Weathering and pedogenesis under coastal (hyper-)aridity deduced from 10Be exposure-dated alluvial fan morphostratigraphies, Atacama Desert

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

Processes and rates of weathering and pedogenesis in the hyperarid Atacama Desert are primarily controlled by the prevailing scarcity of water. In opposition to the interior of deserts, weathering and soil formation along the arid to hyperarid coasts are not well understood and require more in-depth research. The coastal Atacama receives comparatively large amounts of moisture – mainly because of orographic blocking of advective fog by the steep western Coastal Cordillera – and thereby constitutes a contrasting desert environment. We provide new insights into the post-depositional alteration of two Late Quaternary multi-stage alluvial fans at the marine-terrestrial interface of the western Atacama. For this purpose, we established morphochronologies primarily using cosmogenic 10Be exposure dating. By combining those (i) with remote sensing-based spectral, textural, and gravelometric differentiation of the morphostratigraphy at the northern fan complex (~22°S) and (ii) with an evaluation of physicochemical soil properties and micromorphological analyses along the chronosequence at the southern fan complex (~25°S), we inferred the processes and timescales of weathering and soil formation, respectively. The results indicate a formation of weathering rinds associated with the accumulation of secondary iron oxides, clast breakdown due to salt weathering, and denudation expressed in a continuous smoothing of the micro-relief. These processes lead to the development of mature desert pavements over timescales of 10^4 years. The weathering intensity during the Late Quaternary is found to depend on the oceanic moisture supply jointly driven by sea surface temperature variability and sea level fluctuations. Post-depositional alluvial fan alteration is characterized by initial yet clearly identifiable soil formation since the MIS 5e–c. Relationships of physicochemical parameters with age substantiate topsoil desalinization, decalcification coupled with dealkalinization, accumulation of soil organic matter, and initial rubification as well as loamification. Strongest pedogenesis apparently occurred during more humid phases between MIS 5 and the MIS 4/3-transition.

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

Sustainable Development Goals

SDG 14 – Leben unter Wasser

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/a8befe48-1eb6-4840-817a-f58e57eed44d