Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Vertical and Lateral Segmentation of an Evaporite-Detached Normal Fault Array: The Halten Terrace, Offshore Mid-Norway
(1) Basin Studies and Petroleum Geoscience, University of Manchester, Manchester, United Kingdom.
(2) Department of Earth Science and Engineering, Imperial College, London, United Kingdom.
(3) Department of Earth Science, University of Bergen, Bergen, Norway.
(4) Statoil, Harstad, Norway.
(5) Statoil Research Centre, Bergen, Norway.
The Halten Terrace, offshore mid-Norway, is underlain by two evaporitic units of Triassic age, each approximately 380 m thick and separated by approximately 530 m of mudstone. This evaporitic package is rheologically weak, and led to decoupling of fault systems during Middle Jurassic to Early Cretaceous rifting. We use 3D seismic data, constrained by wells, from the Bremstein Fault Complex (BFC) of the Halten Terrace. Mapping of faults and key seismic horizons, and analysis of throw variations along faults, allows us to constrain patterns of fault segmentation and linkage within the BFC.
Supra-salt faults are partly gravity-driven, and controlled by tilting of the evaporitic package. Sub-salt and supra-salt faults act as semi-independent populations, with varying degrees of linkage through the evaporitic package; this leads to a large number of possible fault linkage patterns. The presence of pre-rift salt influences the tectono-stratigraphic development of segment boundaries in faults above the salt, with a much greater variety of patterns than observed in rifts without pre-rift salt. In many cases, the footwall areas of faults in salt-influenced rifts experience little or no uplift compared with salt-free rifts. In some cases, segment boundaries may be associated with footwall highs and hanging wall lows, rather than the footwall lows and hanging wall highs expected in salt free rifts. This has implications for sediment dispersal and deposition in salt influenced rift basins, because i) segment boundaries are less likely to form sediment entry points, as they are typically not sites of topographic lows, and ii) there may be additional depocentres in the hanging wall at segment boundary locations, in contrast to the intra-basinal highs developed at these locations in basins lacking salt. Our observations suggest that generic tectono-stratigraphic models based on rift basins that lack pre-rift salt should be applied cautiously to salt-influenced rift basins.