Brachiopoda: Spiriferida como parâmetro paleoambiental do Devoniano da Bacia do Paraná (estudo de caso)

Abstract

The Spiriferida are Rhynchonelliformea brachiopods characterized by having medium to large, strophic, biconvex, ribbed shells that have a spiral brachidium, the latter being a characteristic that distinguishes them from other brachiopods. Therefore, the main objective of this work was to elucidate the distribution of the representatives of the order Spiriferida in the Devonian deposits of the Ponta Grossa Formation in the Paraná Basin. Thus, characterizing their taxonomy, ecological attributes, stratigraphic position and stratigraphic distribution in the regional sequence framework. 423 samples containing the biological group of interest were processed, this material coming from the Bosque Mistral Paleontological Salvage Technical Project. However, the laboratory work involved curating the fossil material, ensuring its integrity, documentation, accurate taxonomic identification based on the rules of zoological nomenclature and quantitative parameters, as well as descriptions of sedimentary and taphonomic features present in the material. The taxonomic analysis identified three species of the Australospirifer genus: Australospirifer antarcticus, A. iheringi and A. kayserianus. The taphonomic analyses indicated three modes of occurrence for the Spiriferida of the Ponta Grossa Formation (taphonomic class I: random orientation; taphonomic class II: unidirectional flow and taphonomic class III: grouped in a “cluster”, these taphonomic classes can be associated with two distinct taphofacies, characterizing environments ranging from the lower shoreface to the offshore. The paleobathymetric distribution of the specimens analyzed showed that the Spiriferida present in the Devonian of the Paraná Basin can be considered good paleobathymetric indicators and are associated with the end of transgressive cycles.