EVIDENCE OF LONG-LIVED EOLIAN SYSTEMS IN CENTRAL SOUTH AMERICA: OBSERVATIONS FROM THE CHACO PLAINS AND THE SIERRA ACONQUIJA

South America is well known for its eolian deposits. This study provides new observations that hope to constrain the temporal and spatial relationships between eolian deposits in the Aconquija Range and the Chaco Plains to the east. Detrital zircon geochronology provides a tool to constrain the provenance of these deposits between connecting the eolian systems in central South America.

Field observations from the valleys north of the city of Catamarca within the southern Aconquija Range of the Sierra Pampeanas recognize moderately east-dipping paleosol-bearing loessic and fine sand deposits interlayered with volcanic ash and underlying more recent colluvial detritus. Timing of uplift in this region is suggested to be Miocene-Pliocene. This might suggest an earlier history of eolian sediment dispersal across a large swath of the central Andes orogen (near 28⁰ S). This differs greatly in age to the loessic sediments of Tafi del Valle also found in the Aconquija Range, which holds a record of about the last ~1 Ma of eolian deposits. The Tafi del Valle deposits have been shown to be derived from northwesterly winds coming off the Puna Plateau. The Chaco Plain is over 800,000 km² of poly-megafans comprised of eolian, fluvial, and pluvial sediments. Previously generated detrital zircon data demonstrates that the Late Pleistocene - Holocene Chaco eolian sediments are transported by northerly winds recycling sediments from rivers and playa lakes. This region is heavily affected by the South American monsoon system and is generally independent from the Pampean eolian system to the south. The new observations from the Catamarca region suggest that the wind-blown sediment pathways were established earlier than previously defined across the Puna Plateau. Understanding long-lived eolian sediment pathways will help paleoclimatic reconstructions with similar geologic configurations.