Implications for Late Quaternary climate, weathering, and soil formation at Atacama’s hyperarid coast drawn from trapped charge- and cosmogenic nuclide-dated alluvial fans

Autor(en)

Janek Walk, Melanie Bartz, Ariane Binnie, Martin Kehl, Ramona Mörchen, Philipp Schulte, Xiaolei Sun, Georg Stauch, Christopher Tittmann, Roland Bol, Helmut Brückner, Frank Lehmkuhl

Abstrakt

The limited availability of water in the hyperarid Atacama Desert governs the occurrence and magnitude of hydromorphodynamic events, subsequent formation of fluvial and alluvial landforms, biotic activity, weathering, and soil formation. While those aspects have received considerable attention by geoscientists in the core of the desert, they are as yet not well understood especially in the coastal environment. In contrast to the interior, the coast receives much larger amounts of moisture – partly due to slightly higher precipitation but mainly as a result of orographic blocking of advective fog by the Coastal Cordillera between ~500 and ~1,200 m above sea level.

We present a synthesis of six years of research on the coastal alluvial fans of the Atacama Desert (20.5–25.5°S), conducted within the framework of the CRC 1211 “Earth – Evolution at the dry limit”, and provide new insights into the processes and timing of their primary aggradation as well as secondary, post-depositional alteration by weathering and pedogenesis. Therefore, we established a regional geochronological framework based on both trapped charge dating (K-feldspar luminescence and electron spin resonance) and cosmogenic 10Be exposure dating. The latter was additionally applied for chronosequence studies on two specific multi-stage alluvial fans. Combining the morphochronologies with a morphostratigraphy (spectral, textural, and gravelometric surface characteristics) on the one hand, and a pedostratigraphy (physicochemical soil properties) on the other, allowed to deduce the types and rates of weathering and soil formation, respectively.

Our results indicate that increased fan aggradation occurred throughout Late Pleistocene and Holocene periods of higher pluvial activity nourished by the Pacific, while fan generations older than the last interglacial period are absent or only preserved in form of small remnants. Post-depositional formation of weathering rinds, clast breakdown due to salt weathering, and denudation results over timescales of 10^4 years in mature desert pavements. The weathering intensity during the Late Quaternary is found to be related to sea surface temperature variability and sea level variations jointly driving the oceanic moisture supply. Towards the south, higher (palaeo)precipitation resulted in more advanced soil formation characterized by initial humification, decalcification closely coupled with acidification, rubification, and loamification.

Organisation(en)

Institut für Geographie und Regionalforschung

Externe Organisation(en)

Rheinisch-Westfälische Technische Hochschule Aachen, Universität zu Köln, Université de Lausanne, Rheinische Friedrich-Wilhelms-Universität Bonn, Forschungszentrum Jülich

Publikationsdatum

2023

ÖFOS 2012

105404 Geomorphologie, 105127 Geochronologie, 105402 Bodengeographie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/650a6acf-0859-45db-ac48-33ce3a10a3d5