Normal fault control on bedrock channel incision and sediment supply: Insights from numerical modeling

Abstract

[1] The evolution of footwall drainage basins, sediment supply and hanging wall stratigraphy in rift basins is investigated using a coupled numerical model of detachmentlimited stream network evolution and coarse-grained fan delta deposition. The response of bedrock channel networks to repeated footwall uplift events leads to increasing sediment supply over tens of thousands of years as the networks initiate and then expand, followed by relatively constant sediment supply as the stream networks reach their maximum spatial extent. The distinct time lag between the onset of tectonic activity and attainment of maximum sediment supply leads to stratigraphies that are initially aggradational and then progradational. Much of the variation in sediment supply is the product of the complex response and reorganization of the stream networks to faulting-related perturbations and is not directly related to specific faulting events. Increasing fault displacement drives the system toward a new steady state with a higher sediment supply but is initially expressed as a retrogradation as sediment supply lags behind increased displacement. The converse is true for a decrease in fault displacement, which is initially expressed as progradation. Continual stochastic variation in recurrence interval leads to a system that does not achieve a steady state and as a result exhibits continual variation in sediment supply. The model results emphasize the local tectonic controls on stratigraphic architectures developed within extensional basins and the complex manner in which stream network growth and response to tectonic activity can be expressed in the stratigraphic record.INDEX TERMS: 3022 Marine Geology and Geophysics: Marine sediments-processes and transport; 3210 Mathematical Geophysics: Modeling; 5415 Planetology: Solid Surface Planets: Erosion and weathering; 8010 Structural Geology: Fractures and faults; 8105 Tectonophysics: Continental margins and sedimentary basins; KEYWORDS: bedrock, incision, faulting, sediments, stratigraphy Citation: Hardy, S., and R. Gawthorpe, Normal fault control on bedrock channel incision and sediment supply: Insights from numerical modeling,

Characterising the origin, nature and fate of sediment exported from catchments perturbed by active tectonics

“…Our findings therefore provide direct field confirmation of recent numerical modelling studies (Hardy & Gawthorpe, 2002;Cowie et al, 2006) that not only is there a significant pulse in the total volume of sediment exported to neighbouring depositional basins during the transient phase, but also that much of it is sourced from near the fault. Moreover, the fact that sediment is not derived uniformly across the catchment as a function of drainage area underlines the inherent dangers for any studies attempting to derive catchment wide erosion rates from sediment samples using cosmogenic nucleides (c.f.…”

“…Firstly, the response to the uplift rate increase propagates relatively slowly upstream of the fault (8-10 mm/yr , meaning that while part of the catchments has adjusted to the increase in fault uplift rate, the headwaters are yet to "detect" the change in relative base level. Consequently it takes time for the volume of sediment output to increase; in contrast the increase in hanging-wall subsidence rate is felt immediately across the whole basin (Hardy & Gawthorpe, 2002;Cowie et al, 2006). These observations require that much of the coarse fraction sediment derived from erosion since the fault acceleration must be stored in fans just downstream of the Fucino fault, as the basin is internally drained and the sediment has to be deposited somewhere.…”

“…In conjunction with the above work, "upstream" insight into the dynamics of catchment-wise sediment export in recent years has been generated as a product of burgeoning growth in landscape science in the last 10 years (Hardy & Gawthorpe, 2002, Whipple, 2004Cowie et al, 2006). A growing number of field studies (e.g.…”

“…& Stolar, 2006;Whittaker et al 2007a;Cowie et al, 2008) and a considerable body of modelling work (e.g. Tucker & Slingerland, 1996;Allen & Densmore, 2000;Whipple & Tucker, 1999;Willett & Brandon, 2002;Hardy & Gawthorpe, 2002;Simpson, 2006) have evidenced the coupling between tectonics, climate, and erosion through time, and demonstrate that transient landscape response to both tectonic and climatic perturbations can be associated with significant changes in the flux of sediment from upland areas. Recent work by Densmore et al, (2007) for small fans using a mass balance approach explicitly shows for transport-limited (i.e.…”

Three-Dimensional Growth of Flexural Slip Fault-Bend and Fault-Propagation Folds and Their Geomorphic Expression

“…The ratio of m/n is theoretically predicted to lie in a narrow range around 0.5 [89]. This, and related approaches, have been used by many authors to model bedrock channel development [94,[98][99][100]. The model is strictly only applicable to small, mountainous catchments such as those that are commonly found in tectonically active regions and where bedrock channels can be expected to be the dominant channel type.…”