Fan morphodynamics under varying climatic and topographic gradients of the Chilean Andean forearc

Dry conditions in the Atacama and Andean forearc region, prevailing since the early Miocene, vary across geographic gradients and pluvial episodes. Areas of northern Chile experienced inherently different surface processes (e.g. evaporitic, periglacial, glacial), influencing fluvial system evolution and sediment signal propagation. We compare five Chilean alluvial fan sub-environments of varying aridity to assess sedimentary signal preservation. These sub-environments include 1) the hyper-arid, debris flow-dominated Chilean coastal fans that are largely incising and Late Quaternary in age; 2) the hyper-arid core Atacama with Quaternary fans impacted by evaporitic processes and paleolake level alterations; 3) the megascale Precordillera fans that date back to the Miocene; 4) fans in the arid transition from the upper Rio Loa valley to the High Andes that show evidence of periglacial processes and volcanic events; 5) finally, the semi-arid fans on the Altiplano of the western Andes that show evidence of Pleistocene glacio-fluvial aggradation and interfingering with lake sediments in addition to periglacial and volcanic events.

To investigate signal propagation, we assess the timing of terminal fan surface aggradation through terrestrial cosmogenic nuclides and luminescence dating, while documenting landscape processes. We also explore stratigraphic fan architecture, through numerical landscape evolution modeling, sedimentary bedding analysis, and ground-penetrating radar (GPR). Using this multi-method approach, we aim to disentangle how climatic and tectonic drivers shape sediment production and propagation in Andean forearc fan evolution. Results are preliminary, following multiple field campaigns, the latest in March 2025.