GEOCHEMISTRY OF LOW TEMPERATURES

Author: CUBILLAS GONZÁLEZ PABLO.
Year: 2004.
University: OVIEDO.
Place of defense: FACULTAD DE GEOLOGÍA.
Place of preparation: FACULTAD DE GEOLOGÍA.

Summary: The study of the transport of chemical species in natural porous media is of vital importance for a large number of geological disciplines, gaining a special interest knowledge of the mechanisms that govern the interaction between solid and aqueous phases. These interactions result in precipitation processes and incorporation of surface modifying the composition of the aqueous phase and thus affecting transport cash in the middle. This fact, a decisive influence in the implementation of transport models to many geological problems, such as mineral ore deposit, or phenomena diagénesis migration of toxic waste and nuclear weapons. The carbonates are among those most widely distributed minerals in the earth's crust, being present in a large percentage of sedimentary rocks, marine sediments, and so on. The carbonates, also are present throughout, or much of the route of natural waters through the Earth's surface, bringing the study of interactions carbonate aqueous solution is vital. La presente tesis doctoral presenta los resultados de un estudio exhaustivo del proceso de interacción de disoluciones acuosas ricas en cadmio con carbonatos de calcio de diferente composición mineralógica (aragonito y calcita) y distinto origen (biogénico y abiogenico). Cadmium is not an abundant element in the earth's crust under natural conditions, however, its concentration in the air, water and soil has increased due to a multitude of anthropogenic activities such as mining, manufacturing plastics, batteries used in fertilization , and so on. In order to study the interaction process from several points of view and to better understand the threaded through the unfolding process of interaction is used different experimental techniques and instrumental. Some of the techniques used were: 1, - with Atomic Force Microscopy, which can monitor the process of interaction in real time. 2-sorption experiments of macroscopic reactor closed to determine the ability of "entrapment" of different cadmium samples evaluated. 3-Experiments in silica gel, made with a view to obtaining higher-quality secondary stages to study using analytical techniques such as X-ray diffraction, scanning electron microscopy, and so on. 4, closed-reactor experiments, conducted with the objective of measuring the speed of dissolution of calcium carbonate, the rate of precipitation of carbonate cadmium, as well as the effect of the formation of precipitates on the speed of dissolution of calcium carbonate . Our results indicate that the process of interaction between cadmium carbonate used and the different results in a process of precipitation surface, with a precipitous phase solid solution CaxCd1-xCO3 with calcite type structure. However, depending on the degree of similarity between the structures cristalográficas substrate carbonated and solid solution of the process neoformación precipitation takes place through different processes. In the case of calcite, being both very similar structures, precipitation of the solid solution takes place through a process of growing epitaxial, resulting in the formation of a layer with a thickness of a few armstromgs. In the case of experiments with aragonite structures are different so the precipitation takes place through three-dimensional nucleation random, and in this case when the initial concentration of cadmium is large enough, the original windows are covered with a layer the solution 8 No solid 3f4 of thickness up to 10 um. This difference in the process of precipitation has important implications for the ability of sorption and different sample used, the amount of cadmium being hasty in experiments with aragonite and carbonate abiogénico three orders of magnitude higher than in the so-ca experiments with calcite.

Author: Jiménez Espejo Francisco J..
Year: 2006.
University: GRANADA.
Place of defense: Facultad de Ciencias. Universidad de Granada.
Place of preparation: Facultad de Ciencias.

Summary: This thesis includes a multidisciplinary study by which the conditions have been rebuilt paleoclimáticas and paleoceanográficas as well as developments in the different climate responses in the Western Mediterranean during the last glacial cycle. In addition, also discusses the impact that climate variability has had on the human cultural evolution in the south of the Iberian Peninsula. Issues related to the westernmost basin of the Mediterranean basin Algero-Balear and the Alboran Sea, both regions key to the understanding of the interconnections Atlántico-Mediterráneo. Various witnesses have been selected from marine sediments that have been analyzed at very high resolution using mineralogical and geochemical indicators for the reconstruction of climate variability. In the basin Algero-Balear have analyzed sediment survey 975 of the Ocean Drilling Program, "and have used various indicators of sedimentary regime (elements detríticos and mineralogical composition), productivity (in Ba and organic matter), conditions paleoceanográficas in water column (stable isotopes) and oxygenation (relations of trace elements). The results obtained reveal fluctuations in the concentration of elements and phases Detritic home as a result of fluctuations in humidity and aridity. As for productivity, it shows that was greater during cold periods, and Heinrich events "Younger Dryas." By contrast, the interval of time for the deposit of sapropel latest in the eastern Mediterranean does not correspond to any increase in productivity. In this watershed if there is a major event reoxidación to 7.7 thousand years as a result of the change in the movement that is taking place at this time. This event also led to the remobilization of various trace elements, as well as the oxidation of organic matter. Comparing the registration studied in this basin with other Mediterranean basin suggests the existence of marked differences in responses to climate along the Mediterranean. In the Alboran Sea basin has been analyzed an east-west transect for the reconstruction paleoceanográfica this watershed. This reconstruction is based equally on stable isotope profiles, surface water temperatures and chemical composition of sediments. Witnesses were recovered at different depths for the study of the patterns of movement and the conditions of oxygenation. The various indicators show significant swings in productivity, ventilation and fund Detritic contribution to the watershed. The surface water temperatures brought the major climatic oscillations of this period. The comparison of the profiles obtained in the Alboran Sea basin and Algero-Balear indicates that there are significant gradients along the Western Mediterranean. In the Alboran Sea basin productivity was always higher input river here and played an important role in the productivity in wet periods as "Bolling-Allerod" and the beginning of the Holocene, as well as at the beginning of the "Younger Dryas" . The indicators of oxygenation show very significant changes in circulation and oxygenation over the interval studied. They note, moreover, that the waters from the eastern Mediterranean have also been an important driving force in the output current of the Mediterranean. This fact combined with the influence Atlantic has led to North gradients in this basin. In fact in the regions of Southern Alboran recognize events occurring in the eastern Mediterranean as depositing the sapropel latest. Overall, up to 7.9-9.2 thousand years ventilation conditions in this basin were smaller and from this period increased ventilation and settled the 8 patterns 6fb current movement. Finally, the West paleoclimatic records of the Mediterranean are also used to know the impact that climate variability has had on the human cultural evolution in the south of the Iberian Peninsula. In the case of the basin Algero-Balear, variations of the content in Ba and therefore in productivity have been used as an indicator of climatic stability, defined different climatic events according to their coefficient of variation. They also have used indicators of sedimentary regime to reconstruct conditions in the period remplazamiento population in southern Iberia. It shows that reduced oxygenation conditions, a high input, low river and coefficient of variation of the content in Ba associated with the most favorable conditions for the populations of Neandertales. This shows that these populations could survive in southern Iberia to 28.000-30.000 years and that its extinction was strongly influenced by environmental changes.