In lieu of an abstract, here is a brief excerpt of the content:

85 6 The Kaiparowits Formation: A Remarkable Record of Late Cretaceous Terrestrial Environments, Ecosystems, and Evolution in Western North America Eric M. Roberts, Scott D. Sampson, Alan L. Deino, Samuel A. Bowring, and Robert Buchwaldt 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 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 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 (~190-m level), was radiometrically dated by both 40 Ar/39 Ar 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 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 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 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. Introduction The Kaiparowits Formation provides a truly exceptional window into Late Cretaceous terrestrial ecosystems of the Western Interior of North America. A wealth of attention has recently been devoted to the formation, resulting in numerous new and important paleontological discoveries and greatly improved temporal and paleoenvironmental contexts. The renaissance of research in the Kaiparowits Formation over the last 10–20 years has been prompted by a realization of the untapped richness of continental vertebrate, invertebrate , paleobotanical, and trace fossils entombed within the myriad of wet, subhumid channel, overbank, and lacustrine depositional environments that make up this sequence. Arguably , the greatest attribute of the formation, from a paleontological viewpoint, is the outstanding potential for high-resolution evolutionary and ecological investigations of its preserved flora and fauna. The unusually thick (860 m) succession was deposited in a remarkably short ~2 Myr interval, recording one of the fastest sediment accumulation rates of any richly fossiliferous continental sedimentary sequence in the world (Roberts, 2005). The significance of this fact is greatly enhanced by the voluminous and high-quality preservation of most major groups of continental fossils, including aquatic and terrestrial vertebrate skeletal accumulations , macro- and microinvertebrate shelled organisms, plant macro- and microfossils (leaves, wood, palynomorphs), and continental trace fossil assemblages from multiple substrates. Moreover, recent high-precision radioisotopic dating in the formation (and in coeval units) reveals that the Kaiparowits Formation is nearly identical in age (Late Campanian) to many of the other most important fossiliferous Campanian formations or intervals across the Western Interior Basin, including the Dinosaur Park Formation and portions of the Judith River, Two Medicine, Fruitland, and possibly Aguja Roberts et al. 86 formations (Roberts, Deino, and Chan, 2005). This fact has been recognized by various workers as a critical opportunity for high-resolution comparisons of closely coeval floras and faunas across the more than 2000-km north–south-trending corridor of fossiliferous strata, which is well exposed from Alberta to Mexico. Sampson et al. (2004, 2010) and Gates et al. (2010) used this improved chronostratigraphic control to test long-debated hypotheses concerning the distribution patterns and provinciality of subcontinental faunas in the Western Interior Basin. Sampson et al. (2004, 2010) argued that provincialism hypotheses put forward a decade earlier by Lehman...


Additional Information

Related ISBN
MARC Record
Launched on MUSE
Open Access
Back To Top

This website uses cookies to ensure you get the best experience on our website. Without cookies your experience may not be seamless.