Palynofacial analysis in alkaline soils and paleoenvironmental implications: The Paso Otero 5 archaeological site - (Necochea district, Buenos Aires province, Argentina)

GRILL, S., A. M. BORROMEI, G. MARTÍNEZ, M. A. GUTIÉRREZ, M. E. CORNOU Y D. OLIVERA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier Ltd.

Año: 2007 vol. 24 p. 34 - 47

0895-9811

The combination of palynofacial and sedimentological analyses constitutes a valuable method for paleoenvironmental and paleoclimatic reconstructions, especially when fossil pollen information is scarce or absent. This methodology elucidates a late Pleistocene/Holocene sequence at the Paso Otero 5 archaeological site in the middle basin of the Quequén Grande River, Necochea district, Buenos Aires province, Argentina. Although the main factor responsible for the destruction of pollen grains is pH, biochemical and chemical oxidation and mechanical damage contribute to the deterioration as well. The site sequence indicates that extremely arid climatic conditions without vegetation cover prevailed during the late Pleistocene (12,000 14C yr BP),after which the climate changed to semiarid conditions associated with a disturbed environment due to strong eolian activity (Palynofacies 1 and 2; pre-10,400 14C yr BP).During the Pleistocene/Holocene transition (Palynofacies 3 and 4; 10,400 9400 14C yr BP),loamy facies associated with paleosoils reflected stable conditions and temporary ponds (spring deposits).Similar conditions occurred near the end of early Holocene (Palynofacies 5-9; 9400-6600 14C yr BP),whereas sandy and silty facies are associated with the flood margins of streams or rivers in the middle and late Holocene (Palynofacies 10-14; 6600-2500 14C yr BP).The top of the sequence (Palynofacies 15 and 16)consists of alluvium sediments and reflects locally humid conditions and modern vegetation with anthropic influence. One of the earliest Pampean sites with evidence of humans (10,450 -10,200 14C yr BP), Paso Otero 5 provides a variety of megafauna bone specimens associated with fish-tail projectile points, a lithic artifact diagnostic of early human occupations in South America. The site contains a complete stratigraphic record from the late Pleistocene to the present. The evidence presented herein supports the hypothesis that human colonization, at least in some areas of the southern cone, took place within severe, fluctuating climatic conditions.