Mineralogy and diagenesis: Their effect on acoustic and electrical properties of pelagic clays at DSDP Leg 86 Holes

Analysis of pelagic clay samples from Sites 576, 578, and 581 shows that physical, acoustic, and electrical trends with increasing burial depth are related to mineralogical and diagenetic changes. The properties of interest are bulk density (roo), porosity (phi), compressional-wave velocity (Vp) and velocity anisotropy (Ap), and electrical resistivity (Ro) and resistivity anisotropy (Ar). In general, as demonstrated in particular for the brown pelagic clay, the increase in roo, Vp, Ro, and to a lesser extent Ap and Ar with increasing depth is primarily caused by decreasing phi (and water content) as a result of compaction. The mineralogy and chemistry of the pelagic clays vary as a function of burial depth at all three sites. These variations are interpreted to reflect changes in the relative importance of detrital and diagenetic components. Mineralogical and chemical variations, however, play minor roles in determining variations in acoustic and electrical properties of the clays with increasing burial depth.

Debates teóricos en torno a la literatura latinoamericana: el surgimiento de un nuevo proyecto crítico (1975-1985)

Este trabajo se propone indagar en las instancias de emergencia del proyecto crítico que, a principios de los años '70, comienza a perfilarse como un espacio colectivo de reflexión y debate en torno a la necesidad de un discurso teórico y crítico que acompañe la "madurez" de un corpus literario en pleno proceso de expansión y consagración internacional. Se hace especial hincapié en el cruce entre modernización y politización que realiza este proyecto, sus principales actores, los circuitos de las revistas de crítica literaria y cultural que lo consolidó, y los aportes iniciales que luego dieron lugar a las producciones críticas más complejas de los años '80.

Elemental abundance and water content at DSDP Leg 86 Holes

X-ray fluorescence analyses of 1143 samples from Site 576 (32°21.4'N, 164°16.5'E) and 539 samples from Site 578 (33°55.6'N, 151°37.7'E) for the elements Na, Mg, Al, Si, P, K, Ca, Ti, Mn, Fe, Ba, and S show consistent trends from Si-rich surficial deposits to dark brown clays rich in Mn, Fe, P, and Ti in early Cenozoic sections. These data sets form the basis for a detailed paleogeochemical stratigraphy of North Pacific "red" clays.

Las legitimaciones de la dictadura militar de Guatemala (1982- 1985)

Del larguísimo conflicto armado interno guatemalteco (1962-1996) sólo un breve período de tiempo concentra los índices más altos de violencia política desplegados por las fuerzas represivas estatales. Este período de tiempo corresponde al gobierno de un militar democráticamente electo (Fernando Romeo Lucas García, 1978-1982) y a las dictaduras encabezadas por José Efraín Ríos Montt (1982-1983) y Oscar Humberto Mejía Víctores (1983-1985). A nuestro juicio, la comparación de las experiencias represivas latinoamericanas (1964-1990) nos puede dar claves para identificar variables independientes que sirvan para explicar patrones o acontecimientos comunes o contrastantes. Para poder hacerlas comparables hemos utilizado una unidad equivalente, el concepto de dictadura institucional de las Fuerzas Armadas, como concepto históricamente referido y diferenciado de otras experiencias dictatoriales. Nuestra hipótesis general es que durante el período 1982-1985 se constituyó en Guatemala una dictadura institucional de las Fuerzas Armadas fundacional de características notablemente similares a las vistas en el Cono Sur. El objetivo de este artículo en particular es principalmente pedagógico: mostrar algunas de las características similares de esa última dictadura militar guatemalteca (1982-1985) en lo que respecta a las formas de legitimación. Trabajaremos algunas poquísimas dimensiones como la legitimidad de origen, la forma de organización del ejercicio del poder político y la legitimidad de ejercicio

La Historia en la Historieta. La revista Fierro (1984) y la representación de la Guerra de Malvinas

En el siguiente trabajo nos proponemos abordar el caso argentino en el que la historieta operó como un primer vehículo de representación por parte de la industria cultural de un acontecimiento traumático social, mas precisamente de los tópicos o marcas de la dictadura de 1976. Específicamente trabajaremos el caso particular de la revista "Fierro, historieta para sobrevivientes" (1984-1992) durante los años de la transición a la democracia, es decir entre 1984 y 1985. Asimismo hemos elegido de entre todas las historietas publicadas, la serie "Batalla de las Malvinas" (1984), con guión de Ricardo Barreiro, y dibujos de Carlos Pedrazzini, Alberto Macagno y Marcelo Pérez. El objetivo de este trabajo es el de repensar el lugar de la historieta como representación válida del pasado reciente, una representación que incluso puede provocar una mirada crítica y aportar a la consolidación de la memoria

Quartz content and mass accumulation rates at DSDP Hole 86-576A

The amount and the accumulation rate of quartz were measured in 33 samples from Hole 576A. The amount and source of mineral aerosol being deposited in the northwest Pacific during the Cenozoic are evaluated using these data. When Hole 576A is compared to a Cenozoic record in the central North Pacific, a strong uniformity in the composition of the mineral aerosol across the North Pacific is seen. The data suggest that Hole 576A entered the influence of the westerlies about 15 m.y. ago and that since that time the rates of sediment deposition have increased. Only the dramatic change in quartz accumulation 2.5 m.y. ago can be clearly related to a climatic event, but a gradual increase in quartz accumulation through the Miocene and early Pliocene is probably a result of increasing Northern Hemisphere aridity and intensified atmospheric activity associated with global cooling during the interval.

Core alignment and composite depth scale of DSDP Site 86-577

Deep Sea Drilling Project Site 577 on Shatsky Rise (North Pacific Ocean) recovered a series of cores at three holes that contain calcareous nannofossil ooze of latest Cretaceous (late Maastrichtian) through early Eocene age. Several important records have been generated using samples from these cores, but the stratigraphy has remained outdated and confusing. Here we revise the stratigraphy at Site 577. This includes refining several age datums, realigning cores in the depth domain, and placing all stratigraphic markers on a current time scale. The work provides a template for appropriately bringing latest Cretaceous and Paleogene data sets at old drill sites into current paleoceanographic literature for this time interval. While the Paleocene Eocene Thermal Maximum (PETM) lies within core gaps at Holes 577* and 577A, the sedimentary record at the site holds other important events and remains crucially relevant to understanding changes in oceanographic conditions from the latest Cretaceous through early Paleogene.

Age model and stable isotope record of DSDP holes 48-401 and 86-577

Early Paleogene warm climates may have been linked to different modes and sources of deepwater formation. Warm polar temperatures of the Paleocene and Eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters. The possibility of increasing ocean heat transport through the production of warm saline deep waters (WSDW) in the Tethyan region has generated considerable interest. In addition, General Circulation Model results indicate that deepwater source regions may be highly sensitive to changing basin configurations. To decipher deepwater changes, we examined detailed benthic foraminiferal faunal and isotopic records of the late Paleocene through the early Eocene (~60 to 50 Ma) from two critical regions: the North Atlantic (Bay of Biscay Site 401) and the Pacific (Shatsky Rise Site 577). These records are compared with published data from the Southern Ocean (Maud Rise Site 690, Islas Orcadas Rise Site 702). During the late Paleocene, similar benthic foraminiferal delta18O values were recorded at all four sites. This indicates uniform deepwater temperatures, consistent with a single source of deep water. The highest delta13C values were recorded in the Southern Ocean and were 0.5 per mil more positive than those of the Pacific. We infer that the Southern Ocean was proximal to a source of nutrient-depleted deep water during the late Paleocene. Upper Paleocene Reflector Ab was cut on the western Bermuda Rise by cyclonically circulating bottom water, also suggesting a vigorous source of bottom water in the Southern Ocean. A dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest Paleocene in the Southern Ocean. This is a short-term (<100 kyr), globally synchronous event which also is apparent in both the Atlantic and Pacific records as a carbon isotopic excursion of approximately 1 per mil. Faunal analyses from the North Atlantic and Pacific sites indicate that the largest benthic foraminiferal faunal turnover of the Cenozoic was synchronous with the isotopic excursion, lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation. We speculate that the Southern Ocean deepwater source was reduced or eliminated at the time of the excursion. During the early Eocene, Southern Ocean delta13C values remained enriched relative to the North Atlantic and Pacific. However, the Southern Ocean was also enriched in delta18O relative to these basins. We interpret that these patterns indicate that although the Southern Ocean was proximal to a source of cool, nutrient-depleted water, the intermediate to upper deep water sites of the North Atlantic and Pacific were ventilated by a different source that probably originated in low latitudes, i.e., WSDW.

Seasonal variations of contribution of large and fine fractions of phytoplankton to primary production and chlorophyll a in the Sevastopol Bay from April 1985 till March 1986

It has been shown that in the Sevastopol Bay during the year primary production and chlorophyll "a" created by picoplankton (0.45-2.5 µm) consisted on the average 20-44% of total production. It was approximately a half of the level for oligotrophic waters of the ocean. Picoplankton of waters studied is represented by eucaryotes, cell diameter of which is, as a rule, about 2-3 µm. Contribution of the finest fraction of phytoplankton (0.43-0.85 µm) to primary production and con¬tent of chlorophyll "a" was insignificant (0-4%).

Ages at DSDP Site 86-577

A synthesis of paleomagnetic and calcareous nannofossil stratigraphies for the sedimentary sequences recovered at Deep Sea Drilling Project (DSDP) Site 577 on the Shatsky Rise is presented. Numerical ages are estimated for a series of nannofossil datum levels from the late Maestrichtian to middle Eocene period ( about 68 to about 52 m.y. ago) and the late Cenozoic (last about 5 m.y.). Absolute age control is obtained on the basis of the revised geomagnetic polarity time scale of. The results are compared with various sets of data reported in the literature, in particular to magnetobiochronologies derived from marine sections accessible on land in Italy and from recent DSDP boreholes in the South Atlantic, and with the summary by Berggren et al. Although a number of minor discrepancies remain to be resolved, the remarkable general agreement of the data validates the basic concept of this approach to the elaboration of a calibrated geologic time scale.