Abstract
Interpretation of acoustic seismic records have allowed mapping of shallow gas accumulations and gas escape features in the Rías Baixas. X-ray photographs and voids of cores are semi-direct evidence of gassy sediments. Mapping of fluid-escape areas shows that these are related to the gas accumulations or at the intersections of faults. Analyses (GC-MS) of bubble samples collected in Simón Bay (Ría de Vigo) and across the whole ría confirm the presence of methane. The spatial distribution of gas escapes/accumulations and their vertical variations are interpreted as evidence of sedimentary facies control. The appearance of authigenic minerals (gypsum, pyrite and aragonite) and microbiological activity related to the seal facies are taken as evidence of the biogeochemical coupling processes. It is evident that these shallow-water coastal environments make significant contributions to the methane budget of the hydrosphere and atmosphere. It is also suggested that microbiological activity is favoured by gas escapes.
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Acknowledgements
This paper presents updated gas research for the project PGIDT00PXI30105PR. It is also a contribution to REN2000-1102 MAR and, partially, to PGIDT00MAR30103PR, BTE2000-0877 and 464 IGCP projects. Special thanks to José Nogueiras and Sandra Rellán, from the Dept. of Química Analítica y Alimentaria, for helping with the gas chromatography analysis. Thanks also to Jorge Iglesias, Montserrat Martínez and Sandra Rúa for assistance with gas sampling. Special thanks to Dr Bilal Haq, Alan Judd and Vanny Aloisi for their comments that have greatly improved this paper.
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Garcia-Gil, S. A natural laboratory for shallow gas: the Rías Baixas (NW Spain). Geo-Mar Lett 23, 215–229 (2003). https://doi.org/10.1007/s00367-003-0159-5
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DOI: https://doi.org/10.1007/s00367-003-0159-5