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The Upper Cretaceous Iron Springs Formation in southwest Utah consists of 1,000 m of fluvial sandstone, conglomerate, mudstone, and minor lacustrine carbonate rock. The formation was deposited in the proximal reaches of the southern sector of the Sevier foreland basin. These strata record uplift and erosion of thrust sheets in the fold/thrust belt to the west.

Facies associations indicate deposition in alluvial fan and fluvial braidplain environments. Laterally extensive sheets of clast-supported cobble conglomerate were deposited during episodes of unconfined sheetflood flow. Mud matrix-supported boulder conglomerate represents locally derived muddy debris flows. Lenticular bodies of sandstone and conglomerate were deposited in channels of a sandy braided stream system. Sheets of mudstone and siltstone represent floodplain sedimentation during flood events.

To the north, an upward-coarsening trend in conglomerates of the lower part of the section is attributed to eastward advancement of the thrust belt by ramping and erosion of three thrust sheets. A shift in sediment dispersal patterns from east to north-northeast, shown by paleocurrent data, indicates evolution from an earlier lateral drainage pattern to development of a trunk stream system that paralleled the orogenic front. Abrupt fining of sediment concurrent with this shift suggests an increase in the rate of subsidence, which inhibited progradation of coarser material basinward. This trunk system was likely fed by tributary alluvial fans emerging from the fold/thrust belt to the west.

Variances in sandstone and conglomerate composition among different localities reflect deformation of different sedimentary lithologies ranging in age from Precambrian to lower Mesozoic along strike of the mountain belt. At the northernmost studied locality, locally derived basal mudflow deposits show north-directed transport and indicate intraforeland deformation and development of a mudflow-dominated fan. Overlying quartzitic conglomerate and sandstone show east-directed flow and were derived from erosion of Precambrian-Cambrian quartzite in the upper plate of the Wah Wah thrust. An upsection increase in carbonate detritus indicates emplacement of the carbonate-dominated Blue Mountain and Escalante thrusts. In contrast, the Iron Springs Formation at the southernmost studied locality is dominated by fine-grained quartz arenite derived from erosion of the Jurassic Aztec Sandstone during movement on the Weiser syncline and Summit-Willow Tank thrust, located in the Muddy Mountains of southern Nevada. An increase in lithic fragments upsection indicates uplift and erosion of the Muddy Mountain and Glendale thrust system.

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