Stuart Hardy1, Rob L. Gawthorpe2
(1) The University of Manchester, Manchester, United Kingdom
(2) University of Manchester, Manchester, United Kingdom
ABSTRACT: Tectonic Controls on Drainage Networks, Sediment Supply and Syn-rift Stratigraphy Around Normal Fault Zones
The initiation, organisation and evolution of bedrock channel networks, and their response to tectonic activity and climate change, are thought to have a profound effect upon sediment supply to sedimentary basins and resultant basin-fill stratigraphy. However, little is known about either the magnitude or frequency of such variations in sediment supply and their expression in the stratigraphic record. To investigate the effect of channel network growth on sediment supply, in response to tectonic activity, we use a coupled numerical model of: 1) detachment-limited stream network evolution, and 2) coarse-grained fan-delta deposition. A critical threshold shear stress model for fluvial incision and bedrock channel development is used to simulate stream network evolution in the uplifting footwall of an extensional fault. Sediment eroded during stream network evolution is transported to a marine, fault-bounded, hangingwall basin where coarse-grained deltaic deposition occurs.
The response over geological timescales to repeated faulting events (footwall uplift/hangingwall subsidence) is investigated. There is a distinct time-lag between the onset of tectonic activity and the attainment of maximum sediment supply from footwall drainage basins. However, even within periods of approximate equilibrium, large fluctuations in sediment supply are observed that are not in phase with specific faulting (uplift) events. These variations are the product of the complex response and re-organisation of the stream networks to faulting-related perturbations and their occurrence is not predictable. The stratigraphic architectures of the modelled deltas show phases of progradation and aggradation in response to variations in sediment supply caused by stream network initiation and growth.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado