The Tertiary Ebro basin, located in the Northeastern part of the Iberian Peninsula, is framed by three mountain ranges, the Pyrenees to the North, the Iberian Chain to the South-west, and the Catalonian Coastal Ranges to the South-east. The structural development of those chains controlled the basin evolution in tectonic and structural aspects as well as in the stratigraphic and sedimentologic ones. Nevertheless, the Ebro basin evolved mainly as the southern foreland basin of the Pyrenees, and most of its structural features are related to this tectonic situation. It is neatly asymmetric, with its deepest trough under the Pyrenees (the depth of the Tertiary basin increases northwards, reaching values of 4000 m under the sea level below the Pyrenees). The Tertiary stratigraphic units also increase their thickness northwards. Continent-continent collision resulted in the subduction of the lower crust and lithospheric mantle of the Iberian plate below the European one. Thus, the tectonic load of alochtonous units and the formation of a cold lithospheric root during the pyreneean shortening induced the deflection of the Ebro basin, a flexure which created that deep elongated trough, as shown in the ECORS profile.
However, the Ebro basin is also an intraplate basin within the Iberian plate, and was affected by the tectonic evolution of the NE Iberian peninsula during the Neogene age. Of special interest for us will be the tectonic stress conditions created during the Africa-Iberia-Europe convergence, once the collision was locked at the Pyrenees.
The studied area is located in the central part of the Ebro basin. Most rocks exposed within the basin are of Oligocene-Miocene age (including clastic, evaporite, and carbonate facies) of a fluvial and lacustrine origin. They were sedimented during an endorheic period of the evolution of the basin. The beds are almost flat-lying except where there has been local thrusting in the basin margins, or there has been the buoyant rise of evaporites in Quaternary diapirism. The main macrostructural feature is the Logroño-Sástago sincline, a wide NW-SE trending fold of gentle dipping (up to 4-6°).
Our studies in the Ebro basin focused on its Neogene palaeostress evolution. Palaeostress analysis (performed from the analysis of jointing and faulting) shows an evolution of a N-S compressional stress field to a E-W coaxial extension. Also, the application of remote sensing techniques to this area lead to a detailed mapping of actual lineaments. Other topic studied was the stress perturbation patterns caused by macro and mesofractures, as evidenced by fracture (namely joints) patterns. All these studies can be found in the Arlegui's PhD dissertation and papers.
SIMÓN, J.L., 1989: Late Cenozoic stress field and fracturing in the Iberian Chain and Ebro Basin (Spain). Journal of Structural Geology, 11(3): 285-294.
SORIANO, M. A. 1990: Geomorfología del sector centromeridional de la Depresión del Ebro. Institución Fernando el Católico, publicación 1231.
ARLEGUI, L.E., and SIMÓN, J.L., 1993: El sistema de diaclasas N-S del sector central de la Cuenca del Ebro. Relación con el campo de esfuerzos. Revista de la Sociedad Geológica de España, 6(1-2): 115-123.
ARLEGUI, L.E.; SORIANO, A. and SIMÓN, J.L., 1994: Un sistema regional de fracturas NW-SE en el Centro de la Cuenca del Ebro: Com. 2¼ Cong. GET, 39-43.
ARLEGUI, L.E.; SIMÓN, J.L., and SORIANO, M.A., 1997: Estructuración neógena del sector central de la Cuenca del Ebro. In Calvo, J.P. and Morales, J. (Eds.) Avances en el conocimiento del Terciario Ibérico. Museo Nacional de Ciencias Naturales. Madrid, pp: 33-36.
ARLEGUI, L.E., and SIMÓN, J.L., 1997: El sistema de fallas normales de las Bárdenas (Navarra) en el marco del campo de esfuerzos neógeno. En Calvo, J.P. y Morales, J. (Eds.) Avances en el conocimiento del Terciario Ibérico. Museo Nacional de Ciencias Naturales. Madrid, pp: 29-33.
ARLEGUI, L.E., and SORIANO, M.A., 1998, in press: Characterising lineaments from satellite images and field studies in the central Ebro basin (NE Spain). International Journal of Remote Sensing,
