From salt-detached gravity-driven extension of a rifted margin to its inversion: The Cotiella Massif case study (Southern Pyrenees)

The Cotiella Massif is included in the Cotiella-Bóixols thrust-sheet, one of the three imbricated thrust sheets of the South-Pyrenean thrust system. It originated from the inversion of the Cotiella Basin, a post-rift gravity-driven salt-bearing assemblage of isolated sub-basins. On them, upper Albian to lower Coniacian post-rift carbonate platforms collapsed above Upper Triassic evaporites (Keuper facies), and middle Coniacian to lower Santonian minibasins developed during the margin failure due to salt evacuation and gravity-driven extension. Seismic scale rollovers developed in the hanging wall of basinward-dipping listric faults isolating four sub-basins: Cotiella, Armeña, Peña del Mediodia, and Seira. Additionally, structural and sedimentological evidence suggests passive diapirism at the footwall of these faults. Upon the Pyrenean orogeny, diapirs were rejuvenated, squeezed and welded, faults were positively inverted, and the salt-detached gravity system was incorporated into the orogen.

In this work, we present a detailed geological map of the Cotiella Basin around the Reduno downward-facing anticline which represents the basinward northern edge of the Cotiella sub-basin and its contact with the Armeña sub-basin. Based on this map, more than 1.700 dip data, and comprehensive image interpretations, a stepwise restoration of a representative cross-section has been done to unravel the geological evolution of the basin from the early stages of development to its subsequent contractional deformation. On it, a flap and halokinetic sequences can be identified. Furthermore, a regional and a counter-regional extensional fault system affecting early syn-kinematic strata have been recognized, nowadays highly folded and overturned due to inversion. In addition, the later contractional deformation related to the Pyrenean orogeny has also been inferred, highlighting the role of inherited extensional and salt tectonics structures during the inversion.