Evidence for Eocene aridification of the Atacama Desert’s hyperarid core

Abstract The Atacama Desert is the most arid non-polar region on Earth, yet the timing and drivers of its hyperaridity remain debated. The earliest record of extreme aridification is preserved in the Coastal Cordillera of Northern Chile at the Oligocene-Miocene boundary. However, clast exposure ages on low-relief surfaces and supergene mineralisation ages suggest that low precipitation, and thus limited surface activity and weathering, may have been established earlier. To test the Miocene hyperaridity hypothesis, we have established a record of surface activity based on cosmogenic 21 Ne concentrations in 135 locally-derived quartz clasts from low-relief surfaces in the desert’s core. Thirty-two clasts have modelled exposure durations of Oligocene age or older. Their long-term surface preservation suggests exceptionally low landscape evolution rates and implies that aridification initiated earlier than the development of the Humboldt Current and major Andean uplift. We hypothesize that global cooling following the Early Eocene Climatic Optimum was likely a key driver of regional aridification.