Holocene sedimentary history of the Silala River (Antofagasta Region, Chile)

Assessing past and ongoing climate change in the central Andes is critical for understanding the impact of future environmental changes under anthropogenic warming. Emerging from springs located in Bolivia and flowing into northern Chile's Atacama Desert, the Silala River contains inset, terraced wetland (or in-stream) deposits that provide a unique opportunity to study the impact of past hydroclimate change in a sensitive groundwater system with a small catchment area. After an initial (late Pleistocene) period of deep incision to form the present ravine, in-stream wetland fine-grained deposits formed during three phases of aggradation dated to >8.5-1.9 ka (Unit 1), >0.65-0.2 ka (Unit 2), and <0.2 ka to the recent 20th century (Unit 4). These phases of accumulation were coeval with periods of well-dated records of elevated groundwater tables throughout northern Chile. Phases of abrupt downcutting occurred due to a lowering of the water table after 1.9 ka and before 0.2 ka. The cycle of erosion and deposition clearly continues to the present as evinced by the very recent (21st century) incision of Unit 4 (>1.5 m in some areas) throughout sectors of the Silala where dried-out standing vegetation can be seen. Such recent incision may be due to multiple different factors, including recent climate change coupled with intense extraction of groundwater resources by the copper mining industry. This article is categorized under: Human Water > Water Governance Science of Water > Hydrological Processes Science of Water > Water and Environmental Change