Time scales of tectonic landscapes and their sediment routing systems

Abstract

In regions undergoing active tectonics, the coupling between the tectonic displacement field, the overlying landscape and the redistribution of mass at the Earth's surface in the form of sediment routing systems, is particularly marked and variable. Coupling between deformation and surface processes takes place at a range of scales, from the whole orogen to individual extensional fault blocks or contractional anticlines. At the large scale, the attainment of a steady-state between the overlying topography and the prevailing tectonic conditions in active contractional orogens requires an efficient erosional system, with a time scale dependent on the vigour of the erosional system, generally in the range 106–107 years. The catchment–fan systems associated with extensional fault blocks and basins of the western USA are valuable natural examples to study the coupling between tectonic deformation, landscape and sediment routing systems. Even relatively simple coupled systems such as an extensional fault block and its associated basin margin fans have a range of time scales in response to a tectonic perturbation. These response times originate from the development of uniform (steady-state) relief during the accumulation of displacement on a normal fault (c. 106 years), the upstream propagation of a bedrock knickpoint in transverse catchments following a change in tectonic uplift rate (c. 106 years), or the relaxation times of the integrated catchment–fan system in response to changes in climatic and tectonic boundary conditions (105–106 years). The presence of extensive bedrock or alluvial piedmonts increases response times significantly. The sediment efflux of a mountain catchment is a boundary condition for far-field fluvial transport, but the fluvial system is much more than a simple transmitter of the sediment supply signal to a neighbouring depocentre. Fluvial systems appear to act as buffers to incoming sediment supply signals, with a diffusive time scale (c. 105–106 years) dependent on the length of the system and the extent of its floodplains, stream channels and proximal gravel fans. The vocabulary for explaining landscapes would benefit from a greater recognition of the importance of the repeat time and magnitude of perturbations in relation to the response and relaxation times of the landscape and its sediment routing systems. Landscapes are best differentiated as ‘buffered’ or ‘reactive’ depending on the ratio of the response time to the repeat time of the perturbation. Furthermore, landscapes may be regarded as ‘steady’ or ‘transient’ depending on the ratio of the response time to the time elapsed since the most recent change in boundary conditions. The response of tectonically and climatically perturbed landscapes has profound implications for the interpretation of stratigraphic architecture.

Climate, tectonics or morphology: what signals can we see in drainage basin sediment yields?

“…Our findings support previous work indicating long lag times from tectonic changes that are "buffered" by the fluvial system (Allen, 2008;Métivier and Gaudemer, 1999), in particular within areas of valley floor and floodplain (Castelltort and Van Den Driessche, 2003;Métivier and Gaudemer, 1999;Simpson and Castelltort, 2012) as found in our expanding catchment settings. It is worth noting that increases in sediment delivery are generated by all uplift and climate scenarios -but as catchment area and valley floor length grow, peaks in sediment were smoothed, or lost within the noise of the autogenic signals.…”

“…One common theme from the above studies and others (Allen, 2008;Humphrey and Heller, 1995;Métivier and Gaudemer, 1999) is that basin response to external forcings is complex and strongly contingent upon the internal basin processing of these forcings. Therefore, there is clearly a need to disentangle the relative impacts of climate, tectonics and autogenics on sediment delivery and how these may manifest themselves in the sedimentary record.…”

Determinants of modelling choices for 1-D free-surface flow and morphodynamics in hydrology and hydraulics: a review

“…1 and 2b, in which the choice of T and that of δT are somehow left at the modeller's discretion, as degrees of freedom: how different from T 0 should T be to allow longenough observation and/or simulation periods? These points are the subject of detailed investigations into the field of morphodynamics (Paola et al, 1992Howard, 1994;Van Heijst et al, 2001;Allen, 2008). Indicators of "system evolution velocities" with units of a velocity but different definitions may for example be found in Sheets et al (2002), who took the channel depth (H ) divided by the average deposition rate to obtain a relevant, characteristic timescale (T ).…”

“…For the same purpose, Wang et al (2011) took the characteristic bed roughness (ε) instead of channel depth. The objective is often to discriminate what Allen (2008) called the "reactive" (high L/T ) and "buffer" (low L/T ) systems. With or without morphodynamic issues, a reasonable hypothesis here seems that the dispersion in L/T ratios arises from the variety of flow contexts, which may necessitate different modelling strategies.…”

Role of sea-level change in deep water deposition along a carbonate shelf margin, Early and Middle Permian, Delaware Basin: implications for reservoir characterization

“…The character of sedimentation in basins is related to the dynamic processes and feedback mechanisms between the external (allogenic) and internal (autogenic) forcings that govern sediment dispersal in depositional systems (Stow et al 1985;Richards et al 1998;Castelltort & Van Den Driessche 2003;Allen 2008;Sømme et al 2009;Bourget et al 2010). Sea level change, one of the external forcings, is an important parameter influencing the stratigraphic succession and resulting sedimentary architecture in deep water depositional systems (Perlmutter & Matthews 1990 Kamberis et al 2005;Steel et al 2008).…”