Phytolith and pollen analysis of camelids coprolites from Cerro Casa de Piedra 7 (CCP7) archaeological site, Province of Santa Cruz, Argentin

N. BORRELLI; M. OSTERRIETH; L. S. BURRY; M. FUGASSA.

Mar del Plata

Congreso; 7th International Meeting on Phytolith Research (7THIMPR); 2008

Universidad Nacional de Mar del Plata

Cerro Casa de Piedra is a hill of volcanic origin in the river basin of Río Roble, and Burmeister lake, 900m above sea level, with a temperate cold and semiarid climate. The site is in an ecotone located between a forest of Nothofagus sp. and a shrub steppe (Civalero and Aschero, 2003). It has a stratigraphic sequence that includes 19 levels, with human occupation between ca. 9,700 and ca. 3,400 yr (Civalero and Franco, 2003). The site could have been a gather point for human microbands in the summer, when a camelids availability with the highest fast level exists (Aschero, 1996). Before 9000 yr BP, vegetation at CCP7 could have been dominated by a grass steppe, with humid and cooler conditions than the current ones. After 9000 yr BP, the important grasses diminution; and the increase in Nothofagus, shrubs and herbs suggest the forest-steppe ecotone establishment until ca. 3500 yr BP (Mancini, 2005). The aim of this work is to present the preliminary results about phytolith and pollen analysis of camelids coprolites from Cerro Casa de Piedra 7 (CCP7) (Parque Nacional Perito Moreno, province of Santa Cruz). We worked with coprolites recovered in four archaeological layers, associated to the following radiocarbon dating (14C): 1) layer 17: 9640±190 yr BP; 2) layer 14: 8460±400 yr BP; 3) layer 11: 7880±150 yr BP; 4) layer 7: 5610±110 yr BP. Of each coprolite, external and internal parts were separated. For the phytolith analysis, both portions were treated with 30% hydrogen peroxide at 70°C in order to oxidize the organic material. Phytoliths and pieces of amorphous silica (<7,5µm) were discriminated, and about 250–300 phytoliths were counted. Pollen analysis was done in coprolites of the 17, 14 and 7 layers. In both portions of each coprolite, pollen was extracted with an acetolithic mixture (9 parts of (CH3CO)2O and 1 part of SO4H2), and counted under optical microscope. Pieces of amorphous silica content increase from more modern (15,8%) to ancient (25,1%) coprolites, suggesting the importance of taphonomical processes on phytolith conservation. In general, the predominant isolated phytoliths correspond to Poaceae morphotypes: 1) Rectangle (20-35%), 2) Rondel (16-24%), and 3) Elongate psilate (2-8%). In the more modern coprolites, the predominant articulated phytoliths are composed of epidermal polygonal phytoliths and hair cells that could be attributable to dycotiledons; instead, in the ancient coprolites, the predominant articulated phytoliths are composed of Poaceae elongated cells; according to Mancini (2005) vegetation changes description for the study area. Pollen analysis show more abundance of Empetrum taxa (dycotiledon) in the ancient coprolites; while in the more modern coprolites, the representative taxa are Caryophyllaceae, Asteraceae and Nothofagus (all dycotiledons) and Poaceae (monocotyldedons). On camelid coprolites of the same excavation, paleoparasitological analysis were carried out (Fugassa, 2006; Taglioretti, 2008; Fugassa et al., 2008); and some studies of vegetal rest recognition are being carried out (Yagueddú y Arriaga, 2008). The interdisciplinary coprolites study, based on different indicators, will allow us to adjust the results and build interpretations of the past environmental conditions in the study area.