Presentación Orbis Tertius : VII Congreso y Revista digital

Fil: Pastormerlo, Sergio Carlos. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Tramas intergenéricas en el relato Lucaniano del 'día después' (B.C., VII, 786-846)

La escena del campo de batalla tras el enfrentamiento entre pompeyanos y cesarianos en el libro VII del Bellum Ciuile de Lucano (786-846) deja al descubierto el proceso de refuncionalización del tópico tradicional del día después de la lucha. Desde una perspectiva estilística mostramos que la intersección entre los códigos historiográfico, épico y trágico y la manipulación de diversos motivos literarios y culturales en dicho relato pueden leerse como uno de los principales mecanismos de la poética lucaniana del ciuile nefas.

Composition and alteration of volcanic rocks of ODP Hole 119-738C

During ODP Leg 119 one basement hole was drilled at Site 738, on the Southern Kerguelen Plateau. The 38.2 m of basement rocks drilled comprises three basaltic aa-lava flows with basal and top breccias, overlain by Turanian marine carbonates. Site 738 basalts probably erupted near a fracture zone, and were emplaced during the plateau-forming stage of Kerguelen Plateau evolution under quiet, subaerial to shallow water conditions. The basalts are T-MORB, chemically resembling Mesozoic continental flood basalts of the southern hemisphere. Two slightly different magma batches are distinguished by Fe, Ti, Al, Zr, and REE concentrations. Prior to eruption, the magmas had undergone significant olivine and some clinopyroxene fractionation. Incompatible and immobile trace element concentrations and ratios point to a veined upper mantle source, where a refractory mineral assemblage retains Nb, Ta, and the HREE. The basaltic melts derived from this regionally veined, enriched upper mantle have high LREE, and especially Ba and Th concentrations and bear the DUPAL isotopic signature gained from deep- seated, recycled, old oceanic(?) crust. A saponite-celadonite secondary mineral assemblage confines the alteration temperature to <170°C. Alteration is accompanied by net gains of H2O, CO2, K2O, and Rb, higher oxidation, minor Na2O, SiO2 gains, and losses of V and CaO. Released Ca, together with Ca from seawater, precipitated as calcite in veins and vesicles, plumbed the circulation system and terminated the rock/open seawater interaction.

Danian calcareous nannofossils in ODP Hole 119-738C

An apparently complete Danian section was recovered at ODP Site 738 on the southern Kerguelen Plateau. Calcareous nannofossils are abundant and moderately preserved in the section. A number of taxa common in middle or low latitudes, such as Braarudosphaera, Biscutum? romeinii, Biscutum? parvulum, Cyclagelosphaera, Octolithus multiplus, and Toweius petalosus are absent at Site 738. On the other hand, a bloom of Hornibrookina occurs at Site 738 only slightly (15 cm) above the Cretaceous/Tertiary boundary as defined by the iridium peak. Species of Chiasmolithus and Prinsius are very abundant. This gives the nannofossil assemblages distinct high-latitude characteristics and suggests significant latitudinal thermal gradients in the Danian oceans. A Danian nannofossil zonation for the Antarctic region is proposed, which utilizes traditional markers and several nontraditional markers, i.e., the first occurrences of Hornibrookina, Prinsius martinii, and Chiasmolithus bidens, and the last occurrence of Hornibrookina teuriensis. Quantitative analyses of the calcareous nannofossil assemblages from Site 738 reveal four steps of rapid floral changes in the early Danian before relatively stable nannofloral conditions were reached at about 63.8 Ma.

Paleogene and early Neogene planktonic foraminifera of ODP sites 119-738 and 119-744

A virtually complete composite history of Cenozoic pelagic sedimentation was recovered from ODP Sites 738 (62°43' S) and 744 (61°35' S), drilled during Leg 119 on the Kerguelen Plateau. An excellent magnetobiochronologic record was obtained from upper Eocene through Holocene sediments at Site 744, and an expanded lower Paleocene through lower Oligocene sequence was cored at Hole 738. Analysis of the stratigraphic distribution of over 125 planktonic foraminifer taxa from these sites reveals changes in species composition that were strongly influenced by the climatic evolution of Antarctic water masses. Early Paleocene planktonic foraminifer assemblages are nearly identical in species composition to coeval assemblages from low and middle latitude sites, showing the same patterns of post-extinction recovery and taxonomic radiation. Biogeographic isolation, revealed by the absence of tropical keeled species, became apparent by late early Paleocene time. Diversity increased near the Paleocene/Eocene boundary when keeled morozovellids immigrated to the Kerguelen Plateau. Greatest diversity (23 species) was achieved by early Eocene time, corresponding to a Cenozoic warming maximum that has been recognized in lower Eocene deep sea and terrestrial sediments worldwide. A gradual decline in diversity from the late early through middle Eocene, primarily due to the disappearance of acarininids, parallels the record of cooling paleotemperatures in Southern Ocean surface waters. Chiloguembelina-dominated assemblages appeared in the late middle Eocene and persisted through the early Oligocene as Antarctic surface waters became thermally isolated. Late Eocene and early Oligocene assemblages exhibit considerably lower diversity than the older Eocene faunas, and were dominated by chiloguembelinids, subbotinids, and catapsydracids during a time of pronounced climatic cooling and development of continental glaciation on East Antarctica. The small foraminifer Globigerinit? juvenilis replaced chiloguembelinids as the dominant taxon during the late Oligocene. Diversity increased slightly toward the end of the late Oligocene with new appearances of several tenuitellid, globoturborotalitid, and globigerinid species. The trend toward diminishing planktonic foraminifer diversity was renewed during the late early Miocene as siliceous productivity increased in the Antarctic surface waters, culminating with the reduction to nearly monospecific assemblages of Neogloboqu?drin? p?chyderm? that occur in Pliocene-Holocene biosiliceous sediments. An Antarctic Paleogene zonal scheme previously devised for ODP Sites 689 and 690 in the Weddell Sea is used to biostratigraphically subdivide the Kerguelen Plateau sequence. The definition of one Antarctic Paleogene biozone is modified in the present study to facilitate correlation within the southern high latitudes. The ages of 13 late Eoceneearly Miocene datum events are calibrated based on a magnetobiochronologic age model developed for Site 744.