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Extreme depositional events in ancient river systems are often overlooked due to the assumption that the sedimentary record is overwritten by average conditions. However, where these high-energy events are preserved, their study is critical for reconstructing past climates—without it, we risk underestimating the true magnitude of environmental change possible in future climate scenarios. In the Uinta Basin (Utah, USA), the Green River Formation preserves the sedimentary record of an ancient river system with highly variable discharge. Because “average” flow conditions lacked the energy to significantly alter the landscape, deposits from more extreme flow events are preferentially preserved. Here we analyze supercritical flow structures formed by fast, inertia-driven flows that capture one such event during the early Paleogene warm period. Nested scour features, interpreted as cyclic step deposits, show depths (x̃ = 2.19 m, min = 0.74 m, max = 16.41 m, n = 40) statistically distinct (Kruskal-Wallis test, p = 0.3852) from paleo-channel depths measured in the same interval (x̃ = 2.75 m, min = 0.95 m, max = 21.00 m, n = 22). A continuous train of nearly-to-fully-preserved scour fills overlying partially-preserved, nested basal scour complexes indicates that large-scale cyclic steps formed during and persisted throughout a catastrophic flood, serving as the dominant sediment transport mechanism. Rivers such as these, that are dominated by deposition during extreme events, operate under fundamentally different sediment transport and flow mechanisms than those with more consistent, perennial hydrographs. These variable discharge river systems are underrepresented in current fluvial models and need greater recognition and study to improve our understanding of Earth’s climate history and future hazards.
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This content will become publicly available on December 16, 2026
Channel-Scale Froude Supercritical Flow Deposits: Characterizing Catastrophe During A Climate Extreme
Extreme depositional events in ancient river systems are often overlooked due to the assumption that the sedimentary record is overwritten by average conditions. However, where these high-energy events are preserved, their study is critical for reconstructing past climates—without it, we risk underestimating the true magnitude of environmental change possible in future climate scenarios. In the Uinta Basin (Utah, USA), the Green River Formation preserves the sedimentary record of an ancient river system with highly variable discharge. Because “average” flow conditions lacked the energy to significantly alter the landscape, deposits from more extreme flow events are preferentially preserved. Here we analyze supercritical flow structures formed by fast, inertia-driven flows that capture one such event during the early Paleogene warm period. Nested scour features, interpreted as cyclic step deposits, show depths (x̃ = 2.19 m, min = 0.74 m, max = 16.41 m, n = 40) statistically distinct (Kruskal-Wallis test, p = 0.3852) from paleo-channel depths measured in the same interval (x̃ = 2.75 m, min = 0.95 m, max = 21.00 m, n = 22). A continuous train of nearly-to-fully-preserved scour fills overlying partially-preserved, nested basal scour complexes indicates that large-scale cyclic steps formed during and persisted throughout a catastrophic flood, serving as the dominant sediment transport mechanism. Rivers such as these, that are dominated by deposition during extreme events, operate under fundamentally different sediment transport and flow mechanisms than those with more consistent, perennial hydrographs. These variable discharge river systems are underrepresented in current fluvial models and need greater recognition and study to improve our understanding of Earth’s climate history and future hazards.
more »
« less
- Award ID(s):
- 2503863
- PAR ID:
- 10687860
- Publisher / Repository:
- AGU
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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