Organic matter, isotopic composition of calcite veins in basement basalt and pore water at DSDP Leg 78A Holes

Sediments of the Barbados Ridge complex, cored on DSDP Leg 78A, contain low concentrations of acid-insoluble carbon (0.05-0.25%) and nitrogen (C/N 1.5-5) and dispersed C1-C6 hydrocarbons (100-800 ppb). The concentrations of organic carbon and 13C in organic carbon decrease with depth, whereas the concentration of dispersed hydrocarbons increases slightly with depth. These trends may reflect the slow oxidation of organic matter, with selective removal of 13C and slow conversion of the residual organic matter to hydrocarbons. Very minor indications of nitrogen gas were observed at about 250 meters sub-bottom at two of the drilling sites. Basement basalts have calcite veins with d13C values in the range of 2.0 to 3.2 per mil and d18O-SMOW values ranging from 28.5 to +30.6 per mil. Interstitial waters have d18O-SMOW of 0.2 to -3.5 per mil and dD-SMOW of -2 to -15 per mil. The oxygen isotopic composition of the calcite veins in the basement basalts gives estimated equilibrium fractionation temperatures in the range of 11 to 24°C, assuming precipitation from water with d18O-SMOW in the range of +0.1 to -1.0 per mil. This suggests that basalt alteration and precipitation of vein calcite occurred in contact either with warmer Campanian seawater or, later, with pore water, after burial to depths of 200- 300 meters. Pore waters from all three sites are depleted in deuterium and 18O, and dissolved sulfate is enriched in 34S at Sites 541 and 542, but not at Site 543.

Distribution, origin, and hydrocarbon-potential of organic matter in sediments from DSDP Leg 66 Holes

As part of an ongoing program of organic geochemical studies of sediments recovered by the Deep Sea Drilling Project, we have analyzed the types, amounts, and thermal alteration indices of organic matter collected from the Pacific continental margin of southern Mexico on Leg 66. The samples were pieces of core frozen aboard ship. Some of them were analyzed by pyrolysis, heavy C15+ hydrocarbons, and nonhydrocarbons to help determine their origin and hydrocarbon potential. Our main objectives were to find out how much organic matter was being deposited; to establish whether it derived from marine or terrestrial sources; to determine the controls of deposition of organic matter; to estimate the hydrocarbon potential of the drilled section; and to compare and contrast organic sedimentation here with that on other margins.

Sediment paleomagnetism at DSDP Leg 78 Holes

The results of paleomagnetic studies of samples from DSDP Leg 78A are reported. For Site 541, the interval from 60 to 200 m sub-bottom was correlated with the Matuyama through Gilbert polarity epochs. For Site 543, the interval from 150 to 190 m sub-bottom was correlated with marine magnetic Anomalies 5C through 5E. Down-dip directions of tilted beds inferred from declination values for Sites 541 and 542 suggest a pattern of monoclinal folding. Results from basalt samples are comparable to those from other DSDP sites in relatively old basalts.

La experimentación fotográfica como práctica didáctica

Fotografía Experimental consiste en un taller creado para los alumnos del último año de la Orientación Ciencias Naturales del Liceo Víctor Mercante de la U.N.L.P. El aspecto que lo caracteriza es el trabajo interdisciplinario que se realiza durante su desarrollo en el que se articulan aspectos de las ciencias físicas, químicas y sociales para el abordaje de la fotografía como tema a investigar. La experimentación, la modalidad de taller y las consiguientes producciones en clase propician el espacio adecuado para la construcción de los conocimientos teóricos que docentes y alumnos aportan, a la integración de los diferentes saberes, en las conclusiones finales de cada jornada.