Environmental changes during the Upper PleistoceneeHolocene in Mediterranean NE Spain as recorded by the mineralogy and geochemistry of alluvial records Joaquín Bastida a , María Cinta Osácar b , Carlos Sancho b, * , Arsenio Muñoz b a Departamento de Geología, Universidad de Valencia, Doctor Moliner 50, 46100 Burjassot, Valencia, Spain b Departamento de Ciencias de la Tierra, Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain article info Article history: Available online 14 March 2013 abstract Landscape evolution and environmental conditions from Last Glacial Maximum (LGM) to Late Holocene times were reconstructed from the mineralogical and geochemical characteristics of the alluvial mor- phochronostratigraphy, recorded in Bardenas Reales Natural Park (Ebro Basin, NE Spain). Alluvial ar- chitecture includes a LGM-Holocene gravelly unit (z22e9 ka BP), a Lower Holocene siltyemuddy unit (z9e7 ka BP), and an Upper Holocene sandy unit (z5e0.1 ka BP). Increases in illiteesmectite mixed layers, kaolinite, chlorite and modified Chemical Index of Alteration (CIA*), as well as the decrease in illite FWHM(E), are indicators of minor increases in the chemical weathering of the alluvial sediments. The results suggest that this area, although under broad semiarid conditions, underwent the following environmental evolution: i) an increasing trend in moisture availability in the Lower Holocene, and ii) a variable pattern in water disposal at the onset of the Upper Holocene, followed by a decrease in humidity during the last millennium. This reconstruction proves the usefulness of mineralogical and geochemical proxies as indicators of rapid environmental changes under Mediterranean conditions. Ó 2013 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Alluvial geomorphic systems from semiarid lands are highly sensitive to Holocene environmental variability. Their response leads to successive aggradational/erosional phases building com- plex morphopedostratigraphic sequences. The study of Holocene alluvial archives during the last decade has produced relevant regional information to improve palaeoclimatic reconstructions and to recognise past analogue scenarios of future climate pre- dictions. The works carried out in the southwestern U.S. (Waters and Haynes, 2001; Bacon et al., 2010; Jones et al., 2010; Miller et al., 2010) and in the Mediterranean region (Faust et al., 2004; Thorndycraft and Benito, 2006; Sancho et al., 2008a; Zeilhofer and Faust, 2008; Zielhofer et al., 2008, 2010) are key examples. Widespread Holocene alluvial deposits have been documented in the Bardenas Reales Natural Park (Ebro Basin, NE Spain) (Sancho et al., 2008a). This study focuses on mapping, dating and analysis of the sedimentary and pedogenic features of alluvial units to reconstruct regional short-term environmental changes. Alluvial aggradation is essentially associated with increase in aridity and/or high hydrological variability (Sancho et al., 2008a). Moreover, this interpretation has been improved by using additional indicators, such as gastropod content (Murelaga et al., 2012) and magnetic properties (Gómez-Paccard et al., 2013). In this context, mineralogy and geochemistry can become interesting tools for complementary palaeoenvironmental readings. Preliminary data were reported by Osácar et al. (2009) and Bastida et al. (2010). Mineralogical and geochemical analyses from Holocene records have been reported from different sedimentary environments, such as soils (Kirkwood and Nesbitt, 1991), floodplain deposits (Moldenhauer et al., 2008), Mediterranean alluvial soils (Zielhofer et al., 2009; Grygar et al., 2010), colluvial and fan deposits (Blättermann et al., 2012), and marine sediments (Montero-Serrano et al., 2010; Youn and Kim, 2011). These works address the palaeoenvironmental implications, in terms of weathering, and/or evaluations of the source area of sed- iments. Clearly, the available baseline information on alluvial records is very limited. 2. Study area Bardenas Reales Natural Park and World Biosphere Reserve is located in the western sector of the Ebro Basin (Fig. 1), in the * Corresponding author. E-mail address: csancho@unizar.es (C. Sancho). Contents lists available at SciVerse ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ e see front matter Ó 2013 Elsevier Ltd and INQUA. All rights reserved. http://dx.doi.org/10.1016/j.quaint.2013.02.041 Quaternary International 302 (2013) 3e19