REVISED AGE OF THE CLOVERLY FORMATION (CRETACEOUS, WESTERN INTERIOR, USA)
New U-Pb radiometric dates were obtained from euhedral zircons derived from fluvial sandstones and bentonitic claystone layers associated with marginal lacustrine sandstones. The zircons were analyzed using both laser ablation-inductively coupled plasma-mass spectrometry and thermal ionization mass spectrometry. Our results suggest that the Pryor Conglomerate was likely deposited before the Aptian, the Little Sheep Mudstone Member through much of the Aptian–Albian, and portions of the Himes Member, Greybull Sandstone, and overlying the Sykes Mountain Formation and Thermopolis Shale in the late Albian. Our reanalysis of previous biostratigraphic correlations shows that foraminiferal, palynological, and molluscan data independently indicate a late Albian–Cenomanian rather than the Aptian–Albian age for the Himes and Greybull Members that was previously inferred. Faulty biostratigraphic correlations biased subsequent fission track and paleomagnetic studies, in which younger ages tended to be discarded as erroneous. We incorporate refined ages and geological reinterpretations into a new depositional model for the Cloverly Formation.