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Linear-Sourced Slope Channel Systems in High Sediment Supply Basin Margin Clinoforms

Abstract

Current researches on deep water slope channels tend to focus on single channel or channel belt that are fed by a single point source on the continental shelf, and data are biased towards large systems of continental margin-scale (>1km) clinoforms. However, there is good evidence for linear-sourced slope channel systems on the slopes of moderately deep water clinoforms (<1km) that are common for petroleum prolific back-arc, foreland, and lacustrine basins. These basins are characterised by a progradation-dominant shelf edge trajectory, with multiple contemporaneously active slope channels and thick basin floor fans. To show how shelf-edge trajectory influences slope channel systems and deep water sand deposition, we map slope channel distribution of Late Cretaceous Fox Hill-Lewis clinoforms in Washakie basin, and compare the results from the aggradational early clinoforms vs. the progradational late clinoforms. The studied section is the type section for rising and highstand fans. The mapped slope-channel distribution strongly suggests that the basin-floor fan complexes are fed by multiple slope channels confined within well-defined high frequency (fourth and fifth-order) sequences. Channels on the deep water slope merge with basin floor fans as aprons on the lower slope to toe-of-slope. Incisions near the shelf edge, cross-cutting multiple fifth-order sequences, directly link shelf edge deltas to slope channels and fans, especially for the progradation-dominant clinoforms. Channel log motifs are not evenly distributed through the height of any clinoform but tend to cluster, suggesting channel elements within a larger slope channel complex. Channel thickness varies from few meters for each channel element, to fifty meters for the stacked channel complex. The width of channel complexes is mostly within 3-5 km. Local net to gross in the channels can be more than fifty percent. We also evaluate that the progradation rate of the shelf-edge influences the density of slope channels immediately in front of the shelf. Further testing will clarify if the spacing of the slope channels can be related to the density of small rivers, thus controlled by climate and Laramide tectonic uplift rate. Overall the study explores the under-evaluated role of linear-sourced slope channels in source to sink systems in the contest of prograding shelf-edge trajectory.