How Deep is the Sandbox?

Tara Gregg

Whitman College, Walla Walla, WA 99362



A system of geologically young grabens has developed in the Needles District of Canyonlands National Park, Utah. In this region, Pennsylvanian and Permian sandstones overlie evaporites of the Pennsylvanian Paradox Formation. The creation of a deep canyon by the erosion of the Colorado River has removed lateral support for these rocks, producing a series of normal faults whose movement is facilitated by the low-strength evaporite layer. Fault displacement can be inferred based on the thickness of sediment fill within these grabens. Gravity surveys performed in coordination with seismic studies indicate that sediment in Cyclone Graben exceeds 30 meters in thickness and may possibly be as thick as 100 meters. These results indicate that fault displacement exceeds previously reported estimates by at least a factor of 1.5. Faculty Sponsor: Kevin Pogue

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