Archaeological sites of the Guaraní indigenous tradition are recognized in aeolian dunes on the southwestern shore of the Laguna dos Patos, Rio Grande do Sul. However, the occupation of indigenous hunter-gatherers in sandy landscapes lacks explanation. Based on a geoarchaeological study at site RS-LS-45, this paper aims to understand the paleoenvironments of one of the dune sites and what the role of climate was for indigenous permanence, using paleoclimatic reconstructions of the last 1000 years, C14 dating of indigenous occupations, and a sedimentary facies analysis. The results indicate that indigenous settlements occurred during wetter climatic periods, with a Land Reconnaissance during the Medieval Climatic Anomaly and a Littoral Agglutination throughout the Cold Poles and Wet Tropics periods. The paleoenvironments of the archaeological site revealed the remobilization of archaeological materials in erosional events, overlain by an ancient aeolian depositional system (paleodunes) marked by medium sands and preserved in fixed sandy mounds. The erosion of the paleodunes provides sediments for a still-active aeolian sedimentation environment that was reactivated, possibly, during the Little Ice Age. From the study of the pre-colonial setting, it was possible to understand the influence of climate on the native peoples of the region and to refine the stratigraphy and sedimentology of a Guaraní site, in a region not studied from a geoarchaeological perspective. [ABSTRACT FROM AUTHOR]