Sedimentology, Ichnology, Sequence Stratigraphy and Vertebrate Paleontology of the Belly River Group, southwestern Saskatchewan, Canada

The Belly River Group (BRG) in southwestern Saskatchewan records the interplay of accommodation space and base level in an epicontinental seaway. The Belly River Group has been the focus of numerous studies concerned with sedimentology, stratigraphy, and paleontology in Alberta and Montana, due to extensive badlands exposure, exceptional three-dimensional preservation of many sedimentary features, and the vast paleontologic data available from the deposits. The BRG has been studied with far less detail in Saskatchewan, due to the poor and sporadic nature of available outcrop, and comparatively little subsurface data. This study synthesizes all available data for the BRG in southwestern Saskatchewan, effectively characterizing the sedimentology, stratigraphy, ichnology, and paleontology and provides a comprehensive framework for these deposits in the province. This study provides critical insights into the BRG, particularly in regards to sequence stratigraphy. During the Campanian, the Western Interior Seaway bisected North America, and its western shore was located in southern Saskatchewan. This study provides critical insights into shoreline dynamics, both from a geologic and paleontologic perspective, and how these dynamics influence deposits further inland not directly in contact with the seaway. This study highlights the utility of integrating multiple, distinct datasets to understand depositional evolution along coastal plains, and its effects on biodiversity. McLean (1971) characterized the uppermost deposits of the BRG (then called the Judith River Group) in the Cypress Hills as being deposited in an extensive delta plain. In Chapter 3, detailed facies analysis indicates the upper DPF does not record sedimentation in a delta system. A reinterpretation determines the DPF was deposited in a low-relief coastal plain with a wave-dominated, tidally influenced, fluvially modified shoreline. Marginal-marine facies, interpreted as lagoons, tidal flats and estuaries, display a typical brackish-water trace-fossil assemblage, including Asterosoma isp., Chondrites isp., Cylindrichnus concentricus, Teichichnus rectus, and Skolithos isp. Fine-grained sandstone deposited in an estuarine mouth-bar and barrier-island complex protected the coast from wave reworking. As the seaway transgressed across the coast, fully marine wave-dominated parasequences replaced those of the coastal plain. Typical trace fossils include Asterosoma isp., Chondrites isp., Diplocraterion isp., Nereites missouriensis, Phycosiphon incertum, Planolites isp., Rhizocorallium isp., and Zoophycos isp., reflecting open, fully marine conditions. In Chapter 4, the Belly River Group and its associated formations are formally recognized for the first time in Saskatchewan with facies, depositional environments, and sequence stratigraphic framework interpreted to provide a concise treatment of the deposits in southwestern Saskatchewan. A new lithostratigraphic unit within the uppermost Dinosaur Park Formation is recognized based on laterally extensive barrier island, lagoon, and estuary basin deposits. The Manâtakâw Member is established as a means to aide in discussing the transition from nonmarine clastics of the BRG to marine shales of the overlying Bearpaw Formation. Unincised and incised valley systems are explored in detail, with lowstand systems tract deposits compared and contrasted between the Oldman and Dinosaur Park formations. Chapters 5 and 6 discuss microvertebrate localities from the Dinosaur Park Formation, one at Lake Diefenbaker (Ch. 5), and the other at Woodpile Coulee (Ch. 6). Palynology, ichnology, sedimentology, and vertebrate paleontology are integrated to determine paleoenvironmental and paleoecological conditions in the two regions and their stratigraphic positions. Both sites are interpreted as having been deposited at different times during transgression of the encroaching Bearpaw Sea. Though well studied and sampled in Alberta, the Dinosaur Park Formation is poorly exposed with little known associated vertebrate assemblages in Saskatchewan. These discoveries from the microvertebrate sites offer new insights into Late Cretaceous ecosystems near paleocoastlines, allowing for future studies of spatial diversity patterns relative to Albertan faunas