Gravity anomalies and orthogonal box fold development on heterogeneous basement in the Neogene Ronda Depression (Western Betic Cordillera)

Abstract

28 páginas, 6 figuras.-- PDF es el manucristo aceptado del autor (post-print).The Ronda Depression constitutes a Neogene intramontane basin located in the external zones of the Western Betic Cordillera. Major deformation structures affect only the southwestern part of its sedimentary infill and consist of NNE–SSW and WNW–ESE box folds that developed simultaneously. New gravity data reveal two negative NNE–SSW elongated Bouguer anomalies, unrelated to basin depocenters, but corresponding to the accumulation of low-density ductile Triassic basement rocks in the core of antiforms or directly under the northwestern undeformed sedimentary infill. The Subbetic basement is also deformed by early-Burdigalian to Serravallian NNE–SSW folds and thrusts, although there is no clear continuity with those affecting the late-Miocene sedimentary infill. The aim of this contribution is to describe in detail the late-Miocene folds that deform the Ronda Depression, as well as to discuss the role of the basement nature on their reactivation. The reactivation of the pre-Tortonian folds, due to the heterogeneous distribution of evaporitic Triassic rocks in the basement as well as the presence of rigid limestones on the southwestern basin boundary, determined the simultaneous orthogonal fold development that only evidence local deformation.This study was supported by a PhD grant to the first author from Spain´s Ministerio de Educación y Ciencia and the projects CSD2006-00041 and CGL 2006-06001 (MEC) and Junta de Andalucía.Peer reviewe