Drainage evolution of the Ebro Basin (southern Pyrenees, NE Spain).
Interplay between tectonics, climate, and fluvial transport during the Cenozoic evolution of the Ebro Basin (NE Iberia)

location map.                See more information in this publication.

  The Ebro foreland basin (NE Iberia) initiated during the Palaeocene as a result of the tectonic collision and subduction of the Iberian plate underneath the European plate. The basin became landlocked in late Eocene by the Pyrenees, the Catalan Coastal Ranges (CCR) and the Iberian Range, and was subsequently filled with alluvial, fluvial and lacustrine sediments. During the Miocene, the Catalan Coastal Ranges underwent a tectonic extension that opened the Western Mediterranean. Although the topographic barrier constituted by the CCR was significantly reduced, the Ebro Basin remained closed at least until late Miocene times, when the endorheic fluvial system opened through the present Ebro River to the Mediterranean initiating the formation of the delta.

  The causes for this major drainage changes are not well understood. Although tectonic deformation is often invoked to explain changes in drainage patterns, there is no evidence for tectonism coeval in space and time with the breakthrough of the Ebro River across the CCR. Oscillations of the sea level have been argued as a triggeriing mechanism, but regional isostatic behaviour of the lithosphere cannot be dismissed, since it controls the vertical movements during both crustal compression and extension. The role of basin overfilling with sediments and the changes in the hydrological balance precipitation/evaporation (both controling the water level in the closed basin) are equally relevant for the overburdening of the basin. In this work, we link quantitative approaches to these processes in a 3D numerical model of drainage evolution constrained by well logs, geological cross sections and fission track data.
 
The results suggest that the capture of the endorheic drainage was driven by sediment overfilling of the basin and the erosion of up to 2-3 km at the Catalan Coastal Ranges rift flank, which flexural uplift significantly delayed the drainage opening.

Model evolution: 

The models shown here and in the publications are the result of developing and using the software TISC to quantitatively relate lithospheric, crustal and surface processes. The numerical model links quantitatively the drainage evolution with the tectonic evolution, using as a constraint the erosion deduced from isotopic composition and the sediment accumulation dferived from seismic and borehole surveys.
The figure below shows a top view of the calculated drainage network and topography (top left), sediment thickness distribution (top right), and cross section as predicted by the computer simulation. Areas dotted in dark blue are lakes. Time is indicated on the top left corner. The horizontal movement of tectonic blocks is contrained from structural geology studies of the three mountain ranges sorrounding the basin.

Note that the opening of the closed lacustrine basin is predicted at 10 Myr before present, approximately coinciding with the youngest lacustrine sediments found in the basin.

Evolution of the sediment volume within the basin (plain line, left panel) and the sedimentation/erosion rate at the whole Ebro Basin domain (plain line right panel), as calculated with the model.

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