The effect of a pre-deposited mobile substrate on terminal-fan evolution and channel organization: Tank experiments

Depositional processes interact with mobile substrates in nearly all passive-margin settings throughout the world. The interplay between sedimentation and a mobile substrate (e.g., salt layer) results in a complex stratigraphic record, making it difficult to reconstruct basin-fill history. Herein we investigate the dynamic feedback between sediment loading and substrate deformation to understand morphologic change and stratigraphic development. We used simplified tank experiments of a linked fan and terminal-channel system evolving over a deformable substrate. A series of experiments were conducted with controlling variables including mobile substrate thickness, sediment supply rate, and basin slope. Experimental results indicate: (1) an increase in substrate thickness resulted in increased subsidence around the fan that limited sediment transport to its terminal channels, (2) a higher sediment discharge rate on a substrate resulted in faster fan progradation coupled with relatively less subsidence and more sediment transport to terminal channels, and (3) a higher-slope experiment caused the largest amount of sediment transport downstream, while a decrease in basin slope resulted in a larger number of established channels along with a wider fan surface. An analysis of surface processes is also used to determine the expected stratigraphy between a linked fan and terminal-channel system as it interacted with the mobile substrate. We apply the experimental findings to understand the fluvial-dump-wind-redistribute system deposited on top of the Louann Salt layer in the eastern part of the Late Jurassic Gulf of Mexico basin.