CONICET | Buscador de Institutos y Recursos Humanos

The firsts results of the phytolith research carried out for the sedimentary sequence of Alfar archaeological site are presented. The aims of this study were to identify the vegetetation associations and to contribute to the reconstruction of past environments during the hunter-gatherers occupation of the site in mid-Holocene. This siliceous microfossil data is also complemented with other proxy evidence derived from the zooarchaeological study of the bone remains recovered from the site. Alfar site (38 5' 48.9"S, 57 33' 20.7"W) is located in Mar del Plata City, General Pueyrredón County, Buenos Aires province. Is situated in the Pampean plains, on the right margin of Corrientes stream and at 0.65 km north-west from modern littoral (Argentine Sea, Southwestern Atlantic Ocean). In 2006 a total surface of 17 m2 were excavated, where more than 2.139 lithic artifacts and 8.945 faunal remains were recovered. The archaeological remains were deposited on the edge of a lagoon located in the dune line. Radiocarbon age of 5.700 years BP places the human occupation within the range of the Hypsithermal (= Climatic Optimum) warm event. Faunal species associated with warm arid (e.g. Tolypeutes matacus) as much as with warm humid settings (e.g. Holochilus brasiliensis) were recorded in Alfar, forming a not-analogous assemblage. In addition, greater proportions of root etching on bone specimens surfaces were recorded in the sequence's base (19% versus 7.24% on the top), indicating certain landscape stability. It is important to underline the low collagen content of the bones, due to a strong bacterial activity in an aerobic and rich organic matter environment and to temporary water presence in the levels that contains the archaeological remains. The results of the siliceous microremains analysis in four samples (M1, M2, M3 and M4) of Alfar West Profile indicate similar phytolith proportions throughout the sedimentary sequence. The dominant morphotypes are: elongated with smooth or echinate, unciform hair cells, acicular hair cells and air bases (especially in M2), short cells -in particular bilobates in M1-, rondell, trapeziform short cells and trapeziform sinuate and cylindrical polilobated (in M2), etc. All of these morphotypes correspond to the gramineous family, typical of the Pampean grasslands. Saddle phytoliths are recorded in the entire stratigraphic column, increasing their frequency towards the top (M3). These cells are characteristic of C4 gramineous plants that grow in environments with elevated temperatures, hydric stress and/or presence of salts. In sum, the results of the palaeobotanical analyses, complemented with the archaeofaunal studies, show the existence of a permanent cover of gramineous communities on a lagoon margin, a considerable pedogenetic activity and a progressive tendency of drying towards the top of the profile. The obtained data indicates that the human populations occupied Alfar site under dryness conditions, but with warm climate at mid-Holocene Hypsithermal.

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