Published February 2025 | Published
Journal Article

Floodplain topography and avulsion pathfinding control stratigraphic architecture in a numerical model of a fluvial fan

  • 1. ROR icon Indiana University Bloomington
  • 2. ROR icon Geosyntec Consultants (United States)
  • 3. ROR icon California Institute of Technology
  • 4. ROR icon Tulane University
  • 5. ROR icon Pennsylvania State University

Abstract

Buried channel sand bodies are important reservoirs of subsurface water and energy resources, but their arrangement and interconnectedness are difficult to predict. The dominant process that distributes channels and their sediments in alluvial basins is river avulsion, which occurs when a channel seeks a new location on the adjacent floodplain. Floodplain sedimentation, incision, and channel levee growth influence channel pathfinding during avulsion, and should control key aspects of the stratigraphic arrangement of channel bodies, including compensational (spatially and temporally even) deposition, stratigraphic completeness, and facies distributions; however, this impact has been difficult to isolate in natural and experimental basin fills. To test how different avulsion pathfinding parameters influence stratigraphic architecture, we use a numerical model of a fluvial fan to produce synthetic fluvial stratigraphy under seven different runs with progressively more complex channel pathfinding rules. In the simplest models where pathfinding is set by a random walk, the channel rapidly changes position and avulsions spread across the fan surface. The corresponding deposit is dominated by channel facies, is relatively incomplete, and the compensation timescale is short. As rules for pathfinding become more complex and channels can be attracted or repulsed by pre-existing channels, lobe switching emerges. Deposits become more diverse with a mix of channel and floodplain facies, stratigraphic completeness increases, and the compensation timescale lengthens. Previous work suggests that the compensation timescale is related to the burial timescale and relief across the depositional surface, yet we find that compensation approaches the burial timescale only for model runs with high morphodynamic complexity and relatively long topographic memory. Our results imply that in simple systems with limited degrees of freedom, the compensation timescale may become detached from the burial timescale, with uniform sedimentation occurring quickly relative to long burial timescales.

Copyright and License

© 2025 SEPM Society for Sedimentary Geology.

Acknowledgement

DAE, CS, and HKM were funded by National Science Foundation (NSF) grants 1911321 and 2321056. HKM was supported by National Aeronautics and Space Administration (NASA) Future Investigators in NASA Earth and Space Science and Technology (FINESST) grant 80NSSC21K1598. EAH contributions were supported by NSF 1935513. Model code for RiverWalk with the stratigraphic module (RiverWalk-Strat) is available at https://github.com/harrison-martin/RiverWalk-Strat. We thank C. Broaddus for discussion and Associate Editor V. Ganti, reviewer Y. Wang, and an anonymous reviewer whose comments improved this manuscript.

Additional details

Created:
February 25, 2025
Modified:
February 25, 2025