Pedagogía y Ciencias de la Eduación: estudio comparativo, de Mariana Olmedo

Fil: Coscarelli, María Raquel. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Interstitial-water chemistry of ODP Leg 113 sites

Variations in the distribution of major elements and stable oxygen isotopes in ODP Leg 113 pore water are not related to lithology and thus appear to be controlled by minor constituents. Petrographic observations and geochemical considerations indicate that alteration of calc-alkalic volcanic material dispersed in the sediment is an important process. A diagenetic reaction is constructed that involves transformation of volcanic glass into smectite, zeolite (represented by phillipsite), chert, and iron sulfide. Mass balance calculations reveal that alteration of less than 10% (volume) of volcanogenic material may account for the observed depletion of magnesium, potassium, and 18O and enrichment of calcium. Alteration of this amount of volcanic glass produces less than 4% (volume) of smectite and zeolite. Hence, mass balance is obtained without having to invoke unreasonable large amounts of volcanic matter or interactions between seawater and basement.

De la naturaleza mecánica al organismo programado

Tanto las metáforas como los instrumentos informáticos de que se valen las nuevas "ciencias de la vida", cuyos logros son intensamente divulgados por los medios de comunicación, impregnan las formas de percibir, pensar y experimentar el mundo, y llegan a afectar la misma noción de qué significa ser humanos. Junto con los discursos y las soluciones técnicas que proponen la genética y las neurociencias emergen nuevas formas de concebir y tratar la materia orgánica, tanto humana como animal y vegetal. Así, mientras las herramientas mecánicas, estos nuevos relatos cosmológicos abandonan las viejas figuras retóricas de la mecanización para embarcar en un proyecto inédito: la "digitalización" de la vida. Se trata de un sueño inspirado en la compatibilidad entre los cuerpos y el nuevo instrumental técnico, cuya mayor ambición consiste en descifrar la información que define la esencia de cada organismo, con el fin de "reprogramar" sus códigos, circuitos y flujos vitales. Aunque suela presentarse como un proyecto meramente tecnológico y "naturalizado" en sus premisas y objetivos, vale la pena rescatar sus robustas raíces históricas y sus reverberaciones políticas, económicas y socioculturales.

De la naturaleza mecánica al organismo programado

Tanto las metáforas como los instrumentos informáticos de que se valen las nuevas "ciencias de la vida", cuyos logros son intensamente divulgados por los medios de comunicación, impregnan las formas de percibir, pensar y experimentar el mundo, y llegan a afectar la misma noción de qué significa ser humanos. Junto con los discursos y las soluciones técnicas que proponen la genética y las neurociencias emergen nuevas formas de concebir y tratar la materia orgánica, tanto humana como animal y vegetal. Así, mientras las herramientas mecánicas, estos nuevos relatos cosmológicos abandonan las viejas figuras retóricas de la mecanización para embarcar en un proyecto inédito: la "digitalización" de la vida. Se trata de un sueño inspirado en la compatibilidad entre los cuerpos y el nuevo instrumental técnico, cuya mayor ambición consiste en descifrar la información que define la esencia de cada organismo, con el fin de "reprogramar" sus códigos, circuitos y flujos vitales. Aunque suela presentarse como un proyecto meramente tecnológico y "naturalizado" en sus premisas y objetivos, vale la pena rescatar sus robustas raíces históricas y sus reverberaciones políticas, económicas y socioculturales.

Lower Cretaceous nannofossils of ODP Holes 113-682B and 113-693A

Organic-rich, moderately to sparsely nannofossiliferous Lower Cretaceous claystones ("black shales") were cored at two Ocean Drilling Program Leg 113 sites on the continental slope of East Antarctica off Dronning Maud Land. A 39 m section at Site 692 yielded a Neocomian assemblage of limited diversity with rare Cyclagelosphaera deflandrei, Diadorhombus rectus, and Cruciellipsis cuvillieri, and is probably Valanginian in age. A 70-m section at Site 693 is assigned to the Rhagodiscus angustus Zone (late Aptian-early Albian in age). The latter zone is represented at DSDP sites on the Falkland Plateau, but equivalents to the Neocomian section are absent there, probably due to a disconformity. Watznaueria barnesae is the dominant species at both ODP sites, but it shares dominance with Repagulum parvidentatum at Site 693, where they total 70%-90% of the assemblage; their dominance is attributed to a paleogeographic setting within a restricted basin rather than to postdepositional dissolution of other species. The evolutionary development of this restricted basin and its eventual ventilation in early Albian times is discussed in terms of the regional stratigraphy and the breakup and dispersal of southwestern Gondwanaland. One new species, Corollithion covingtonii, is described.

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.

Pliocene-Pleistocene biostratigraphy in the Tyrrhenian Sea

The distribution of stratigraphically important calcareous nannofossils and planktonic foraminifera has been investigated in the Pliocene-Pleistocene sequences of ODP Sites 652, 653, and 654 (Tyrrhenian Sea-western Mediterranean). Semiquantitative and quantitative methods have been used, and an optimum relative sequence of bioevents based on the calcareous plankton groups has been established. About 30 bioevents in an interval of 5.0 m.y. are considered widely traceable in the area and reasonably synchronous. On the basis of those events, a correlation among the three investigated sequences is presented.

Middle Eocene to Pleistocene calcareous nannofossils of ODP Leg 113 holes

Long sequences of Upper Cretaceous through Quaternary sediments rich in calcareous and siliceous microfossils were recovered at Ocean Drilling Program Sites 689 and 690 on Maud Rise off East Antarctica. These sites have become the southernmost anchor in the Atlantic Basin for bio-, magneto-, chemostratigraphic, and paleobiogeographic studies. ODP Sites 692 and 693 on the Weddell Sea margin of East Antarctica and Site 696 on the South Orkney microcontinent of West Antarctica yielded calcareous nannofossils within some stratigraphic intervals. Sites 691, 692, 694, 695, and 697 did not recover Cenozoic calcareous nannofossils. Calcareous nannofossil biostratigraphy suggests a major hiatus across the Paleogene/Neogene boundary at Sites 689 and 690, and two additional hiatuses in the middle Eocene-lower Oligocene section at Site 690. Correlation with magnetostratigraphy reveals: the last occurrence (LO) of Reticulofenestra umbilica at Maud Rise is over 1 m.y. younger than that at the middle-latitude sites; the LO of Isthmolithus recurvus is synchronous in the middle-latitude and high-latitude areas (about 34.8 Ma); Reticulofenestra oamaruensis ranges from 38.0 to 36.0 Ma at Maud Rise; Reticulofenestra reticulata has a shorter range at Maud Rise (42.1 to 38.9 Ma) than at the middle-latitude DSDP Site 516; the range of Chiasmolithus oamaruensis is diachronous over different latitudes; and the LO of Chiasmolithus solitus is a good datum at 41.3 Ma from 30°S to 65°S in the South Atlantic Ocean. Comparison of calcareous nannofossil abundances in a latitudinal transect shows: Reticulofenestra bisecta is a temperate-water species and its LO, which crosses below that of Chiasmolithus altus at Maud Rise, is not applicable for the Paleogene/Neogene boundary in high southern latitude areas; Clausicoccus fenestratus is rare or absent at Maud Rise and can not be used as a marker; Coccolithus formosus is a warm-water species which disappeared earlier toward higher latitudes. Calcareous nannofossil assemblages indicate that by at least the middle Eocene, surface water temperatures became considerably lower in the high southern latitudes than in the middle-latitude areas and that there have been more extreme cold events in the high latitudes during the Neogene. Bicolumnus ovatus n. gen., n. sp. is proposed in this paper.