Mesoscopic phase separation in La2CuO4.02 - a 139La NQR study

In crystals of La2CuO4.02 oxygen diffusion can be limited to such small length scales, that the resulting phase separation is invisible for neutrons. Decomposition of the 139La NQR spectra shows the existence of three different regions, of which one orders antiferromagnetically below 17K concomitantly with the onset of a weak superconductivity in the crystal. These regions are compared to the macroscopic phases seen previously in the title compound and the cluster-glass and striped phases reported for the underdoped Sr-doped cuprates.Comment: 4 pages, RevTeX, 5 figures, to be published in PR

Benzoylpivaloylmethanide precursors for the chemical beam epitaxy of oxide thin films:1. Synthesis, characterization, and use of yttrium benzoylpivaloylmethanide

The new complex yttrium benzoylpivaloylmethanide and its acetonitrile adduct have been characterized by IR, NMR, mass spectroscopy, X-ray structure analysis, and thermogravimetric/differential thermal analysis. In situ flux measurements and mass spectroscopic studies have been performed to test the suitability of this compound as a precursor for the deposition of complex oxide thin films under molecular beam conditions. Finally it has been used to deposit epitaxial Y2O3 (001) thin films on SrTiO3 (001) substrates. </p

Discs and discord: The paleontological record of Ediacaran discoidal structures in the south American continent

Discoidal sedimentary structures are commonly described in Proterozoic strata, and even more common in Ediacaran to lower Cambrian sedimentary successions. Many abiotic processes are able to produce such circular or discoidal structures in bedding planes, however, their abundance in Ediacaran strata suggests a possible correlation with the evolution and preservation of epibenthic metazoans that emerged at the end of this period. In the South American paleontological record, studies regarding the Ediacaran soft-bodied organisms are meager and restricted to few reports in Brazil, Paraguay, and Argentina. In many cases, such “fossils” were only tentatively characterized in terms of their general morphology and putative taxonomic affinity. Thus, considering the almost absence of work on these enigmatic structures in South America, this paper aims to make a critical analysis on the main occurrences of Ediacaran-Cambrian discoidal structures described in this continent. Based on a detailed review and unpublished data, it was possible to provide a general picture concerning the main paleoenvironmental and sedimentary significance of this structures, as well as on the most promising prospects in terms of the paleontological record of Ediacaran soft-bodied metazoans in South American. In this sense, it was settled that occurrences such as those in the Jaibaras and Itajaí basins should be reassessed in order to establish reliable criteria of biogenicity. In the case of the material from the Sete Lagoas and Tagatiya Guazu formations, it is considered more parsimonious to interpret the discoidal features as resulting from microbial processes. Similarly, the discoidal structures of the Cerro Negro Formation presents a series of internal laminations and textures that resembles those developed by processes of microbial grain binding and trapping suggesting that, at least part of this material, can be related to microbially induced sedimentary structures. Finally, for the ichnologically diversified Puncoviscana and Camaquã basins, two different scenarios were identified. The first presents an ichnological assemblage strongly indicative of lower Paleozoic, and possibly Cambrian affinity. Thus, the discs in association with these traces, should be viewed with caution and interpretations made in light of a Paleozoic context. The second possesses an ichnological association typical of that expected for the Ediacaran-Cambrian transition, and the diversity of discoidal forms can potentially represent imprints of macroorganisms on a microbially bounded substrate, thus deserving a more detailed approach.Fil: Inglez, L.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Warren, L. V.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Okubo, J.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Simões, M. G.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Quaglio, F.. Universidade de Sao Paulo; BrasilFil: Arrouy, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Netto, R. G.. Universidade do Vale do Rio dos Sinos; Brasi

Paleomagnetism of the Ediacaran Avellaneda Formation (Argentina), part I: Paleogeography of the Río de la Plata craton at the dawn of Gondwana

A paleomagnetic and rock magnetic study was carried out in the Ediacaran Avellaneda (∼570 Ma) and Cerro Negro (∼555 Ma) Formations belonging to the La Providencia Group, in the upper part of the Neoproterozoic sedimentary cover of the Tandilia region, in the Río de la Plata craton. The Avellaneda Formation was studied at outcrop level and in three drill cores, yielding a mean characteristic remanence direction of Dec: 21.4°, Inc: 67.1°, α95: 4.2°, k: 23.9, N: 51 and a paleomagnetic pole at 1.0° S, 313.4° E, A95: 5.9°. The Cerro Negro Formation yielded a mean characteristic direction of Dec: 22.0°, Inc: 68.5°, α95: 10.3°, k: 20.8, N: 11 obtained from a single drill core, from which a paleomagnetic pole at 3.6° S, 307.8°E, A95: 16.6° was computed. Rock magnetic data indicates that magnetic remanence is mainly associated with magnetite and hematite. The paleomagnetic information presented here results in a change in the previously accepted Late Ediacaran apparent polar wander path of the Río de la Plata Craton. The newly obtained poles indicate that Río de la Plata Craton experienced a rapid drift from a low latitudes location (ca. 19° S) at ca. 600 Ma to moderately higher latitudes (between 50° and 42°S) from around 580 to 550 Ma.Fil: Franceschinis, Pablo Reinaldo. 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; ArgentinaFil: Afonso, J. W.. Universidade de Säo Paulo, Säo Paulo; BrasilFil: Arrouy, M. J.. Universidade de Sao Paulo; BrasilFil: Gómez Peral, Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Trindade, R. I. F.. Universidade de Sao Paulo; BrasilFil: Rapalini, Augusto Ernesto. 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; Argentin

Paleomagnetism of the Ediacaran Avellaneda Formation (Argentina), Part II: Magnetic and chemical stratigraphy constraints on the onset of the Shuram carbon excursion

Magnetostratigraphy is a powerful technique for high-resolution stratigraphic correlation and accurate dating of the polarity history of the magnetic field. Up to now, magnetostratigraphic studies have been underutilized in Ediacaran successions. Here, we present a magnetostratigraphy coupled with a carbon isotope study in Ediacaran Avellaneda Formation (∼570 Ma), a sedimentary cover sequence in the Tandilia orogenic belt, of the Río de la Plata craton. Paleomagnetic results and δ13C profiles were obtained from three drill cores that cut across the sedimentary record of the Avellaneda Formation. Paleomagnetic results plotted stratigraphically allowed the identification of a prevalent reverse polarity separated by normal polarity interval. Our findings show a coincident correlative polarity transition at each drill core analyzed. δ13C values demonstrate that the magnetostratigraphic polarity pattern is laterally consistent. Furthermore, C-isotope curves show a transition from positive to negative values near the top of the Avellaneda Formation. This excursion is likely correlative with the onset of the Shuram excursion (ca. 570 Ma). Our findings suggest that the onset of Shuram excursion took place during a reverse polarity chron. Comparison with other coeval sequences validate this correlation. Geomagnetic polarity reversals pattern in the Avellaneda Formation and its correlative pattern, validates a magnetostratigraphy as a potential method to correlate Precambrian strata. Our new findings shed further light on the possible use of magnetic polarity reversals to correlate Ediacaran successions.Fil: Afonso, J. W. L.. Universidade de Sao Paulo; BrasilFil: Franceschinis, Pablo Reinaldo. 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; ArgentinaFil: Rapalini, Augusto Ernesto. 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; ArgentinaFil: Arrouy, Maria Julia. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff". - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff". - Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff"; ArgentinaFil: Gómez Peral, Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Poiré, Daniel G.. 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. Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff". - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff". - Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto de Hidrología de Llanuras "Dr. Eduardo Jorge Usunoff"; ArgentinaFil: Caetano Filho, S.. Universidade de Sao Paulo; BrasilFil: Trindade, R. I. F.. Universidade de Sao Paulo; Brasi