Abstract

The Duchesne fault zone (DFZ) in the Uinta basin of northeastern Utah is a system of normal faults and joint zones that forms prominent, east-trending lineaments tens of kilometers long. The Duchesne graben, an asymmetrical fault-bounded trough in the western part of the DFZ, is the focus of this article. A master fault bounds the southern margin of the structural half graben, dips steeply northward, and accommodates about 200 m of slip. This fault either terminates downward by 1400 m depth or flattens into a north-dipping, low-angle detachment fault at about 1000 m depth. The half graben is developed along the crest of an open, low-amplitude flexure in the southern limb of the Uinta basin syncline. This faulted flexure trapped hydrocarbons that migrated southward from depth in the Uinta basin. Intense fracturing within the half graben also created migration pathways for hydrocarbons and generated shallow reservoirs in the Green River Formation.

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