126 research outputs found
Advances in Cambrian studies: A meeting in the Andes, VI field meeting of the Subcomission on Cambrian Stratigraphy, Argentina 2000 (IUGS-UNESCO)
The Cambrian System in Northwestern Argentina: stratigraphical and palaeontological framework
Cambrian sequences are widespread in the early Paleozoic of the Central Andean Basin. Siliciclastic sediments dominate these sequences although several minor occurrences of carbonates and volcanic rocks have been observed. The rocks assigned to the Cambrian System in NW Argentina are recognized in the Puna, Eastern Cordillera, Subandean Ranges and the Famatina System. This paper gives a general overview of the Cambrian formations outcropping in the northern provinces of Jujuy, Salta, Tucumán, Catamarca and La Rioja. Special emphasis has been given to the stratigraphical and biostratigraphical framework of the sequences. Late Precambrian-Early Cambrian thick sedimentary wackes dominate the basal Puncoviscana Formation (s.l.), characterized by a varied ichnofauna that includes the Precambrian-Cambrian transitional levels. Thick packages of sandstone facies characterize the overlying highly ichnofossiliferous Mesón Group. A rich shelly fauna included in sandstones, shales and volcaniclastics, dominate in the Cambrian-Ordovician transitional levels of the overlying Cambro-Ordovician Santa Victoria and Cachiyuyo Groups. Palaeogeographic aspects dealing with the position and development of Cambrian basins are discussed. Several synthetic biostratigraphic tables are presented displaying the known record for the Cambrian System, including the transitional levels to the lowermost Ordovician in the above-mentioned regions
El Alisal: a new locality with trace fossils of the Puncoviscana Formation (late Precambrian-early Cambrian) in Salta Province. Argentina
The Puncoviscana, Suncho and Las Aguaditas/Negro Peinado formations represent a thick siliciclastic folded succession that crops out on a strip about 800 km long and 150 km wide in northwestern Argentina (Jujuy, Salta, Tucumán, Catamarca and La Rioja provinces). These sequences are lithologically characterized by very lowgrade metamorphic sediments grading from slates to schists; turbidites, pelagic clays, limestones and volcanic rocks. On the basis of paleoichnological data, these units have been assigned to the late Precambrian-early Cambrian. A new locality bearing well preserved trace fossils from the Puncoviscana Formation is described herein. The outcrop is located about 45 km west of Salta city (Salta Province), displaying an alternation of colored differentiated grayish-bluish slates and fine sandstones. Ichnofossils include Cochlichnus anguineus HITCHCOCK, Helminthoidichnites tenuis FITCH, Helminthoida isp., Monomorphichnus lineatus CRIMES, LEGG and MARCOS ARBOLEYA, Planolites isp. and Torrowangea? isp., as well as some limb marks and a few slightly bended smooth trails (indet.). An Early Cambrian age for the succession at El Alisal as well as some environmental considerations are allowed by the ichnological association. In addition, the ichnogenus Planolites is mentioned for the first time from the “red shales and conglomerate type” facies at the neighbor locality of Chorrillos
Ordovician conodonts of the Devendeus Formation at the Angosto de La Quesera (Cordillera Oriental of Salta, Argentina) : Taxonomic considerations and biostratigraphic significance
Conodonts recovered from the Devendeus Formation at the Angosto de La Quesera locality (Cordillera Oriental of Salta) in northwestern Argentina include Nogamiconus sp., Problematoconites perforatus, Drepanoistodus sp., Oneotodus sp., Scolopodus filosus, Teridontus nakamurai and Variabiloconus sp., as a part of an association that defines a pre-Paltodus deltifer Zone. The material most likely represents the Cordylodus angulatus and/or the lower part of the Rossodus manitouensis Zone. These microfossils support the dating of the Devendeus Formation as Tremadocian (Early Ordovician)
Estructuras de fijación de pelmatozoas (equinodermos) en el Ordovícico Medio de la Zona Centroibérica española
Se describen diversas estructuras discoidales a subcónicas, cementadas a restos esqueléticos de braquiópodos, moluscos, trilobites y cistideos. que constituyen los primeros elementos de fijación de pelmatozoos a sustratos firmes encontrados en el Ordovícico Medio de la Zona Centroibérica del Macizo Hespérico. El material proviene de cinco localidades de edad comprendida entre el Oretaniense inferior y el Dobrotiviense superior, y ha sido asignado a los morfogéneros Podolithus y Lichenocrinus?, el primero
de los cuales se conocía previamente en las calizas del Ashgill de la Rama Aragonesa de la Cordillera Ibérica. Los ejemplares de Podolithus encontrados en las Capas con Tristani pertenecen al menos a dos morfoespecies distintas, tratadas en nomenclatura abierta, que sc diferencian por sus caracteres morfológicos y los fragmentos pluricolumnales
asociados.
[ABSTRACT]
Pelmatozoan holdfasts, in Ihe form of discoid to subeonical multiplated structures, have been observed attached to shelly fragments ol articulate brachiopods. molluscs, trilobites and cystoids from five localities of the Central Iberian Zone of the Hesperian Massif. The described material ranges from lower Oretanian to upper Dobrotivian in
age, and represents the first evidence of hard substrate colonization by echinoderms in the Middle Ordovician of Spain. The identified taxa belong to the morphogenera Podolithus and ?Lichenocrinus, the former also recorded from Ashgill limestones in the eastern Iberian Cordillera. At least two morphospecies of Podolithus, which have been
left in open nomenclature, are distinguished on the basis of their overall morphology and stem characteristies
Nutrient resorption in dominant species of forests in the 'Espinal Mesopotámico' (Argentina)
Se estudió durante dos años (2009 y 2010) la retranslocación de nutrientes en especies dominantes de bosques correspondientes a una secuencia sucesional del Espinal Mesopotámico. El objetivo fue comparar la retranslocación de nutrientes (nitrógeno, fósforo, potasio, calcio, magnesio y azufre) entre especies de familias fabáceas (Acacia caven, Prosopis affinis y Prosopis nigra; con capacidad de fijar biológicamente el nitrógeno atmosférico) y celtidáceas (Celtis tala, sin capacidad de fijar biológicamente el nitrógeno atmosférico). Se analizaron químicamente las muestras de hojas maduras (recolectadas en primavera) y senescentes (recolectadas en otoño) para determinar la concentración de nutrientes y luego se calcularon los índices de retranslocación (Rc1 y Rc2). Se determinó que la mayor retranslocación del nitrógeno estuvo asociada la imposibilidad de fijar biológicamente el nitrógeno atmosférico, observándose que ambos índices denotaron una máxima retranslocación de nitrógeno en C. tala y mínima en A. caven. Contrariamente, los demás elementos (P, K, Ca, Mg y S) mostraron diferencias en la retranslocación en uno de los índices utilizados, indicando mayor resorción en fabáceas respecto a celtidácea, asociado a una mayor demanda foliar de estos elementos.The resorption of nutrients of dominant species in a successional sequence of forests of the Argentinean Mesopotamian Espinal was studied for two years (2009-2010). The aim was to compare nutrient resorption (nitrogen, phosphorus, potassium, calcium, magnesium and sulphur) among species of the Fabaceae (Acacia caven, Prosopis affinis and Prosopis nigra with the capacity of biologically fixing the atmospheric nitrogen) and Celtidacea families (Celtis tala, without the capacity of biologically fixing the atmospheric nitrogen). Samples of mature leaves (collected in spring) and senescent leaves (collected in autumn) were chemically analyzed to determine nutrient concentration; afterwards, resorption rates were calculated (Rc7 and Rc2). It was found that the higher nitrogen resorption was associated with the inability of biologically fixing the atmospheric nitrogen, having both indexes a maximum nitrogen resorption in C. tala and a minimum in A. caven. On the contrary, the other elements (P, K, Ca, Mg and S) showed resorption differences in one of the indexes used, indicating a higher resorption in Fabaceae in contrast with Celtidaceae, associated with a higher foliar demand of these elements.Fil: Mendoza, Carlos A.. Universidad Autónoma de Entre Ríos. Facultad de Ciencia y Tecnología; ArgentinaFil: Turrión, M. Belén. Universidad de Valladolid; EspañaFil: Aceñolaza, Pablo Gilberto. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentina. Universidad Autónoma de Entre Ríos. Facultad de Ciencia y Tecnología; ArgentinaFil: Gallardo, Juan F.. Consejo Superior de Investigaciones Cientificas; EspañaFil: Pando, Valentín. Universidad de Valladolid; Españ
Spatial distribution modeling for invasive exotic trees in the Pre-Delta National Park (Entre Ríos, Argentina)
Se estudió la distribución espacial de árboles exóticos invasores (AEI) en el Parque Nacional Pre-Delta (PNPD-Entre Ríos, Argentina) mediante el empleo de técnicas de muestreo a distancia. Se modeló la distribución potencial mediante la técnica de interpolación Kriging. Se comparó la cartografía generada con un mapa de zonificación del PNPD y con cartografía de unidades ambientales identificadas en función de un gradiente topográfico. Se registraron datos estructurales del bosque, fenológicos de los árboles y de las acciones de control por parte del personal del PNPD, a fin de caracterizar los procesos de invasión. Se obtuvo cartografía de la distribución potencial de Melia azedarach L., Broussonetia papyrifera (L.) L'Hér. ex Vent., Ligustrum lucidum W.T. Aiton, Brachychiton populneus (Schott & Endl.) R. Br., Fraxinus sp. L. y Morus alba L. Esta última resultó ser dominante en el PNPD en los tres sectores estudiados (barrancas, islas y zona alta). En cuanto a las acciones de manejo de especies exóticas de los agentes del PNPD, cerca del 50% de los ejemplares de M. alba sujeto a aplicaciones de control mecánico (técnica de anillado) presentaron rebrotes, indicando su alta capacidad de supervivencia.Spatial distribution of alien trees was studied on Pre-Delta National Park (PNPD-Entre Ríos, Argentina), by distance sampling techniques. Potential distribution was modelled by Kriging interpolation technique. Generated maps were overlapped with PNPD zonification map and environmental units map. We recorded forest structural data, tree phenology and tree control management actions, in order to characterize the processes of invasion. We obtained maps of potential distribution of Melia azedrach, Broussonetia papyrifera, Ligustrum lucidum, Brachychiton populneus, Fraxinus sp. and Morus alba L. The latter was the dominant species in all studied sectors (cliffs, islands and highlands). As for the management actions carried out with trees of the PNPD, about 50% of the specimens of M. alba subjected to mechanical control (banding technique) showed regrowth, indicating its high survival capacity.Fil: Torresin, Jerónimo A.. Provincia de Misiones. Ministerio de Ecología; ArgentinaFil: Zamboni, L. Pamela. Universidad Autonoma de Entre Rios. Facultad de Ciencia y Tecnologia; ArgentinaFil: Sione, Walter F.. Universidad Autonoma de Entre Rios. Facultad de Ciencia y Tecnologia; Argentina. Universidad Nacional de Luján; ArgentinaFil: Rodriguez, Estela Elizabeth. Universidad Autonoma de Entre Rios. Facultad de Ciencia y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Aceñolaza, Pablo Gilberto. Universidad Autonoma de Entre Rios. Facultad de Ciencia y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentin
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