Assessing the lateral and vertical variability of shelf-margin depositional systems and associated forcing mechanisms: A forward modeling approach

Understanding the primary drivers of lateral and vertical variability in the stratal architecture of shelf-margin settings is key to understanding how sediments are partitioned from the shelf to the slope and the basin floor in source-to-sink systems. In this study, we model the 4-D evolution of a shelf margin over a period of 18.5 m.y. using Badlands stratigraphic forward modeling software. The modeled system is analogous to the Hammerhead shelf margin developed in the Bight Basin (southern Australian margin) during the Late Cretaceous, with forcing parameters interpreted from “real world” 3-D seismic data. A series of seven models were designed and tested to investigate potential drivers of shelf-margin variability, which include shoreline process regime (i.e., fluvial, wave, or mixed coastal processes), uplift, rainfall, and source area extent. We find that shoreline processes, which in the context of this study include fluvial and wave processes, may significantly impact shelf-margin architecture although they are less likely to affect the long-term evolution of a shelf margin. The addition of either fluvial or wave processes increases along-strike lateral variability with mixed-process shorelines resulting in the most variability. We propose that these hydrodynamic processes affect sediment supply locally leading to “out-of-phase” supply influencing both shelf-margin architecture and the character of sequence stratigraphic surfaces laterally. Rainfall is also shown to have a much more immediate effect on shelf-margin architecture compared to changes in tectonics (uplift). The results of this study are particularly applicable to the Hammerhead shelf margin and may also be applied to other shelf margins where eustasy is not the primary control on shelf-margin architecture and/or paleoclimatic conditions are poorly constrained.