Catena 103 (2013) 30–43 Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena Environmental response of a fragile, semiarid landscape (Bardenas Reales Natural Park, NE Spain) to Early Holocene climate variability: A paleo- and environmental-magnetic approach M. Gómez-Paccard a,⁎, J.C. Larrasoaña a,b, C. Sancho c, A. Muñoz c, E. McDonald d, E.J. Rhodes e, M.C. Osácar c, E. Costa f, E. Beamud g a Institut de Ciències de la Terra Jaume Almera, CSIC, C/Solé i Sabarís s/n, 08028 Barcelona, Spain b Instituto Geológico y Minero de España, Unidad de Zaragoza, C/Manuel Lasala 44, 9B, 50006 Zaragoza, Spain c Departamento de Ciencias de la Tierra, Universidad de Zaragoza, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain d Division of Earth and Ecosystem Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 USA e Department of Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095-1567, USA f Grup de Geodinàmica i Anàlisi de Conques (GGAC), GEOMODELS Research Institute, Departament d'Estratigrafia, Paleontologia i Geociències Marines, Universitat de Barcelona, C/Martí i Franquès s/n, 08028 Barcelona, Spain g Grup de Geodinàmica i Anàlisi de Conques (GGAC), GEOMODELS Research Institute, Laboratori de Paleomagnetisme CCiTUB-CSIC, Institut de Ciències de la Terra Jaume Almera, CSIC, C/Solé i Sabarís s/n, 08028 Barcelona, Spain article info abstract Article history: The Bardenas Reales Natural Park (western Ebro Basin, NE Spain) constitutes a fragile landscape where the Received 14 May 2010 prevailing semiarid climate and erodability of the bedrock have resulted in high sensitivity to Received in revised form 10 March 2011 erosion/sedimentation oscillations during the Holocene. In this paper, we present new chronologic, Accepted 13 May 2011 sedimentologic, paleomagnetic and environmental magnetic results from the oldest unit (Qah1) of a system of nested cut-and-fill alluvial sequences, which is 18 m thick and crops out extensively in the central part of Keywords: the natural park at the Bardena Blanca Depression. Radiocarbon dating indicates that Early Holocene unit Paleomagnetism Environmental magnetism Qah1 is younger than 9.38–8.89 cal kyr BP and gives ages of 8.92–8.42 and 7.59–7.37 cal kyr BP in the middle Early Holocene and uppermost parts of the unit, respectively. Sedimentologic data indicate that distal alluvial sediments of Alluvial sediments unit Qah1 accumulated in sandy mud flats and ephemeral playa lakes under arid conditions. The coincidence Climate variability of enhanced magnetite content with moderate to intense root bioturbation in the lowermost and likely also Iberian Peninsula uppermost sediments of unit Qah1 suggests that magnetite formed authigenically in response to relatively wetter conditions at the beginning and end of this dry period. These results indicate that onset and cessation of alluvial aggradation mark the passing of a geomorphologic threshold, most likely plant cover in the watershed, during a progressive drying–wetting event. The radiocarbon-based age model of unit Qah1 indicates that alluvial aggradation under arid conditions began at 9.13 cal kyr BP and ended at 7.16 cal kyr BP. This period is strikingly centered at around the 8.2 kyr cold event but spans a longer time period, supporting the notion of a global climatic deterioration as the underlying cause for this event. Paleomagnetic directions do not clearly display the characteristic patterns recognized in paleosecular variation curves derived from other European lacustrine sediments and cannot be used to refine the radiocarbon-based age model for unit Qah1. Our results demonstrate a quick and strong response of alluvial systems to Early Holocene climate variability in fragile Mediterranean landscapes such as those at the semiarid Bardenas Reales Natural Park. © 2011 Elsevier B.V. All rights reserved. 1. Introduction mean temperatures, decreased precipitation, and an increase in high temperature and drought events resulting from enhanced interannual Climate models predict that global change will preferentially affect variability (Born et al., 2008; Giorgi and Lionello, 2008). The Ebro semiarid landscapes such as those within the Mediterranean area Basin (Fig. 1) is a semiarid region located in NE Spain and is therefore (Intergovernamental Panel on Climate Change, 2007). Projected expected to be especially vulnerable to future climate change. The conditions for southern European semiarid regions indicate higher Bardenas Reales de Navarra in the western sector of the Ebro Basin constitutes a Natural Park and World Biosphere Reserve aimed at preserving fragile semiarid landscapes and ecosystems typical of the ⁎ Corresponding author. Tel.: +34 934095410; fax: +34 934110012. Mediterranean region. The Lower Miocene bedrock of the central E-mail address: [email protected] (M. Gómez-Paccard). sector of Bardenas Reales consists of easily erodable clayey units that 0341-8162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2011.05.013 M. Gómez-Paccard et al. / Catena 103 (2013) 30–43 31 a o 2 W 44o b PamplonaPamplona PYRENEESPYRENEES 42o TudelaTudela E bro RiverEBRO BASIN IBERIANIBERIANZaragozaZaragoz RANGEa Ebro Barcelona Tres RAN River G Mugas E Ebro Basin 40o o o Cornialto Mountain ranges 2 E 4 E Estroza Bardena Blanca Depression Ebro River Rallón Arguedas Tripa Azul Holocene (alluvial & Pilatos fluvial sediments) Pleistocene (terraces & piedmonts) continental Tudela formations Miocene Ujué N Lerín Tudela 0 10 km c Arroyo Vedado Grande o y o r r A 300 m Fig. 1. a) Location of the study area within the context of the NE Iberian Peninsula. b) Geological sketch map of the Bardenas Reales Natural Park area, with location of the Bardena Blanca Depression watershed (dashed line). c) Aerial picture of the studied section at the Arroyo Vedado section whose location is indicated by a white circle (UTM Coordinates ED50/Zone 30N, x: 623001; y: 4675808). The location of the Arroyo Vedado section within the Bardena Blanca Depression is marked by the small rectangle in (b). have conditioned, along with the prevailing semiarid climate, a sensitivity in terms of erosion and sedimentation oscillations, which particular landscape characterized by a wide depression bordered by have resulted in development of several nested cut-and-fill alluvial high-gradient water divides. These characteristics impose high sequences in response to Holocene climate variability (Sancho et al., 32 M. Gómez-Paccard et al. / Catena 103 (2013) 30–43 2008a). While the basic lithostratigraphic, chronostratigraphic and (Tripa Azul, 630 m) to the south and Lower Miocene buttes and mesas paleoenvironmental framework for these sequences has been capped by remnants of Plio-Pleistocene cover pediments to the north addressed in several studies (Muñoz et al., 2006; Sancho et al., (La Estroza, 462 m; Cornialto,510m)andeast(Rallón,470m). 2008a, 2008b), details of the link between surface processes and Bedrock of the Bardena Blanca consists of the uppermost landscape evolution with Holocene climate change remain to be sediments of the Lerín Formation, the lowermost sediments of the firmly established. This information would complement available overlying Tudela Formation, and their lateral equivalents to the north knowledge of paleoenvironmental conditions derived from other (Ujué Formation) (Larrasoaña et al., 2006). These sediments consti- alluvial (Gutiérrez and Peña, 1998; Peña et al., 2000, 2004) and tute thick mudstone sequences with sporadic intercalations of lacustrine (Davis and Stevenson, 2007; González-Sampériz et al., gypsum, sandstone, and limestone beds deposited in distal alluvial 2008; Valero-Garcés et al., 2000) archives from the Ebro Basin. and palustrine environments that occupied the central fringe of the Disentangling paleoclimatic oscillations from the Holocene sedi- land-locked Ebro Basin during the Early Miocene (Larrasoaña et al., mentary record requires development of high resolution and accu- 2006; Muñoz et al., 2002). Connection of the Ebro Basin with the rate chronologies, which are typically based on radiometric (14C and Mediterranean Sea during the Late Miocene (Muñoz et al., 2002) U–Th) and luminescence dating. In recent years, paleomagnetism marked the beginning of Quaternary downcutting of the fluvial has been increasingly used as an ancillary tool to date Holocene network. Nevertheless, short periods of aggradation led to formation sediments through recognition of secular changes in the intensity of Early Pleistocene terraces of the Ebro and Aragón rivers and related (relative paleointensity: RPI) and direction (i.e., paleosecular varia- cover pediments (Léranoz, 1993). tion: PSV) of the Earth's magnetic field. Thus, PSV and RPI curves have The Bardena Blanca Depression constitutes a singular semiarid contributed to establishing the chronology of both marine (e.g., Evans landscape with intensive processes driven by high erodibility of the et al., 2007; Lise-Pronovost et al., 2009; Rolph et al., 2004; Willmott bedrock, heavy rainfall, and scarce vegetation cover. In addition, this et al., 2006) and lacustrine (e.g., Chaparro et al., 2008; Gogorza et al., area has been the focus of historical human impact due to intensive 2002; Haberzettl et al., 2009; Irurzun et al., 2009; Rolph et al., 2004; agricultural and grazing practices, especially during the last 10 cen- Snowball et al., 2007) records worldwide. Paleoclimatic