Detailed Thrust Fault Architecture: Cedar Mountain Thrust, N San Rafael Swell, Utah

Christine Souque¹, Russell K. Davies², Rob J. Knipe¹, Michael Welch¹, and Henry Lickorish^2
1Rock Deformation Research Ltd., Leeds, United Kingdom
²Rock Deformation Research USA Inc., McKinney, TX

A thrust fault with a displacement of 30 meters exposed in three directions around a block of sandstone and shale in central Utah allows the detailed evaluation of multi-scale fault zone evolution in a layered sequence. The thrust is exposed in the north central San Rafael Swell as a splay from the N-S striking, easterly directed Cedar Mountain / Ketobe thrust system. The faulting involves the Slick Rock and Moab Members of the Entrada Sandstone Fm. and the Tidwell and Salt Wash Members of the Morrison Fm. The rheological contrasts of the multi-layered succession influences the fault related deformation with broad folding and smearing followed by faulting and discrete partitioning of deformation styles. The deformation shows a combination of jointing and faulting in the competent layers and folding, smearing and eventually faulting in the less competent layers. A model for the transition from ductile folding to faulting in the less competent units depends on the position of the weak layer in the stacking sequence and the ratio of fault propagation to overall slip for the fault zone with the potential for faults to propagate from above and below the folded succession. The mechanisms of fault propagation in the sequence are shown to control the final architecture of the fault zone, the nature of the inner fault zone, as well as the width and intensity of deformation of the damage zone. The models and description have implications for the deformation styles and shale and sand smear continuity for predicting the fault seal potential in thrust zones.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas