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Postglacial alluvial fan dynamics in the Cordillera Oriental, Peru, and palaeoclimatic implications

Published online by Cambridge University Press:  18 December 2018

Kevin Ratnayaka
Affiliation:
Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstraße 24, 48149 Münster, Germany
Ralf Hetzel*
Affiliation:
Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstraße 24, 48149 Münster, Germany
Jens Hornung
Affiliation:
Technische Universität Darmstadt, Institut für Angewandte Geowissenschaften, Schnittspahnstraße 9, 64287 Darmstadt, Germany
Andrea Hampel
Affiliation:
Institut für Geologie, Leibniz Universität Hannover, Callinstraße 30, 30167 Hannover, Germany
Matthias Hinderer
Affiliation:
Technische Universität Darmstadt, Institut für Angewandte Geowissenschaften, Schnittspahnstraße 9, 64287 Darmstadt, Germany
Manfred Frechen
Affiliation:
Leibniz Institute for Applied Geophysics, Geochronology & Isotope Hydrology, Stilleweg 2, 30655 Hannover, Germany
*
*Corresponding author at: Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Corrensstraße 24, 48149 Münster, Germany. E-mail address: rahetzel@uni-muenster.de (R. Hetzel).

Abstract

Alluvial fans record climate-driven erosion and sediment-transport processes and allow reconstructing past environmental conditions. Here we investigate the sedimentation history of two alluvial fans located in formerly glaciated valleys of the Cordillera Oriental, Peru. 10Be exposure ages from the fan surfaces and radiocarbon ages from the fan interiors constrain the final stages of fan formation. The 10Be and 14C ages cluster mainly between 13.3–9.3 ka and 11,500–9700 cal yr BP, respectively. Our age data set indicates that—after deglaciation—large amounts of fan sediment were deposited until ∼10 ka, when sedimentation rates declined rather abruptly. This pattern is supported by 10Be erosion rates for the fan catchments, because under the assumption of constant erosion the time needed to erode the material stored in the fans significantly exceeds their age. Correlating our ages with regional climate records indicates that precipitation exerts the primary control on fan sedimentation. Two periods with elevated lake levels and increased precipitation between 18 and 14.5 ka and from 13 to 11.5 ka resulted in rapid deposition of large fan lobes. Subsequently, lower precipitation rates decreased erosion in the catchments and sediment delivery to the fans, which have remained largely inactive since ∼9.5 ka.

Type
Research Article
Copyright
Copyright © University of Washington. Published by Cambridge University Press, 2018. 

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