Abstract

Results from a newly developed numerical model incorporating tectonic subsidence, eustasy, and sedimentation are presented for rift-basin settings. In particular, we simulate contemporaneous fan-delta deposition, subsidence, and eustatic sea-level variations to investigate the three-dimensional nature of depositional sequences in the hanging wall of a normal fault. A random-walk algorithm is used for sediment delivery from source to shoreline, together with a nonlinear three-dimensional diffusion equation for sediment movement on steep delta foresets. Three sediment sources are modeled; they are located along strike in areas of low, medium, and high subsidence. Rates of hanging-wall subsidence, eustatic sea-level variation, and sediment supply are derived from studies of active extensional basins. The resulting stratigraphy contains three fan deltas with distinct morphologies and internal stacking patterns. Sequence boundaries and offlap (forced regression) are restricted to areas of low subsidence, toward the fault tip; aggradationally stacked deltaic wedges are along strike where subsidence rates are high, near the fault center. The simulated geometries compare well to natural examples and highlight along-strike sequence variability and the importance of local controls in such settings.

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