Late Cretaceous deposits of the North American Western Interior represent the best, if not only, opportunity to construct a high-resolution chronostratigraphic framework within which to conduct continental-scale geological and paleontological analyses. This is due to the serendipitous combination of large areas of outcrop, interfingering marine units with biostratigraphically informative fossils, and a consistent scattering of radiometric dates due to synorogenic volcanic activity. Accurate correlation is essential for testing a large number of current geological and paleobiological hypotheses; however, despite the large amount of data available, many published correlations suffer from inaccuracies or are simply based on outdated information.
Here I present a comprehensive high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. For the first time, nearly two hundred 40Ar / 39Ar radiometric dates are recalibrated to both current standard and decay constant pairings, correcting errors in previous recalibrations. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and miscalculations in recently published analyses are corrected which in particular affects the relative age positions of the Belly River Group, Alberta; Judith River Group, Montana, Kaiparowits Formation, Utah, and Fruitland and Kirtland Formations, New Mexico.
This work represents the most extensive and accurate interbasinal correlation currently available for the North American Western Interior and should replace all previously published similar works and diagrams.
The stratigraphic ranges of selected dinosaur clades are plotted on the chronostratigraphic framework, typically forming stacks of short-duration species which do not overlap stratigraphically with preceding or succeeding forms. This is the expected pattern which is produced by an anagenetic mode of evolution, suggesting that true branching (speciation) events were rare and may have geographic significance. Purported north-south provinciality of dinosaurs is shown to be mostly an artifact of stratigraphic miscorrelation. Rapid stepwise acquisition of display characters in many dinosaur clades, in particular chasmosaurine ceratopsids, suggests that they may represent the highest resolution biostratigraphic markers to be used where radiometric dates are not available.