(Table 1) Uranium and Thorium concentrations, activity ratios and calcium carbonate content of DSDP Site 54-424

The geochemical behaviour of uranium and thorium in metalliferous sediments and hydrothermal deposits has been widely studied and the main results have been summarised by Boström and Rydell. These isotopes may be used to clarify how the metal-rich solutions are introduced into sediment cover and seawater. Using radiochemistry followed by alpha spectrometry, we have measured uranium concentrations as high as several hundred p.p.m., which must clearly be associated with ocean ridge thermal activity, in sediments interbedded between the basaltic basement and the green hydrothermal mud at DSDP Site 424. These high uranium concentrations indicate the path followed by the hydrothermal fluid which, debouching at the sediment-water interface, formed the green mud.

Alejandro Bekes. Breviario filológico. Términos usuales en Lingüística y Teoría Literaria. Segunda edición ampliada y corregida. Entre Ríos, EDUNER, 2013, 424 pp.

Fil: Zubiría, María Isabel. Universidad Nacional de Cuyo

Poder y gobierno local en México, 1808-1857 : (Reseña de) María del Carmen Salinas Sandoval, Diana Birrichaga Gardida y Antonio Escobar Ohmstede (coordinadores) Poder y gobierno local en México, 1808-1857, Zinacantepec, Estado de México: El Colegio Mexiquense-El Colegio de Michoacán-Universidad Autónoma del Estado de México, 2011, 424 p.

Este libro es fruto de un esfuerzo colectivo por comprender el poder como una construcción social, destacando los aportes de la historia local para una mejor comprensión de la historia nacional mexicana en su primer medio siglo de independencia.

Esquilo, Tragédias (ediçâo bilingüe). Estudo y traduçâo de Jaa Torrano, Sâo Paulo, Iluminuras, Coleçâo Dionísias, 2009, 424 pp.

Fil: Hamamé, Graciela Noemí. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación. Instituto de Investigaciones en Humanidades y Ciencias Sociales (UNLP-CONICET); Argentina.

Poder y gobierno local en México, 1808-1857 : (Reseña de) María del Carmen Salinas Sandoval, Diana Birrichaga Gardida y Antonio Escobar Ohmstede (coordinadores) Poder y gobierno local en México, 1808-1857, Zinacantepec, Estado de México: El Colegio Mexiquense-El Colegio de Michoacán-Universidad Autónoma del Estado de México, 2011, 424 p.

Este libro es fruto de un esfuerzo colectivo por comprender el poder como una construcción social, destacando los aportes de la historia local para una mejor comprensión de la historia nacional mexicana en su primer medio siglo de independencia.

Composition and origin of sediments at DSDP Site 54-424

The sediments recovered on Deep Sea Drilling Project Leg 54 appear to be mixtures of the normal pelagic sediments of the area and hydrothermally produced manganese and iron phases. The latter are mineralogically and chemically very similar to phases recovered from surficial sampling of the mounds. The hydrothermal nontronite which is approximately 15 meters thick in the three holes is essentially free of carbonate or detrital contaminants. The basal sediments are similar to the carbonate oozes presently being deposited in the region, but are enriched in Mn and Fe. This enrichment appears to be the result of hydrothermal deposition that took place at or near the spreading center and may not be associated with the mounds formation. Three different hypotheses for the formation of the nontronite layer and the mounds deposits are considered. An initial deposition of a widespread nontronite layer and subsequent diapiric-like movement of the layer into carbonates could account for the observed stratigraphy; however, if this be correct, analogous deposits should be present in other DSDP sites. The second hypothesis - replacement of the normal sediments by nontronite - may be feasible, but the high purity of the nontronite requires dissolution and removal of refractory elements. The third hypothesis, metal deposition in an advancing oxidation gradient, is compatible with submersible observations of the mounds; however, it can account only for the high purity of the nontronite by very rapid deposition of the hydrothermal phases.

Esquilo, Tragédias (ediçâo bilingüe). Estudo y traduçâo de Jaa Torrano, Sâo Paulo, Iluminuras, Coleçâo Dionísias, 2009, 424 pp.

Fil: Hamamé, Graciela Noemí. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación. Instituto de Investigaciones en Humanidades y Ciencias Sociales (UNLP-CONICET); Argentina.

Poder y gobierno local en México, 1808-1857 : (Reseña de) María del Carmen Salinas Sandoval, Diana Birrichaga Gardida y Antonio Escobar Ohmstede (coordinadores) Poder y gobierno local en México, 1808-1857, Zinacantepec, Estado de México: El Colegio Mexiquense-El Colegio de Michoacán-Universidad Autónoma del Estado de México, 2011, 424 p.

Este libro es fruto de un esfuerzo colectivo por comprender el poder como una construcción social, destacando los aportes de la historia local para una mejor comprensión de la historia nacional mexicana en su primer medio siglo de independencia.

Esquilo, Tragédias (ediçâo bilingüe). Estudo y traduçâo de Jaa Torrano, Sâo Paulo, Iluminuras, Coleçâo Dionísias, 2009, 424 pp.

Fil: Hamamé, Graciela Noemí. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación. Instituto de Investigaciones en Humanidades y Ciencias Sociales (UNLP-CONICET); Argentina.

Marine barite in sediments of DSDP Site 54-424

The distribution of barite in sediments from D.S.D.P. sites 424 and 424A at the Galapagos hydrothermal mounds field is determined and the process of its formation is deduced. Barite in these deposits is associated with calcareous sediments and is completely absent from the hydrothermal material (manganese crusts and nontronite). Its concentrations tend to increase in the deeper sediments. Since manganese crusts contain significant amounts of Ba, a lack of barite in them is probably due to low concentrations of [SO4]2 in the sediment-seawater interface where they form. The formation of barite occurs within buried sediments, the interstitial waters of which are saturated with [SO4]2. The most probable source of [SO4]2- is the oxidation of H2S which is released from the hydrothermal fluids percolating upwards through the sediments. Although nontronite is formed within buried sediments the environmental conditions occurring during its formation (reducing) prevent barite formation. The association of barite with calcareous sediments is due to the release of Ba by calcareous microorganisms and/or to high concentrations of Ca in the pore waters which maintain a high pH and hence [SO4]2- is stable.