Late Pleistocene alluvial fan evolution along the coastal Atacama Desert (N Chile)

Due to their sensitivity to both tectonic activity and climatic variations, coastal alluvial fans (CAF) along the western flank of the Coastal Cordillera in the Atacama Desert (northern Chile) are important geo-archives for unravelling Quaternary environmental change. Our study focuses on terrestrial and marine deposits of five CAF complexes between 20° and 25°S along the coastal zone of the Atacama to identify phases of alluvial fan activity during the Late Quaternary. Based on a combination of luminescence dating and 10Be cosmogenic nuclide exposure dating as well as existing chronological data in the area, insights into climatic variations along the hyper-arid coast are presented for the Late Pleistocene derived from CAF morphodynamics. Activity of alluvial fans could be documented during time spans 95–80 ka, 60–45 ka, 35–20 ka, as well as the Holocene. Numerical dating of marine terrace deposits gives insights into the tectonic uplift of the Coastal Plain in northern Chile during the Late Quaternary period, for which estimated uplift rates between ~0.06 and ~0.57 m/ka were derived. While tectonic activity induces base-level changes, long-term tectonic activity rather indirectly controls alluvial fan activity. We suggest that alluvial fan activity is mainly controlled by atmospheric changes from the Pacific Ocean. Based on our observations, CAF in the hyper-arid Atacama Desert serve as suitable geo-archives for reconstructing climate changes during the Quaternary. In particular, the usefulness of alluvial fan systems in a water-limited environment is important for understanding the palaeoenvironmental evolution in a coastal desert. •The alluvial fan evolution along the coast of Chile from 20°-25°S in the Atacama Desert is presented for the last 100 ka.•Activity of alluvial fans could be documented during time spans 95–80 ka, 60–45 ka, 35–20 ka, as well as the Holocene.•Estimated uplift rates between ~0.06 and ~0.57 m/ka were derived from marine formations for the Late Quaternary period.•Long-term tectonic activity only indirectly controls alluvial fan activity (base-level changes).•Alluvial fan activity is mainly controlled by atmospheric changes from the Pacific Ocean.