The Madrid Basin and the Central System: A tectonostratigraphic analysis from 2D seismic lines

Data from deep boreholes, seismic surveys, and surface geology are used to reconstruct the sedimentary infilling of the Cenozoic Madrid Basin. Eight main depositional sequences and seismic units are recognised. From the Paleogene, the latter four of these sedimentary sequences were deposited in a continental environment, under the influence of tectonic activity in the Central System, the Toledo Mountains, the Iberian Chain, and the Sierra de Altomira. The sedimentary infill shows an overall coarsening-upward trend from upper Cretaceous formations to syn-tectonic conglomerate deposits, followed by a fining-upward sequence and moderate reactivation of some faults during the late Miocene–Pliocene. The syn-tectonic sediments are Oligocene–early Miocene in age. The foredeep is oriented northeast–southwest and shows a sediment thickness of up to 3800 m in areas close to the Central System. Several types of tectonic structures are recognised, including imbricate thrust systems, thrust triangle zones, fault-propagation folds, back-thrust systems, and pop-up structures. The frontal thrusts were subjected to significant erosion, and late Miocene sediments onlap the anticlines of the onshore foreland. NW–SE-trending positive flower structures have been recognised in the eastern part of the basin. The total northwest–southeast shortening across the contact between the Madrid Basin and the Central System is approximately 5 km, of which 2–3 km occurred across the Southern Border Thrust. The simultaneous basement uplift of the Central System and the tectonic escape of the Sierra de Altomira have been interpreted as a consequence of constrictive deformation within the “Pyrenean” foreland of the Iberian microplate