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Spatial and Temporal Evolution of an Ancient Fluvial Meanderbelt (Upper Cretaceous Dinosaur Park Formation, Southeastern Alberta, Canada) With Emphasis on Characterization of Counter Point Bar Deposits


Counter point bar, or concave-bank bench, deposits have historically been overlooked relative to other meanderbelt elements. Although they have been sporadically described from modern river systems, until recently their stratigraphic expression has not been explored. Recent identification in subsurface datasets has relied on recognition of their characteristic concave-downstream accretion surfaces in seismic reflection volumes, calibrated by well data. However, they have largely been elusive in the outcrop record. In this study, a meanderbelt deposit is examined in badlands-style outcrops of the Cretaceous Dinosaur Park Fm in SE Alberta, Canada. The dissected landscape offers sedimentological details of the 7.5–8.0 m thick meanderbelt deposit over 3 km2. In the outcrop, counter point bar deposits consist of siltstone-dominated inclined heterolithic stratification, which are present immediately downstream from and adjacent to convex-shaped, sandstone-dominated point bar elements. The evolution of fluvial meanderbelts results in a complex amalgam of architectural elements in the stratigraphic record (e.g., point bars, etc.), which when unraveled, provide insight into formative sedimentological processes. A predictive linkage between morphodynamics and stratigraphic product is critical for interpretation of the rock record, particularly in instances of limited data such as subsurface reservoirs. Refined fine-scale facies and architectural element transitions deduced from the field study are considered for the analysis of analogous deposits, including those of the Athabasca Oil Sands. At Dinosaur Provincial Park, detailed sedimentologic characteristics were compiled from over 40 measured sections and abundant paleoflow indicators; key stratigraphic surfaces, including meanderbelt bounding contacts, component architectural element contacts, and intra-bar accretion and erosion surfaces, were surveyed using a high resolution (10 cm) differential GPS unit. Outcrop data was then imported into modeling software, and surfaces extrapolated and projected into the third dimension in order to constrain geometrical information (e.g., surface orientations, which reveal bar accretion directions). Architectural element and component geobody volumes are also constrained. The study area is characterized by at least five meanderbelt elements, including point bars and abandoned channel fills – emphasis is placed on characterization of a counter point bar deposit.