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

Abstract

Chitinozoans from Silurian strata in the Tarija Basin were investigated from the Zapla and Santa Bárbara ranges, Jujuy province, northwestern Argentina, and from an early Givetian section in the subsurface of Santiago del Estero 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-lower Wenlock) succession of Paraná Basin in Brazil and eastern Paraguay applies to the Argentinian faunas as well. The Lower Silurian Zapla Formation yields a chitinozoan assemblage of Aeronian s.l. to early Telychian age. It corresponds to all or part of the Cancañiri Formation in Bolivia, the Vila Maria Formation in Brazil, and the Vargas Peña Formation in Paraguay. In the Zapla Range the overlying Lipeón Formation is late Telychian to Sheinwoodian in age, and is coeval with the Cariy Formation of Paraguay and also with the lower part of the Cachipunco Formation in the Santa Bárbara Range. The upper part of the Cachipunco Formation is dated as Ludlow s.l. to early Pridoli, 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 also known from contemporary strata in Brazil, Bolivia and Paraguay.