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

Paleoenvironments and age of the Talampaya Formation: The Permo-Triassic boundary in northwestern Argentina

© 2015 Elsevier Ltd. The Talampaya Formation is the basal unit of the Ischigualasto-Villa Unión rift system and has been traditionally assigned to the Triassic based on stratigraphic relationships. A median U-Pb age of 252.38 (+0.09/-0.22) Ma was obtained from volcanic zircons collected from a tuff bed close to the top of this unit at the Bordo Atravesado locality in the Cuesta de Miranda area (La Rioja, Argentina). This radiometric age is very close to the accepted Permian-Triassic boundary indicating that, at least in this locality, sedimentation occurred during the Late Permian but may have extended into the earliest Triassic. This new evidence indicates that the onset of the extensional event that gave rise to the rift basins in western Argentina started during the Permian. Detailed sedimentological studies of the 260 m thick Talampaya Formation allowed subdividing the succession into seven facies associations grouped into three evolutionary stages indicating that sedimentary environments initially evolved from alluvial fans to a braided river system. Subsequent intrabasinal volcanism associated with sediment deposition by low-to moderate-sinuosity rivers is recorded in the lower third of the column. The middle and upper part of the unit captures the evolution from ephemeral fluvial systems with an eolian interval to an ephemeral clastic lake with intermittent volcanic ash deposits. These changes indicate a progressive lowering of the landscape and a transition towards arid or semiarid conditions

The Villacorta Formation (nov. nom.): A new late Silurian unit in the Famatina Province

En la parte media de la quebrada de Villacorta, sobre el faldeo occidental de la sierra del Famatina a la latitud del poblado de Casa Pintada (Valle Hermoso, provincia de La Rioja), aflora una espesa sucesión de areniscas cuarzosas que se propone denominar Formación Villacorta (nov. nom.). La misma apoya en discordancia erosiva sobre areniscas verdes de la Formación Suri (Ordovícico) y es cubierta en marcada discordancia angular por las rocas de la Formación Agua Colorada (Carbonífero superior). La sección inferior de la nueva unidad se caracteriza por el predominio de cuarcitas blanquecinas, en el sector medio son conspicuas las areniscas verdes oscuro y por encima niveles arenosos castaños con desarrollo anillos de Liesegang, mientras que en el tramo superior predominan areniscas feldespáticas con estratificación entrecruzada. La geometría mayormente plano-convexa o tabular de los cuerpos, el predominio de estratificación entrecruzada algunas con cortinas de fango, y laminación ondulítica, localmente formando niveles heterolíticos, sugieren que la depositación tuvo lugar en un ambiente marino litoral con acción mareal que grada a un ambiente transicional, muy probablemente deltaico. La posición y relaciones estratigráficas de la Formación Villacorta, sumado a la asociación palinológica recuperada en el tope de la unidad sugieren una edad silúrica tardía, probablemente wenlockiana-ludloviana para esta nueva formación.A thick succession of quartz-rich sandstones is here proposed to be named Villacorta Formation (Nov Nom.). This unit crops out in the middle part of the quebrada de Villacorta, on the western slope of the Sierra del Famatina at the latitude of the Casa Pintada hamlet (Valle Hermoso, La Rioja province). The sandstone package disconformably rests on greenish sandstones of the Ordovician Suri Formation and is covered in marked angular unconformity by rocks of the Late Carboniferous Agua Colorada Formation (Paganzo Group). The lower section of this new unit is characterized by the predominance of whitish quartzites, the middle interval consists of dark green sandstones that pass upwards to brown sandy levels with conspicuous liesegang rings, and the upper section comprises cross-bedded feldspathic sandstones. The mostly flat-convex or tabular geometry of the sandstone bodies, the predominance of cross-bedding with some mudstone drapes, and ripple-cross lamination, locally forming heterolithic levels, suggest deposition in a tide-influenced environment grading into a transitional, most probably deltaic environment. The position, and stratigraphic relationships of the Villacorta Formation, in addition to the palynological assemblage recovered from the uppermost part of the unit, indicate a late Silurian (Wenlock-Ludlow) age for this new formation.Fil: Marenssi, Sergio Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Limarino, Carlos Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Ferreyra, Luis C.. Comisión Nacional de Energía Atómica; ArgentinaFil: Ciccioli, Patricia Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; ArgentinaFil: Scarlatta, Leonardo. Comisión Nacional de Energía Atómica; ArgentinaFil: Cesari, Silvia Nelida. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; ArgentinaFil: Bello, Fanny C.. Comisión Nacional de Energía Atómica; Argentin

The inventory of geological heritage of the state of São Paulo, Brazil: Methodological basis, results and perspectives

An inventory of geological sites based on solid and clear criteria is a first step for any geoconservation strategy. This paper describes the method used in the geoheritage inventory of the State of São Paulo, Brazil, and presents its main results. This inventory developed by the geoscientific community aimed to identify geosites with scientific value in the whole state, using a systematic approach. All 142 geosites representative of 11 geological frameworks were characterised and quantitatively evaluated according to their scientific value and risk of degradation, in order to establish priorities for their future management. An online database of the inventory is under construction, which will be available to be easily consulted and updated by the geoscientific community. All data were made available to the State Geological Institute as the backbone for the implementation of a future state geoconservation strategy.The authors acknowledge the Science Without Borders Programme, Process 075/2012, which supported this study and the São Paulo Research Foundation (FAPESP), Process 2011/17261-6. We also thanks C. Mazoca for his help with maps and figures.info:eu-repo/semantics/acceptedVersio

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