Paleomagnetic of basalts from the Kerguelen Plateau

Paleomagnetic measurements were performed on 106 basalt samples collected from Holes 747C, 748C, 749C, and 750B. Basalt samples were recovered from the southern portion of the Kerguelen Plateau and the transitional zone between the northern and southern plateau in the south central Indian Ocean. The ages of basalts range from 100 to 115 Ma. In addition to the preliminary shipboard measurements (Schlich, Wise, et al., 1989, doi:10.2973/odp.proc.ir.120.1989), characteristic inclinations of the magnetization were obtained using mainly stepwise thermal demagnetization of the samples. Reliable paleomagnetic results were obtained from three sites (Sites 747, 748, and 749). The paleomagnetic inclinations of Sites 747, 748, and 749 are -51°, -63°, and -62°, respectively. The considerable differences between the paleomagnetic and present inclinations of about 70° at Sites 747, 748, and 749 indicate that displacement in the direction of the geomagnetic meridian has taken place since formation of the basalt. Shallower paleomagnetic inclinations than the present inclinations at each site imply a southward movement of the sites with respect to the geomagnetic pole. By comparing the apparent polar wander path of Antarctica with the virtual geomagnetic pole (VGP) of the Southern Kerguelen Plateau, we have concluded that no major tectonic movement has taken place between the Kerguelen Plateau and Antarctica since formation of the basalt (i.e., 100-115 Ma). The angular dispersion of the VGP for the Kerguelen Plateau is calculated as 17°.

Sedimentology, magnetics and chemistry on palaeolake core D100 from the Gobi Desert

The Gaxun Nur Basin in arid China is tectonically influenced by the left-lateral displacements along the Gobi-Altay and Qilian Shan shear zones, resulting in a large pull-apart basin with strong subsidence in the interior. The up to 300 m thick basin fills consist of fluvio-lacustrine fine-grained deposits mainly transported by river discharges from the Tibetan Plateau. They led to a large depositional area of more than 28,000 qkm in size with presently dry terminal lakes at the outer edges. This vast area serves as a main source for loess transport to south-eastern regions of China (Loess Plateau) caused by the variable winter monsoon. Based on geochemical and sedimentological analyses of the sediment core D100 retrieved from a deep drilling in the centre of the Gaxun Nur Basin following questions have to be answered: 1. Reconstruction of the water balance and determination of hydrological cycles during interglacial and glacial periods. 2. Reconstructing variations in lacustrine environment and aeolian activities with respect to transitional phases fro, warm to cold stages (MIS 4 to 5 and older stages). 3. Establishing a sustainable chronology for the last 250 ka.

Paleomagnetic of the Cobb Mountin event sections

Detailed paleomagnetic investigations are reported for 283 specimens, sampled from three closely spaced Ocean Drilling Program Leg 135 cores from the Lau Basin. These specimens cover three rather similar records of the reversed Cobb Mountain short polarity event, having an age of about 1.12 m.y. On the basis of a very detailed subsampling every 0.6 cm, we found that the transition times for the Cobb Mountain geomagnetic polarity event, as seen in the three Lau Basin sediment records, appear to have been as short as 0.6-1.0 k.y., although the duration of the normal-polarity event itself lasted only about 17 ± 4 k.y. The older (R to N) transition as well as the younger (N to R) transition show virtual geomagnetic paths roughly along the Americas, but shifted some 30° ± 10° to the east. These paths conflict with Cobb Mountain transition paths recorded in sediments from the Labrador Sea and the North Atlantic, but they are in fair accordance with sediment records from the Celebes and Sulu seas when corrected for differences in site longitude, suggesting that the transitional fields are dominated by nonaxial, high-order spherical harmonics.

Neogene planktonic foraminifera of ODP Site 130-806

The Neogene biostratigraphy presented here is based on the study of 230 samples through 737 m of pelagic sediment in Hole 806B. Sediment accumulation is interrupted only once in the uppermost lower Miocene (Zone N6), apparently coincident with a widespread deep-sea hiatus. Preservation of planktonic foraminifers through the section ranges from good to moderately poor. One hundred and ten species of planktonic foraminifers were identified; taxonomic notes on most species are included. All of the standard low-latitude Neogene foraminiferal zones are delineated, with the exceptions of Zones N8 and N9 because of a high first occurrence of Orbulina, and Zones N18 and N19 because of a high first occurrence of Sphaeroidinella dehiscens. Good agreement exists between the published account of the variation in planktonic foraminiferal species richness and the rates of diversification and turnover, and measurements of these evolutionary indexes in the record of Hole 806B. The global pattern of change in tropical/transitional species richness is paralleled in Hole 806B, with departures caused by either ecological conditions peculiar to the western equatorial Pacific or by inexactness in the estimation of million-year intervals in Hole 806B. Temporal changes in the relative abundance of taxa in the sediment assemblages, considered in light of their depth habitats, reveal a detailed picture of historical change in the structure of the upper water column over the Ontong Java Plateau. The dominance of surface dwellers (Paragloborotalia kugleri, P. mayeri, Dentoglobigerina altispira, Globigerinita glutinata, and Globigerinoides spp.) throughout the lower and middle Miocene is replaced by a more equitable distribution of surface (D. altispira and Globigerinoides spp.), intermediate (Globorotalia menardii plexus), and deep (Streptochilus spp.) dwellers in the late Miocene, following the closing of the Indo-Pacific Seaway and the initiation of large-scale glaciation in the Antarctic. The shoaling of the thermocline along the equator engendered by these climatic and tectonic events persisted through the Pliocene, when initial increases in the abundance of a new set of shallow, intermediate, and deep dwelling species of planktonic foraminifers coincide with the closing of the Panamanian Seaway.

Planktonic foraminifera of IODP Site 306-U1314

Surface water conditions at the Integrated Ocean Drilling Program (IODP) Site U1314 (Southern Gardar Drift, 56° 21.8' N, 27° 53.3' W, 2820 m depth) were inferred using planktic foraminifer assemblages between Marine Isotope Stage (MIS) 19 and 11 (ca. 800-400 ka). Factor analysis of the planktic foraminifer assemblages suggests that the assemblage was controlled by three factors. The first factor (which explained 49% of the variance) is dominated by transitional and subpolar species and points to warm and salty surface water conditions (Atlantic water). The second factor (37%) is dominated by Neogloboquadrina pachyderma sin and has been associated with the presence of cold and low saline surface waters (Arctic water). Finally, the third factor (9%), linked to a significant presence of Turborotalita quinqueloba, reflects the closeness of the Arctic front (the boundary between Atlantic and Arctic water). The position of the Arctic and Polar fronts has been estimated across the glacial-interglacial cycles studied according to planktic foraminifer abundances from Site U1314 (and their factor analysis) combined with a synthesis of planktic foraminifer and diatom data from other North Atlantic sites. Regarding at the migrations of the Arctic front and the surface water masses distribution across each climatic cycle we determined five phases of development. Furthermore, deep ocean circulation changes observed in glacial-interglacial cycles have been associated with each phase. The high abundance of transitional-subpolar foraminifers (above 65% at Site U1314) during the early interglacial phase indicated that the Arctic front position and surface water masses distribution were similar to present conditions. During the late interglacial phase, N. pachyderma sin and T. quinqueloba slightly increased indicating that winter sea ice slightly expanded southwestwards whereas the ice volume remained stable or was still decreasing. N. pachyderma sin increased rapidly (above 65% at Site U1314) at the first phase of glacial periods indicating the expansion of the Arctic waters in the western subpolar North Atlantic. During the second phase of glacial periods the transitional-subpolar assemblage throve again in the central subpolar North Atlantic associated with strong warming events that followed ice-rafting events. The third phase of glacial periods corresponds to full glacial conditions in which N. pachyderma sin dominated the assemblage for the whole subpolar North Atlantic. This division in phases may be applied to the last four climatic cycles.

(Table 1) Paleomagnetic of ODP Site 136-842

Paleomagnetic studies on sediments recovered during Leg 136 have yielded a polarity reversal sequence that can be compared with the global magnetic reversal time scale to establish a sedimentation rate for Hole 842B. This sedimentation rate is substantially higher than that normally observed in the central Pacific basin probably as a result of the contribution of volcanic ash to the normal pelagic sources of sediment. The basalt samples from the oceanic crust at Site 843 have been used to determine a paleolatitude of 10.2°S for the 110±2 m.y.-old crust from this site. Detailed studies of the polarity transitions yielded few intermediate directions, but these few records provide support for the "Americas" transitional path observed at other continental and marine sites in Europe and North America.

Petrological parameters of sands and sandstones from DSDP and ODP holes in arc-related areas

Detrital modes for 524 deep-marine sand and sandstone samples recovered on circum-Pacific, Caribbean, and Mediterranean legs of the Deep Sea Drilling Project and the Ocean Drilling Program form the basis for an actualistic model for arc-related provenance. This model refines the Dickinson and Suczek (1979) and Dickinson and others (1983) models and can be used to interpret the provenance/tectonic history of ancient arc-related sedimentary sequences. Four provenance groups are defined using QFL, QmKP, LmLvLs, and LvfLvmiLvl ternary plots of site means: (1) intraoceanic arc and remnant arc, (2) continental arc, (3) triple junction, and (4) strike-slip-continental arc. Intraoceanic- and remnant-arc sands are poor in quartz (mean QFL%Q < 5) and rich in lithics (QFL%L > 75); they are predominantly composed of plagioclase feldspar and volcanic lithic fragments. Continental-arc sand can be more quartzofeldspathic than the intraoceanic- and remnant-arc sand (mean QFL%Q values as much as 10, mean QFL%F values as much as 65, and mean QmKP%Qm as much as 20) and has more variable lithic populations, with minor metamorphic and sedimentary components. The triple-junction and strike-slip-continental groups compositionally overlap; both are more quartzofeldspathic than the other groups and show highly variable lithic proportions, but the strike-slip-continental group is more quartzose. Modal compositions of the triple junction group roughly correlate with the QFL transitional-arc field of Dickinson and others (1983), whereas the strike-slip-continental group approximately correlates with their dissected-arc field.

Stable isotope record and lithic fragments distribution in sediments of MIS9-14 of the North Atlantic

Stable isotope and ice-rafted debris records from three core sites in the mid-latitude North Atlantic (IODP Site U1313, MD01-2446, MD03-2699) are combined with records of ODP Sites 1056/1058 and 980 to reconstruct hydrographic conditions during the middle Pleistocene spanning Marine Isotope Stages (MIS) 9-14 (300-540 ka). Core MD03-2699 is the first high-resolution mid-Brunhes record from the North Atlantic's eastern boundary upwelling system covering the complete MIS 11c interval and MIS 13. The array of sites reflect western and eastern basin boundary current as well as north to south transect sampling of subpolar and transitional water masses and allow the reconstruction of transport pathways in the upper limb of the North Atlantic's circulation. Hydrographic conditions in the surface and deep ocean during peak interglacial MIS 9 and 11 were similar among all the sites with relative stable conditions and confirm prolonged warmth during MIS 11c also for the mid-latitudes. Sea surface temperature (SST) reconstructions further reveal that in the mid-latitude North Atlantic MIS 11c is associated with two plateaus, the younger one of which is slightly warmer. Enhanced subsurface northward heat transport in the eastern boundary current system, especially during early MIS 11c, is denoted by the presence of tropical planktic foraminifer species and raises the question how strongly it impacted the Portuguese upwelling system. Deep water ventilation at the onset of MIS 11c significantly preceded surface water ventilation. Although MIS 13 was generally colder and more variable than the younger interglacials the surface water circulation scheme was the same. The greatest differences between the sites existed during the glacial inceptions and glacials. Then a north - south trending hydrographic front separated the nearshore and offshore waters off Portugal. While offshore waters originated from the North Atlantic Current as indicated by the similarities between the records of IODP Site U1313, ODP Site 980 and MD01-2446, nearshore waters as recorded in core MD03-2699 derived from the Azores Current and thus the subtropical gyre. Except for MIS 12, Azores Current influence seems to be related to eastern boundary system dynamics and not to changes in the Atlantic overturning circulation.

Siliceous microfossils in middle Eocene sediments of ODP Holes 120-748B and 120-749B

The Middle Eocene Climatic Optimum (MECO) is a major transient warming event that occurred at ~ 40 Ma and reversed a long-term cooling trend through the early and middle Eocene. We report the results of a high-resolution, quantitative study of siliceous microfossils at Ocean Drilling Program Sites 748 and 749 (Southern Kerguelen Plateau, Southern Ocean, ~ 58°S) across a ~ 1.4 myr interval spanning the MECO event. At both sites, a significant increase in biosiliceous sedimentation is associated with the MECO event. Rich siliceous planktonic microfossil assemblages in this interval are unusual in that they are dominated by ebridians, with radiolarians as a secondary major component. Silicoflagellates and diatoms comprise only a minor fraction of the assemblage, in contrast to siliceous microfossil assemblages that characterize modern Southern Ocean sediments. Based on our new siliceous microfossil records, we interpret two ~ 300 kyr periods of elevated nutrient availability in Southern Ocean surface waters which span the peak warming interval of the MECO and the post-MECO cooling interval. A diverse assemblage of large silicoflagellates belonging to the Dictyocha grandis plexus is linked to the rapid rise in sea-surface temperatures immediately prior to peak warmth, and a pronounced turnover is observed in both ebridian and silicoflagellate assemblages at the onset of peak warming. The interval of peak warmth is also characterized by high abundance of cosmopolitan ebridians (e.g., Ammodochium spp.) and silicoflagellates (e.g., Naviculopsis spp.), and increased abundance of tropical and subtropical diatom genera (e.g., Asterolampra and Azpeitia). These observations confirm the relative pattern of temperature change interpreted from geochemical proxy data at multiple Southern Ocean sites. Furthermore, rapid assemblage changes in both autotrophic and heterotrophic siliceous microfossil groups indicate a reorganization of Southern Ocean plankton communities in response to greenhouse warming during the MECO event.

Palinoestratigrafía, paleoambientes y cambios climáticos durante el Cretácico final y Paleógeno de la Cuenca del Grupo Salta, República Argentina

El objetivo principal de la presente tesis es la búsqueda de nuevos registros palinológicos para las formaciones del Grupo Salta, especialmente para aquellas que cuentan con poco o ningún registro de palinomorfos, tales como las Formaciones La Yesera, Las Curtiembres, Yacoraite y Olmedo. Los resultados palinológicos permitieron evaluar algunos aspectos geológicos como las relaciones estratigráficas, edad y ambientes de depósito. El muestreo se centró principalmente en el período comprendido entre el Neocomiano y Daniano, correspondiente a los subgrupos con mayor escasez de datos (Pirgua y Balbuena). 157 muestras palinológicas de la Cuenca del Grupo Salta y áreas relacionadas se trataron en laboratorio, 31 resultaron fértiles. Se brindan los primeros registros palinológicos de la Formación La Yesera (localidad valle de Pucará) que consisten en 35 especies. Las inferencias aleoambientales obtenidas a partir de la palinoflora apoyan las conclusiones que provienen de los datos sedimentológicos: presencia de un lago perenne al momento de la depositación del Miembro Brealito y sequías estacionales cuando se acumuló el Miembro Don Bartolo. La palinoflora indica un clima subtropical con presencia de cierta aridez. A partir de los rangos estratigráficos de algunas especies y de las dataciones radimétricas del Basalto de Isonza, se estima una edad entre el Albiano y el Cenomaniano. Para la Formación Las Curtiembres (Miembro Morales) se describen 19 especies provenientes de la quebrada de Palo Seco, que constituyen la primer asociación palinológica registrada. El predominio de Ephedraceae y Cheirolepidiaceae, junto a la escasa representación de pteridofitas, sugieren condiciones ambientales de aridez a semiaridez, en coincidencia con la sedimentología que indica que la sección superior del Miembro Morales es transicional con las capas rojas de la parte superior de la Formación Las Curtiembres. La asociación palinológica contiene representantes de amplia distribución espacial y temporal. Es relevante la presencia de Peninsulapollis gillii que indica una edad no mayor al Campaniano para la asociación estudiada. Sólo una muestra de la Formación Yacoraite en la localidad de Tres Cruces fue productiva en cuanto al contenido de palinomorfos. La asociación consta solamente de los géneros Leiosphaeridia y Pediastrum que se asocian a condiciones de agua dulce o mixtas. Para la Formación Olmedo se registran 34 especies de palinomorfos y 39 especies para la Formación Tunal (localidades de Garabatal y El Chorro respectivamente). Ambas formaciones comparten un 49 % de taxa. El marcado predominio de algas clorococales indica condiciones lacustres y un ambiente palustre se infiere por la presencia de Pandaniidites texus y Mtchedlishvilia saltenia. El elevado porcentaje de Verrustephanoporites simplex indica que la selva de ulmáceas, era la unidad fitogeográfica más ampliamente distribuida, comparable con la actual Selva de Transición de la Provincia de Yungas. La coincidencia de facies y contenido palinológico indicarían similares condiciones ambientales para las Formaciones Olmedo y Tunal. Mtchedlishvilia saltenia permiten circunscribir las Formaciones al Daniano. Los cambios climáticos acontecidos durante el desarrollo de la Cuenca del Grupo Salta quedaron evidenciados en la palinoflora. Durante el Cretácico Tardío, habrían prevalecido condiciones de aridez y a partir del Maastrichtiano, el clima se torna más húmedo. Las asociaciones del Daniano se caracterizan por una palinoflora de clima subtropical húmedo. Entre el Paleoceno Superior y hasta el Eoceno Inferior, continúa el registro de la flora de clima subtropical pero con una leve disminución en la humedad. Las especies Peninsulapollis gillii, Rhoipites sp. A, Rousea patagonica, Spinitricolpites jennerclarkei, Verrustephanoporites simplex y Azolla sp., pasan el límite Cretácio-Paleógeno registrándose en sedimentos pre- y post-danianos. Se requieren mayores estudios de detalle en aquellos niveles donde está contenido el límite para esclarecer los posibles cambios vegetacionales que hayan ocurrido.

(Table 1) Sulfur isotopes, total sulfur, and degree of oxidation of basalt samples from DSDP Hole 69-504B and 70-504B

About 150 basalt samples from Hole 504B, near the Costa Rica Rift were analyzed for sulfur content and sulfur-isotope composition. The basement in Hole 504B can be divided into an upper part, which has oxidative alteration (274.5-550 m below sea floor), and a lower part, which has nonoxidative alteration (550-835 m below sea floor) (the interval from 540 to 585 meters actually is transitional). This division is reflected in both the sulfur content and the sulfurisotope composition. Oxidative alteration of basalts by sea water at low temperatures has resulted in a depletion in sulfur in the upper part of the hole (mostly less than 600 ppm S) as compared to fresh sulfur-saturated oceanic tholeiites (900-1200 ppm S). High amounts of sulfur in the lower part of the hole are a result of precipitation of secondary pyrite under non-oxidative or weakly oxidative conditions from solutions which dissolved igneous sulfides. The average sulfur-isotope composition of the primary igneous sulfides is d34S = -0.01 per mil, which is close to the assumed mantle sulfur composition (d34S = 0 per mil. Pyrite and sulfate sulfur extracted together in a separate preparation step (as "pyrite-sulfate" sulfur) indicate addition of sea-water sulfate to the upper part of the basalts. The d34S of secondary pyrite isolated by hand-picking varies between -8.0 and +5.8 per mil; the "pyrite-sulfate" sulfur (d34S = -4.8 to +10.5 per mil), as well as that of the isolated pyrite, may have originated in the precipitation of pyrite from solutions containing sulfur from the dissolution of igneous sulfides, but addition of sulfur transported by hydrothermal solutions cannot be excluded.

Abordaje preventivo de la resistencia infantil a la atención odontológica a través del juego

La resistencia de algunos niños a la atención odontológica constituye un problema para los profesionales, el niño y sus padres. Una forma de prevenirla es preparar al niño con anticipación utilizando el juego como espacio transicional para la aceptación de los procedimientos de curación. La experiencia nos ha demostrado su eficacia en la construcción de representaciones en la mente del niño del diagnóstico y del tratamiento. Al anticipar la experiencia a través del juego disminuye su temor. La metodología implementada es la técnica de juego en grupos pequeños de pares. Los niños comprenden la situación odontológica a través de dramatizaciones, dibujos y juegos con instrumental y juguetes En un clima Iúdico, aprenden el uso del instrumental odontológico, se familiariza con el mobiliario y aparatología del consultorio y posteriormente se evalúa la disposición para recibir atención odontológica.

El encuentro del verdadero amor de María Mercedes Carranza : la pasión por la escritura

El discurso retórico que utiliza la voz poética en el poemario de María Mercedes Carranza, De amor y desamor (1994), expresa a lo largo de la obra un estado de transición entre estos dos sentimientos que sugiere el título. Esta transición entre amor y desamor se esclarece en el poemario según el orden que la autora estableció para cada uno de sus poemas. En ellos, el desencanto ayuda al otro ser humano a reconocer el verdadero amor en la escritura de la literatura.