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Micromorphology of South American shell sites: archaeostratigraphy and formation processes of sambaquis (Santa Catarina, Brazil) and concheros (Tierra del Fuego, Argentina)

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Author(s):
Ximena Suarez Villagran
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Geociências (IG/BT)
Defense date:
Examining board members:
Paulo Cesar Fonseca Giannini; Jordi Estevez Escalera; Raquel Pique Huerta; Carlos Ernesto Gonçalves Reynaud Schaefer
Advisor: Paulo Cesar Fonseca Giannini
Abstract

To understand site formation processes in shell sites, eight sambaquis(shell mounds) from the southern coast of Santa Catarina and one shell midden (conchero) from Tierra del Fuego were studied. For the sambaquis of Santa Catarina, the aim was to understand the cultural and natural formation processes (human activities and taphonomy) and the way they changed through time through the whole period of prehistoric human occupation in the region (c. 7400-1000 years BP). In Tierra del Fuego, the micro-stratgraphic study of an ethnohistoric shell midden was done to serve as model for hypothesis on formation processes of shell sites. The methods used for characterization of archaeological sediments included: grain-size analyses, zooarchaeology, C and N isotopy (\'? POT.13\'C e \'? POT.15\' N), micromorphology and scanning electron microscopy. Experimental archaeology was done using different hearths lit on known contexts and by controlled burning of mollusk shell. Three types of sambaquis were analyzed: four shell mounds; two sand mounds; and two fish mounds. Formation of the first and third group followed a recurrent and continuous pattern of reworking of items, accumulated and burnt in a different location than the final. These items included food refuse, like shell, fish remains (bone and tissue) and plant material (charcoal and residues of \'C IND.3\' plants), as well as terrigenous components from the sedimentary substrate of the surroundings of the site and from the exploredshell beds. Sand mounds are ephemeral but planned occupations. Their formation involved rising of a sand mound and/or occupation over sand dunes, with deposition of shells and plant remains on top. Two substantial implications are extracted from this analyses: 1) the reworking of food residues may be destructing the remains of daily occupations associated with the large sambaquis, that have never been found to this moment; 2) the correspondence of formation process in shell mounds and fish mounds suggests continuity in the depositional activities, besides the change in material (substitution of shell by fish remains) and adoption of ceramic technology in recent times. The ethnohistorical site analyzed for geo-ethnoarchaeological comparison was formed by recurrent domestic occupations that lasted for a century. Analyses of the peripheral shell ring allowed the micromorphological characterization of episodes of massive shell deposition, trampling and site abandonment. Analyses of hearths located in the central habitation area showed micromorphological indicators of high temperature and moderate temperature combustion structures (over and under 500° C, respectivley). Comparison of microfacies from the fueguian shell midden and microfacies from the sambaquis shows different pre-depositional trajectories. In the first case, deposition is related with the immediate and secondary discard of food refuse around the living space. In the second case, formation is related with an intricate succession of deposition, burning and transport of items that resulted in a tertiary deposit. These observations corroborate the great complexity in the formation processes of sambaquis. (AU)