Descripción y génesis de los bancos de oolitas ferruginosas en la base del Silúrico de la precordillera Argentina

Abstract

Detailed outcrop and microscopic descriptions and current ideas about factors controlling the origin of oolitic ironstones coming from the Lower Silurian of the western Argentina Precordillera Basin are given. Chamosite and goethite comprise around 20 to 98 % of the oolitic ironstones. Phosphatic nodules are common components in these deposits. Lithofacies arrangement, outcrop architecture and bioturbation patterns allow to interpret them as shallow marine bars, which typically constitute parasequences boundaries. They are associated with widespread detrital facies. Their origin is related to sea-level fluctuations and a good correlation with global events can be established. The origin and distribution of the ironstones in the Precordillera basin is related with cool-water seas in high southern latitudes, during a high stand of sea-level, occurring after the Late Ordovician glacial event.