Miocene orographic uplift forces rapid hydrological change in the southern central Andes

Rainfall in the central Andes associated with the South American Monsoon and the South American Low-Level Jet results from orographic effects on atmospheric circulation exerted by the Andean Plateau and the Eastern Cordillera. However, despite its importance for South American climate, no reliable records exist that allow decoding the evolution of thresholds and interactions between Andean topography and atmospheric circulation, especially regarding the onset of humid conditions in the inherently dry southern central Andes. Here, we employ multi-proxy isotope data of lipid biomarkers, pedogenic carbonates and volcanic glass from the Eastern Cordillera of NW Argentina and present the first long-term evapotranspiration record. We find that regional eco-hydrology and vegetation changes are associated with initiation of moisture transport via the South American Low-Level Jet at 7.6 Ma, and subsequent lateral growth of the orogen at 6.5 Ma. Our results highlight that topographically induced changes in atmospheric circulation patterns, not global climate change, were responsible for late Miocene environmental change in this part of the southern hemisphere. This suggests that mountain building over time fundamentally controlled habitat evolution along the central Andes.Fil: Rohrmann, Alexander. Universitat Potsdam; AlemaniaFil: Sachse, Dirk. Universitat Potsdam; Alemania. German Research Centre for Geosciences; AlemaniaFil: Mulch, Andreas. Goethe Universitat Frankfurt; AlemaniaFil: Pingel, Heiko. Universitat Potsdam; AlemaniaFil: Tofelde, Stefanie. Universitat Potsdam; AlemaniaFil: Alonso, Ricardo Narciso. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Salta. Facultad de Ciencias Naturales; ArgentinaFil: Strecker, Manfred R.. Universitat Potsdam; Alemani

Recording of multiple lake-marsh paleoenvironments during the middle Holocene in the Quebrada del Toro, NW Argentina

Registro de múltiples episodios lacustre-palustres durante el Holoceno medio en la Quebrada del Toro,En el noroeste argentino durante el Cuaternario se desarrollaron sistemas lacustres asociados con 38 deslizamientos, avalanchas de roca y desarrollo de grandes abanicos aluviales, generados por la 39 actividad tectónica andina, los cambios climáticos y/o lluvias extraordinarias. En la localidad de El 40 Candado, tramo inferior de la Quebrada del Toro (provincia de Salta, Argentina), se reconocen 41 afloramientos pelíticos que son interpretados en base a sus características sedimentológicas y 42 paleontológicas como acumulaciones lacustres-palustres someras. Estos depósitos se habrían producido 43 a partir de la instalación de un ambiente lacustre-palustre como consecuencia del desarrollo de un gran 44 abanico aluvial que obstruyó al río Toro. La sedimentación ocurrió durante el Holoceno medio de 45 acuerdo con la datación de gasterópodos y materia orgánica que arrojaron edades entre 8-4.8 ka. Según 46 los restos paleobotánicos y palinológicos así como los atributos sedimentológicos, la acumulación 47 ocurrió en ambientes lacustre-palustre temporarios, somero bajo condiciones húmedas que habría 48 alternado con las condiciones paleoclimáticas áridas y secas que caracterizaron al Holoceno medio de 49 esta región de los Andes Centrales.Quaternary lake systems have developed in many Andean intermontane valleys in northwestern 20 Argentina in association with landslides, rock avalanches, and the development of large alluvial fans, 21 caused either by tectonics, climate change, and/or increased rainfall. At the El Candado location, in the 22 narrow, southern sector of the Quebrada del Toro (Salta Province, Argentina), fine-grained sedimentary 23 deposits are recognized, which, based on their sedimentological and paleontological characteristics, are 24 interpreted as the sedimentary infill of shallow lakes-marshes that were generated by the development 25 of large alluvial fans that dammed the Río Toro. Based on AMS 14 C dating of gastropod shells and 26 organic matter (ca. 8-4.8 ka), this region experienced multiple lacustrine-marsh paleoenvironments 27 during the middle Holocene. Pollen analysis and paleobotanical investigations of these deposits suggest 28 that the accumulation of the lake sediments occurred under relatively humid conditions that alternated 29 with semi-arid periods as is typical for the Andean Holocene.Fil: Veizaga Saavedra, Juan Gonzalo. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sánchez, María Cristina. Universidad Nacional de Salta. Facultad de Ciencias Naturales; ArgentinaFil: Martinez, Olga Gladys. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Pingel, Heiko. Universitat Potsdam; AlemaniaFil: de Francesco, Claudio German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Exhumation and structural evolution of the high-elevation Malcante Range, Eastern Cordillera, NW Argentina

As an integral part of the Eastern Cordillera, the fault-bounded Malcante mountain range (up to 5100 m) in the NW Argentine Andes (ca. 25°S) is located in the transition between the arid Puna Plateau to the west and the humid broken foreland to the east. At this latitude, the topographic gradient of the eastern Andean margin forms an efficient orographic barrier that causes pronounced east–west rainfall and surface-process gradients. In this setting, the Malcante Range is an important, yet poorly studied structural high formed during the Cenozoic topographic growth of the Central Andes. In this study, we combine (a) detailed field observations, (b) a two-dimensional structural reconstruction, (c) apatite fission track and (U–Th-Sm)/He thermochronology of bedrock samples from a vertical transect across the western flank of the Malcante Range, and (d) inverse thermal modelling using QTQt software with the aim of deciphering the exhumation history of this mountain range. Field data indicate the presence of an angular unconformity between Cenozoic foreland deposits and older sedimentary strata, suggesting an initial episode of deformation during the middle-late Eocene, while our thermal model constrains the onset of exhumation at ~10 Ma. We suggest that exhumation was related to the unroofing of the easily erodible sedimentary cover, which prevented significant initial surface uplift. This may have changed as more resilient bedrock was exposed at ~5 Ma according to the thermal model, promoting rapid rock uplift. In combination with published data, our thermochronology allows us to speculate on the existence of a zone of deformation concentrated in the area of the present-day Pasha (24.5°S), Malcante (25°S), and Agua de Castilla (25.4°S) mountain ranges by ca. 10 Ma.Fil: Payrola Bosio, Patricio Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Zapata, Matias Sebastian. Smithsonian Tropical Research Institute; Panamá. University of Missouri; Estados UnidosFil: Sobel, Edward Robert. Universitat Potsdam. Mathematisch Nautrwissenschaften Fakultat. Institut für Geowissenschaften; AlemaniaFil: del Papa, Cecilia Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Pingel, Heiko. Universitat Potsdam. Mathematisch Nautrwissenschaften Fakultat. Institut für Geowissenschaften; AlemaniaFil: Glodny, Johannes. German Research Centre for Geosciences; AlemaniaFil: Ledesma, Jonathan Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

Development of an incipient Paleogene topography between the present-day Eastern Andean Plateau (Puna) and the Eastern Cordillera, southern Central Andes, NW Argentina

The structural and topographic evolution of orogenic plateaus is an important research topic because of its impact on atmospheric circulation patterns, the amount and distribution of rainfall, and resulting changes in surface processes. The Puna region in the north-western Argentina (between 13°S and 27°S) is part of the Andean Plateau, which is the world's second largest orogenic plateau. In order to investigate the deformational events responsible for the initial growth of this part of the Andean plateau, we carried out structural and stratigraphic investigations within the present-day transition zone between the northern Puna and the adjacent Eastern Cordillera to the east. This transition zone is characterized by ubiquitous exposures of continental middle Eocene redbeds of the Casa Grande Formation. Our structural mapping, together with a sedimentological analysis of these units and their relationships with the adjacent mountain ranges, has revealed growth structures and unconformities that are indicative of syntectonic deposition. These findings support the notion that tectonic shortening in this part of the Central Andes was already active during the middle Paleogene, and that early Cenozoic deformation in the region that now constitutes the Puna occurred in a spatially irregular manner. The patterns of Paleogene deformation and uplift along the eastern margin of the present-day plateau correspond to an approximately north-south oriented swath of reactivated basement heterogeneities (i.e. zones of mechanical weakness) stemming from regional Paleozoic mountain building that may have led to local concentration of deformation belts.Fil: Montero López, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Hongn, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: López Steinmetz, Romina Lucrecia. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; ArgentinaFil: Aramayo, Alejandro José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Pingel, Heiko. Universitat Potsdam; AlemaniaFil: Strecker, Manfred R.. Universitat Potsdam; AlemaniaFil: Cottle, John M.. University of California; Estados UnidosFil: Bianchi, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentin