Quantitative geomorphic analysis of vegetated dunes of Western Pampa plain of Argentina: The role of aeolian legacy and hydroclimatic variability in landscape evolution

Abstract

The temperate grassland and cultivated soils of the Western Pampa of Argentina,southern South America, developed over Late Pleistocene–Holocene aeolian sands,shifted from semiarid to dry subhumid in the past 120 years with an increase ofprecipitation variability, concordant with significant changes in agricultural land use.This Western Pampean Dunefield (WPD) is a dormant system, mostly stabilised byvegetation and agriculture, with extensive reactivations during the 1930s ‘PampasDust Bowl’ and the current formation of new dunes in an anthropogenically disturbed landscape. Analysis of the complex assembled aeolian landforms of the WPDwith quantification of vegetated dunes provides new associations for landscape evolution and aims to contribute to science-based land management. The methodologyincludes field surveys, remote sensing imagery, dune morphometry, site stratigraphyand optically stimulated luminescence (OSL) dating. Main aeolian bedforms are blowout dunes and sinuous ridges, associated with aeolian streaks, sand sheets andfluvial-aeolian plains. The blowout dunes (simple, compound and complex) reach tensto thousands of meters in diameter, have commonly superimposed dunes on thedepositional lobes, and sand transport directions towards the NW, NNW-NNE andSW. The sinuous ridges, continuous for 100s m to 1–2 km, have nearly symmetrical profiles and two main crest orientations (NW-SE and SW–NE). Cross-dune patterns and associated OSL chronology allow proposing a morphostratigraphy scheme of compound and complex blowout dunes developed during the Late Pleistocene and growing since then, while sinuous ridges probably accreted in the Holocene. Young blowout dunes are penecontemporaneous and post-date sinuous ridges, reflecting significant aeolian reworking processes. Patches of barchanoid and reversing dunes superimposed on blowout dunes, which have been active since at least the CE 1970s, and the new dune formation in the past two decades, often in intensively cultivated areas, indicate that synergistic biogeomorphic processes may yield irreversible changes in semi-arid to dry subhumid landscapes with an aeolian legacy.