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Trudgill, Bruce1, David Dutton2 
(1) Colorado School of Mines, Golden, CO 
(2) Imperial College, London, United Kingdom

ABSTRACT: Evolution of Relay Ramps in Salt Detached Settings: Examples from the Canyonlands Grabens SE Utah and Offshore West Africa

The geometry and evolution of a number of relay ramps from two contrasting salt detached structural regimes have been studied using 3-D seismic analyses, 3-D structural restorations and displacement modelling coupled with field analysis. This study is illustrated with field examples of relay ramps from the Canyonlands Grabens, SE Utah and seismic examples of relay ramps from offshore West Africa (Angola). 
In the Angola study, a relatively thin salt layer results in listric normal faults developing welded fault surfaces that reduce their ability to accrue displacement, and may counter the influence of mechanical interaction. Restorations indicate that partial welding of a listric fault surface from a Pliocene aged relay ramp resulted in the by-pass of a footwall/hangingwall breach in favour of an intra-ramp breaching style. 
In the Canyonlands Grabens, the underlying salt layer is relatively thick compared to the overlying zone of brittle deformation. Relay ramps are developed between overlapping fault segments in an active, growing fault array. The maximum length of fault segments appears to be related to the thickness of the brittle plate, and this may therefore exert a control on the spatial development of relay ramps. 
The results of this study indicate that the salt layer thickness (and in Angola, evacuation) constrains both the temporal and spatial ability of faults to accrue displacement and controls the genesis, evolution and breaching of relay ramps.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.