Hallazgo de un fósil silúrico en los depósitos auríferos cenozoicos de la mina romana de Las Médulas (León, NO de España)

Abstract

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