Dr. Martin Stange
Project: Climatic versus tectonic drivers of intense catchment erosion in the southern Pyrenees, fincanced by Bremen TRAC,
Martin Stange (in cooperation with J. Kuss & C. Spiegel)
This study investigates the coupling of earth surface processes, climate, and tectonics, particularly focussing on fluvial incision and sediment routing in the river systems of the Pyrenees. Extensive terrace staircases in the foreland domains formed in the deeply entrenched valleys of the transverse river network of the Pyrenees. The paired (bilateral) terrace staircases in the southern Pyrenees foreland (i.e. Ebro basin) show striking similarities between the major southern Pyrenean tributary rivers as to the number and elevation of individual terrace levels and the inferred long-term (Quaternary) incision magnitudes. The amplitudes of valley entrenchment are consistent in northern Pyrenean rivers but valley cross-sections disclose asymmetric staircase geometries and non-uniform terrace extent and preservation. Aiming at unravelling the drivers of fluvial valley entrenchment and terrace staircase formation in the Pyrenees two major river systems have been investigated (i) the prominent Segre River in the southeastern Pyrenees and (ii) the Garonne River which drains large parts of the central northern Pyrenees. Terrace staircases are composed of successions of abandoned river floodplains separated by incision scarps that result from alternating periods of extensive floodplain aggradation during cold-climate periods and phases of vertical and lateral erosion associated with climatic transitions (e.g., Vandenberghe, 2001, 2008). Such climate-triggered terrace formation is superimposed on a long-term incision trend by a river that is stream-power controlled and determined by the base level position of the fluvial network (e.g., Whipple and Tucker, 1999; Blum and Törnqvist, 2000). Long-term river incision is commonly a response to base level lowering or catchment scale uplift (Merritts et al., 1994; Maddy et al., 2001) and, hence, can only be evaluated considering the specific climatic, tectonic and base level setting of a drainage network. At first, numerous sediment outcrops were investigated for (post)depositional structures and deformations. Major terrace levels were sampled for exposure dating via 10Be cosmogenic nuclides. Field-based geomorphological mapping was combined with GIS-based DEM and stream profile analyses. In a second step, results were integrated in a numerical landscape evolution model (TISC; Garcia- Castellanos et al., 2003) that was used to assess the relative impacts of Quaternary climate change, tectonic uplift, lithospheric flexural isostasy, and differential bedrock erodibility on stream (terrace) profile development in the southern Pyrenean drainage system.