ABSTRACT Dinosaur Provincial Park (DPP) was designated as a UNESCO World Heritage Site in 1979, but in 1955 the exceptional quality and abundance of dinosaur fossils were already recognized with 80 km 2 of the richest fossil beds being set aside as an Alberta, Canada, provincial park. DPP represents possibly the best window into the biology of the Late Campanian anywhere in the world. At present, more than 35 species of dinosaurs, 32 species of fish, 10 species of amphibians, 29 taxa of non-dinosaurian reptiles, 1 bird, and 20 taxa of mammals are known to have been discovered in DPP. The dinosaur fossils of DPP were first seriously collected in 1912, with many “trophy” specimens being sent to museums in Ottawa, Toronto, New York, Washington, and London among others. This initial rush of dinosaur fossil collecting persisted until the 1930s, but with declining effort and results. In the late 1960s and early 1970s, scientific study of the park resumed in earnest, and by the 1980s, the park was receiving the full attention of staff from the newly created Royal Tyrrell Museum of Palaeontology, based in Drumheller. With modern scientific thinking and techniques being applied to its dinosaurian, and especially non-dinosaurian, fossils, the park is as important a resource as ever. Hydrocarbon exploration in Alberta has contributed immensely to our knowledge of the geological history of the province during the Cretaceous, thus enabling a better understanding of the factors, both physical and biological, that contributed to the creation, preservation, and subsequent exposure of the extensive fossil resources contained within DPP.

The interval spanning the uppermost Hell Creek Formation to the overlying lowermost Fort Union Formation in north-central Montana encompasses a marked paleoenvironmental change (associated with the formational contact), the Chicxulub impact event, and the Cretaceous-Paleogene boundary. We have examined the record of this transition at the Hell Creek Formation lectostratotype to determine the placement of these events using a series of lithological, geochemical, palynological, and 40 Ar/ 39 Ar geochronological analyses. The claystone derived from the Chicxulub impact is identified based on lithological criteria, enrichment of iridium and osmium, and osmium isotope ratios. The impact claystone also contains a Cyathidites fern spike. The first continuous lignite horizon in the section immediately overlies this claystone and represents the Hell Creek–Fort Union formational contact. A tuff ~3 m above the impact layer is dated to 66.024 ± 0.059 Ma. Given this evidence, at the lectostratotype the Cretaceous-Paleogene boundary is coincident with the impact claystone and therefore with the formational contact. Due to poor preservation and apparent reworking of palynomorphs surrounding the formational contact, the Cretaceous-Paleogene boundary is difficult to identify based on biostratigraphically significant taxa. The presence of marine dinoflagellates is suggestive of reworking of older marine sediments during the deposition of the Cretaceous-Paleogene boundary interval.

Abstract The Virgelle Member of the Milk River Formation, Alberta, Canada represents a sandy progradational depositional systems tract that contains linkages between offshore, estuarine, and coastal plain environments. Distinct upward-shoaling depositional successions include regional erosion surfaces that punctuate transitions from storm- and fair-weather-dominated deposition to tidal sand bars and estuarine channel complexes that developed as the systems tract prograded basinward. The lower part of the Virgelle Member is characterized by hummocky and swaley cross-bedded sandstones depicting the transition from offshore to storm-dominated middle shoreface. A sharp, regionally flat erosion surface separates middle shoreface deposits below from two end-member upper shoreface/foreshore lithofacies associations above: (1) rare fair weather wave-reworked deposits or, (2) common tidally reworked deposits represented by outer estuarine tidal bars. The upper shoreface unconformity is thus dominantly a tide-cut source diastem (TSD), overlain by bathymetrically equivalent subtidal to intertidal sand bars typified by planar-bound, herringbone, cross-bedded sandstone. The erosive base of extensive, laterally accreted estuarine channels (ECh) cuts into middle shoreface deposits and truncates the flat disconformity and the above-mentioned shoreface and esmarine successions. Tidal influence within the channels is recorded by carbonaceous bundles and couplets, reactivation surfaces, and subordinate, flood-directed, three-dimensional dunes. In addition, a restricted ichnofauna documents the influence of an estuarine environment. The resulting depositional model depicts a west-northwest/east-southeast trending estuarine system, open to the east, that truncates the storm-dominated middle shoreface, and is itself cut by a belt of meandering estuarine channels merged into overlying supralidal coastal plain mudstones. The genera] distribution of palynomorphs is consistent with the progression of marine dinoflagellate-rich assemblages in outer estuarine tidal bars to mostly terrestrial assemblages in ebb-dominated estuarine channels. A qualitative analysis of depositional regime variables Q, M, D and R within the supply-dominated depositional systems tract of the Virgelle Member highlights the critical importance of the sediment dispersal function D, in this case controlled by tides and storms. The corresponding relationship may be expressed as Q M ≥ D R. The proposed model for a progradational estuary contrasts with sequence stratigraphic models of transgressive estuaries because it is not restricted to specific relative sea-level stages, and because it arises from the linkage of depositional processes along the entire systems tract, from offshore to coastal plain.