The “Lagoa do Camargo 1” Paleoindian site: some implications for tropical geomorphology, pedology, and paleoenvironments in southeastern Brazil (original) (raw)

Lagoa do Camargo 1, a Paleoindian archaeological site located in southeast Brazil dated between 10.5 and 8.3 ka, was studied using a variety of analyses: artifact and charcoal frequencies, soil morphology and micromorphology, magnetic analysis, optically stimulated luminescence, and radiocarbon dating. Our results show that the sandy tropical Oxisol present at the site was accumulated by episodic erosion and accumulation of materials along the slope, by means of diffuse runoff (sheet wash), and that bioturbation, albeit present, played a minor role in the soil formation. From a geoarchaeological point of view, the site poses an important problem, which is the presence of a deeply buried archaeological site almost at the top of a plateau. Our conclusions are relevant for understanding the genesis of sandy Oxisols that cover a large portion of southeast Brazil, where charcoal fragments are abundant, and whose genesis is considered by some authors to be strongly related to pedoturbation. 1 INTRODUCTION The assessment of the cultural characteristics and chronology of Paleoindian sites (sites older than 8500 yr BP) in South America is of upmost importance for understanding the timing and processes related to the peopling of the Americas (Araujo, 2015; Gruhn & Bryan, 2011; Meltzer, 2003; Webb & Rindos, 1997). In the eastern portion of South America, large areas are still devoid of data, including São Paulo State, southeastern Brazil. The aim of this research is to address this gap by employing a geoarchaeological approach, based on the specific character of biological, physical and chemical processes that are often found in tropical areas (Araujo, 2014). Paleoindian sites in eastern South America are generally found inside caves and rockshelters (Araujo, Strauss, Feathers, Paisani, & Schrage, 2013) and here we avoid such bias by studying an open-air site. We conducted an intensive, systematic subsurface survey program in the vicinity of Lagoa do Camargo, a lake in Rio Claro County, São Paulo State, southeastern Brazil. The choice of Lagoa do Camargo as a pilot area was based on the hypothesis that lakes can provide a stable water source for humans and also be exploited as fishing and hunting areas. We also based this choice on our former successful attempts to find open-air Paleoindian archaeological sites in central Brazil (Araujo, Neves, & Kipnis, 2012). From a geoarchaeological point of view, lakes can be considered as traps for sediment, artifacts, and microartifacts (Sonnenburg, Boyce, & Reinhardt, 2011), and are therefore not subject to the strong erosional and depositional cycles that are common in fluvial systems. However, lake margins and the slopes that surround them can also be subject to both erosion and sedimentation, and our research design took these possibilities into consideration. The understanding of slope processes affecting tropical soils are important for establishing accumulation and erosion rates and for estimating potential depth of burial of archaeological sites. These processes can encompass a variety of factors that are well known (e.g., creeping, slope-wash, biological turnover , in situ weathering, and so on), but the role of these different factors in specific settings is not always straightforward. Results of our work at Lagoa do Camargo I are somewhat surprising, because we were able to find archaeological materials buried in a upper slope section at depths of more than