Troisi Melean, Jorge. (2012). El oro de los jesuitas. La compañíade Jesús y sus esclavos en la Argentina colonial.Saarbrücken: Editorial Académica Española, 172 pgs.

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

Arturo Carrera, El vespertillo de las parcas. Buenos Aires, Tusquets Editores, 1997, 172 páginas

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

Arturo Carrera, El vespertillo de las parcas. Buenos Aires, Tusquets Editores, 1997, 172 páginas

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

Mineralogy and major element oxide composition of sediments from ODP Hole 172-1063D

Dansgaard-Oeschger (D-O) cycles in sediment at Site 1063 are characterized by distinct fluctuations in physical properties. Stadials are marked by low bulk density and interstadials by high bulk density. Compressional (P-)wave velocity is in phase with bulk density over some but not all depth intervals. Four of the D-O cycles straddling the oxygen isotope Stage 4/5 boundary have been studied in detail to understand the origin of the physical properties changes. Sediment on the Bermuda Rise is comprised of three main components: calcite, aluminosilicate minerals, and biogenic silica. Calcite concentrations vary from 1% to 43% of bulk sediment and are highest during interstadials. Aluminosilicate concentrations vary from 52% to 92% of bulk sediment and are highest during stadials. The major element ratios Al2O3/TiO2 and K2O/Al2O3 show increases across bulk density cycles, suggesting a change in the composition of aluminosilicates. This interpretation is supported by mineralogical analyses, which show a subtle change in clay composition. Biogenic silica concentrations vary from 0% to 23% of bulk sediment and are also highest during stadials. However, the abundance of silica varies significantly from one D-O cycle to another. Silt and fine sand abundance also increase during the first of the four stadials. This coarsening of sediment coincides with the increase in biogenic silica. The low grain density and high porosity associated with biogenic silica result in intervals of low bulk-sediment density. The abundance of biogenic silica closely matches P-wave velocity, suggesting that silica imparts a greater rigidity to the sediment.

Troisi Melean, Jorge. (2012). El oro de los jesuitas. La compañíade Jesús y sus esclavos en la Argentina colonial.Saarbrücken: Editorial Académica Española, 172 pgs.

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

Paleomagnetic, stable oxygen isotope ratios, and U/Th activities of ODP Site 172-1062

Geomagnetic excursions are recognized as intrinsic features of the Earth's magnetic field. High-resolution records of field behaviour, captured in marine sedimentary cores, present an opportunity to determine the temporal and geometric character of the field during geomagnetic excursions and provide constraints on the mechanisms producing field variability. We present here the highest resolution record yet published of the Blake geomagnetic excursion (~125 ka) measured in three cores from Ocean Drilling Program (ODP) Site 1062 on the Blake-Bahama Outer Ridge. The Blake excursion has a controversial structure and timing but these cores have a sufficiently high sedimentation rate (~10cm/ka) to allow detailed reconstruction of the field behaviour at this site during the excursion. Palaeomagnetic measurements of the cores reveal rapid transitions (<500 yr) between the contemporary stable normal polarity and a completely reversed state of long duration which spans a stratigraphic interval of 0.7 m. We determine the duration of the reversed state during the Blake excursion using oxygen isotope stratigraphy, combined with 230Th excess measurements to assess variations in the sedimentation rates through the sections of interest. This provides an age and duration for the Blake excursion with greater accuracy and with constrained uncertainty. We date the directional excursion as falling between 129 and 122 ka with a duration for the deviation of 6.5±1.3 kyr. The long duration of this interval and the fully reversed field suggest the existence of a pseudo-stable, reversed dipole field component during the excursion and challenge the idea that excursions are always of short duration.

Troisi Melean, Jorge. (2012). El oro de los jesuitas. La compañíade Jesús y sus esclavos en la Argentina colonial.Saarbrücken: Editorial Académica Española, 172 pgs.

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