Aridization, dune dissipation and pedogenesis in the Quaternary of Eastern Pampean Sand Sea

IRIONDO, M., KROHLING, D. AND BRUNETTO, E.

Sand Dunes: Conservation, Shapes/Tyes, Enhancement

Nova Science Publishers Inc

Lugar: New York; Año: 2011; p. 1 - 43

The Pampa region is a large plain of aeolian origin which forms the central part of Argentina. After a warm and humid environment established during the Last Interglacial, a cold and dry climate provoked by the glaciations in the Andes Cordillera generated a desert formed by a sand sea (the Pampean Sand Sea, PSS) and loess deposits (the Peripherial Loess Belt, PLB). Later climatic oscillations produced reworking of the sand structures, with destruction, reshaping and dissipation of dunes, pedogenesis and new deflation of the soil. Such a sequence occurred several times in the Pampa. This chapter describes the processes and dune types of the northeast of the PSS, with an area covering some 10,000 km A sequence of six desert climates intercalated with humid or subhumid pulses were recognized in the region. Three basic processes were responsible for the evolution of the sand sea: deflation, dune dissipation and pedogenesis, each of them recognizable in morphology and internal sedimentary structures. Deflation was provoked by strong winds originated in the Patagonian ice cap, that formed longitudinal mega-dunes during the Oxigen Isotopic Stage 4 (OIS 4) and other dune types in OIS 2 and Late Holocene. Dune dissipation, a process produced by the pluvial action on loose sand in semiarid climates, was particularly important in the climatic change occurred during OIS 3 (between 65 and 36 ka. BP). Pedogenesis dominated during the middle Holocene Hypsithermal and a Late Holocene (3,5-1,4 ka. BP) dry climate deflated again the PSS, generating composed parabolic mega-dunes. Typical weather scenarios of the Holocene past climates are sporadically reproduced today during extreme humid or dry short periods (one year or two), which allows to reasonably know the basic meteorological parameters of those past systems: Dry periods similar to that of Late Holocene are characterized by a large thermal amplitude, frosts and stronger winds than normal, reproducing a continental anticyclonic circulation. Humid extremes similar to the Holocene Optimum Climaticum are warmer than normal, with lower thermal amplitude, with rains produced by local convection processes.