Versiones de la Matrona (Catulo 66-68)

Fil: Galán, Lía Margarita. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Electron spin resonance (ESR) and 14C dating in sediments of Bonaire, Leeward Antilles

The coastal deposits of Bonaire, Leeward Antilles, are among the most studied archives for extreme-wave events (EWEs) in the Caribbean. Here we present more than 400 electron spin resonance (ESR) and radiocarbon data on coarse-clast deposits from Bonaire's eastern and western coasts. The chronological data are compared to the occurrence and age of fine-grained extreme-wave deposits detected in lagoons and floodplains. Both approaches are aimed at the identification of EWEs, the differentiation between extraordinary storms and tsunamis, improving reconstructions of the coastal evolution, and establishing a geochronological framework for the events. Although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive-related processes, insufficient separation, superimposition or burying of coarse-clast deposits and restricted dating accuracy limit the use of both fine-grained and coarse-clast geoarchives to unravel decadal- to centennial-scale events. At several locations, distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin. Coastal landforms on the western coast have significantly been influenced by (sub)-recent hurricanes, indicating that formation of the coarse-clast deposits on the eastern coast is likely to be related to past events of higher energy.

La formación de la CGT de los Argentinos en La Plata, Berisso y Ensenada al calor del '68 platense : La experiencia de la intersindical de gremios y sus relaciones con el movimiento obrero y estudiantil

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

México 68, la lucha por la democracia en los fondos del Archivo Histórico de la Universidad Nacional Autónoma de México

Este artículo analiza los documentos que contienen información sobre las luchas universitaria resguardados en el Archivo Histórico de la Universidad Nacional Autónoma de México (AHUNAM). Este archivo es custodio de fondos universitarios y acervos provenientes de particulares, recibidos por donación, compra o legado, cuyo contenido se caracteriza por su pluralidad temática y por resultar claves para entender momentos históricos coyunturales en la historia de México, tales como la colección hemerográfica que guarda la memoria sobre la lucha por la autonomía de la universidad, la colección movimientos estudiantiles, entre los cuales destaca el movimiento de 1968 y el Paro Estudiantil 1999-2000. Específicamente este artículo se enfoca sobre los fondos y colecciones del movimiento estudiantil ocurrido en 1968, el cual comenzó con una serie de protestas nacionales que culminaron con la matanza de decenas de estudiantes y ciudadanos en la Plaza de las Tres Culturas, Tlalelolco; acontecimiento que sangró la vida universitaria y de la sociedad mexicana y de la cual el AHUNAM reúne documentación, hemerográfica, gráfica y fotografía que coadyuvan a la investigación y contribuyen a que no perdamos la memoria en la lucha por la democracia

Composition of sediment pore water and isotopes in carbonate and benthic foraminifera at DSDP Holes 68-501, 69-505 and Site 69-504

Two sites on the southern flank of the Costa Rica Rift were drilled on DSDP Legs 68 and 69, one on crust 3.9 m.y. old and the other on crust 5.9 m.y. old. The basement of the younger site is effectively cooled by the circulation of seawater. The basement of the older site has been sealed by sediment, and an interval in the uppermost 560 meters of basement recently reheated to temperatures of 60 to 120°C. Although the thickness of the sediments at the two sites is similar (150-240 m versus 270 m), the much rougher basement topography at the younger Site 505 produces occasional basement outcrops, through which 80 to 90% of the total heat loss apparently occurs by advection of warm seawater. This seawater has been heated only slightly, however; the temperature at the base of the sediments is only 9°C. Changes in its composition due to reaction with the basement basalts are negligible, as indicated by profiles of sediment pore water chemistry. Bacterial sulfate reduction in the sediments produces a decrease in SO4 (and Ca) and an increase in alkalinity (and Sr and NH3) as depth increases to an intermediate level, but at deeper levels these trends reverse, and all of these species plus Mg, K, Na, and chlorinity approach seawater values near basement. Si, however, is higher, and Li may be lower. At the older site, Site 501/504, where heat loss is entirely by conduction, the temperature at the sediment/basement contact is 59°C. Sediment pore water chemistry is heavily affected by reaction with the basaltic basement, as indicated by large decreases in d18O, Mg, alkalinity, Na, and K and an increase in Ca with increasing depth. The size of the changes in d18O, Mg, alkalinity, Ca, Sr, and SO4 varies laterally over 500 meters, indicating lateral gradients in pore water chemistry that are nearly as large as the vertical gradients. The lateral gradients are believed to result from similar lateral gradients in the composition of the basement formation water, which propagate upward through the sediments by diffusion. A model of the d18O profile suggests that the basement at Site 501/504 was sealed off from advection about 1 m.y. ago, so that reaction rates began to dominate the basement pore water chemistry. A limestone-chert diagenetic front began to move upward through the lower sediments less than 200,000 yr. ago.