Abstract
Dating of extensive alluvial fan surfaces and fluvial features in the hyperarid core of the Atacama Desert, Chile, using cosmogenic nuclides provides unrivalled insights about the onset and variability of aridity. The predominantly hyperarid conditions help to preserve the traces of episodic climatic and/or slow tectonic change. Utilizing single clast exposure dating with cosmogenic 10Be and 21Ne, we determine the termination of episodes of enhanced fluvial erosion and deposition occurring at ~19, ~14, ~9.5 Ma; large scale fluvial modification of the landscape had ceased by ~2–3 Ma. The presence of clasts that record pre-Miocene exposure ages (~28 Ma and ~34 Ma) require stagnant landscape development during the Oligocene. Our data implies an early onset of (hyper-) aridity in the core region of the Atacama Desert, interrupted by wetter but probably still arid periods. The apparent conflict with interpretation that favour a later onset of (hyper-) aridity can be reconciled when the climatic gradients within the Atacama Desert are considered.
Highlights
The Atacama Desert of northern Chile is one of the driest places on Earth, with an extreme hyperarid core (Coastal Cordillera & Central Depression between 19° and 22°S), receiving less than 2 mm/yr modern precipitation[1,2]
The absence of fluvial erosion means that long-term tectonic activity is a prominent control on landscape evolution in the hyperarid core of the Atacama Desert
The Atacama Fault System (AFS) was active throughout the Cenozoic[23,25]; the topographically subtle surface expressions of its trace are preserved throughout the hyperarid core of the Atacama Desert
Summary
The Atacama Desert of northern Chile is one of the driest places on Earth, with an extreme hyperarid core (Coastal Cordillera & Central Depression between 19° and 22°S), receiving less than 2 mm/yr modern precipitation[1,2]. The Andes Mountains to the east (Fig. 1) cast a rainshadow over the Atacama Desert as moisture originating from the Atlantic becomes orographically elevated, causing precipitation on the eastern Andean flank and a relative absence westwards[4]. These effects, coupled with high evaporation rates in most areas of the Atacama Desert strengthen hyperarid conditions[4,5]. The absence of fluvial erosion means that long-term tectonic activity is a prominent control on landscape evolution in the hyperarid core of the Atacama Desert. Preservation of Early Miocene alluvial fan surfaces indicate a predominantly (hyper-) arid climate conditions since the Early Miocene
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