Research Article Paleoenvironmental Evolution of a Forearc in Response to Forcings by Drainage, Climate, Volcanism, and Tectonics: The Quillagua Depocenter, Chile Teresa Jordan , 1 Andrés Quezada , 2 Nicolás Blanco , 2 Arturo Jensen , 3 Paulina Vásquez , 2 and Fernando Sepúlveda 2 1 Earth & Atmospheric Sciences, Snee Hall, Cornell University, Ithaca, NY 14853, USA 2 Servicio Nacional de Geología y Minería, Avenida Santa María 0104, Providencia, Metropolitana 7530263, Chile 3 Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta 1240000, Chile Correspondence should be addressed to Teresa Jordan; tej1@cornell.edu Received 23 August 2021; Accepted 2 December 2021; Published 18 January 2022 Academic Editor: Alexander R. Simms Copyright © 2022 Teresa Jordan et al. Exclusive Licensee GeoScienceWorld. Distributed under a Creative Commons Attribution License (CC BY 4.0). The Late Miocene and Pliocene Quillagua depocenter lake system existed in a forearc basin on the west side of the Andes Mountains in northern Chile, alternating between standing-water and salar conditions. Quaternary incision of the Loa River Canyon resulted in bypass of the prior depositional surface and drainage of groundwater from the abandoned depocenter. Systematic regional geological mapping, 32 new chronological constraints on the strata in the basin, outcrop-scale facies analyses, and geophysical data underpin a revised evaluation of the controls on the lake system. The progressive stages, ages, and causes of the Quaternary destruction of the lake system are reconstructed based on mapped distributions of superficial fluvial sediments, chronological studies of terrace deposits, and landform analysis. The lake system occurred at the junction of small catchments draining the slowly rising western Andean foothills and the large paleo-Loa River catchment draining the Andean volcanic arc, during a time span of intense caldera activity. Small magnitude climate variability affected both the hyperarid low elevation sectors and arid upper sectors of the catchments. By 10 Ma, the regional climate was extremely arid, limiting water and sediment to small amounts, and during the Late Miocene and Pliocene, there was no surface-water outlet to the Pacific. Hydrological variations from 9 to 2.6 Ma led to sediment accumulation in variable lake environments, alternating with long hiatuses. Minor deformation within the Quillagua depocenter shifted the topographic axis and groundwater outlets. Simultaneous headward erosion from the Pacific shore captured the Loa River, which triggered large-magnitude incision that persists today. The progression of surface water environmental change was accompanied by changing composition and amount of surface and groundwater, which determined deposition of primary evaporite minerals, extensive diagenesis, and eventually, complex patterns of dissolution expressed as karst. 1. Introduction The Quillagua depocenter in the hyperarid Atacama Desert of the southern Tropics in Chile (Figure 1) shifted over the last 9 million years among conditions ranging between internal drainage that created a lake which was at times fully evaporated and other times fresh water, to the erosion of a 260 m deep canyon. In this paper, we dissect the complex roles of drainage basin evolution, deformation, volcanic activity, and climate change during the accumulation of 200 m of upper Miocene to Pliocene fluvial, shallow lacus- trine, and evaporite deposits, as well as during their postde- positional diagenetic alternation and partial erosional destruction. This paper’s new analysis is based largely on new regional mapping, tephra dating, and facies descriptions by the Chilean geological survey [1]. The Quillagua depocenter is a distal part of the latest Oligocene to present Pampa del Tamarugal (PdT) forearc basin (Figures 1 and 2) [2–4]. The 400 km long Loa River drains through the Quillagua depocenter. Today, the entire GeoScienceWorld Lithosphere Volume 2022, Article ID 1024844, 27 pages https://doi.org/10.2113/2022/1024844 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/doi/10.2113/2022/1024844/5514759/1024844.pdf by guest on 20 January 2022