Neogene strike-slip faulting in southeastern Spain: the deformation of the pull-apart basin of Abaran

Abstract

The Abarán Basin is interpreted as a Neogene pull-apart basin that developed along an east-striking right-slip fault zone in the thin-skinned fold-and-thrust belt of the Betic foreland (External Zone). Apart from showing well known strike-slip characteristics, the fault zone is typified by drag and imbrication along subvertical faults. Considerable right-slip faulting before, during and after basin development is demonstrated by the unconformable contact between the basin and its faulted 'basement', by the formation and deformation of the basin, and by the lateral separation between basin and hinterland. The Abarán Basin shows a typical rhombic shape determined by synsedimentary faults. The fault configuration is interpreted as a releasing overstep: the northern and southern basin margin were controlled by two major right-hand stepping, east-striking right-slip faults connected by minor northwest-striking normaloblique slip faults bounding the basin in the east and the west. The progressive opening of the basin in response to the right-slip along the fault zone, generated lateral shear and extension parallel to the strike-slip basin margins throughout the sedimentation history. Right-slip led to en-echelon folds and progressive drag. Extension resulted in an overall deepening of the basin and activated normal faults. Due to movements along normal faults dipping away from the basin centre, older sediments were torn apart while being tilted. The resulting depression in the centre of the basin was subsequently filled by younger sediments that accumulated next to older deposits. Repetition of this mechanism with basinward fault progradation, generated downlapping sediment packages that step over normal faults.