Quaternary evolution of the Cordillera Frontal piedmont between c. 33° and 34°S Mendoza, Argentina

Abstract

The piedmont of Cordillera Frontal between c. 33° and 34°S (Mendoza, Argentina) is a highly populated area deeply modified by human activities, known as Valle de Uco. It is situated within the borderland region of the geological provinces of Cordillera Frontal and Cuyo basin. The landscape is dominantly composed of both erosional and depositional landforms made of fluvio-aeolian deposits fractured and folded by tectonic processes together with some landforms of volcanic origin. Alluvial fans, related to several aggradational cycles of Quaternary age, are the most remarkable geomorphological units. Several tectonic features are present giving rise to conspicuous morphological features. Some of the streams are structurally controlled by faults while several drainage anomalies that indicate active tectonic processes have been identified. The Late Quaternary alluvial sequences, dominantly comprising sandy and silty deposits of volcaniclastic composition and secondarily metamorphic rocks, represent the fine-grained sedimentary facies of the fluvial systems accumulated in a distal fan environment. The alluvial deposits have been incised by several episodes of erosion since Pleistocene time. The Andes Cordillera and the piedmont of Mendoza province (Argentina) are an active tectonic area characterized by a complex geological setting that determines a heterogeneous landscape. Of particular environmental and human significance is the piedmont of Cordillera Frontal between c. 33° and 34°S. Known as Valle de Uco, it is a highly populated area deeply modified by human activities and constitutes one of the three man-made agricultural oases of Mendoza province (Fig. 1). Consequently, the reconstruction of the piedmont evolution and the understanding of the processes involved are essential to evaluate possible environmental responses under the present climatic fluctuations in a densely populated area. Several contributions have demonstrated the environmental sensitivity of the region during Quaternary time as documented by the record of Pleistocene and Holocene glacial advances in the Andean headwaters of the fluvial systems (e.g. Espizúa 2004, 2005; Espizúa & Pitte 2009; Messager 2010) along with geomorphological, palaeoenvironmental and palaeoclimatic studies (Baker et al. 2009; Paez et al. 2010). In order to understand the nature and characteristics of the present landscape, analysis of the Late Pleistocene and Holocene period is especially important. This key time interval covering the recent geological past includes a dramatic climatic change: the transition of the last glacial cycle to the present interglacial (Saltzman 2002). In addition, the Cordillera Frontal piedmont is considered as one of the source areas of the aeolian deposits of central Argentina (Zárate 2003; Mehl et al. 2012). Knowledge of the sedimentary record is therefore significant to validate the current models of aeolian sedimentation. These issues have renewed interest in the area and instigated multidisciplinary analysis by our research team. The studies, still under progress, include stratigraphical, sedimentological, geochronogical, morphostructural and palaeontological analysis, with the general aim of reconstructing the environmental and climatic conditions during Late Quaternary time across the Cordillera Frontal piedmont (e.g. Mehl & Zárate 2012; Rojo et al. 2012) and the eastern piedmont of San Rafael block, situated to the south (Tripaldi et al. 2011). Simultaneously, other authors (e.g. Pepin 2010; Pepin et al. 2013; Casa et al. 2011) have focused on tectonic, geomorphological and geochronological analyses in the study area (e.g. Cordón del Carrizalito piedmont, Las Tunas fluvial system). The purpose of this paper is to provide a general overview of the Quaternary stratigraphy and evolution of the Cordillera Frontal piedmont at Valle de Uco. Special emphasis is placed on Late Pleistocene and Holocene alluvial sequences that exhibit a suitable stratigraphic resolution for palaeoenvironmental reconstructions. The chronology and morphotectonic of the area are also analysed, along with the composition and provenance of the sediments. The final aim is to contribute to the understanding of the landscape dynamics in an active tectonic setting within the context of the Quaternary climate cycles.