Pedoarchaeology and hillslope evolution at a Late Pleistocene/Holocene human settlement in Southeastern Brazil: Bastos site study case

The arrival of humans in the Americas is a controversial topic, especially in South America. Several works have successively moved back the first arrival age in the Late Pleistocene, but little knowledge remains about the paleoenvironments associated with the first human settlements. Pedoarcheology approach on such cases may support paleoenvironmental reconstructions, combined with slope dynamics, to identify the paleosurfaces associated with archaeological sites. The Bastos archeological site is currently the oldest in the state of São Paulo, located at the foot slopes of an alluvial cone, and presents lithic artifacts ranging between 12.9 and 3.9 ka. A combination of soil morphological description, archaeological survey, chemical and granulometric analysis, soil micromorphology and Carbon-14 dating, was applied. Three profiles of buried B textural (Bt) and one the surface have been described. The buried profiles are separated by paleo-surfaces that truncated the A horizons from the three bottom profiles. The time intervals between deposits allowed the formation of Bt with well-developed blocky structures with abundant clay skins, indicating that the time interval (between 4,000 and 5,000 years) was sufficient to form thick Bt with highly developed pedofeatures. A concentration of lithic artifacts closes to the contact with the paleosurface, indicate colluvial deposition at 12.9, 8.7 and 3.9 ka. In addition to the upper deposits, the bottom alluvial deposit has undated archaeological artifacts indicating that maybe the settlement is earlier than 12.9 ka. The slope dynamics indicates that periodic short-term mass movements events mobilize soils from the upper slopes forming alluvial cones downslope, not necessarily associated with changes in climatic conditions.

Financing: Fapesp 2019/18664-9