Three-dimensional quantitative modeling of clinoform development

Clinoform geometry pervades stratigraphic sequences across a variety of scales. It is a composite surface, which records the complex interplay between accommodation, sediment supply, physiography, and hydrodynamics. Much of the sequence stratigraphic technique employs clinoform geometry to discriminate between the various systems tracts that constitute depositional sequences. However, many sequence stratigraphic models treat the generation of accommodation and the input of sediment supply as a two-dimensional problem, by assuming a line source of sediment entering a system impacted by relative sea-level fluctuations. One common attribute of clinoforms, regardless of size and/or shape, is that their formation is inherently three-dimensional. Therefore, the clinoform geometry varies spatially and temporally throughout a region depending on the proximity to the sediment source and the character of the hydrodynamic regime. We present a three-dimensional stratigraphic model that combines both diffusion and advection to simulate across- and along-margin sediment transport and deposition. This model allows us to examine how the morphology and internal clinoform geometry of deltas vary away from the sediment source. In this application, we simulate the development of a delta in a low-energy environment to understand the importance of along-shelf diffusion on clinoform geometry and the morphology of the delta. We predict the three-dimensional geometry and how it varies throughout a relative sea-level cycle. Our model indicates that when the clinoform rollover is spatially coincident with the shoreline position, the clinoform geometry changes dramatically along strike away from the sediment source region throughout a relative sea-level cycle. For example, oblique clinoforms develop near the source region and evolve into an onlapping sequence along strike. On the basis of stratal geometry and the technique of sequence stratigraphy, this deposit would be interpreted as two different sequences with very different connotations for their formation. We surmise that when the clinoform rollover and the shoreline position are separated (e.g., a subaqueous delta), the along-strike variability of the clinoform geometry diminishes because of the hydrodynamic forces operative across the shelf. Consequently, it is important to determine how clinoforms develop in three dimensions and to ensure that our window of observation is sufficient to discern between local and regional variability. (C) 1999 Elsevier Science B.V. All rights reserved.