Fluvial responses to climate and tectonics throughout the Quaternary in the semi-arid Andes

• Increased erosion at the beginning of the Quaternary. • Asymmetrical erosion of the Andes due to linked changes in atmospheric circulation. • Major climate changes impact fluvial incision paced by tectonic uplift on long term. • Potential link between climate driven onshore erosion and subduction processes. How major shifts in climate over the Quaternary have affected topography is unclear, especially in tectonically active regions. This shortcoming is largely due to a lack of robust chronologies of landscape evolution over the last few million years. Here we document a rare case, where a fluvial landscape has been preserved well enough to record its responses to tectonic and climatic shifts throughout the Quaternary. Our results show that aggradation of sediment fill near the Huasco River mouth in the semi-arid Central Andes at the beginning of the Quaternary corresponds to an increased upstream erosion rate and we propose that this was due to glacial expansion. At 1.3 Ma, the river began to incise into these sediments, and at 1.0 Ma the rate of downcutting increased notably. The fluvial incision coincides with the Early-Middle Pleistocene Transition, when the periodicity of global climate cycles lengthened. We integrate these findings with marine terrace dating in the same region and find that, although fundamental changes of aggradation and incision were coeval with global climate change, the average rates of fluvial incision over million-year timescales are comparable to rates of uplift. Our findings imply that the Central Andean landscape has responded to major shifts in the frequency of orbitally-driven climatic cycles, impacting topography that is governed by tectonic uplift over longer timescales. As the supply of sediments offshore to subduction zones is considered to exert a control on uplift, our results have broader implications for feedbacks between climatic and tectonic processes.