Morphology and Timing of Submarine Mass Movements on the Northwest British Continental Margin

• Main Author: Owen, Matthew John
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University College London 2013
• Subjects: Barra; Rockall Trough; Storegga; North Atlantic; Planktonic foraminifera
• Online Access: https://archimer.ifremer.fr/doc/00499/61041/64448.pdf; https://archimer.ifremer.fr/doc/00499/61041/

A variety of factors influence the stability of submarine slopes and this thesis investigates those operating on the northwest British continental margin and Barra Fan. Through analysis of North Atlantic sector submarine mass movements, a conceptual model of continental slope failure is proposed and examined against the Peach slide case study. Situated on the eastern flank of the Rockall Trough, the Barra Fan is subject to cyclonic ocean circulation and has experienced growth since continental uplift during the mid-Pliocene. Surface and shallow-subsurface morphology of the fan is determined using pinger sub-bottom profile (paper records scanned and converted to SEGY format), sidescan sonar and multibeam echosounder data. A number of different acoustic facies are mapped, including: contourites, hemipelagites and debris flows. Analysis of gravity core 56/-10/239 identifies a debris flow containing material of glacial age and AMS ¹⁴C dating of planktonic foraminifera constrain emplacement prior to 11.9 ka cal BP. Reference to additional sediment cores located in the Barra Fan region (MD95-2006 and 56/-10/36) allows the development of a chronology for the contourites and hemipelagites interpreted during geophysical investigation. This allows constraint of two periods of slope failure during the late Pleistocene: the first between 21 and 20 ka cal BP, shortly after the British ice sheetʼs maximum advance; and the second between 12 and 11 ka cal BP at the termination of the Younger Dryas stadial. Processes similar to those on the Norwegian continental margin seem to operate on the northwest British continental margin, the morphology and setting of the Peach slide is similar to Storegga and Trænadjupet, suggesting that similar processes initiated failure. Important roles seem to be played by contouritic and glaciogenic sedimentation, producing excess pore pressure in the fanʼs sediments with fluid expulsion visible in the acoustic data.