Universität zu Köln

Maßon, Linda ORCID: 0009-0008-1501-3134 (2025). Developing luminescence-based inventories to decipher particle histories in hyperarid alluvial landforms (Atacama Desert, Chile). PhD thesis, Universität zu Köln.

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Abstract

Deciphering particle histories in hyperarid alluvial landforms is crucial to reconstruct depositional and post-depositional dynamics. This is essential to understand landscape evolution and climatic variability in the Late Quaternary. In the Atacama Desert, the driest non-polar desert on Earth, such reconstructions are scarce since suitable chronological tools are lacking. Organic material for 14C dating is usually absent and cosmogenic nuclide dating methods cannot resolve subsurface processes related to post-depositional mixing. Single-grain feldspar luminescence dating can overcome those challenges, as feldspar grains are abundant and can record both deposition and post-depositional processes. However, this method also has limitations: Atacama Desert feldspars i) display unfavourable luminescence properties, ii) have heterogeneous geochemical compositions, and iii) experience heterogeneous bleaching, which is common in alluvial deposits. This thesis presents methodological refinements of single-grain feldspar luminescence dating techniques. These techniques are tested by applying them to decipher particle histories along a climatic and elevational transect in the Coastal Cordillera of the Atacama Desert. The overall aim is to establish a chronological toolset for complex alluvial settings in hyperarid regions and to apply it to improve the understanding of palaeoclimatic variability and landscape evolution in the Coastal Cordillera. The challenging luminescence properties of Atacama Desert feldspars result in time-consuming measurements, as many grains have to be analysed to obtain a sufficient number of suitable luminescence signals. In a first study the application of a standardised growth curve (SGC) was successfully tested on Atacama Desert samples. Measurement times were reduced by at least 60 %. It was further shown that the geochemical composition of feldspar grains is not correlated with their luminescence characteristics. This finding motivated a second study of the internal potassium (K) concentration of feldspar and its effects on dose rate calculations. A comparison of the three most cited literature-based values with measurement-based K-concentrations revealed that literature values overestimate the K-concentration in nine out of ten analysed samples. This results in systematic one-directional errors in the dose rate determination and consequently in the age calculation. To address this, a time- and cost-efficient approach was developed to routinely measure the K-concentration in feldspar for luminescence dating. In the third study of this thesis, this approach was successfully applied to samples from alluvial deposits along the climatic and elevational transect in the Atacama Desert. However, the SGC approach yielded unreliable results when applied to these samples. Therefore, in the third study a conventional single-aliquot regenerative-dose (SAR) approach was used for equivalent dose (De) estimations. The luminescence analyses were integrated into a multi-method framework that included granulometric and geochemical analyses as well as field surveys. Five soil and surface profiles along the climatic and elevational transect were examined. Depositional phases as well as post-depositional processes, including bioturbation and desert pavement formation, were identified. The results indicate wetter phases around 50 ka and since 5 ka, as well as prolonged geomorphic stability under presumably extremely arid conditions around 6 ka. These reconstructions are consistent with other palaeoenvironmental archives from the region and suggest a strong influence of regional climate variability, likely linked to (ENSO-related) weather anomalies. Overall, this thesis demonstrates that in complex alluvial landforms, which are prone to heterogeneous bleaching and contain feldspars with heterogeneous chemical compositions, special precautions are required. Dose rates must be determined accurately, accounting for variable internal K-concentrations. Furthermore, luminescence results must be interpreted holistically. This involves considering the shape of De distributions, age estimates, luminescence-related proxies, and geomorphological evidence, rather than focussing on a single age per sample. Applied in this way, single-grain feldspar luminescence dating provides a robust tool to decipher particle histories and thereby reconstruct the paleoenvironment, thus contribution to an improved understanding of Late Quaternary climatic fluctuations and landscape evolution in the hyperarid Atacama Desert.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Maßon, Linda linda.masson@gmx.de https://orcid.org/0009-0008-1501-3134 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-793552
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Geographisches Institut
Subjects:	Natural sciences and mathematics Earth sciences Geography and travel
Uncontrolled Keywords:	Keywords Language CRC1211 English Atacama Desert English Single-grain feldspar luminescence English
Date of oral exam:	28 November 2025
Referee:	Name Academic Title Reimann, Tony Prof. Dr. Tsukamoto, Sumiko Prof.Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/79355