Ordovician and Silurian graptolite assemblages from Cerro del Fuerte, San Juan Province, Argentina

A description is given of three transects through the Silurian strata of Cerro del Fuerte, San Juan Province, Argentina. All are in the Precordillera structural belt; the Silurian strata probably have conformable boundaries with the Ordovician and Devonian, and there is a regional angular unconformity at the base of the Carboniferous. The Silurian includes two formations, the La Chilca below and the Los Espejos above. Both formations exhibit a coarsening upwards sequence: the Los Espejos Formation spans the Wenlock, Ludlow and, probably, Pridoli epochs, the first being of relatively fine sediments and the latter two of coarser sediments. The third transect also includes Devonian sediments which seem to represent, albeit incompletely, a third coarsening upwards cycle. The graptolite faunas have been extensively collected and form the basis of the systematic section of the paper. Late Ordovician, Llandovery and Ludlow faunas are described.