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Title: The timing of alluvial fan deposition along the Northern coast of Chile constrained by luminescence and electron spin resonance dating
Authors: Bartz, Melanie
Duval, Mathieu
Brill, Dominik
Zander-Heinz, Anja Christina
King, Georgina
Walk, Janek
Stauch, Georg
Lehmkuhl, Frank
Brückner, Helmut
Issue Date: 2019
Publisher: International Union for Quaternary Research
Citation: 20th Congress of the International Union for Quaternary Research (INQUA), 2019, O-4114
Abstract: Coastal alluvial fans (CAFs) in northern Chile are of crucial interest for studying the Quaternary environmental evolution of the hyper-arid Atacama Desert. This research, however, is limited by the small amount of chronological data currently available to constrain these CAF deposits. Optically stimulated luminescence (OSL) dating of quartz has proven challenging in these deposits due to unsuitable OSL signal properties. Therefore, we aim to establish a chronostratigraphic framework for CAFs between 21°S and 25°S by using a combination of post-infrared infrared (pIRIR) stimulated luminescence dating of K-feldspar and electron spin resonance (ESR) dating of quartz. Samples were taken from alluvial deposits, as well as from marine and aeolian sediments embedded in the CAF. Preliminary numerical dating results can be summarized as follows: pIRIR dose distributions of alluvial fan samples are characterised by relatively high overdispersion and positive skewness, in contrast to marine and aeolian deposits. Measurement of modern analogue sediments indicates that this can be attributed to partial signal resetting, due to different transport mechanisms. Following the quartz multiple centre (MC) ESR dating approach, both the Al and the Ti centres were measured in order to evaluate whether full bleaching of the different centres has been achieved prior to deposition. While the Ti-H centre provides lower doses than the Ti-Li centres, in most cases the Al centre provides the highest dose values. This pattern is consistent with their respective bleaching kinetics and suggests that the Ti-H signal most likely provides the closest estimate to the true burial dose. ESR ages (Ti-H, Ti-Li) are consistent with the luminescence dating results at 1σ for most of the samples. Differences between pIRIR and ESR age estimates might be explained by incomplete bleaching of the ESR signals during short-term debris-flow transport. First numerical ages date the lowermost marine terrace to the MIS 5, providing a maximum age for alluvial fan deposition directly at the coast. Marine terraces give insights into the tectonic activity in the area during the Late Pleistocene, leading to estimated uplift rates of ~0.3 m/ka. Aeolian sand interbeds in the alluvial fan complex and alluvial fan deposits date to ~60-30 ka and ~15 ka, giving insights into the palaeoclimate, regional geomorphology and wind pattern in the study area. To conclude, our results show the need to develop reliable dating approaches in environments where the standard OSL dating procedures do not work. In this context, the conjunction of pIRIR and MC ESR dating can be considered as a promising tool to decipher Late Pleistocene landscape dynamics along the northern coast of Chile.
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Type: Presentation
Appears in Collections:Congresos, encuentros científicos y estancias de investigación

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