arenal Central, located on Martin Garcia Island within the Rio de la Plata estuary, along with a new set of radiocarbon dates. This settlement represents the southernmost point reached by an Amazonian canoeing population in South America, illustrating colonization processes carried out by founder populations in suboptimal social and natural environments. Thus, the objectives of this work are to refine the chronology of the Guarani occupation of the site and analyze its material record, comparing it with other Guarani assemblages. The results show that Arenal Central was occupied around 1400 CE, during the final phase of the Guarani expansion across the La Plata Basin. From this settlement, a vast territory was incorporated as a catchment area, including the lower Uruguay River, the Parana Delta islands, and the adjacent Uruguayan steppe. This extensive territorial use appears to have been essential due to the limited carrying capacity of the island and the scarcity of critical resources required to sustain the Guarani ecological niche. While the recovered assemblage retains the fundamental characteristics of Guarani material culture, a noticeable decline in the complexity of pictorial expressions, particularly in painted ceramics, is evident. This apparent simplification may reflect limited intra-ethnic interaction, likely due to the low density of the Guarani population in the surrounding area, as well as the challenges posed by a suboptimal insular environment. Finally, we incorporate these new results into the broader process of occupation of the Parana Delta and the Rio de la Plata estuary, for which we provide a brief synthesis.