Evolución tectonoestratigráfica de la cuenca Cenozoica de El Bierzo (NO de España)

Abstract

The roman gold mines (Médulas) of the SW border of the El Bierzo basin provide good exposures of its Cenozoic succession. The sedimentological and structural study of these outcrops has allowed determining the role of the major alpine structures in the evolution and infill of the basin. This basin is a portion of the much larger Duero foreland basin and was originated from the Oligocene, during the uplift of the Cantabrian Cordillera (CC) and, later, of the Galician-Leonese Mountains (MGL). Both mountain ranges delivered siliciclastic sediments into the basin, whose basal unit, the Toral Fm, was fed from a distant source area as the uplift of the CC began in the N. Conversely, the overlying Médulas Fm was fed from the growing MGL in the S. Both units consists of coalescent alluvial fans, developed under semiarid conditions. The last deformation stages by thrusts emplacing from S to N led to the fragmentation of the basin, with only parts of its sedimentary record being preserved nowadays. Also, deformation led to the uplifting of the southern fault blocks, where the base of the El Bierzo sucession is found up to 500 m higher than in the central part of the basin.