Geochemistry, SiO2 minerals and isotopes at DSDP Hole 72-516F

Cherts recovered during DSDP Leg 72 from Rio Grande Rise sediments (Site 516) consist of both cristobalite and quartz, and contain ghosts of foraminifers and (more rare) radiolarians. Porcelanite made of disordered cristobalite is found in most old enclosing sediments. Local dissolution of siliceous microfossils during diagenesis is the most likely source of the silica required for the chert formation. As sediment age increases, the proportion of biogenic silica decreases and authigenic silica increases.

La memoria colectiva de los adolescentes de la ciudad de La Plata sobre la última dictadura militar

En la presente investigación, realizada como trabajo final de la Licenciatura en Sociología de la Facultad de Humanidades y Ciencias de la Educación de la Universidad Nacional de La Plata, se aborda el tema de la memoria colectiva de los adolescentes de entre 17 y 18 años de la ciudad de La Plata sobre la última dictadura militar argentina iniciada en 1976. El objetivo principal del trabajo consiste en indagar la memoria colectiva de estos adolescentes, explorar las representaciones que construyeron acerca de dicho momento particular de la vida social y política de nuestro país, teniendo en cuenta que estos jóvenes no lo han vivido, es decir, no han sido testigos ni han sufrido en carne propia el terrorismo de Estado. La totalidad de estos chicos ha nacido entre los años 1984 y 1985, cuando la democracia ya estaba vigente. Para la realización de esta exploración se seleccionaron grupos de adolescentes de cuatro escuelas medias de la ciudad de La Plata, distribuidas en distintas zonas geográficas y con diversas características socioeconómicas

Foraminiferal study of ODP Hole 189-1171

Sequence boundary ages determined in shallow-water sediments obtained from ODP (Ocean Drilling Program) Leg 189 Site 1171 (South Tasman Rise) compare well with other stratigraphic records (New Jersey, United States, and northwestern Europe) and d18O increases from deep-sea records, indicating that significant (>10 m) eustatic changes occurred during the early to middle Eocene (51-42 Ma). Sequence boundaries were identified and dated using lithology, bio- and magnetostratigraphy, water-depth changes, CaCO3 content, and physical properties (e.g., photospectrometry). They are characterized by a sharp bioturbated surface, low CaCO3 content, and an abrupt increase in glauconite above the surface. Foraminiferal biofacies and planktonic/benthic foraminiferal ratios were used to estimate water-depth changes. Ages of six sequence boundaries (50.9, 49.2, 48.5-47.8, 47.1, 44.5, and 42.6 Ma) from Site 1171 correlate well to the timings of d18O increases and sequence boundaries identified from other Eocene studies. The synchronous nature of sequence boundary development from globally distal sites and d18O increases indicates a global control and that glacioeustasy was operating in this supposedly ice-free world. This is supported by previous modeling studies and atmospheric pCO2 estimates showing that the first time pCO2 levels decreased below a threshold that would support the development of an Antarctic ice sheet occurred at ca. 51 Ma. Estimates of sea-level amplitudes range from ~20 m for the early Eocene (51-49 Ma) and ~25 m to ~45 m for the middle Eocene (48-42 Ma) using constraints established for Oligocene d18O records.