Basin Stratigraphic Response to Variable Fault Geometry and Tectonic Kinematics: An Investigation of Extensional Basin Development

Engelder, Todd M.¹, Mark Person¹, John Swenson², Brad Ritts¹ (1) Indiana University, Bloomington, IN (2) University of Minnesota Duluth, Duluth, MN

Fault geometry and fault block rotation rates impose a significant impact on the distribution of coarse and fine grained facies during extensional basin evolution. To date, however, quantitative sediment transport models have only considered vertical movement of nodes through time. In this study, we consider the effects of extensional tectonics on strata infilling using forward models of fault block kinematics and diffusion controlled sediment transport. A sensitivity study is presented where we consider the effects of fault block rotation, geometry, temporal variations in sediment supply and climate on the distribution of fine and coarse grained facies. Half-graben basins with relatively large basin-bounding fault dips and slow subsidence rates are generally dominated by footwall fans. However, basins with relatively small basin-bounding fault dips and fast extension rates generate a more significant sediment flux from the footwall. In addition to controlling the total potential area for erosion, fault geometry has a significant impact on the migration of boundaries between grain-size dominated, depositional regimes. Current, sediment transport models show that basins with low fault dip magnitudes and fast extension create a significant volume of accommodation space on the footwall. The generation of accommodation near the upstream boundary of a fluvial sediment wedge should induce the boundary between a gravel dominated regime and a sand dominated regime to migrate upstream as the sediment flux remains constant through time.