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The role of previous rift basin geometry in the postrift and contractional evolution of the Organyà basin and the Bóixols thrust sheet, South-central Pyrenees


The Early Cretaceous extensional period in the Bay of Biscay-Pyrenean domain is well known and has been object of several studies (Berástegui et al., 1990; García-Senz, 2002; Jammes et al., 2009; Carola et al., 2013). The extensional features developed during this period had influenced the subsequent Late Cretaceous contractional Alpine structures of the Pyrenean Orogen (Muñoz, 2002).

The Lower Cretaceous rift system of the Pyrenees show a right-lateral stepped geometry with different basins (García-Senz, 2002). The Organyà basin constitutes one of the most important basins of this rift system, which is located in the Southern Central Pyrenees. The inversion of its W-E southern margin has been related to the development of the Bóixols thrust sheet, the northernmost of the South-Pyrenean thrust sheets (Bond and McClay, 1995; García-Senz, 2002).

Despite this well-known influence, the detailed study here presented revealed the presence of a NNW-SSE trending relay area which corresponds to the western boundary of the Organyà basin (Figure 1). The objective of this study is to understand the role played by this extensional margin into both the postrift facies distribution and the geometry and evolution of the subsequent contractional structures. This work has been carried out by using seismic, well and field data, which have been incorporated into a 3D structural model in order to better understand the 3D geometry of the study area.

The 3D study of the geometry and facies distribution of the different tectonostratigraphic units highlights the presence of this extensional margin, and corroborates its influence in the subsequent stages of the evolution of the area. The main features which lead to these conclusions are: the parallelism between the postrift facies belts and the western boundary of the Organyà basin, the geometry of the contractional structures which shows changes in the structural relief, the plunge and the wavelength across this relay area, and the thickness distribution and onlap geometries of the syntectonic sediments (Figure 1).