LATE QUATERNARY PALEOSOLS, LANDSCAPE EVOLUTION AND CLIMATE CHANGE IN THE NORTHERN PAMPA, ARGENTINA

The presence and characteristics of paleosols within loess sequences are often interpreted in terms of regional and even global climatic changes. In addition, they can be used to provide important insights into the pedosedimentary evolution of a landscape. Despite containing the most extensive loess cover in the Southern Hemisphere, there have been few detailed studies of paleosols in the Argentinian Pampa. This paper reports a pedosedimentary investigation of two Late Quaternary loess-paleosol sections from the northern part of this region.

Field and micromorphological data indicate that the landscape at both sites has experienced a cyclical development with relatively stable land surfaces associated with significant soil formation (e.g. bioturbation, weathering, leaching and clay translocation processes) being interspersed with phases of instability, erosion, loess accumulation and accretionary pedogenesis. The 7 m section at Baradero contains two paleosol units, the older one is a pedocomplex whose upper part is correlated on the basis of optically-stimulated luminescence dates to Oxygen Isotope Stage (OIS) 5a of the marine record. The surface soil developed in Late Pleistocene loess is significantly less developed than both paleosols, thus opening up the intriguing possibility that the climate during the Holocene may have been drier and/or milder than earlier warm stages and sub-stages. The only paleosol recorded in the 9 m section at the Lozada site appears to date from OIS 5a and is again more developed than the surface soil. In this case, however, significant amounts of loess have accumulated throughout the Holocene, perhaps supporting the notion that the comparative developments reflect differences in length of ‘soil-forming intervals’ rather than climate. This study not only emphasises the potential value of a pedosedimentary approach to the interpretation of loess-paleosol sections, but also highlights some of the difficulties of inferring regional climatic changes from pedosedimentary reconstructions.