A model of rift basin evolution constrained by first-order stratigraphic observations

The stratigraphy of many nonmarine rift basins records a common sedimentological history consisting of a relatively abrupt increase of water depth followed by a slower shoaling upward trend. We explore in this paper the origin of these sequences through a three-dimensional physical model that incorporates the affects of fault growth, flexure, erosion, sedimentation, and isostasy. Fault growth is assumed to occur in a self-similar manner and is treated as dislocations inducing flexure in a thin elastic plate. Topography generated by faulting and flexure is allowed to undergo diffusion to simulate erosive and sedimentary processes. Isostatic response, to the redistribution of mass results in additional flexure of the thin plate. The model is tested using two models of fault growth, and we compare the numerical results with the stratigraphy observed in nonmarine rifts. Basins generated using a constant-lengthening-rate mode of fault growth fail to reproduce the stratigraphy pf continental rift basins. We find that the commonly observed stratigraphic Succession of lacustrine to fluvial conditions requires the displacement rate of the bounding fault to decrease with time, consistent with opening at a relatively constant areal extension rate.