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In order to better constrain the age and provenance of the Upper Cretaceous Wahweap and Kaiparowits formations in southern Utah, U-Pb SHRIMP ages were obtained for detrital zircons from three sandstone samples, in addition to the first 40Ar-39Ar age for the Wahweap Formation, obtained from a devitrified volcanic ash horizon (bentonite). The ash horizon, located 40 m above the base of the Wahweap Formation, yields an age of 80.1 ± 0.3 Ma. The new radiometric data improve upon previous biostratigraphic age estimates for the Wahweap Formation and indicate that the formation was deposited between approximately 81 and 76 Ma. The youngest population of detrital zircons from the base of the Wahweap Formation clusters...
The Kaiparowits Formation is an unusually thick package of Upper Cretaceous (late Campanian) strata exposed in Grand Staircase-Escalante National Monument of southern Utah, USA. The formation was deposited within the rapidly subsiding Cordilleran foreland basin as part of a thick clastic wedge derived from sources in the Sevier orogenic belt, thrust sheets in southeastern Nevada and southern California, and the Mogollon slope in southwestern Arizona. Channel systems in the Kaiparowits Formation shifted from northeastward to southeastward flow over time, and for a short period of time, sea level rise in the Western Interior Seaway resulted in tidally influenced rivers and/or estuarine systems. Thick floodbasin pond...