Analysis of the relation between tectonics, erosion and topographic evolution over a long time scale in the Ardennes Massif.

Description

Relief and landscape formation have been a matter of debate in geosciences. One important hypothesis that was put forward in this research field is the dynamic equilibrium that might exist between three factors that control relief formation: the tectonic activity of a region (vertical movements), erosion and depositional processes, and the climate and its evolution. 

Relief = Tectonic + Erosion + Climate

Since the beginning of the twentieth century, various research projects have started to look at the relations between those factors at regional or local scale. Different conceptual models have been created in the past, but the development of numerical methods (GIS¹, digital models, databases) in the '80s has strongly stimulated this research field.

Most often, the relation between tectonics, erosion and relief was studied in active mountain regions with steep topography (i.e.: Andes, Himalaya, Alps, etc.), and various authors have analysed the interactions between erosion and tectonic activity (Whipple and Tucker, 2002; von Blanckenburg et al., 2004); morphometry and tectonic activity (Burbank, 2005; Whittacker et al., 2007); and erosion and morphometry (Norton et al, 2008; Whipple, 2004; Tibaldi and Leon, 2000). But in general, there is a clear lack of information on regions of moderate to low relief (Tebbens, 2000; Demoulin, 1998; Lague et al. 2000)

The scientific question that this research project will tackle is the following :

"Are hillslope and channel morphology of the Ardennes Massif indicators of the transient response of the area to slow tectonic uplift" 

We focus on the Ardennes Massif for the following reasons:

1. Ancient mountain chain with well-documented geology and information on neotectonic evolution
2. Differential uplift since late Oligocene (23MY), see Figure 1 below for illustration.
3. Rather homogeneous climatic evolution during the Quaternary (as the studied area is relatively small, the spatial differences in climate can be neglected) 

Figure 1 : Map of the selected catchments in the lower Meuse watershed. Inset map locates the Ardennes Massif

in the western part of the Rhenish Shield (dark grey). Numbers refers to the post YMT uplift (meters). 

This work is therefore based on three main hypotheses we will test:

1. Increased tectonic activity can be inferred from the morphometry of the present landscape.
2. Morphological indices of river channels and slopes can be used to infer long-term erosion processes
3. The present morphology is the result of the balance between erosion and tectonic activity.

Figure 2 : Threefold analysis between Tectonic Activity, Erosion and Morphometry.

In order to quantify the long term erosion rates, we are using in-situ produced cosmogenic nuclides. Cosmogenic nuclides are nuclides that are formed by the interaction of a specific atom with cosmic radiation. The accumulation of nuclides in rock fragments at the earth surface provides the basis for exposure 'dating' of landforms, and the quantification of long-term erosion rates (Bierman, 1994; Gosse and Phillips, 2001).

In other words, the higher the concentration of cosmogenic nuclides that we measure in rock fragments or soil material, the longer the material has been close to the earth surface and the lower the rate of erosion of that particular surface. 

In the laboratory, we separate Be from river and soil samples, and prepare material for ¹⁰Be analysis. ¹⁰Be has a half life of 1,500,000 years, which is almost 250x the half life of ¹⁴C, and permits more longer term analysis.

Figure 3 : Relation between the ¹⁰Be concentration and the exposure time / derived erosion rates (R. Braucher, 1998)

Figure 4 : The belgian Ardennes landscape (respectively the Bocq, the Lesse and the Semois rivers).

This project is funded by an FSR grant of the UCL.   

¹ GIS : Geographical Information System : computer program that presents, manages, stores and analyzes data based on their spatial location. GIS is the merging of cartography, statistical analysis, and database technology.

Contacts

• Sougnez Nicolas
• Vanacker Veerle

References

Bierman, P.R. (1994), Using in-situ produced cosmogenic isotopes to estimate rates of landscape evolution: a review from the geomorphic perspective, J. Geophys. Res. 99, pp. 13885–13896.

Braucher, R. (1998), Utilisation du ¹⁰Be cosmogénique produit In-Situ pour l'étude de la dynamique des latérites en zone intertropicale. PhD thesis presented the 8 june 1998 at Université d'Aix Marseille III. 

Burbank, D. W. (2005), Cracking the Himalaya, Nature, 434, 963– 964.

Demoulin, A. (1998), Testing the tectonic significance of some parameters of longitudinal river profiles: the case of the Ardenne (Belgium, NW Europe), Geomorphology 24, pp. 189–208.

Demoulin, A., and Hallot, E. (2009). Shape and amount of quaternary uplift of the Western Rhenish shield and the Ardennes. Tectonophysics 474, 696-708. 

Gosse, J.C., Phillips, F.M. (2001), Terrestrial cosmogenic nuclides: theory and applications, Quat. Sci. Rev. 20.

Lague, D., Davy, P., and Crave, A. (2000) Estimating uplift rate and erodability from the area–slope relationship: examples from Brittany (France) and numerical modelling, Physics and Chemistry of the Earth 25A (2000), pp. 543–548.

Norton KP, von Blanckenburg F, Schlunegger F, Schwab M, Kubik PW. (2008), Cosmogenic nuclide-based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the Swiss Alps. Geomorphology  95: 474–486. DOI. 10.1016/j. geomorph.2007.07.013

Tebbens, L.A, Veldkamp,A., Van Dijke, J.J.  and Schoorl, J.M. (2000), Modeling longitudinal-profile development in response to late Quaternary tectonics, climate and sea-level changes; the River Meuse, Global and Planetary Change 27, pp. 187–206.

Tibaldi, A., and J. R. Leon (2000), Morphometry of late Pleistocene-Holocene faulting and volcanotectonic relationship in the southern Andes of Colombia, Tectonics, 19(2), 358–377, doi:10.1029/1999TC900063.

von Blanckenburg, F., T. Hewawasam, and P. W. Kubik (2004), Cosmogenic nuclide evidence for low weathering and denudation in the wet, tropical highlands of Sri Lanka, J. Geophys. Res., 109, F03008, doi:10.1029/2003JF000049.

Whipple, K. X. (2004), Bedrock rivers and the geomorphology of active orogens, Ann. Rev. Earth Planet. Sci., 32, 151-185

Whipple, K. X., and G. E. Tucker (2002), Implications of sediment-flux-dependent river incision models for landscape evolution, J. Geophys. Res., 107(B2), 2039, doi:10.1029/2000JB000044.

Whittaker, A.C., Cowie, P.A., Attal, M., Tucker, G.E. and Robert, G.P. (2007), Bedrock channel adjustment to tectonic forcing: implications for predicting river incision rates. Geology 35, 103–106.