1. University of the Highlands and Islands, Inverness IV2 5NA, UK
2. CASP, West Building, Madingley Rise, Madingley Road, Cambridge CB3 0UD, UK
3. HM Research Associates Ltd., Giddanmu, St. Ishmaels SA62 3TJ, UK
4. Department of Earth Sciences, University of the Western Cape, Bellville 7530, South Africa