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The Axhandle basin in central Utah is a piggyback basin that formed above the Gunnison thrust system. The basin contains-1 km of upper Cretaceous-to-Eocene strata of the North Horn and lower Flagstaff Limestone formations. A significantly more exact chronology, based on magnetic polarity stratigraphy, has been developed for the basinfilling strata. The new data provide a detailed temporal framework for the interpretation of the depositional and tectonic evolution of the basin during chrons 33-21 (-75-49 Ma). Tectonic subsidence curves and stratigraphic relations along the eastern basin margin define two episodes of motion on the Gunnison thrust system. The majority of tectonic shortening on the system occurred between 83-75 Ma and caused widespread non-deposition within the Axhandle basin. A second episode of motion, in detail comprising of four separate periods of backthrusting, occurred between 70-60 Ma. The Canyon Range, Pavant, and Nebo thrust sheets were emplaced 30-50 km to the west of the Axhandle basin between 97 and 74 Ma. The initial episode of motion on the Gunnison thrust system was thus partly coeval with the emplacement of these thrust sheets. Uplift and erosion above the San Rafael Swell, a basement flexure located-100 km east of the Axhandle basin, occurred at the same time-between 70 and-60 Ma-as the second episode of motion on the Gunnison thrust system. These age constraints clearly demonstrate coeval motion on multiple contractional structures. Episodes of thrust wedge reorganization with durations of 5-10 m.y. appear to be separated by quiescent periods of up to 5 m.y. Evolution of the thrust belt in NE Utah and Wyoming was remarkably similar to that in central Utah 300 km to their south. This similarity suggests that the tectonic stresses driving the thrust wedge were relatively uniform along strike.

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