Silurian and lower devonian chitinozoan biostratigraphy of the paraná basin in brazil and Paraguay

Abstract

The taxonomy and distribution of Chitinozoa from Silurian (Llandovery) and Lower Devonian strata are reported from the Paraná Basin in southern Brazil and eastern Paraguay. The pre‐Carboniferous sequences of the Paraná Basin in this area are present in three sub‐basins viz., the Alto Garças (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in east Paraguay. There is more similarity in the lithology between the Alto Garças and “East Paraguay”; sub‐basins, than between the former and the Apucarana sub‐basin. Llandoverian and Lochkovian to Pragian beds are present in all sub‐basins. So far, no Emsian beds have been found in outcrops from the north‐northwest margin of the Alto Garças Sub‐basin, and no early Emsian beds in the outcrops on the northeast margin. Furthermore, Emsian beds could not be identified from the “East Paraguay Sub‐basin”; in the present study. The Early Devonian sequence is more complete in the Apucarana Sub‐basin. It seems that the Apucarana Sub‐basin endured a different evolution compared to the two other sub‐basins during the Ordovician, Silurian and lower Devonian. Of the 39 chitinozoan species encountered, 24 species are left in open nomenclature, and the following five species are newly described: Ancyrochitina paranaensis, Angochitina daemoni, Sphaerochitina silurica, Spinachitina harringtoni, and Spinachitina wolfarti. A chitinozoan biozonation, with five zones and three subzones, is proposed for the investigated interval, and compared with the spore zonation. In addition we infer that the Furnas Formation could correspond to two chitinozoan zones found in Bolivia and Argentina (zones of Urochitina loboi and Angochitina aff. A. comosa), ranging in age from late Lochkovian to earliest Pragian. The zones are, from oldest to youngest: total range zone of Belonechitina postrobusta (upper Rhuddanian); total range zone of Conochitina elongate (Aeronian); concurrent range subzone of Spinachitina wolfarti n. sp. and Plectochitina sp. A (lower Aeronian); concurrent range subzone of Conochitina proboscifera and Spinachitina harringtoni n. sp. (upper Aeronian s.l.); concurrent range subzone of Conochitina proboscifera and Desmochitina cf. D. densa (lower Telychian s.l.); concurrent range zone of Salopochitina monterrosae and Conochitina proboscifera (upper Telychian‐lower Sheinwoodian); total range zone of Urochitina loboi (upper Lochkovian); total range zone of Angochitina aff. A. comosa (lowermost Pragian); total range zone of Ramochitina magnifica (Pragian s.l.), and total range zone of Ancyrochitina parisi (upper Emsian).