A Silurian fossil has been collected from sandstone pebbles in the red Cenozoic deposits of the famous
Roman gold-mine of Las Médulas. It consists on an articulated shell of the cardiolid bivalve Cardiola
gibbosa Barrande, of basal Gorstian age (Ludlow). This species is considered as an exotic element to the
neighboring Paleozoic outcrops, being most probably reworked from an unknown area souther of the
Ollo de Sapo anticlinorium. This hypothesis agrees with the recent geological reinterpretation of the goldbearing
units as a system of Paleogene fluvial terraces. The fossiliferous pebble is attributed to the third
terrace scoured by an ancient river flowing to the NE, being progressively entrenched during the initial
stages of the Alpine convergence which ends with the formation of the compressive El Bierzo Cenozoic
basin