Geophysical and geochemical survey of a large marine pockmark on the Malin Shelf, Ireland
Szpak, Michal T.
Simpson, A. J.
Evans, Rob L.
Allen, C. C. R.
McNally, D. J.
Kelleher, B. P.
MetadataShow full item record
Marine pockmarks are a specific type of seabed geological setting resembling craters or pits and are considered seabed surface expressions of fluid flow in the subsurface. A large composite pockmark on the Malin Shelf, off the northern coast of Ireland was surveyed and ground truthed to assess its activity and investigate fluid related processes in the subsurface. Geophysical (including acoustic and electromagnetic) data confirmed the subsurface presence of signatures typical of fluids within the sediment. Shallow seismic profiling revealed a large shallow gas pocket and typical gas related indicators such as acoustic blanking and enhanced reflectors present underneath and around the large pockmark. Sulphate profiles indicate that gas from the shallow reservoir has been migrating upwards, at least recently. However, there are no chimney structures observed in the sub-bottom data and the migration pathways are not apparent. Electromagnetic data show slightly elevated electrical conductivity on the edges of the pockmarks and a drop below regional levels within the confines of the pockmark, suggesting changes in physical properties of the sediment. Nuclear Magnetic Resonance (NMR) experiments were employed to characterize the organic component of sediments from selected depths. Very strong microbial signatures were evident in all NMR spectra but microbes outside the pockmark appear to be much more active than inside. These observations coincide with spikes in conductivity and the lateral gas bearing body suggesting that there is an increase in microbial activity and biomass when gas is present.
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q01011, doi:10.1029/2011GC003787.
Showing items related by title, author, creator and subject.
Newman, Kori R.; Cormier, Marie-Helene; Weissel, Jeffrey K.; Driscoll, Neal W.; Kastner, Miriam; Solomon, Evan A.; Robertson, Gretchen; Hill, Jenna C.; Singh, Hanumant; Camilli, Richard; Eustice, Ryan M. (2007-11)Detailed near-bottom investigation of a series of giant, kilometer scale, elongate pockmarks along the edge of the mid-Atlantic continental shelf confirms that methane is actively venting at the site. Dissolved methane ...
Seabed fluid expulsion along the upper slope and outer shelf of the U.S. Atlantic continental margin Brothers, Daniel S.; Ruppel, Carolyn D.; Kluesner, J. W.; ten Brink, Uri S.; Chaytor, Jason D.; Hill, Jenna C.; Andrews, Brian D.; Flores, Claudia H. (John Wiley & Sons, 2014-01-08)Identifying the spatial distribution of seabed fluid expulsion features is crucial for understanding the substrate plumbing system of any continental margin. A 1100 km stretch of the U.S. Atlantic margin contains more than ...
Lithospheric structures and Precambrian terrane boundaries in northeastern Botswana revealed through magnetotelluric profiling as part of the Southern African Magnetotelluric Experiment Miensopust, Marion P.; Jones, Alan G.; Muller, Mark R.; Garcia, Xavier; Evans, Rob L. (American Geophysical Union, 2011-02-03)Within the framework of the Southern African Magnetotelluric Experiment a focused study was undertaken to gain improved knowledge of the lithospheric geometries and structures of the westerly extension of the Zimbabwe ...