La ludoteca escolar, ¿sólo un espacio para el juego? : Secuencia didáctica sobre escritura de reglamentos

Fil: Fernandez, Adriana Miriam. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

La Crónica del Perú : testimonio de la transformación de un género

Los primeros cronistas -entre ellos Pedro Cieza de León (1522-1558)- vivían bajo el paradigma renacentista, con respecto al perentorio impulso de acción que los encaminó por territorios desconocidos en la geografía, lo cultural, el arte o la concepción filosófica y cósmica del universo. La impronta de la época permitió al hombre recuperar la confianza en sus propias aptitudes y vigorizó su individualidad; por esa razón logró la asombrosa hazaña de prolongar la vida terrena en textualidades que lo mantuvieron vivo a través de los tiempos. Entonces podemos suponer que Cieza de León, cronista del Siglo de Oro, produjo con su Crónica del Perú una serie de relaciones que aportaron los datos de un viaje fundacional hacia el nuevo continente por aquellos años ignorado. Esta trayectoria exigía actos de enunciación dinamizadores de un género que se estaba transformando. En esta ponencia podríamos diferenciar los elementos residuales -que remiten al Medioevo- y aquellos que impactan sobre dicha textualidad a partir de los procesos de transculturación desatados por el descubrimiento y la conquista.

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.

Stable carbon isotope ratios and the formation of dolomite in ODP Leg 175 sites

We examine the link between organic matter degradation, anaerobic methane oxidation (AMO), and sulfate depletion and explore how these processes potentially influence dolomitization. We determined rates and depths of AMO and dolomite formation for a variety of organic-rich sites along the west African Margin using data from Ocean Drilling Program (ODP) Leg 175. Rates of AMO are calculated from the diffusive fluxes of CH4 and SO4, and rates of dolomite formation are calculated from the diffusive flux of Mg. We find that the rates of dolomite formation are relatively constant regardless of the depth at which it is forming, indicating that the diffusive fluxes of Mg and Ca are not limiting. Based upon the calculated log IAP values, log K(sp) values for dolomite were found to narrowly range between -16.1 and -16.4. Dolomite formation is controlled in part by competition between AMO and methanogenesis, which controls the speciation of dissolved CO2. AMO increases the concentration of CO3[2-] through sulfate reduction, favoring dolomite formation, while methanogenesis increases the pCO2 of the pore waters, inhibiting dolomite formation. By regulating the pCO2 and alkalinity, methanogenesis and AMO can regulate the formation of dolomite in organic-rich marine sediments. In addition to providing a mechanistic link between AMO and dolomite formation, our findings provide a method by which the stability constant of dolomite can be calculated in modern sediments and allow prediction of regions and depth domains in which dolomite may be forming.