Phytolith and FTIR studies applied to combustion structures: The case of the Middle Paleolithic site of El Salt (Alcoy, Alicante)

The combination of phytolith and FTIR analyses is a powerful tool to investigate the use of fire by past human populations. Here, we apply these methods to study the hearths of the subunit Xb at the Middle Palaeolithic site of El Salt, in Alcoi. El Salt is characterized by recurrent Neanderthal occupations that produced a succession of combustion structures and other anthropogenic remains. Using FTIR analysis we have been able to detect the presence of ashes, thermally altered clay, and phosphatic minerals in the sediments. Phytolith results point to the use of wood as fuel in subunit Xb. However, most of the phytoliths have been deposited in the site by natural agents, probably in the form of bird guano characterized by the presence of distinctive phytoliths of seed coats from Celtis sp. Differentiating between natural and anthropogenic deposited phytoliths is essential to evaluate the impact produced by human activities in the archaeological sediments.