Quaternary International 162–163 (2007) 158–165 Soil genesis related to medieval climatic fluctuations in southern Patagonia and Tierra del Fuego (Argentina): Chronological and paleoclimatic considerations Cristian M. Favier-Dubois CONICET-INCUAPA, Departamento de Arqueologı´a, Universidad Nacional del Centro, Avenida Del Valle 5737, (B7400JWI) Olavarrı´a, Argentina Available online 20 February 2007 Abstract Coastal and continental localities analyzed in southern Patagonia and Tierra del Fuego (Argentina) demonstrate the ubiquitous presence of a late Holocene Mollisol in eolian and colluvial deposits. This soil is buried in many places by a sandy layer of variable thickness, indicating a further reactivation of morphogenetic processes. Maximum and minimum ages obtained by 14 C and oxidizable carbon ratio (OCR) methods place the beginning of this pedologic event about 1000 years ago. The regional character of this soil and the evidence of climatic fluctuations supplied from paleohydrological, pollen, and multi-proxy studies in the area suggest that the soil’s origin could be related to a pulse of increasing humidity following an episode of drought during medieval times. r 2006 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction and research objectives Geoarcheological work carried out in coastal and continental areas in southern Patagonia (south of the Santa Cruz river basin) and northern Tierra del Fuego has shown the recurrent presence of a pedologic event in the upper section of extended late Holocene eolian and colluvial deposits, frequently associated with archeological material (Favier-Dubois, 2001). This soil is buried in those places where erosional processes have acted or are still active, as in coastal dune areas, but it is exposed in other positions on the landscape. On a regional scale, the analyzed sequences indicate an active morphogenesis after the Middle Holocene, character- ized by abundant eolian deposits, which may be related to arid conditions (Rabassa and Clapperton, 1990; Markgraf, 1993; Aniya, 1996). At about 1000 years ago, there is a pedogenetic interval represented by a soil having an A–AC–C profile and a mollic epipedon, which may be classified as a Mollisol (see stratigraphy). The soil’s development may indicate an important change in the environmental conditions due to the stabilization of regional eolian and colluvial systems at that time. Furthermore, changes in the distribution of the archeological record are linked to this development (Favier-Dubois, 2003). There- fore, the aim of this paper is to analyze the morphology, chronology, and distribution as well as the paleoclimatic implications of this soil in the region under analysis. 2. Methods Geoarcheological surveys are a part of the archeological research projects carried out in the region for the purpose of studying the evolution of hunter-gatherer populations (Borrero, 1998). The analysis of the environ- mental dynamics was based on the identification of landforms, the drawing of stratigraphic profiles, the correlation of litho- and pedostratigraphic units, and the study of sedimentary facies. Soil profiles were described and characterized according to soil taxonomy (Soil Survey Staff, 2003). Two different methods were used to obtain numerical ages: (1) radiocarbon dating, using both conventional and AMS techniques, and (2) oxidizable carbon ratio (OCR) dating, a method based on the effect of the biochemical degradation of charcoal and soil humic material, measured as a ratio of the total carbon to the readily oxidizable carbon in the sample (Frink, 1994, 1995). Textures were determined by sieving and pipetting. ARTICLE IN PRESS 1040-6182/$ - see front matter r 2006 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2006.10.044 E-mail address: cfavier@coopenet.com.ar.