[Extract] Updated Sedimentological and paleontological data support earlier assertions that the Kaiparowits Formation was deposited in a wet alluvial to coastal plain setting with an abundance of large river channels and perennial ponds, lakes, and wetlands. A synthesis of available geochronological data from contemporaneous Upper Cretaceous continental sedimentary units was compiled, and many ages were recalibrated on the basis of new standards to provide\ud
the most up-to-date correlations of coeval strata and associated faunas across the Western Interior Basin. Recalibration of Kaiparowits Formation ash beds demonstrates that the\ud
formation is approximately half a million years older than previously suggested, deposited ~76.6-74.5 Ma. In addition, a new ash bed (bentonite) from the Horse Mountain area, collected in the lower portion of the middle unit of the Kaiparowits Formation (~19o-m level), was radiometrically dated by both 40Ar/39Ar and U-Pb techniques, resulting in similar ages of 75.97 ± 0.18 Ma and 76.26 ± 0.05 Ma. Importantly, both ages are consistent with dated ash beds sitting above and below this level. Measured sections from throughout the outcrop expanse of the Kaiparowits Formation are correlated by an updated tephrostratigraphy, and key vertebrate\ud
fossil sites from throughout the formation are precisely tied into this stratigraphy. Updated geochronology and stratigraphy reveals that many of the most richly fossiliferous intervals\ud
across the Western Interior Basin are constrained to extremely narrow temporal intervals. The term taphozone was coined to describe broad geographic zones of exceptional and elevated continental fossil preservation within narrow temporal windows. Taphozones imply the existence\ud
of regional or basin-scale controls on fossil preservation. The Kaiparowits-Dinosaur Park-upper Two Medicine taphozone is assigned to the widespread interval of middle to late Campanian strata in the Western Interior Basin defined by the Kaiparowits, Dinosaur Park, and upper Two Medicine formations. Preliminary analysis of this phenomenon suggests that synchronous deposition of large volumes of volcanic ash across the basin during this time may be the primary driver of elevated fossil preservation in the Kaiparowits-Dinosaur Park-upper Two Medicine taphozone
