Evaluating the Influence of Floodplain-filling Styles on Channel-belt Stacking and Basin-scale Fluvial Architecture

Abstract:

Recent work in modern and ancient systems has shown a range of characteristic floodplain sedimentation patterns acting over a range of temporal and spatial scales. In aggradational fluvial systems floodplain sedimentation style influences where rivers relocate during avulsion, which in turn influences the distribution of channel-belt sandstones in stratigraphy over long timescales. Exploring the link between floodplain-sedimentation patterns and avulsions is therefore important for both predicting stratigraphic architecture and using stratigraphy to interpret paleo-floodplain sedimentation dynamics. Here we use an object-based model of basin filling to explore how different floodplain aggradation styles (including both uniform and exponential decay) affect the stratigraphic preservation of three different avulsion patterns: random (channels are equally likely to relocate anywhere on the floodplain), compensational (channels relocate to the lowest point on the floodplain), and clustered (channels relocate to a point near the previous channel position). Preliminary modeling results suggest that only clustered avulsion patterns are identifiable under uniform floodplain aggradation conditions, but that different avulsion patterns generate unique sand-body distributions under exponential floodplain sedimentation. This suggests that floodplain-aggradation styles influence how well we can interpret paleo-avulsion patterns in ancient deposits. We apply these insights to the Paleocene-Eocene Wasatch Formation in western Colorado to explore the relationship between preserved floodplain deposits and basin-scale sand-body architecture. We compare proxies for paleo-floodplain-aggradation patterns (including paleosol development, lateral continuity of paleosol horizons, and occurrence and distribution of splays) in three different members with quantitative metrics of channel-body organization at both sand-body and outcrop scales. Changes in floodplain deposits and sand-body organization between members of this formation suggest a link between floodplain-filling styles and large-scale channel-avulsion patterns.