Basin-scale predictive models of alluvial architecture: Constraints from the Palaeocene–Eocene, Bighorn Basin, Wyoming, USA

Amanda Owen* (Corresponding Author), Adrian J. Hartley, Alena Ebinghaus, Gary S. Weissmann, Maurício G.M. Santos

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)
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Basin-scale models are required to interpret ancient continental sedimentary successions, and reduce uncertainty in assessing geological resources in basins. Recently, modern studies show distributive fluvial systems to comprise a substantial proportion of modern sedimentary basins, but their role in ancient basin fills has yet to be quantitatively documented at the basin scale. This study analysed key fluvial characteristics to construct a detailed basin-wide model of the Palaeogene Fort Union and Willwood formations (Bighorn Basin, Wyoming), using observations from modern studies, and ancient system scale studies of distributive fluvial systems, to guide interpretations. Mapping showed these formations to be highly heterogeneous with channel-body proportion (from 12 to 81%) and geometry types (large amalgamated bodies to isolated channels), grain size (silt to conglomerate), average channel-body thickness (4 to 20 m) and average storey thickness (3 to 10 m) varying significantly across the basin. Distributive fluvial systems in the form of alluvial and fluvial fans in transverse configurations were recognized as well as a wide axial system, with heterogeneity in the formations being closely aligned to these interpretations. Furthermore, numerous individual depositional systems were identified within the formations (Beartooth Absaroka, Washakie, Owl Creek and axial). Predicted downstream distributive fluvial system trends (i.e. downstream decrease in channel proportion, size and grain size) were identified in the Beartooth, Absaroka and Owl Creek systems. However, predicted trends were not identified in the Washakie system where intrabasinal thrusting disturbed the sequence. Importantly, a wide axial fluvial system was identified, where reverse downstream distributive fluvial system trends were present, interpreted to be the result of the input of transverse systems of variable size. This study provides a new level of detail in the application of basin-scale models, demonstrating their usefulness in trying to understand and predict alluvial architecture distribution and heterogeneity, with important implications for economic resources and palaeogeographic reconstructions.

Original languageEnglish
Pages (from-to)736-763
Number of pages28
Issue number2
Early online date19 Aug 2018
Publication statusPublished - 28 Feb 2019

Bibliographical note

This work was supported by Phase 2 of the Fluvial Systems Research Group (BP, BG, Chevron, ConocoPhillips and Total). AE thanks the University of Aberdeen for additional funding and MGMS thanks the São Paulo Research Foundation (FAPESP 2014/13937‐3). The authors also wish to thank numerous residents of the Bighorn Basin for their kind hospitality and access to land, and Isobel Buchanan and Alistair Swan for assistance in the field. The authors also thank reviewers Luca Colombera and Sian Davies‐Vollum and AE Christopher Fielding for helpful comments on this manuscript.


  • Basin scale
  • Bighorn Basin
  • distributive fluvial system
  • fluvial
  • Fort Union Formation
  • Willwood Formation


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