EARLY SILURIAN MALVINOKAFFRIC BRACHIOPODS (LA-CHILCA FORMATION), ARGENTINE PRECORDILLERA

A study of brachiopods collected from the La Chilca Formation of the P recordillera mountain belt reveals the presence of ten genera belongin g to the Dalmanellacea, Strophomenacea, Rhynchonellacea and Retziacea. Twelve species are distinguished, of which eight are new although two are not formally established. Because the fine-grained sandstones fro m which the brachiopods were collected are interbedded with or occurs stratigraphically above the Atovograptus atavus graptolite biozone, an Early Llandovery (Rhuddanian) age is indicated. The biogeographical a ffinities between the La Chilca fauna and other Llandoverian malvinoka ffric associations are briefly analyzed.