DTI Strategic Environmental Assessment Area 4 (SEA4) : geological evolution Pilot Whale Diapirs and stability of the seabed habitat

• Main Authors: Holmes, R., Hobbs, P.R.N., Leslie, A.B., Wilkinson, I.P., Gregory, F.J., Riding, J.B., Hoult, R.J., Cooper, R., Jones, S.M.
• Format: Report
• Language: English
• Published: British Geological Survey 2003
• Subjects: Fugloy; Fugloy*
• Online Access: http://nora.nerc.ac.uk/id/eprint/509851/; https://nora.nerc.ac.uk/id/eprint/509851/1/CR03082N.pdf; http://webservices.bgs.ac.uk/sea/documents/64

The DTI 2002 programme of new deep-water seabed multibeam and sample data acquisition in SEA4 included surveys of a field of seabed mud mounds, collectively named the Pilot Whale Diapirs. The largest of these occur over a buried anticline and they are set in sediment debris flows that originated from grounded ice and submarine landslides. Other diapirs and mud mounds are sited on and adjacent to the north-east plunging Fugloy Ridge and buried transfer fault zones within a region subject to modern earthquakes. The focus of this study is on the SW group of the five main groups of large-scale mud diapirs with seabed elevation of 30m or more above the surrounding seabed and with very complex seabed geometries. Diapiric sediment has been transferred to seabed from deep sources, in places from more than 500m below modern seabed and from strata more than 24 million years old. Interpretations of the fossil biota, sediment properties and seismic reflection profiles indicate that there is submetre scale heterogeneity in the composition and age of sediments cropping at or near seabed on the large-scale mud diapirs. Interpretations from the seismic reflection profiles and the fossil data from one site on the large-scale diapirs indicate that the large-scale mud diapirism postdates approximately 5 million years ago and might have been initiated as late as 1.1 million years ago. The evidence suggests that rapid large-scale mud diapirism is not occurring at the present day. In contrast, interpretations of the regional geological setting and the sub-seabed data indicate that there are large areas with potential for modern, active and small-scale diapirism. Reconnaissance sample surveys indicate that some of the steepest slopes on the large-scale diapirs are composed of rock and overlain by thin soft sediments with gravel at seabed. A numerical static stability model is presented that predicts the general conditions under which the modern seabed will become unstable on the large-scale diapirs. The model predicts that thin-skin ...