Chemistry of upper Eocene microtektites

Late Eocene microtektites and crystal-bearing microkrystites extracted from DSDP and ODP cores from the Atlantic, Pacific, and Indian oceans have been analyzed to address their provenance. A new analysis of Nd and Sr isotopic compositions confirms previous work and the assignment of the uppermost microtektite layer to the North American tektites, which are associated with the 35.5 Ma, 85 km diameter Chesapeake impact structure of Virginia, USA. Extensive major element and Nd and Sr isotopic analyses of the microkrystites from the lowermost layer were obtained. The melanocratic microkrystites from Sites 216 and 462 in the Indian and Pacific oceans possess major element chemistries, Sr and Nd isotopic signatures and Sm-Nd, T CHUR, model ages similar to those of tagamite melt rocks in the Popigai impact structure. They also possess Rb-Sr, T UR, model ages that are younger than the tagamite TCHUR ages by up to ~1 Ga, which require a process, as yet undefined, of Rb/Sr enrichment. These melanocratic microkrystites are consistent with a provenance from the 35.7 Ma, 100 km diameter Popigai impact structure of Siberia, Russia, while ruling out other contemporaneous structures as a source. Melanocratic microkrystites from other sites and leucocratic microkrystites from all sites possess a wide range of isotopic compositions (epsilon (143Nd) values of -16 to -27.7 and epsilon (87Sr) values of 4.1-354.0), making the association with Popigai tagamites less clear. These microkrystites may have been derived by the melting of target rocks of mixed composition, which were ejected without homogenization. Dark glass and felsic inclusions extracted from Popigai tagamites possess epsilon (143Nd) and epsilon (87Sr) values of -26.7 to -27.8 and 374.7 and 432.4, respectively, and T CHUR and T UR model ages of 1640-1870 Ma and 240-1830 Ma, respectively, which require the preservation of initially present heterogeneity in the source materials. The leucocratic microkrystites possess diverse isotopic compositions that may reflect the melting of supra-basement sedimentary rocks from Popigai, or early basement melts that were ejected prior to homogenization of the Popigai tagamites. The ejection of melt rocks with chemistries consistent with a basement provenance, rather than the surface ~1 km of sedimentary cover rocks, atypically indicates a non-surficial source to some of the ejecta. Microkrystites from two adjacent biozones possess statistically indistinguishable major element compositions, suggesting they have a single source. The occurrence of microkrystites derived from a single impact event, but in different biozones, can be explained by: (1) diachronous biozone boundaries; (2) post-accumulation sedimentary reworking; or (3) erroneous biozonation.

Hunefeldt, Christine: Liberalism in the Bedroom: Quarrelling Spouses in Nineteenth -Century Lima; The Pennsylvania State University Press, University Park, Pennsylvania, 2000. XVII + 388 p.

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

La Argentina neoliberal. Acciones estatales y clase dominante : Del modelo de la convertibilidad al modelo productivo-exportador

El trabajo final analiza la instauración y desarrollo del neoliberalismo en Argentina a partir de la interacción entre los actores de clase dominante y las acciones desplegadas por el Estado. Efectuamos análisis de las principales fracciones del capital, pensando sus estrategias a partir de la posición ocupada en la estructura socio-económica, tensada por una particular correlación de fuerzas. Observamos las acciones estatales atendiendo a las que representaban mayor incidencia en la interacción entre la esfera política y la socio económica, centrándonos en las políticas económicas, y cómo en una interacción compleja con los actores de clase iban dando lugar a la construcción de 'reglas de juego', de patrones que reglamentaban esas interacciones al tiempo que eran producto de las mismas. Indagamos cómo estas interacciones y las reglas de juego emergentes iban dando lugar a distintos modelos dentro del modo de acumulación neoliberal. Así buscamos detectar el desarrollo de distintos momentos de la acción de los actores de la clase dominante: un momento de convergencia donde primaban la confluencia entre los principales actores, y un momento de divergencia, donde destacaba la disputa de intereses y se abría un escenario de luchas interburguesas. Estos se articulaban complejamente con otros momentos de la acción estatal: un momento de la gestión, donde la gobernabilidad aparece estable, y momento de intervención fuerte, donde el Estado debe desarrollar un rol activo para incidir en las reglas de juego y en las relaciones de clase. Desde esta perspectiva realizamos un breve recorrido que buscaba dar cuenta de la instauración del neoliberalismo en Argentina, iniciado con el golpe de Estado de 1976 y deteniéndonos particularmente en el modelo de la convertibilidad, de modo de abstraer un esquema del 'neoliberalismo real' para contrastarlo con el modelo post-convertibilidad, con el fin de analizar sus rupturas y continuidades, concentrando el análisis de la clase dominante y las acciones estatales durante el gobierno de Néstor Kirchner

Sporomorphs and dinoflagellate cysts of ODP Leg 113 holes

Palynological studies were carried out on Paleogene sections from Sites 693 and 696 of Ocean Drilling Project Leg 113 in the Weddell Sea region. Dinoflagellate cysts and sporomorphs were recovered at Site 696 (61°S, 42°W) indicating a middle Eocene to late Eocene/earliest Oligocene age for a glauconitic silt/sandstone. At Site 693 (70°S, 14°W) early Oligocene siliciclastic mud contains a low diversity palynoflora. In an upper Oligocene section (Site 693) only rare, reworked Mesozoic palynomorphs were encountered. Palynological data from Kerogen analyses, dinocysts, and sporomorphs are used to reconstruct the climatic change on the South Orkney microcontinent from the middle Eocene to the late Eocene/earliest Oligocene at Site 696 and the late early Oligocene/early late Oligocene time interval at Site 693 near the continental margin. The middle Eocene was a warm period in the Orkney region with good growing conditions for a warm temperate Nothofagus/conifer forest with an admixture of Proteaceae. Temperate surface water masses, which allowed the growth of a reasonably diverse dinocyst assemblage (ca. 15-20 species), persisted until the end of the Eocene at Site 696. Late early Oligocene sediments of Site 693 (Antarctic continental margin) contain only a low diversity dinocyst flora (two species). The major Cenozoic cooling event in the Weddell Sea region probably occurred at the Eocene/Oligocene boundary. A second dramatic climatic deterioration seems to have taken place during the late early/early late Oligocene, when dinocysts disappeared at the Dronning Maud Land margin area.