Análisis multidisciplinar de las acumulaciones de metano en relación con la arquitectura estratigráfica y los cambios del nivel del mar durante el Cuatenario en la ría de Vigo

Resumo

The economic and environmental impact of shallow gas in marine sediments has led to an increase in the number of studies of this subject over the last twenty years. Shallow gas in marine sediments is mainly composed of methane that can be generated by biogenic or thermogenic processes (Flodgate and Judd, 1992), although most shallow gas is biogenic in origin. Gas accumulates in marine sediments worldwide, mainly associated with muddy sediments rich in organic matter (Hovland and Judd, 1988). Acoustic methods are a very useful tool for detecting them due to the masking effect on the seismic records caused by the presence of free gas in sediments. The Galician Rías Baixas are ancient fluvial valleys affected by seasonal upwelling events that make them highly productive. Also, the oceanographic conditions and morphology of the Ría de Vigo favor the sedimentation of muddy sediment along its axis, making it a propitious environment for the generation of biogenic gas in the sedimentary infill. The main objectives of the present thesis are (1) to reinterpret the seismic records of the ria in order to determine the stratigraphic context in which methane accumulations take place, and (2) to study gas accumulations and seepages in seismic records and to perform a geochemical and sedimentological characterization of the sediment containing the gas. The study of the location of the gas accumulations and seepage inside the stratigraphic context of the Ría de Vigo, the methane concentrations in sediment and the methane fluxes to the water column further our knowledge of the methane budget in the ria.