A hierarchical approach for evaluating fluvial systems: Architectural analysis and sequential evolution of the high net-sand content, middle Wasatch Formation, Uinta Basin, Utah

Well-exposed three-dimensional fluvial outcrops of the high net-sand content middle Wasatch Formation in Three Canyon, Uinta Basin, Utah, were used to create and develop a new methodology for describing the architecture of fluvial systems. The methodology builds on the works of Campbell, Jackson, Allen, and Miall, and addresses sedimentary processes, scale, and temporal context for reservoir and non-reservoir bodies. The methodology developed herein is a three-level hierarchical framework that classifies meso- and macroscale architecture of fluvial systems. The three-level hierarchy contains, from smallest to largest: stories, elements, and archetypes. Eight story types provide the foundational building blocks of this framework and account for sedimentation in both channel-belt and floodplain-belt elements, including (1) downstream accreting; (2) laterally accreting; (3) erosionally-based fine-grained fill; (4) fine-grained fill associated with laterally accreting; (5) levee; (6) splay; (7) crevasse or overbank channels; and (8) floodplain fines. Two types of elements are recognized: (1) channel belt and (2) floodplain belt. An archetype consists of a channel-belt element and its genetically related floodplain-belt elements. Two distinct upward-stacking patterns differentiate braided and meandering archetypes. In deconstructing the evolution of archetypes, three distinct associations between channel-belt elements and their adjacent splays are documented: (1) unassociated splays; (2) associated coeval splays; and (3) associated non-coeval splays.Width and thickness for stories, channel-belt elements, and archetypes are documented providing dimensional constraints for analog high-net-sand-content fluvial systems. Additionally, this methodology provides object-based models with shape-defined reservoir and nonreservoir geobodies that realistically compare to fluvial systems.