Deconvolving Provenance Signatures of Pliocene-Pleistocene Coastal Loess Deposits Along the Atlantic Margin of Argentina

Dust derived from southern South America provides critical nutrients for autotropic marine biota in the South Atlantic Ocean, such that fluxes of wind-blown sediment may ultimately affect the concentration of atmospheric CO2. Expansive sand, silt, and loess deposits are exposed in Central Argentina, recording millions of years of eolian processes; however, the provenance and transport pathways of this dust remains unclear. Coastal loess deposits ranging in age from Pliocene to upper Pleistocene are present along the Atlantic margin of Argentina and provide information on sediment transport pathways for the last 4 million years. Nine samples of loess were collected and analyzed using detrital zircon U-Pb geochronology to better understand the source of these coastal loess deposits. All nine samples have similar provenance with most samples containing an age population from 0 – 30 Ma, 60 – 120 Ma, 160 – 200 Ma, 240 – 290 Ma, 350 – 400 Ma, 440 – 480 Ma, 520 – 640, and 960 – 1200 Ma. The age populations present in the coastal loess deposits are indistinguishable from detrital zircon age populations in late Miocene eolian and fluvial deposits from central Argentina, as well as late Pleistocene/Holocene eolian and fluvial deposits in the Pampas of central Argentina. This correlation indicates the coastal loess deposits are part of the same eolian system that deposited eolian sand and loess in central Argentina. A vertical trend is present throughout the coastal loess deposits suggesting that sediment sources may have changed over time. The data indicate an increased influx of sediment from northern Patagonia relative to other portions of the Andes. The cause of this trend remains unclear; however, dynamic climatic conditions during the Pleistocene may have been a primary driver of this provenance shift. Several hypotheses can explain how the coastal loess deposits received relatively greater influxes from more southerly locations. Overall, the coastal loess deposits represent an important record of eolian deposits from an eolian system that has been active in central Argentina for the last 7 million years.