Chemical composition of clay minerals from ODP Leg 168 sites

The exchangeable cation compositions of organic-poor terrigenous sediments containing smectite as primary ion exchanger from a series of holes along ODP Leg 168 transect on the eastern flank of the Juan de Fuca Ridge have been examined as a function of distance from the ridge axis and burial depth. The total cation exchange capacity (CEC) values of the sediments ranged from 2 to 59 meq/100 g, increasing with increases in the wt.% smectite. At the seafloor, the exchangeable cation compositions involving Na, K, Mg, and Ca, expressed in terms of equivalent fraction, are nearly constant regardless of the different transect sites: XNa = 0.21 ± 0.04, XK = 0.08 ± 0.01, XMg = 0.33 ± 0.09, and XCa = 0.38 ± 0.09. The calculated selectivity coefficients of the corresponding quaternary exchange reactions, calculated using porewater data, are in log units -5.45 ± 0.39 for Na, 1.97 ± 0.49 for K, 0.42 ± 0.41 for Mg, and 3.06 ± 0.69 for Ca. The exchangeable cation compositions below the seafloor change systematically with distance from the ridge crest and burial depth, conforming to the trends of the same cations in the porewaters. The selectivities for Na and Mg are roughly constant at temperatures from 2 to 66°C, indicating that the equivalent fractions of these two cations are independent of sediment alteration taking place on the ridge flank. Unlike Na and Mg, the temperature influence is significant for K and Ca, with Ca-selectivity decreases being coupled with increases in K-selectivity. Although potentially related to diagenetic and/or hydrothermal mineral precipitation or recrystallization, no evidence of such alteration was detected by XRD and TEM. In sites where upwelling of hydrothermal fluids from basement is occurring, the K-selectivity of the sediment is appreciably higher than at the other sites and corresponds to the formation of (Fe, Mg) rich smectite and zeolites. Our study indicates that local increases in K-selectivity at hydrothermal sites are caused by the formation of these authigenic minerals.

Clelia Maria Piastra y Francesco Santi, Figure poetiche e figure teologiche nella mariología dei secoli XI e XII (Atti del Secondo Convengo mariologico della fondazione Ezio Franceschini con la collaborazione della Biblioteca Palatina di Parma. Parma, 19-20 maggio 2000), Firenze: Sismel-Edizioni del Galluzzo, 2004, xii + 168 pp.

Fil: Disalvo, Santiago Aníbal. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Mario Presas, Del Ser a la Palabra. Ensayos sobre estética, fenomenología y hermenéutica, Buenos Aires, Biblos, 2009, 168 p., ISBN 978-950-786-707-1

Fil: Solas, Silvia Angélica. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Juan Orbe (compilador), La situación autobiográfica. Buenos Aires, Corregidor, 1995, 168 páginas

Fil: Páez, Roxana Haydée. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Chemical and isotope compositions of bottom sediments from ODP Leg 168, Eastern Flank of the Juan de Fuca Ridge

Ten sites were drilled in the eastern flank of the Juan de Fuca Ridge (North East Pacific) along a 100 km-long east-west transect during Leg ODP 168. This study focuses on the mineralogical and chemical study of sediments that overly basaltic basement through which seawater circulates. Silicate authigenesis was observed in the sediment layer just above basement at sites located more than 30 km from the ridge axis. This sediment alteration is particularly abundant at ODP Sites 1031 and 1029 where authigenic formation of Fe-Mg rich smectite and zeolite and the dissolution of biogenic calcite are observed. Comparison of the distribution of the alteration in the basal sediment collected along this transect suggests that diffusional transport of aqueous solutes from the basement into the overlying sediment cannot produce the mineralogical and chemical changes in the basal sediments at Sites 1031 located on a basement topographic high, and at Site 1029 located at about 50 km from the ridge axis on a buried basement area. Vertical advection of basement fluid though the sediment section is required to produce this alteration. These processes are still active at Site 1031, based on systematic variations in pore-water profiles and temperatures obtained from stable isotopic data on calcium carbonates and the nature of authigenic minerals. At Site 1029, there is no present-day advection of basement fluids though the sediment section, suggesting that this is a relic site for fluid flow.

Clelia Maria Piastra y Francesco Santi, Figure poetiche e figure teologiche nella mariología dei secoli XI e XII (Atti del Secondo Convengo mariologico della fondazione Ezio Franceschini con la collaborazione della Biblioteca Palatina di Parma. Parma, 19-20 maggio 2000), Firenze: Sismel-Edizioni del Galluzzo, 2004, xii + 168 pp.

Fil: Disalvo, Santiago Aníbal. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Juan Orbe (compilador), La situación autobiográfica. Buenos Aires, Corregidor, 1995, 168 páginas

Fil: Páez, Roxana Haydée. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Mario Presas, Del Ser a la Palabra. Ensayos sobre estética, fenomenología y hermenéutica, Buenos Aires, Biblos, 2009, 168 p., ISBN 978-950-786-707-1

Fil: Solas, Silvia Angélica. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.