The first record of Hirnantian Ostracoda in South America: implications for the biostratigraphy and paleozoogeography of the Paraná basin

Abstract

AbstractHerein is reported the first occurrence of ostracodes from the Iapó Formation, an uppermost Ordovician unit of the Rio Ivaí Group in the Paraná basin, Brazil. Two ostracode species were identified in the Três Barras Farm section:Harpabollia harparum(Troedsson, 1918) andSatiellina paranaensisAdôrno and Salas in Adôrno et al., 2016 were recovered from dropstone-bearing shale overlying glaciogenic diamictites, a feature typical of Hirnantian (uppermost Ordovician) strata throughout Gondwana. The taxonomy of the GenusHarpabollia, as well as its type speciesHarpabollia harparum, was reviewed, and emended and new diagnoses were respectively proposed for each taxon. Occurrences ofHarpabollia harparumandSatiellinaspecies were common in areas influenced by cold waters. Additionally, the occurrence ofHarpabollia harparum, an index species to the uppermost Ordovician of several stratigraphic units in Baltica and southern Gondwana, allowed us to infer a Hirnantian age for the deposits of the Iapó Formation. Other than being associated withHarpabollia harparumin Iapó Formation of the Paraná basin,Satiellina paranaensisis also found in lower levels of the Vila Maria Formation; therefore, these are also considered Hirnantian in age. Above these lower levels of the Vila Maria Formation, a well-dated Rhuddanian (lowermost Llandovery, Silurian) palynomorph assemblage is observed within the formation. These occurrences are evidence of a continuous process of sedimentary deposition during the Ordovician–Silurian transition in the Paraná basin.