Investigating the surface process response to fault interaction and linkage using a numerical modelling approach

Abstract

In order to better understand the evolution of rift-related topography and sedimentation, we present the results of a numerical modelling study in which elevation changes generated by extensional fault propagation, interaction and linkage are used to drive a landscape evolution model. Drainage network development, landsliding and sediment accumulation in response to faulting are calculated using CASCADE, a numerical model developed by Braun and Sambridge, and the results are compared with ¢eld examples.We ¢rst show theoretically how the '£uvial length scale' , L f , in the £uvial incision algorithm can be related to the erodibility of the substrate and can be varied to mimic a range of river behaviour between detachment-limited (DL) and transport-limited (TL) end-member models for river incision.We also present new hydraulic geometry data from an extensional setting which show that channel width does not scale with drainage area where a channel incises through an area of active footwall uplift.We include this information in the coupled model, initially for a single value of L f , and use it to demonstrate how fault interaction controls the location of the main drainage divide and thus the size of the footwall catchments that develop along an evolving basin-bounding normal fault.We show how erosion by landsliding and £uvial incision varies as the footwall area grows and quantify the volume, source area, and timing of sediment input to the hanging-wall basin through time.We also demonstrate how fault growth imposes a geometrical control on the scaling of river discharge with downstream distance within the footwall catchments, thus in£uencing the incision rate of rivers that drain into the hanging-wall basin.Whether these rivers continue to £ow into the basin after the basinbounding fault becomes fully linked strongly depends on the value of L f .We show that such rivers are more likely to maintain their course if they are close to theTL end member (small L f ); as a river becomes progressively more under supplied, i.e. the DL end member (large L f ), it is more likely to be de£ected or dammed by the growing fault.These model results are compared quantitatively with real drainage networks from mainland Greece, the Italian Apennines and eastern California. Finally, we infer the calibre of sediments entering the hanging-wall basin by integrating measurements of erosion rate across the growing footwall with the variation in surface processes in space and time. Combining this information with the observed structural control of sediment entry points into individual hanging-wall depocentres we develop a greater understanding of facies changes associated with the rift-initiation to rift-climax transition previously recognised in syn-rift stratigraphy.

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

“…In contrast, rivers that cut across faults which have moved at a constant rate for the past 3 My appear to have reached topographic steady-state and do not display these transient characteristics (Whittaker et al, 2007b). Because transient landscape responses should theoretically have a substantial impact on the rates and characteristics of sediment export from catchments (section 1.2; Cowie et al, 2006), the Central Apennines is an excellent natural laboratory to study the control of tectonics on sediment production, transport and deposition in normal fault bounded terrains..…”

“…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.…”

“…To make progress in this area, we therefore need to link the growing insight into the geomorphic response of catchments to boundary condition change (e.g. Cowie et al, 2006;Whittaker et al, 2007a) with existing sedimentological data of where and when material is actually deposited in basins (e.g. Horton et al, 2004).…”

Natural experiments in landscape evolution

“…Another approach is to focus on landscape evolution on time scales much longer than a glacial-interglacial cycle. For example, the central Apennines rivers analyzed by Whittaker et al (2007aWhittaker et al ( , 2007bWhittaker et al ( , 2008 and modeled by Attal et al (2008) and Cowie et al (2006Cowie et al ( , 2008 involve transient response extending over about 18 marine oxygen isotope stages. A model calibrated to such a case might therefore be said to represent a weighted average of glacial and interglacial conditions, though understanding the nature of such averaging, and the relative importance of cold versus warm phases, deserves further research.…”

A study of fold characteristics and deformation style using the evolution of the land surface: Zagros Simply Folded Belt, Iran

“…In fact, a complex feedback system operates, which modifies this simple interaction. Elevation changes related to rifting or to folding drive the evolution of the landscape (Cowie et al 2006;Whittaker et al 2007). Drainage systems adapt to changes in the surface slope, recording fold growth and evolution (Jackson et al 1996).…”