Sedimentology, petrology and permeability characterization of the Upper Cretaceous, Virgelle Member, Milk River Formation, Writing-On-Stone Provincial Park, Alberta, Canada

In this study I present a comprehensive geological model of the Upper Cretaceous (Santonian) Virgelle Member, Milk River Formation at Writing-on-Stone Provincial Park (WOSPP) in southern Alberta. The model integrates the multi-scale sedimentologic and petrologic description of Virgelle Member sandstones with the characterization of permeability distributions. The ultimate goal is to offer a physical and conceptual model that may be applied to recognize and describe similar sedimentary deposits that constitute fluid reservoirs in the subsurface.; The Virgelle Member at WOSPP is a progradational depositional systems tract representing environments from marine offshore through shoreface and foreshore, subtidal to intertidal estuarine channels, and capped by thick units of terrestrial, supratidal, muddy hydromorphic paleosols. Regional erosion surfaces punctuate the transitions from storm- and fair-weather dominated deposition to tidal sand bars and estuarine channel complexes. The characteristics of the system provide evidence to propose a new model for estuarine depositional systems in general, the progradational estuary, as an alternative to widely considered transgressive models.; The lithology of the Virgelle Member in the study area is relatively homogeneous, but nonetheless, with very few exceptions, lithofacies-scale (0.5 to 2 metres) permeability populations are sufficiently distinct to be statistically significant. Both permeability magnitudes and distributions closely reflect expected depositional processes and the associated physical structures, to some extent modified by syn-depositional biogenic activity and by subsequent diagenetic events. Besides evaluating the influence of the physical framework on permeability characteristics, samples of Virgelle Member sandstones are used to present experimental evidence for the fluid velocity-dependence of gas permeability applicable to natural and induced subsurface flow conditions.; The study includes analyses of provenance and diagenetic history, significantly widening the spatial and temporal scope of the depositional model. By assuming typical mineralogical and geochemical changes that occur during weathering, the detrital composition of Virgelle Member sandstones and mudstones has been successfully linked to largely plutonic source rocks in the Omineca Belt west of the study area. The sandstones are immature, and the distribution of authigenic minerals appears to be largely substrate-controlled due to the high proportion of labile grains. The resulting paragenetic sequence emphasizes the prevalence of early diagenesis.