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International Journal of Earth Sciences

, Volume 107, Issue 8, pp 2907–2929 | Cite as

Downslope-shifting pockmarks: interplay between hydrocarbon leakage, sedimentations, currents and slope’s topography

  • Sutieng Ho
  • Patrice Imbert
  • Martin Hovland
  • Andreas Wetzel
  • Jean-Philippe Blouet
  • Daniel Carruthers
Original Paper

Abstract

Pockmarks in Pliocene-Quaternary continental slope deposits offshore Angola show features related to: (1) fluid leakage craters that formed repeatedly, (2) authigenic methane-derived carbonates that indicate the (former) presence of hydrocarbons and (3) erosional–depositional structures that are clearly related to current activity. Depending on topography, the pockmarks show differing development: “Advancing Pockmarks” preferentially developed on regional slopes or inclined topography (> 2.5°–3°). They arranged in a chain-like pattern and mimic the outline of buried turbidite channels below. These pockmarks and their infill migrated downslope in response to shifting vents. “Nested Pockmarks” occur in gently sloping areas (< 2°). Their isolated conical infill records slope-parallel migration within a specific depth range pointing to the influence of contour currents. Both pockmark types are long-lived and they record preferential fluid migration along specific pathways, which developed at the downcurrent sidewalls of pockmarks due to flow separation initiating “cavity flow” within the pockmarks. The durable specific migration paths include pockmark sidewalls, vertically stacked erosional-interface of sediment waves, or entire pockmark bodies. The vertical extent of both pockmark types from End Miocene to the present-day seafloor documents various intensities of episodic fluid bursts followed by periods of quiescence and fill.

Keywords

Pockmark migration Pockmark infill Hydrocarbon leakage Angola 

Notes

Acknowledgements

We thank Total S.A. for providing data, funding and its partner for publication permission, and the Ministry of Science and Technology of Taiwan for the Grant MOST1052914I002069A1. Our work is based on and extended from S. Ho’s PhD. The scientific work was fully carried out in Total S.A. and under its direction. S. Ho thanks Benoit Paternoster for his supervision on Geophysics. S. Ho also thanks Cardiff University and JA Cartwright for his great interest in this work and general support. Thanks also for the advices and the enormous support from Gordon Lawrence, David Hutchings, Ludvig Löwemark, and Char-Shine Liu.

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© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of GeosciencesNational Taiwan UniversityTaipeiTaiwan
  2. 2.Total-CSTJFPauFrance
  3. 3.Center for GeobiologyUniversity of BergenBergenNorway
  4. 4.Geological InstituteUniversity of BaselBaselSwitzerland
  5. 5.Unit of Earth SciencesUniversity of FribourgFribourgSwitzerland
  6. 6.Companie Genéral GéophysiqueLlandudnoUK

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