Quaternary landscape evolution and human occupation in Northwestern Argentina

NEDER, L; SAMPIETRO, M. M.

Oslo - Noruega

Congreso; International Geological Congress Oslo 2008; 2008

Our study area is located in the occidental piedmont of Calchaquí Summits (Tucumán ? Northwestern Argentina). It is a semiarid valley, representative of this kind of environment in the region, where most developed agricultural prehispanic settlements were located. The objectives of our research were to establish its geomophological characteristics together with its chronological development, and the relationships between geomophological development and prehispanic settlements. The area was analyzed through photointerpretation of aerial photographs scale 1:50,000 and visual interpretation of satellite images. Pedestrian control surveys were made and thematic maps were digitalized using ILWIS 3.4 software. Landscape units were classified according to its genesis. Slopes, as well as piedmont, reflect different lithologies and tectonic activity that make it possible the presence of Tertiarian outcroppings in terrain surface. Among the recognized landscape units we identify by its origin: structural denudational; denudational; fluvial-alluvial, and eolian landforms. Most characteristic deposits are cenoglomeratic and fanglomeratic. The first ones are located in the apical piedmont forming three levels of covered glacis, developed at different times, during Early and Middle Pleistocene. By the Late Pleistocene and Holocene higher amounts of available water favoured the transport of solids that produced the exhondation of previously deposited materials. As a result of this process is possible to find thin fanglomeradic deposits in the shape of alluvial fans. After that, and coincident with a drier regional period dune fields evolved. These dunes are located between distal piedmont area and bottom valley. Besides landscape composition is complex, it was possible to arrive to a relative chronology according to landform location and size. This chronology was related with regional paleoenvironmental dynamics and slopes regionally located on similar positions. Identified archaeological sites are located on the south part of the study area. They belong to Formative (500 BC to 1000 AC) and Regional Development (1000 AC to 1500 AC) periods. These settlements are located over the oldest covered glacis level. It is very significant that earlier settlements are over smaller basins while latter ones are over larger basins, probably because the drier period during Regional Development develops making impossible agricultural practices on smaller basins.