Tridimensional ostracoda assemblage from Vila Maria Formation, Ordovician/Silurian, Paraná Basin Brazil

REILY, LIVIO; ADÔRNO, RODRIGO RODRIGUES; DO CARMO, DERMEVAL APARECIDO; SALAS, MARIA JOSE; SILVIA RODRIGUEZ L.; MATHEUS DENEZINE; ZABINI, CAROLINA

Río de Janeiro

Congreso; 49º Congreso Brasilero de Geología; 2018

The Rio Ivaí Group is attributed to the Upper Ordovician / Silurian interval, composed of threeformations: Alto Garças, Iapó and Vila Maria. The Vila Maria Formation is composed of blackshales at its base and sandstone at its top. The black shales have the most important fossilrecord of the Lower Paleozoic of the Paraná Basin. Little attention was given to the stratigraphicdistribution, as well as the correlation studies of the fossil record on this formation so far.Satiellina paranaensis Adorno & Salas, 2016 and Conchoprimitia brasiliensis Adorno & Salas,2016, are ostracod species that occurr at the parastratotype section of the Vila Maria Formation,in the village stream, Bom Jardim de Goiás, State of Goiás, Central Brazil. These two speciesbelong to genera that are restricted to the Ordovician, in all of the Gondwana basins (Africa,Europe and the Middle East). The present work record occurrences of four ostracod specimensin three additional species: HapabolliaH. harparum, Gen. 1 et sp. 1 and Gen. 2 et sp. 2. Thesenew occurrences were recovered from Vila Maria Formation at Fazenda Três Barras, BomJardim de Goiás, 7 km distant from the parastratotype section of the Vila Maria Formation.Carapaces of this ostracod assemblage are all replaced by pyrite. Carapaces are complete,with both valves articulated and closed. They are well preserved, but some specimens showpartial dissolution and deformation. In addition to these ostracods assemblages, it was possibleto recover brachiopods, molluscs, palynomorphs, pyritized coprolites and other fossils. As finalremarks, it is observed an increment of biodiversity among ostracod species recovered fromVila Maria Formation. Thisindicate that the outcrops at Fazenda Três Barras are very importantfor paleontological and geochronological studies. Mizusaki et al. (2002), related this section toEarly Silurian. Nonetheless, when considering previous data on ostracods (Adôrno et al., 2016),Satiellina paranaensis and Conchoprimitia, both suggest a late Ordovician age. The preliminarytaxonomic study herein presented is under development and could bring new data to evaluatethe biodiversity and dating of the Vila Maria Formation. New data can clarify the possibility ofthis section yield the Ordovician/Silurian limits in South America.