Stratigraphic signatures of forearc basin formation mechanisms

Abstract

AbstractTectonic deformation of accretionary wedges is often interpreted using stratigraphic patterns observed in forearc basins. However, similar stratigraphic patterns could evolve from different deformational processes making it difficult to uniquely reconcile stratigraphic patterns and the geodynamic history of natural accretionary wedges. Therefore, it is important to test the dynamic consistency of interpreted deformation histories. One approach is to compare synthetic stratigraphy of forearc basins generated in numerical accretionary wedge models, to the stratal patterns observed in natural fore arcs. We present a simple method to simulate synthetic stratigraphy in numerical accretionary wedge models, comparable to the stratigraphic patterns observed in seismic reflection data. As calibration, we use reflection seismic and borehole data for the Kumano forearc basin in Nankai. We observe that the stratigraphy in retro‐forearc basins remains predominantly undisturbed and unaffected by wedge deformation. Sediment‐stabilized wedge‐top basins in wedges with trenchward surface slope typically form landward of an active out‐of‐sequence thrust, leading to a landward tilting of the basin. These stratigraphic characteristics are diagnostic of the forearc basin forming mechanism. We also infer that sedimentation in the trench can potentially influence the generation/reactivation of Megasplay Fault activity in the Nankai accretionary wedge. Activity on the Megasplay Fault helps create accommodation space landward to it that leads to the formation of Kumano forearc basin.