Deirdre C Commins1, Sanjeev Gupta1, Joseph A. Cartwright2
(1) Imperial College, London, United Kingdom
(2) Cardiff University, Cardiff, United Kingdom
ABSTRACT: Fluvial Response to Faulting: Insights into the Growth History of Normal Fault Arrays using Geomorphic Criteria
Late Quaternary-Holocene fluvial systems in the Canyonlands Grabens, Utah, have been dramatically altered by the growth of normal fault segments that formed as a result of gravity gliding above a ductile salt layer. Analysis of fault displacement variations and geomorphic features (e.g., windgaps, waterfalls) permit reconstruction of the growth history of multi-segment fault arrays.
We present data from a fault array that comprises two linked paleo-segments. The presence of an abandoned ('breached') relay ramp in the hangingwall of the linked faults indicates the position of a paleo-fault tip prior to hard linkage taking place.
The displacement profile of the fault is characterised by linear tip gradients, with zero displacement at the tips increasing uniformly to a maximum of 27m near the centre of the fault. The displacement profile approximates that of an ideal isolated fault. The presence of ~11m of post breaching displacement suggests that the fault accrued a significant amount of displacement for its new length, in order to attain this ideal profile.
A stream that traverses the footwall of the fault exhibits a waterfall at the fault trace that separates two graded sections. The height of the waterfall corresponds to the post-breaching displacement of the fault. We propose that the waterfall formed as a result of rapid displacement addition following hard linkage. The formation of the waterfall indicates that post-linkage displacement accumulation is relatively rapid. Analysis of stream profiles in conjunction with fault displacement data thus enables reconstruction of the evolution of fault arrays and the relative timing of displacement accumulation.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado