PALEOMAGNETISM

Author: MOHAMED FALCÓN KAIS JACOB.
Year: 2005.
University: VIGO [www.uvigo.es].
Place of defense: FACULTAD DE CIENCIAS JURÍDICAS DEL TRABAJO.
Place of preparation: FACULTA DE CIENCIAS DEL MAR, UNIVERSIDAD DE OVIEDO.

Summary: The analysis of the spatial and temporal variability of the magnetic properties, geochemistry and sedimentológicas of sediment from the Rias de Vigo, Pontevedra and its continental shelf, has helped to establish a model of evolution diagenética for the Rias Baixas, and the identification a signal paleoclimática on the continental shelf. According to the model diagnético for the Rias Baixas proposed in this thesis, the magnetic properties show a vertical zonation mineralogical characteristics, confirmed by geochemical analysis and the comments made by electron microscopy. The upper part shows a high concentration of magnetic minerals, primarily magnetite. In the intermediate area, (oxihidr) Fe oxides dissolve rapidly due to the processes of sulfatorreducción. Minerals low coerctividad are more susceptible to dissolution, increasing the proportion of meatites and goetita, with a consequent increase in the magnetic hardness. The priritas framboidales are a common component of these sediments along with the freigita his precursos ferrimagnético. The dissolution of oxides in this area, and neoformación of freigita monodominio are the processes responsible for the observed decrease in size at this level. Finally, in greater depth occurs virtually complete dissolution of oxihidr (oxides) of magnetic Fe, as well as the transformation of greigita in pyrite. This zone is characterized, for both, for a low concentration of magnetic minerals, a decrease of the magnetic hardness and an increase defendant's grain size. The establishment of this zoning is ultimately controlled by the resuspension of sediment due to the waves, and especially by the reoxidación of organic matter in the water column. This process is longer in areas outside of the estuaries, deeper, thus delaying the establishment of conditions diagnéticas reductive in these areas. In addition, magnetic techniques have helped detect anthropogenic impacts on the estuaries consisting of a variation of the magnetic characteristic zoning in an area influenced by a filler port and subjected to a heavy traffic of ships of large tonnage. In the continental shelf, the magnetic properties showed an alteration diagenética more moderate that the estuaries, but its importance gradually increases with depth and to the Deposit Fangoso of Galicia. The adjustment of the concentration profile of magnetic minerals in a simple model of stationary diagénesis allowed to estimate the relative importance of processes diagenéticos compared with detríticos establishing a fundamentally Detritic origin of the magnetic signal from these environments. This has led to interpret these results in terms of the evolution paleoclimática locally. Thus, increases in concentration of magnetic minerals related to the Holocene warm periods, particularly with the Roman and Medieval warm periods. These increases would an increase in precipitation under warmer and wetter conditions, as well as a further erosion due to human activities, empowered under this more benign climate. Moreover, the dominance of southern winds during the period 975 BC-1000 AD, power sediment transport to the area from the Douro river Minho and the south. Finally, the increased presence of water subtropical poorer in nutrients derived from this climate, limiting productivity, decreasing the dissolution diagenética of Fe oxides and preserving therefore, the information paleoclimátic 8 a.