Andradina Alloformation: the Anthropocene expression in the Western Plateau of São Paulo

Abstract

The geological frame of the Western Plateau of the State of São Paulo (Planalto Ocidental Paulista), with an area of 220,000 km², has sedimentary deposits on first-order valley bottoms resulting from recent and excessive regional sediment production over a few decades. These sediments were formed by intense erosion as a consequence of the devastation of the primitive forests due to European colonization in the 20^th century. The deposits can be identified in the field by alternating sandy and clayey layers with artifacts that indicate anthropic origin. They can be observed in satellite images and aerial photographs and, thus, their size on valley bottoms can be estimated and their dynamics can be analyzed over time. They occur in the entire drainage network of the Western Plateau, although individually their size is relatively small in each drainage. Because of their regional occurrence and persistent characteristics, and because they represent a very important geotechnogenic epicycle, these deposits, which mark the colonization of the Western Plateau, should be defined as a new formation, named “Andradina Alloformation”, according to the Brazilian stratigraphic lexicon. The term “Andradina” refers to the city where the first deposit was studied in 1994, to one of the most important sites where Pierre Monbeig conducted pioneering research in the 1940’s, and to the site where the Andradina stratigraphic unit was identified. This unit is not the result of a fortuitous or localized event, but represents a geological feature formed in the Anthropocene, which is a new geological epoch of the Quaternary defined by humanity as a geological agent and proposed by the International Union of Geological Sciences (IUGS).