Print this pageDetermination of Palaeoslope Using Small-Scale Remobilization Fabrics in Core: Britannia Field, United Kingdom North Sea
A. Del Pino Sanchez1, R.W.H. Butler1, W.D.
McCaffrey1, P.D.W. Haughton2, W.G. Hakes3, and E.
Hailwood4
1 University of Leeds, Leeds, United Kingdom
2 University College Dublin, Dublin, Ireland
3 Britannia Operator Ltd, Aberdeen, United Kingdom
4 COREMAGNETICS, United Kingdom
Post-depositional remobilisation is an important control on sand body architecture and flow properties at a variety of scales. A range of small-scale structures is identified in core and outcrop that record creep processes occurring at or near the palaeo seabed. The kinematics of deformation in poorly consolidated sediments can be used to deduce orientations of subtle slopes and complex sea-floor topographies that impact on sand deposition and distribution. Different origins for seabed deformation - due to shear coupling from over-riding flows or due to down-slope mass-wasting processes are investigated and criteria are developed to differentiate between them.
Here we present new data from sandstones of the Lower Cretaceous Britannia Formation. This confined turbidite system was locally deposited against a south facing palaeoslope with palaeo-flow directions obtained from grain alignment within coherent beds. Asymmetric dewatering sheets, sand injections and subtle shear fabrics have been measured in oriented core sections. Such features allow the kinematics of sediment remobilisation to be quantified, and the orientation of palaeoslopes to be deduced. In addition a remobilisation index has been developed, based on categorising the intensity of shear to which sediments have been subjected. Both these approaches can aid the understanding of sand body architecture from subsurface core.
Changes arising from small-scale remobilisation may be precursors of larger scale development of heterogeneity through slope failure. Emplacement of material from large-scale failures into basin lows may cause changes in bathymetry and thus influence subsequent sediment distribution patterns which, in subsurface scenarios, has implications for reservoir quality.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005