A westerly wind dominated Puna Plateau during deposition of upper Pleistocene loessic sediments in the subtropical Andes, South America

Abstract

The Tafí del Valle depression (~27° S) in the eastern Andes of Argentina provides a record of late Pleistocene dust deposition in the subtropics of South America. We present large-n U-Pb geochronology data for detrital zircons from upper Pleistocene loess-paleosol deposits. When compared to regional data, the age spectra from the Tafí del Valle samples are most like the southern Puna Plateau, supporting derivation largely from the west and northwest. This runs counter to hypotheses suggesting these loessic sediments were derived from the low elevation plains to the east or extra-Andean Patagonia. Mapping of linear wind erosion features on the Puna Plateau yield a mean orientation of 125.7° (1 s.d. = 12.4°). These new data and existing records are consistent with a westerly-northwesterly dominated (upper- and lower-level) wind system over the southern Puna Plateau (to at least ~27° S) during periods of high dust accumulation in Tafí del Valle.

Fig. 1. Maps of southern South America.

A Simplified geologic map of Argentina and central and southern Chile based on compilation maps^,. Distribution of La Pampa loess and Pampean Sand Sea after Iriondo (^,) and Zárate (). B Digital elevation model for southern portion of South America. Color filled stars denote locations of U-Pb zircon samples for comparison with Tafí del Valle samples: southern Puna Plateau^,; central Puna Plateau^–; Chaco^,; Sierras Pampeanas^–; Precordillera^–; Neuquén basin; northern Patagonia; southern Patagonia; Ríos Neuquén, Salado, Limay, Colorado, Negro Chubut, Gallegos, Santa Cruz, Chico, and Deseado. Area of wind erosion study of Puna Plateau reported here highlighted by dashed red line; linear wind erosion data shown in inset rose plot.

Fig. 2. U-Pb detrital zircon data.

A U-Pb detrital zircon cumulative density functions for Tafí del Valle samples and comparison data. References for comparison data in the Fig. 1 caption with descriptions in Supplementary Table S2. B 3-dimensional multi-dimensional scaling (MDS) plot of U-Pb detrital zircon data for Tafí del Valle samples and comparison data. Measured and sampled stratigraphy, correlated with magnetostratigraphic timescale from Schellenbreger et al. (ref. ); tan denotes loess and crimson denotes paleosol layers. 0 meters represents the top of the section and youngest strata.

Fig. 3. The zonal components of wind at 500 hPa and 850 hPa for 1979–2021.

Data from the ERA5 Reanalysis product. Positive values (red) denote westerly winds, whereas negative values (blue) denote easterly winds. The white star indicates the field location in Tafí del Valle.