Aguirre Rojas, Carlos Antonio. La escuela de los Annales. Ayer hoy, mañana. España, Montesinos, 1999, 235 páginas

Fil: Sorgentini, Hernán Antonio. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Francisco Caudet. Zola, Galdós, Clarín. El naturalismo en Francia y en España. Madrid, Ediciones de la Universidad Autónoma de Madrid, 1995, 305 págs.

Fil: Macciuci, Raquel. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Graciela Salto (compiladora y editora), Memorias del silencio: literaturas en el Caribe y en Centroamérica Buenos Aires, Corregidor, 2010, 349 páginas/ Graciela Salto (coordinadora y editora), Insulas y poéticas: figuras literarias en el Caribe. Buenos Aires, Biblos, 2012, 235 páginas

Fil: Novau, Julieta. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Francisco Caudet. Zola, Galdós, Clarín. El naturalismo en Francia y en España. Madrid, Ediciones de la Universidad Autónoma de Madrid, 1995, 305 págs.

Fil: Macciuci, Raquel. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Aguirre Rojas, Carlos Antonio. La escuela de los Annales. Ayer hoy, mañana. España, Montesinos, 1999, 235 páginas

Fil: Sorgentini, Hernán Antonio. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Measurements of trace metal abundances and isotopes in carbonate sediments, Exuma, Bahamas

In order to validate the use of 238U/235U as a paleoredox proxy in carbonates, we examined the incorporation and early diagenetic evolution of U isotopes in shallow Bahamian carbonate sediments. Our sample set consists of a variety of primary precipitates that represent a range of carbonate producing organisms and components that were important in the past (scleractinian corals, calcareous green and red algae, ooids, and mollusks). In addition, four short push cores were taken in different depositional environments to assess the impact of early diagenesis and pore water chemistry on the U isotopic composition of bulk carbonates. We find that U concentrations are much higher in bulk carbonate sediments (avg. 4.1 ppm) than in primary precipitates (avg. 1.5 ppm). In almost all cases, the lowest bulk sediment U concentrations were as high as or higher than the highest concentrations found in primary precipitates. This is consistent with authigenic accumulation of reduced U(IV) during early diagenesis. The extent of this process appears sensitive to pore water H2S, and thus indirectly to organic matter content. d238/235U values were very close to seawater values in all of the primary precipitates, suggesting that these carbonate components could be used to reconstruct changes in seawater U geochemistry. However, d238/235U of bulk sediments from the push cores was 0.2-0.4 per mil heavier than seawater (and primary precipitates). These results indicate that authigenic accumulation of U under open-system sulfidic pore water conditions commonly found in carbonate sediments strongly affects the bulk U concentrations and 238U/235U ratios. We also report the occurrence of dolomite in a tidal pond core which contains low 234U/238U and 238U/235U ratios and discuss the possibility that the dolomitization process may result in sediments depleted in 238U. From this initial exploration, it is clear that 238U/235U variations in ancient carbonate sediments could be driven by changes in global average seawater, by spatial and temporal variations in the local deposition environment, or subsequent diagenesis. To cope with such effects, proxies for syndepositional pore water redox conditions (e.g., organic matter content, iron speciation, and trace metal distributions) and careful consideration of possible post-deposition alteration will be required to avoid spurious interpretation of 238U/235U data from ancient carbonate sediments.

Aguirre Rojas, Carlos Antonio. La escuela de los Annales. Ayer hoy, mañana. España, Montesinos, 1999, 235 páginas

Fil: Sorgentini, Hernán Antonio. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Graciela Salto (compiladora y editora), Memorias del silencio: literaturas en el Caribe y en Centroamérica Buenos Aires, Corregidor, 2010, 349 páginas/ Graciela Salto (coordinadora y editora), Insulas y poéticas: figuras literarias en el Caribe. Buenos Aires, Biblos, 2012, 235 páginas

Fil: Novau, Julieta. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Strontium isotope data from DSDP Sites 32-305 and 62-463 and ODP Sites 113-689 and 113-690

Fluctuations in oxygen (d18O) and carbon (d13C) isotope values of benthic foraminiferal calcite from the tropical Pacific and Southern Oceans indicate rapid reversals in the dominant mode and direction of the thermohaline circulation during a 1 m.y. interval (71-70 Ma) in the Maastrichtian. At the onset of this change, benthic foraminiferal d18O values increased and were highest in low-latitude Pacific Ocean waters, whereas benthic and planktic foraminiferal d13C values decreased and benthic values were lowest in the Southern Ocean. Subsequently, benthic foraminiferal d18O values in the Indo-Pacific decreased, and benthic and planktic d13C values increased globally. These isotopic patterns suggest that cool intermediate-depth waters, derived from high-latitude regions, penetrated temporarily to the tropics. The low benthic d13C values at the Southern Ocean sites, however, suggest that these cool waters may have been derived from high northern rather than high southern latitudes. Correlation with eustatic sea-level curves suggests that sea-level change was the most likely mechanism to change the circulation and/or source(s) of intermediate-depth waters. We thus propose that oceanic circulation during the latest Cretaceous was vigorous and that competing sources of intermediate- and deep-water formation, linked to changes in climate and sea level, may have alternated in importance.