BRACHIOPODS AND BIOSTRATIGRAPHY OF THE LOS-ESPEJOS FORMATION, SILURO-DEVONIAN OF THE PRECORDILLERA (NW ARGENTINA)

The detailed biostratigraphic analysis of five sections in the Los Espejos Formation in the San Juan Precordillera (NW Argentina) brings a substantial complement to the Silurian faunal list in this region. The study of brachiopods allows one to recognize four faunal assemblages and to establish correlations between the sections. For the first time, the presence of Wenlock, Ludlow and Pridoli strata appears most probable, while the top of the Los Espejos Formation, with the fourth faunal assemblage, is assigned to the Lower Lochkovian. The Silurian-Devonian boundary is tentatively placed for the first time near the top of the formation. Eleven new species are described : Orthostrophia meridionalis nov. sp., Isorthis (Protocortezorthis) cuyanum nov. sp., I. (Tyersella) megamyaria nov. sp., Molongella keideli nov. sp., Dedzetina ? silurica nov. sp., Salopina sanjuanensis nov. sp., L. (Leangella) mutabilis nov. sp., P. (Plectodonta) minima nov. sp., Amosina paolae nov. sp., A. pediculorum nov. sp. and Australocoelia intermedia nov. sp.; Chonetes fuertensis is revised, and three other forms are provisionally left in open nomenclature.