107-1 Reverse-Engineering in the Quantitative Reconstruction of Wave Base Depths and Extents in an Epicontinental Setting: A Case from the Middle Member of the Bakken Formation, North Dakota, USA.

Session: Sedimentary Geology Division/SEPM Student Research Poster Competition: Dynamics of Stratigraphy and Sedimentation

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Abstract:

Understanding the energy regimes that governed sediment transport in epicontinental seas remains a persistent challenge in sedimentology. Traditional reconstructions rely on preserved sedimentary structures to infer relative wave conditions; however, no prior work has quantitatively estimated fair-weather and storm wave base depths in ancient basins.

A novel, grain-specific reverse-engineering approach—guided by the principle of uniformitarianism (“the present is the key to the past”)—is applied to reconstruct wave dynamics in the Late Devonian–Early Mississippian Williston Basin. The case study focuses on the middle member of the Bakken Formation, deposited in a low-gradient intracratonic basin within the tropical belt. Data from more than 70 hydrocarbon wells in the North Dakota portion of the basin, including 24 slabbed cores and 52 petrographic thin sections, reveal four distinct facies associations whose sedimentary structures reflect deposition under both fair-weather and storm wave conditions.

Irregularly sub-parallel bedded silt-rich mudstone to siltstone represents the deepest reach of fair-weather wave-induced bottom currents, preserving tractional structures composed of ~50 µm silt. In contrast, a clay-rich siliciclastic mudstone contains stacked laminae of similar grain size (~50 µm) and is interpreted as the deepest facies within the storm-influenced mudbelt, deposited under episodic storm-driven bottom currents.

Wave parameters for fair-weather and storm conditions are derived from modern semi- to fully enclosed shallow seas, including the Baltic Sea, Yellow Sea, and northern Gulf of Mexico. Using Flemming’s (2024) orbital velocity-based model—which equates seabed orbital velocity with the critical threshold required to mobilize specific grain sizes—fair-weather and storm wave base depths are estimated at ~12 m and ~66 m, respectively. When projected across a characteristic seafloor gradient of 0.005°, the lateral extent of wave influence reaches ~140 km (fair-weather) and ~760 km (storm) from the shoreline during deposition of the middle member of the Bakken Formation.

These estimates provide the first quantitative constraints on wave base depths in an ancient epicontinental shelf. The methodology offers a transferable framework for reconstructing wave-dominated depositional systems in other ancient shallow-marine settings.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5934

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