Near seabed geology in a shallow environment in the Malin Sea (Ireland) using a geophysical multidisciplinary approach

Abstract:

Background and Aims: During the Irish National Seabed Survey (INSS) in 2003, a gas related pockmark field was discovered and extensively mapped in the Malin Shelf region (NW Ireland). In summer 2006 additional complementary data were acquired in specific locations in the area. Objective: To study near-seabed composition, pathways and presence of gas by using an approach on the basis of shallow EM data, high frequency acoustics and short sediment cores in a known shallow gas bearing area. The combination of these various methods have enabled us correlate the main geophysical signatures and some geological properties of the seabed, providing a unique tool for geohazard identification, multibeam seabed characterization, fluid flow migration paths and sediment porosity. Methods: The multidisciplinary approach consisted in core sample analysis, multibeam and single-beam backscatter classification, and a marine controlled-source electromagnetic survey. Results: The results from the EM survey have been plotted in terms of conductivity and have been integrated in GIS software with other geological and geochemical information for interpretation. The maps of conductivities of the upper 20 m of the sub- seafloor show a high sensitivity to the presence of gas in sediments. At a regional scale, areas with gas charged sediments show a decrease in conductivity, this correlates well with gas related echo-facies (SBP). Although there are areas in which gas echo-facies correlates with high conductivities and we have associated this to the presence of microbial activity feeding on methane. The crossings of the EM instrument over the …

Año de publicación:

2012

Keywords:

Fuente:

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