Speaking for the opposing view, John Underhill presented a detailed analysis of the structural trends in this part of the North Sea, including new data on the presence of NW-SE trending dykes (related to the igneous centres on the Isle of Mull, invisible on older, low-resolution scans). These, he believes, are what mobilised the salt and then initiated its withdrawal in the Paleogene. Underhill maintains that his theory is consistent with aeromagnetic results, the known extent of the distribution of devolatissed coal and unusual Chalk diagenesis, and velocity effects. Underhill further suggested that the correct interpretation of these structures would have commercial implications for prospectivity through depth conversion and the understanding of Bunter gas occurrence – and, crucially, of the gas’s chemical and isotopic composition.
The audience, made up dominantly of hydrocarbon industry seismic interpreters with a scattering of researchers and academics, preferred the Underhill model - for which, after a 20-minute period of debate, they voted overwhelmingly, 80:20.