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Quaternary accumulation and erosion of sediment in the drainage basins of the western escarpment of the Peruvian Andes: The role of climate variations

English title Quaternary accumulation and erosion of sediment in the drainage basins of the western escarpment of the Peruvian Andes: The role of climate variations
Applicant Schlunegger Fritz
Number 105188
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geology
Start/End 01.06.2005 - 31.05.2008
Approved amount 169'493.00
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Keywords (4)

QUATERNARY TERRACES; SURFACE PROCESSES; OSL DATING; PERU

Lay Summary (English)

Lead
Lay summary
We analyze whether sediment aggradation and erosion and in Peruvian valleys leading to the formation of cut-and-fill terraces is related to a particular climate, or a climate change. We concentrate on the Pisco valley in southern Peru and combine morphometric data from the landscape with sedimentological data and OSL ages from the cut-and-fill terraces to identify the processes leading to accumulation and removal of sediment in a detailed temporal framework. These data is then compared with the known pattern of climate changes on the Altiplano.
The sedimentological analysis of the terrace fill deposits displays a distinct sedimentary architecture that is characterized by polymict conglomerates with distal sources at base and monomict, locally sourced breccias at the top. This indicates the progradation of the locally sourced fans. Interestingly, the feldspar ages suggest that the time of aggradation is synchronous with wet periods on the Altiplano (Minchin and Tauca wet phases). However, sediment aggradation started earlier in the lower reaches than in the upper reaches. The phases of aggradation are synchronous with time periods of enhanced precipitation. Sediment aggradation started during the first half of a wet period and ended before the wet period was finished. This suggests that erosion also started before the end of a wet period.
The following scenario is therefore probable for the Rio Pisco drainage basin. As the climate is getting wetter, sediment that was previously build and stored on the hillslopes was transported into the trunk stream and transported towards the outlet of the basin. Because of the flattening of the river gradient, sediment starts to accumulate from down- to upstream. After the hillslopes are liberated from sediment, the free capacity of the trunk river to entrain and transport sediment increased leading to erosion of the previously deposited sediments. We think that erosion of the sediments, similar to aggradation, started in the lower reaches, and that the location of sediment entrainment migrated upstream with time. This implies that sediment aggradation occurred because of a change of climate rather than in response to a particular climate.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
121680 Chronology of sediment accumulation and surface erosion in the western Peruvian Andes in response to climate variations during the Quaternary: cosmogenic nuclide analysis, OSL dating and modelling 01.01.2009 Project funding (Div. I-III)
119615 Quaternary accumulation and erosion of sediment in the drainage basins of the western escarpment of the Peruvian Andes: The role of climate variations 01.06.2008 Project funding (Div. I-III)
126784 Quaternary glaciation and environmental history of the Alps: Establishing chronologies for proglacial deposits from northern Switzerland 01.02.2010 Project funding (Div. I-III)

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