Bruce D. Trudgill1
(1) Imperial College, London, London, England
Abstract: Drainage development within the Canyonlands Grabens of SE Utah in response to relay ramp evolution: An analog for the early stratigraphic development of rift basins
The Canyonlands Grabens in southeast Utah form an active extensional fault array covering 200 km southeast of the Colorado River. Th fault array formed as a result of gravity gliding above a thick layer of salt. Growth of this fault array within the last 0.5 my (possibly last 0.1 my) has resulted in major changes in the stream drainages across the area through processes of stream capture and diversion. These changes are a direct response to the growth of the fault array through time by linkage of overlapping segments.
Relay ramps between overlapping fault segments form topographic lows along the graben margins, and act as access points for streams entering a graben system. As fault segments continue to propagate laterally, linkage leads to breaching of the ramp structures. This causes changes in both the course and gradient of the streams, often shifting the locus of alluvial sedimentation away from grabens that were previously infilling.
This complex evolution of drainage networks and alluvial sedimentation patterns in a growing fault array is an excellent example of the stratigraphic response to evolving structures. It also provides a valuable analogue to the early structural and stratigraphic development of larger continental rifts systems. Reservoir distribution is a key element of many hydrocarbon plays, and understanding the relationship between active fault growth and drainage evolution may help predict reservoir distribution and quality.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana