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The 100 m thick stratigraphic section exposed at Dinosaur Provincial Park (DPP; southern Alberta) contains bentonites that have been used for more than 30 years to date DPP's rocks and fossils using the K–Ar decay scheme. Limited reproducibility among different vintages of K–Ar and 40Ar/39Ar ages inhibited the development of a high-resolution chronostratigraphy. Here, we employ and further test a recently completed U–Pb geochronology and associated age-stratigraphy model to update temporal constraints on the Park's bentonites, formational contacts, and other markers. In turn, we document rock accumulation rates and calibrate ages and durations of informal megaherbivore dinosaur assemblage zones and other biozones. Weighted mean 206 Pb/238 U ages from five bentonites range from 76.718 ± 0.020 to 74.289 ± 0.014 Ma (2σ internal uncertainties) through an interval of 88.75 m, indicating a duration of ∼2.43 Myr and an overall rock accumulation rate of 3.65 ± 0.04 cm/ka. An increase in rate above the Oldman–Dinosaur Park formational contact conforms to a regionally expressed pattern of increased accommodation at ∼76.3 Ma across Alberta and Montana. Palynological biozone data suggest a condensed section/hiatus in the uppermost portion of the Oldman Formation. Dinosaur assemblage zones exhibit durations of ∼700–600 kyr and are significantly shorter than those in the overlying Horseshoe Canyon Formation. A decreased rate in dinosaur assemblage turnovers in the last eight million years of the Mesozoic in western Canada may be explained by withdrawal of the Western Interior Seaway and the expansion of ecologically homogenous lowlands in its wake. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Santonian Deadhorse Coulee Member of the Milk River Formation preserves the oldest dinosaur body fossils found in Alberta. However, vertebrate remains consist almost exclusively of isolated elements and microvertebrate assemblages. Here, 1572 relatively complete shed non-avian theropod teeth from 20 localities in the Deadhorse Coulee Member are measured and analyzed to assess species diversity. Teeth are referred to or similar to Tyrannosaurinae indet., cf. Richardoestesia gilmorei, cf. Richardoestesia isosceles, Dromaeosauridae indet., Dromaeosaurinae indet., Velociraptorinae indet., and cf. Paronychodon lacustris. For the taxa identified, the large sample size allows for the assessment of their range of variation and accurate identification, without the benefit of comparable material of this age. Multivariate statistics, including a principal component analysis and a canonical variate analysis, provide reasonable separation of all taxa, although better results are achieved by separate analyses based on qualitative observations of denticle shape. The best results of the canonical variate analysis identified 96.0% of specimens correctly. This corroborates the qualitative identification of specimens and illustrates a valid way of evaluating diversity in areas and formations from which no described jaw material is known. Le membre santonien de Deadhorse Coulee, de la Formation de Milk River, renferme les plus anciens fossiles corporels de dinosaures trouvés en Alberta. Toutefois, les restes de vertébrés sont constitués presque exclusivement d’éléments isolés et d’assemblages de microvertébrés. Dans la présente étude, 1572 dents perdues relativement complètes de théropodes non-aviens provenant de plus de 20 localités dans le membre de Deadhorse Coulee ont été mesurées et analysées afin d’évaluer la diversité spécifique. Ces dents sont attribuées à Tyrannosaurinae indet., cf. Richardoestesia gilmorei, cf. Richardoestesia isosceles, Dromaeosauridae indet., Dromaeosaurinae indet., Velociraptorinae indet., et cf. Paronychodon lacustris. Pour les taxons identifiés, la taille importante de l’échantillon permet l’évaluation de leur variabilité et de l’exactitude d’une identification réalisée sans le recours à du matériel comparable du même âge. Des méthodes de statistique multivariée, dont l’analyse en composantes principales et l’analyse canonique, permettent une séparation raisonnablement fiable de tous les taxons, bien que des analyses basées sur la description qualitative de la forme des denticules donnent de meilleurs résultats. Dans les meilleurs cas, l’analyse canonique permet l’identification exacte de 96,0 % des spécimens. Ceci corrobore l’identification qualitative des spécimens et illustre une approche valide d’évaluation de la diversité dans des régions ou formations dont du matériel maxillaire n’a pas encore été décrit. [ABSTRACT FROM AUTHOR]

U–Pb geochronology, palynology, and lithostratigraphy were employed on the Late Cretaceous rocks in southern Alberta and Montana to solve litho- and chronostratigraphic correlation problems. In the outcrop area around Writing-On-Stone Provincial Park, southern Alberta, the Milk River Formation has a Santonian to possibly very earliest Campanian age and was deposited between ~84.5 Ma and 83.5 Ma. In southern Montana, the Eagle Formation was deposited from ~83.5 Ma to 81.2 Ma, and contains different lithologies and depositional environments as opposed to southern Alberta. In north-central Montana, the Telegraph Creek Formation and Virgelle and Deadhorse Coulee members are equivalent in depositional environments and time to those of the Milk River Formation in southern Alberta. The upper Eagle member, however, has no time- or facies-equivalent rocks around Writing-On-Stone Provincial Park, but is time equivalent to the Alderson Member of the Lea Park Formation in southeastern Alberta. A hiatus of ~2.5 Ma is present between the top of the Milk River Formation in the outcrop area and the basal beds of the Pakowki Formation. The Pakowki transgression occurred at around 81.0 Ma based on a U–Pb zircon age of 80.7 ± 0.2 Ma from bentonite beds just above the bottom of the Pakowki Formation in southern Alberta. This age agrees with previous ages of 80.7 ± 0.6 Ma for the Ardmore Bentonite Beds and ~81.0 Ma for the Claggett transgression in southern Montana.Afin de résoudre des problèmes de corrélations lithostratigraphiques et chronostratigraphiques, on s'est servi de géochronologie U–Pb, de palynologie et de lithostratigraphie sur des roches du Crétacé tardif du sud de l'Alberta et du Montana. Dans la région des affleurements autour du parc provincial de Writing-On-Stone, au sud de l'Alberta, la Formation de Milk River date possiblement du Santonien au Campanien très précoce et aurait été déposée il y a environ 84,5 à 83,5 Ma. Dans le sud du Montana, la Formation Eagle a été déposée il y a environ 83,5 à 81,2 Ma; elle présente des lithologies et des milieux de déposition différents de ceux du sud de l'Alberta. Dans le centre-nord du Montana, la Formation de Telegraph Creek et les membres Virgelle et Deadhorse Coulee ont des milieux et des temps de déposition équivalents à ceux de la Formation de Milk River du sud de l'Alberta. Toutefois, le membre supérieur de Eagle n'a d'équivalent ni dans le temps ni dans les faciès dans les roches autour du parc provincial de Writing-On-Stone, mais il est équivalent dans le temps au membre Alderson de la Formation de Lea Park dans le sud-est de l'Alberta. Il existe un hiatus d'environ 2,5 Ma entre le sommet de la Formation de Milk River dans la région des affleurements et les lits à la base de la Formation de Pakowki. La transgression de Pakowki a eu lieu vers 81,0 Ma selon une détermination d'âge U–Pb de 80,7 ± 0,2 Ma sur un échantillon de zircon provenant de lits de bentonite juste au-dessus de la base de la Formation de Pakowki dans le sud de l'Alberta. Cet âge concorde avec des âges obtenus antérieurement de 80,7 ± 0,6 Ma pour les lits de bentonite Ardmore et d'environ 81,0 Ma pour la transgression de Claggett dans le sud du Montana.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]