Silurian and Middle Devonian Chitinozoa from the Zapla and Santa Barbara Ranges, Tarija Basin, northwestern Argentina

Chitinozoans from Silurian strata in the Tarija Basin were investigated fro m the Zapla and Santa Barbara ranges, Jujuy province, northwestern Argentin a, and from an early Givetian section in the subsurface of Santiago del Est ero Province, northwestern Argentina. The chitinozoan faunas show striking similarities to contemporary assemblages from Bolivia, Paraguay and Brazil. The chitinozoan biozonation proposed for the Lower Silurian (Llandovery-lo wer Wenlock) succession of Parana Basin in Brazil and eastern Paraguay appl ies to the Argentinian faunas as well. The Lower Silurian Zapla Formation y ields a chitinozoan assemblage of Aeronian s.l, to early Telychian age. It corresponds to all or part of the Cancaniri Formation in Bolivia, the Vila Maria Formation in Brazil, and the Vargas Pena Formation in Paraguay. In th e Zapla Range the overlying Lipeon Formation is late Telychian to Sheinwood ian in age, and is coeval with the Cariy Formation of Paraguay and also wit h the lower part of the Cachipunco Formation in the Santa Barbara Range. Th e upper part of the Cachipunco Formation is dated as Ludlow s.l. to early P ridoli, thus it is coeval with the Kirusillas Formation in Bolivia, and is overlain by the Arroyo Colorado Formation (late? Ludlow-earliest Lochkovian ), which could correspond to the Catavi and Tarabuco Formations of Bolivia. A total of 44 chitinozoan species have been recorded, most of which are al so known from contemporary strata in Brazil, Bolivia and Paraguay.