Landscape and environmental conditions for the late Holocene in the eastern Pampa-Patagonia transition (Argentina): a phytolith analysis of the El Tigre archaeological site

Abstract

The El Tigre archaeological site (39°46′49″ S; 62°22′32″ W) is located in the south of Provincia de Buenos Aires, Argentina, on an ancient delta of the Río Colorado. Its sedimentary sequence shows periods of landscape stability and soil formation processes during the period ca. 1,000?400 years bp. The aim of this paper is to investigate the evolutionary history of the vegetation in order to understand palaeoenvironmental changes during the late Holocene. The study of microremains, mainly phytoliths, from the sedimentary sequence indicates that cold and dry conditions predominated at 2,700?2,200 cal bp, from deposition of non-pedogenetic, aggradational sediments in arid or semi-arid environments and/or sparse vegetation cover. Then the climate became much warmer at ca. 2,200?1,200 cal bp, with greater availability of moisture and the presence of xerophytic shrubs and halophytic grasslands, and also extra-regional trees and shrubs. The records indicate that for ca. 1,500?300 cal bp the climate conditions changed to temperate with periods of greater water availability and the presence of a saline steppe and a greater abundance of Monte-Caldenal scrub vegetation elements. This climatic trend is also in agreement with the soil formation processes defined in the archaeological site sequence. The upper layers of the El Tigre site show lower temperatures in the last 300 years, accompanied by variations in the availability of moisture, with alluvial processes characterized by the presence of saline grasslands with xerophytic shrubs and an increase in Asteraceae and Poaceae, continued by the recent top samples with ruderal communities and sandy grasslands.