Abstract

The Canyonlands grabens in southeast Utah form an active extensional fault array covering 200 km2 southeast of the Colorado River. The 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 m.y. (possibly last 0.1 m.y.) has resulted in major changes in the stream drainages across the area through processes of stream capture and diversion. During growth of the fault array, relay ramps between overlapping fault segments form topographic lows along the graben margins. These commonly act as access points for captured streams to enter a graben system. As fault segments continue to propagate laterally, linkage leads to breaching of the relay ramp structures. This causes changes in the course and gradients of the streams, com monly shifting the locus of alluvial sediment deposition away from grabens that were previously infilling. This complex evolution of drainage networks in a growing fault array may provide a valuable analog to the early structural and stratigraphic development of larger continental rift systems. Reservoir distribution is an essential element of many hydrocarbon plays, and understanding the relationship between active fault growth and drainage evolution may help predict reservoir distribution and quality.

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