Resolving Facies Architectures of the Fraser River Delta - Past and Present

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Deltas are important depositional environments, both on modern coastlines and in the rock record. In the subsurface, they host significant quantities of water and hydrocarbon resources. Delta systems are complex; they are affected by wave, tidal and river processes, and their architectures are partly controlled by grain size, depositional slope, climate and tectonics. Constraining the range of depositional morphologies that can be expected in deltaic systems is challenging, yet it is necessary in order to predict the morphologies of reservoir bodies in the subsurface and to model fluid flow. Resolving the architecture of modern deltas and the depositional processes that control sedimentation is essential if development and refinement of predictive models are to be achieved for interpreting paleo-deltaic successions. Through this research program a comprehensive sedimentological and ichnological process-response model and a three-dimensional facies architecture of the Fraser River Delta will be developed. The process-response model will provide baseline data on the modern delta for comparison in understanding delta evolution. The 3D architectural model can be used to map fluid flow through permeable sediments, refine estimates of slope failures based on historical data and refine the depositional history of the delta based on facies analysis. The facies model will also act as an analogue for deep-water deltas, particularly those that are tide influenced but also form in high gradient settings. To reach the final goal of a process-response model and a 3D delta architecture, six research projects are defined: 1) sedimentological characterization of the tide-dominated, freshwater Pitt River and Pitt River Delta; 2) quantification of channel migration and sediment accumulation rates in tidal creeks in Mud Bay and development of a depositional model for the bay; 3) characterization of the Boundary Bay sand flats and comparison to the Mud Bay mud flats; 4) determination of the conditions under which mud deposition and muddy bedload transport occurs in the Fraser River; 5) completion of a sedimentological-ichnological model for the entire Fraser River Delta from the landward limit of the tidal backwater to the seaward limit of the prodelta; and 6) construction of a three-dimensional subsurface model of the delta, focused on the recognition of delta subenvironments using geophysical-log data, seismic profiles, and the re-interpretation of core data. A seventh project will also be undertaken to extend subsurface facies mapping of the Fraser River Delta up the Fraser valley and into Washington, USA (i.e., across the Fraser lowlands). Research on Mud Bay, Boundary Bay and the Pitt River will "complete" the dataset already acquired for the delta, and will enable us to model sedimentological and ichnological trends from the landward limit of the tidal backwater to the base of the Strait of Georgia. The complete Fraser dataset will enable us to define criteria for differentiating delta subenvironments in vibracore and on geophysical logs. The models developed for the present delta will be used to construct and refine existing subsurface models, and to map out sedimentary facies. Sedimentary facies constitute the dominant control on fluid flow through the delta, and the 3D architecture of the delta provides a high-resolution framework for mapping fluid flow. Finally, the facies architecture will be extended across the Fraser lowlands to define the extent of sediment deposition from the Fraser River.