Adriana Mehl

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.

Soils of the Cuyo Region

Cuyo is a heterogeneous environmental region with two major domains, the Western mountain ranges and the Eastern lowlands. The variety of environmental conditions is clearly reflected by the soils. Entisols are regionally dominant resulting from the balance of prevalent arid conditions together with coarse texture parent materials, and the relative young age (late Holocene) of the parent material. Humification and melanization are the dominant pedogenetic processes. Aridisols, the second most dominant soil order, reflect a long-lasting and complex evolution with evidences of calcification, gypsification and clay illuviation. Paleoenvironmental conditions (fossil criopedoturbation) are documented in the mountain domain, indicative of past glacial conditions as well as a wider extension of periglacial conditions (present and fossil Gelisols). Mollisols and Histosols are also present with a limited areal extension at some piedmont settings. The irrigated agricultural oasis of Cuyo, deeply transformed by human activities, has generated new conditions for soil development both in their physico-chemical properties (OM, P, N, texture and alkalinity) and the parent material. Negative colateral effects as salinization, piping, rill and gully erosion are now active. Consequently, soil management, particularly in the fragile ecotonal ambiance of Cuyo, is a major priority in land environmental programmes as elsewhere.

The Continental Record of Marine Isotope Stage 3 (MIS 3; ~60–25 ka) in Central Argentina: Evidence from Fluvial and Aeolian Sequences

Marine Isotope Stage 3 (MIS 3) is characterized by high climatic variability resulting from numerous centennial to millennial scale events. The environmental and climatic reconstruction of this interval is restricted by the sparsity of high-resolution (centennial-scale) terrestrial records in most of South America. This contribution is an attempt to reconstruct the general environmental and climatic conditions of southern South America during MIS 3 by means of continental records located in central Argentina; this is an extensive and heterogeneous region made up of diverse geomorphological settings under different climatic conditions. Therefore, the main features of several aeolian and fluvial records situated in different geomorphological settings across the region are overviewed. The results indicate the predominance of regional aggradation during MIS 3 with differences in the accumulation rates and dominance of either aeolian or fluvial deposits depending on the geomorphological setting. The aggradation process was interrupted by stability intervals evidenced by paleosols in the San Rafael plain, the San Luis paleo-dunefield, the eastern Sierras Pampeanas piedmont and the eastern Pampean plain. The paleosols might represent lapses of decreasing aeolian input and perhaps more humid conditions. In addition, paleobiological indicators from alluvial sequences suggest higher temperatures and water availability between 35 and 31 ka in the Andean piedmont, while dry subhumid or strongly seasonal conditions with alternating subhumid-humid phases were inferred in the eastern Pampean plain during MIS 3. These intervals tend to cluster during the second part of MIS 3, and might reflect the environmental responses to some of the climatic oscillations that occurred during MIS 3. Detailed analysis and a more adjusted chronology are needed to correlate the aeolian and fluvial episodes along with the stability intervals at regional and continental scales.