Late Pleistocene fans and terraces in the Majes valley, southern Peru, and their relation to climatic variations Damian Steffen • Fritz Schlunegger Frank Preusser
Received: 19 November 2008 / Accepted: 10 October 2009 / Published online: 15 November 2009 Ó Springer-Verlag 2009
Abstract This study investigates the connection between sediment aggradation, erosion and climate in a desert environment of the Majes valley, southern Peru. Luminescence dating of terraces and fans shows that sediment aggradation correlates with wet time intervals on the Altiplano, suggesting a climatic inﬂuence on the aggradation–degradation cycles. Major periods of aggradation occurred between *110–100, *60–50 and 12–8 ka. More precipitation in the Majes catchment resulted in increased erosion and transportation of sediment from the hillslopes into the trunk river. As a result, the sediment loads exceeded the transport capacity of the Majes River and aggradation started in the lower reaches where the river gradient is less. Depletion of the hillslope sediment reservoirs caused a relative increase in the capacity of the trunk river to entrain and transport sediment, resulting in erosion of the previously deposited sediment. Consequently, although climate change may initiate a phase of sediment accumulation, degradation can be triggered by an autocyclic negative feedback and does not have to be driven by climatic change. Keywords Alluvial fan Á Terrace Á Luminescence dating Á Peru Á Paleoclimate
Introduction and motivation The response of geomorphic systems to climate change has been a challenging research ﬁeld in ﬂuvial geomorphology. D. Steffen (&) Á F. Schlunegger Á F. Preusser ¨ Institute of Geological Sciences, Universitat Bern, Bern, Switzerland e-mail: firstname.lastname@example.org
Records of change are preserved in stratigraphic archives, and successful reconstructions of response require a correct interpretation of these archives, which, in turn, crucially depends on the chronological framework. In their review paper on ﬂuvial response to climate and sea-level changes, ¨ Blum and Tornqvist (2000) conclude that the majority of research has focused on the past 20 ka at most because of a lack of adequate tools to assess the age of older deposits. Therefore, very little is known about how sediment transfer in a drainage network changes with external forcing, in general, and climate change, in particular, which operate at longer time scales. Luminescence dating is an important tool for studies over longer time spans, because the material required (i.e. quartz and feldspar minerals present as ﬁne- to medium-grained sand) is abundant in almost all sedimentary environments, which is not always the case with organic matter necessary for radiocarbon dating. Furthermore, the age range of luminescence dating is in the order of several hundred thousand years, depending on the luminescence properties of the sample (e.g. Wallinga 2002). The western escarpment of the Andes in southern Peru has proven to be an ideal region to study the response of the sediment transfer system to climate perturbations because Late Pleistocene cut-and-ﬁll terraces that are recorders of change are abundant (e.g. Steffen et al. 2009a), and the aridity allows for the preservation of these archives. Previous studies have been limited to the Peruvian coast and, with few exceptions, to late Holocene time scales (e.g. Fontugne et al. 1999; Keefer et al. 2003; Magilligan and Goldstein 2001; Magilligan et al. 2008; Sandweiss 2003; Wells 1990). Most of this research relates sediment depo˜ sition to warm El Nino-Southern Oscillation (ENSO) ˜ events (El Nino), although assignments of sedimentary deposits to high magnitude precipitation events have been
Int J Earth Sci (Geol Rundsch) (2010) 99:1975–1989
challenged (Ortlieb and Vargas 2003; Vargas et al. 2006)....