Constraining the paleoclimate of the Northern Atacama Desert, Chile using luminescence dating of alluvial fan stratigraphy

Despite the modern hyperaridity of the Atacama Desert (mean annual rainfall <1 mm), evidence for wetter climates during the Holocene have been found in cores from salars (i.e., salt flats) and sedimentary basins. There are several major discrepancies in the Holocene climate of the Atacama Desert after the Last Glacial Maximum, including asynchronous wet phases in the Coastal Cordillera and the Altiplano as well as a discordance between paleo-wetland and Salar de Atacama chronology. We address the following research question: How did fluvial and mass flow activity in the Atacama Desert respond to regionally fluctuating hyperaridity throughout the Quaternary period?  A series of large alluvial fans sourcing from the western Andean foothills that terminate at these salars remain largely underutilized as a paleoclimate record, though alluvial fan stratigraphy is often used to reconstruct past environmental conditions. These alluvial fans, which may serve as a bridge between competing paleoclimate signals, have modern transport and depositional processes that include layered, overbank mudflows that extend laterally for up to hundreds of meters from the channel, aeolian reworking of inactive fan surfaces, and terminations in playa-like environments. To determine how fan activity is tied to Quaternary climate change, we made detailed stratigraphic correlations of 6 sedimentary facies across 18 study sites along the fan sourcing from Quedabra de Chacarilla. We then used single-grain post-infrared infrared stimulated luminescence (post-IR IRSL) to precisely date 11 samples taken from interpreted aeolian-deposited facies within the stratigraphy. Detailed chronology of the fan stratigraphy using post-IR IRSL will allow us to compare with other regional climate proxies and understand how Atacama alluvial fans record and preserve evidence of past climate evolution. This will advance our understanding for how future climatic changes in the region may impact people and infrastructure due to mudflow-based flooding.