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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]

The Cretaceous in the Brazilian Platform records events of magmatism, tectonism and sedimentation coupled to the Gondwana breakup. Some of these events are registered as sedimentary sequences in interior basins, such as in the Cretaceous sequence of the Alto Xingu Sub-basin, Parecis Basin, Central Brazil. This article proposes the faciologic characterization and paleoenvironmental reconstruction of the Cretaceous sequence of the eastern portion of the Parecis Basin and its relation with some reactivated structures as, for instance, the Serra Formosa Arch. Based on both data from outcrops and core drillings a paleoenvironmental and evolutionary reconstruction of the sequence is herein presented. The base of the studied section is characterized by chemical and low energy clastic sedimentation of Lake Bottom and Shoreline, in a context of fast initial subsidence and low sedimentation rate. As the subsidence process decreased, a deltaic progradation became dominant with deposition in a prodelta environment, followed by a deltaic front and deltaic plain interbedded with fluvial plain, and aeolian deposition completing the sequence. The inferred Coniacian–Santonian age is based on vertebrate (fishes and notosuchians) and ostracod fossils with regional chrono-correlates in the Adamantina (Bauru Group), Capacete (Sanfranciscana Basin), and Bajo de la Carpa (Neuquén Group, in Argentina) formations. The formation of a Coniacian depocenter in the Alto Xingu Sub-basin is associated to the Turonian–Coniacian reactivation event in the Peruvian Orogenic Phase of the Andean Orogeny, with the transference of stresses to interplate setting, reactivating Proterozoic structures of the basement. [ABSTRACT FROM AUTHOR]