The Betic External Zone, classically divided into the Prebetic and Subbetic Zones, forms a 100 km scale fold-and-thrust belt in the northern periphery of the Betic-Rif arc, the western end of the Alpine belt of southern Europe. Thrusting and folding in the Betic External Zone initiated in the latest Oligocene to early Miocene, and has continued to the present. This study addresses an almost complete stratigraphic record from the early to the late Miocene preserved in three narrow, elongate basin fragments in the western part of the Prebetic Zone around Pontones and Santiago de la Espada. The Miocene basin fill is folded and disrupted by thrusts but, noticeably, also by extensional normal faults. Previous and new biostratigraphic data are used to establish an updated stratigraphic correlation of the different basin fragments, whilst the sedimentary facies are used in combination with paleobathymetry estimates to asses first-order vertical motions. Our stratigraphic and structural study indicates that prior to late Miocene thrusting in the Prebetics, the three basin fragments formed part of a large marine basin in the early-middle Miocene which made up the northern Atlantic-Mediterranean connection commonly known as the North Betic Strait. Paleobathymetry on the basis of single samples suggests an abrupt subsidence of this basin of several hundreds of meters during the middle Miocene, presumably in response to progressive loading of the Iberian plate by the emplacement of the Subbetic and Betic Internal Zones. Subsequent shallowing of the basin in the late Miocene was immediately followed by the onset of folding and thrusting in the western Prebetics. The development of outcrop and map-scale extensional structures is interpreted as being inherent to the process of thrusting and reverse faulting. Some of the reverse faults probably initiated as Mesozoic extensional faults, and were reactivated as reverse faults through late Miocene thrusting. We suggest that during fault propagation upwards, the reverse faults became progressively less inclined, which inevitably led to extension in the hanging wall and consequent development of normal faults. This implies that irrespective of the extensional nature of some of the faults, the Miocene basins in the Prebetics in essence developed in a compressive setting, eventually leading to segmentation of the large basin into smaller basins and closure of the northern Atlantic-Mediterranean connection.
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