3D modeling of accretionary bodies on a Late Cretaceous point bar in Dinosaur Provincial Park, Alberta, Canada using architectural-element analysis

Traditional models commonly record point bar preservation as continuous accretionary bodies with continuous bounding surfaces that extend along the entire bar face. Although preservation of point bars in this fashion is common, fragmentary bar accretion, whereby accretionary units are preserved as incomplete and dispersed fragments, is also found in both ancient and modern river deposits. Accretionary events in the proposed model are regular and frequent, but are consistently eroded and reworked by subsequent accretion events leading to a complex fragmental architecture. This process generates a complex internal architecture and internal heterogeneity recorded by a hierarchy of bounding surfaces. This hierarchy is documented by 3D architectural-element analysis on a Terrestrial Laser Scanning (TLS) model of a 9m point bar in the Late Cretaceous Dinosaur Park Formation within the Steveville area of Dinosaur Provincial Park, Alberta, Canada. Results from this study reveal seven distinct architectural orders that make up the Steveville point bar. Sixth order surfaces bind channel belts. Fifth order surfaces bind a single point bar story. Fourth order surfaces represent the channel abandonment phase. Third order surfaces record lateral accretion of the point bar and represent accretionary bodies. Geometry of these bodies in a fragmentary point bar are discontinuous in both strike and dip view. Accretionary bodies may accrete as discrete or phase-driven events. Within accretionary bodies are 2 nd order surfaces that record the migration of individual unit bars. Units bars record pulses of sediment during flood events and may show individual fining upward trends depending on the competence of the river. First order surfaces record the migration of individual dune bodies and zero order surfaces record individual laminae. Changes in strike and dip, as measured by pole variation, between successive surfaces drives bar fragmentation. Composite constructional surfaces formed from selective and local stacking of multiple unit bars with local scour and truncation of underlying unit bars tend not be parallel to underlying surfaces and contribute to the pole deviation between accretion surfaces that drives fragmentation.