Geoarqueologia da área da Volta Grande do Alto Rio Uruguai, Sul do Brasil: morfoestratigrafia, geocronologia e sequência arqueológica da Foz do rio Chapecó.

The objective of this PhD was to define the formation of the sedimentary deposits, as well as the chronological sequence of the Volta Grande of the Upper Uruguay River (region of Chapecò river mouth). This research was developed in order to contribute to the definition of the diachronic, sedimentary and stratigraphic context of the archaeological occupations. In order to succeded these goals a geoarchaeological prospection by land and water focusing on the bottom of valleys, in the whole area of Volta Grande, was realized. It comprehended the characterization of surface sedimentary deposits; the exposure and analysis of stratigraphic profiles as well as sedimentological analysis (comprehending granulometry and mineralogy with X-ray diffraction of clays). Four deposits superficially exposed were identified: i.e. fluvial conglomerates, fine sediments with sandy texture, clay colluviums and current and recent alluvial deposits. Seven interesting point for the opening of stratigraphic profiles were identified, and subsequently resulted in the identification of 10 sedimentary facies associated with river-bed, colluvial and colluvial-alluvial deposits. Five of these profiles presented archaeological levels in stratigraphy. Four of them were further selected for the collection of sediment samples. The results indicated that the local sediments are predominantly composed of a variable mixture of silt and clay, with sands occurring predominantly in an interdigitated form. The stratigraphic structure of the identified layers led to the establishment of 8 sedimentary facies, associated with colluvium (gM), colluvium-aluvium (gMyS) and aluvium (S, G, GS, GyS, gMyS). The XRD analyzes indicate the homogeneity of clay fraction minerals, with a high percentage of amorphous minerals and crystalline peaks of quartz, kaolinite and illite, with different intensities in the vertical quartz reflections, indicating different degrees of weathering and possibly different dynamics associated to genesis of the sourcing materials. The radiocarbon dating realized in the project POPARU gives an age between 12.0-0.3 cal Ka BP. Thus indicating that the filling of the local valley occurred during the end of the Pleistocene and during all the Holocene by means of both fluvial and colluvial systems. In the project POPARU nine distinct archaeological levels, with a clear stratigraphic, chronological and technological characterization were identified. The pre-ceramic archaeological sequence shows the following chronological indications: the oldest occupation between 12.0-11.0 cal Ka BP (deposit gM); followed by an occupation between 10.5-9.5 cal Ka BP (gM and x₁GyS in three archaeological sites with ten C¹⁴ data). Then an occupation between 8.7-8.5 cal Ka BP (gM); another between 5.7-5.5 cal Ka BP one more between 4.8-4.6 cal Ka BP (gM); and finally between 3.4-3.3 cal Ka BP (gM and gMyS). The ceramist occupation seems to be sole and dense, with dates between 0.5-0.3 cal Ka BP, (gMyS) with the possibility of anthropogenic soil formation. To sum up, it was observed that the application of the geoarchaeological methodology in the area was important to clarify sediment characteristics and to infer the processes of local bottom valley formation and filling. These data present chronostratigraphic sequence unpublished and unique for the context of open air sites in the inner southern Brazil.