Internal anatomy of an erg sequence from the aeolian-fluvial system of the De La Cuesta Formation (Paganzo Basin, northwestern Argentina)

Permian red beds of the De La Cuesta Formation in the Sierra de Narváez (Paganzo Basin, northwestern Argentina) are essentially composed of sandstones associated with mudstones and subordinate conglomerates. Facies distributions and stacking patterns indicate that these sediments resulted from the interaction between aeolian and ephemeral fluvial systems, and are represented by aeolian dune, dry aeolian interdune and Aeolian sand sheet, mudflat, wet aeolian interdune, and fluvial deposits. The De La Cuesta Formation is characterized by aeolian (erg) sequences alternating with non-aeolian (terminal alluvial fan - mudflat) sequences. Each erg sequence is bounded at its base by a regionally extensive sand-drift surface and at the top by an extinction surface. A number of architectural elements, including aeolian dunes limited by interdunes, grouped crescentic Aeolian dunes, longitudinal dunes, and draa with superimposed crescentic dunes are recognised in the erg sequences. The sand sea developed during phases of increasing aridity, whereas non-aeolian deposition might have occurred during more humid phases. Thus, the styles of aeolian-fluvial interaction are considered to result from cyclical climatic changes. Within the drier hemicycles, the rhythmic alternation between draa deposits and aeolian dune and interdune deposits indicates higher frequency cycles that could be attributed to subtle climatic oscillations and/ or changes in sand supply and availability. The development of the Permian sand sea in the inland Paganzo Basin seems to be related to the growth of a volcanic chain to the west. This topographic barrier separated the Paganzo Basin from the Chilean Basin, located along the western margin of Gondwana and characterised by shallow marine carbonate sedimentation. The correlation between the Permian erg and the shallow marine carbonates suggests a regional warming period during the Middle Permian in western Gondwana

Climbing dunes deposits in sierra de Los Tarjados, La Rioja province, Argentina

Eolian climbing dunes found in the sierra de Los Tarjados (south of the La Rioja province> Argentina) are described in this paper. According to their morphology two mayor types of dunes have been recognized: 1) climbing dunes associated to ramp deposits, which can ascent the mountain front; and 2) climbing dunes do not related to ramps and where deflationary channel developed between the dune front and the cliff. Climbing dunes sands show finer mean grain-size, better sorting and lower skewness than associated sand sheet deposit

Internal anatomy of an Erg sequence from the aeolian-fluvial system of the De La Cuesta Formation (Paganzo Basin, northwestern Argentina)

Permian red beds of the De La Cuesta Formation in the Sierra de Narváez (Paganzo Basin, northwestern Argentina) are essentially composed of sandstones associated with mudstones and subordinate conglomerates. Facies distributions and stacking patterns indicate that these sediments resulted from the interaction between aeolian and ephemeral fluvial systems, and are represented by aeolian dune, dry aeolian interdune and aeolian sand sheet, mudflat, wet aeolian interdune, and fluvial deposits. The De La Cuesta Formation is characterised by aeolian (erg) sequences alternating with non-aeolian (terminal alluvial fan - mudflat) sequences. Each erg sequence is bounded at its base by a regionally extensive sand-drift surface and at the top by an extinction surface. A number of architectural elements, including aeolian dunes limited by interdunes, grouped crescentic aeolian dunes, longitudinal dunes, and draa with superimposed crescentic dunes are recognised in the erg sequences. The sand sea developed during phases of increasing aridity, whereas non-aeolian deposition might have occurred during more humid phases. Thus, the styles of aeolian-fluvial interaction are considered to result from cyclical climatic changes. Within the drier hemicycles, the rhythmic alternation between draa deposits and aeolian dune and interdune deposits indicates higher frequency cycles that could be attributed to subtle climatic oscillations and/ or changes in sand supply and availability. The development of the Permian sand sea in the inland Paganzo Basin seems to be related to the growth of a volcanic chain to the west. This topographic barrier separated the Paganzo Basin from the Chilean Basin, located along the western margin of Gondwana and characterised by shallow marine carbonate sedimentation. The correlation between the Permian erg and the shallow marine carbonates suggests a regional warming period during the Middle Permian in western Gondwana

Palinología del evento transgresivo pennsylvaniano en la Quebrada de la Herradura, San Juan, Argentina

En la Quebrada de La Herradura, ubicada aproximadamente a 10km al noroeste de Huaco, se encuentra expuesta una secuencia continua de rocas neopaleozoicas referidas a las formaciones Guandacol, Tupe y Patquía. La presencia de invertebrados marinos y paleofloras en la Formación Tupe fue reportada a mediados del siglo pasado y más recientemente la fauna fue referida a la Biozona Tivertonia - Streptorhynchus con su estratotipo en esta localidad. Originalmente esta biozona fue referida al Carbonífero tardío; sin embargo, en la última década algunos autores la refieren al Pérmico Temprano. Con el propósito de esclarecer la antigüedad del intervalo marino considerado se ha efectuado un perfil estratigráfico de detalle sobre el que se ha identificado: 1) la posición de las muestras palinológicas fértiles, 2) la ubicación de superficies guía para la correlación estratigráfica con el hipoestratotipo de Huaco y 3) los cambios en los paleoambientes sedimentarios (materializados en la definición de cuatro asociaciones de facies sedimentarias). El análisis sistemático detallado de numerosas muestras palinológicas de los mismos niveles portadores de la fauna permiten corroborar la edad originalmente propuesta. Las palinofloras pueden ser referidas a la Subzonas B y C de la Biozona Raistrickia densa - Convolutispora muriornata de edad pennsylvaniana. Sobre la base del reconocimiento de una superficie de discontinuidad estratigráfica de valor regional y de dos superficies de inundación marina se ha podido establecer un esquema de correlación con las secuencias aflorantes en el anticlinal de Huaco. En esa región los depósitos correspondientes a la transgresión, caracterizada por la fauna de Tivertonia - Streptorhynchus, poseen una edad moscoviana de acuerdo a dataciones radimétricas (método 206Pb/238U en zircones). La información presentada tiende a confirmar las asignaciones originales de la biozona, y por lo tanto de la sección superior de la Formación Tupe al Pennsylvaniano tardío.Sesiones libresFacultad de Ciencias Naturales y Muse

High-Precision U-Pb Calibration of Carboniferous Glaciation and Climate History, Paganzo Group, NW Argentina

The duration and geographic extent of Carboniferous glacial events in southern Gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered. We report 10 high-precision (2σ ± \u3c0.1%) U-Pb ages for the Permian-Carboniferous Paganzo Group, NW Argentina, that redefine the chronostratigraphy of the late Paleozoic Paganzo and Río Blanco Basins, and significantly refine the timing of glacial events and climate shifts in the western region of southern Gondwana. Radiometric calibration of the Paganzo Group indicates three pulses of Carboniferous glaciation in the mid-Visean, the late Serpukhovian to earliest Bashkirian, and between the latest Bashkirian to early Moscovian. An abrupt shift in depositional style from high-sinuosity single-storied fluvial deposits and clay-rich paleosols to low-sinuosity multistoried feldspathic fluvial deposits intercalated with eolianites and calcic paleosols is constrained to the latest Moscovian and earliest Kasimovian. These constraints indicate a relatively abrupt climate shift from humid-subhumid to nonseasonal semiarid regional climate conditions that occurred significantly earlier than previously inferred (Early Permian). This period of high-latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the Pangean paleotropics in the Pennsylvanian

Recent advances on tectonics of the Andes and their foreland and southern North America, as part of special issues published in the Journal of South American Earth Sciences in the last three years (2019-20-21)

International audienceThis Editorial is based on the recent advances presented in the Special Issues related to tectonics across South America, released in the last three years. Its objective is to display the intense work focused on different lines of research of the Andean and Pre-Andean tectonic field and also to summarize key aspects extracted from these volumes in one single document. These Special Issues describe recent advances related to supercontinent Gondwana formation and posterior peripheral accretions during the Early Paleozoic, the instalment of coetaneous arc along the paleo-Pacific trench, the development of Late Paleozoic basins in the retro-arc region, Early Mesozoic extension related to the break-up of Gondwana, Late Cretaceous-Cenozoic closure of main retroarc depocenters, conformation of the proto-Andes, the growth of their structure and temporal destabilization during the Cenozoic, exhumation degree, paleoenvironmental changes experienced during these processes, and their neotectonic and seismological behavior. In the following paragraphs we will describe their general content and main achievements reached in these volumes