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

Abstract

Depositional processes and interactions with a mobile substrate are seen in passive margins throughout the world. The interplay between brittle stratigraphic layers and a deformable substrate resulted in a complex stratigraphic record due to dynamic feedback influences. During the Late Jurassic, a fluvial-dump-wind-redistribute system deposited sediment on top of the pre-deposited Louann Salt layer in the eastern part of the early Gulf of Mexico basin. By using simplified, scaled-tank experiments we are able to investigate the evolution of a linked fan and terminal channel system in response to subsidence in a mobile substrate. A series of experiments were conducted with controlling variables including salt substrate thickness, sediment supply rate, and basin slope. Fan surface area and morphology, number of terminal channels, channel longevity, and geometry were measured along each experiment. 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 thin substrate resulted in faster fan progradation coupled with less subsidence and more sediment transport to terminal channels, and (3) a higher-sloped 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. Furthermore, we utilize the experimental findings to improve the current depositional model for the Jurassic Norphlet Sandstone.