Ichnological aspects of the Aquidauana Formation (Upper Carboniferous, Itarare Group, Brazil): An arthropod-colonized glacial setting

The Late Paleozoic Ice Age (LPIA) in Brazil has an extended sedimentary record, mainly in the Parana Basin. Ichnological records are the main biotic evidence in such an environment, and the Itarare Group (Parana Basin) is important in this regard. However, the Aquidauana Formation, one of the formations in the Itarare Group, is understudied regarding its trace fossil record. Thus, here we present the first ichnotaxonomic characterization of the Aquidauana Formation. We identified ten ichnospecies: Cruziana problematica, Cruziana cf. carbonaria, Diplichnites gouldi, Diplopodichnus biformis, Helmintoidichnites tenuis, cf. Kouphichnium isp., Monomorphichnus lineatus, Rusophycus carbonarius, Umfolozia sinuosa, and Warvichnium ulbrichi. Moreover, we also observed the presence of different morphotypes distributed among two ichnogenera: Monomorphichnus and Warvichnium. We also identified microbially induced sedimentary structures (Arumberia). According to these results, the paleoichnocoenosis of the Aquidauana Formation is characterized by the dominance of activity of small arthropods (probably benthic crustaceans), presenting a low richness of functional morphology. This depauperate ichnocoenosis may reflect environmental stress related to glacial environments and short colonization periods, corroborated by the absence of mixed-layer activity. Compared to other Gondwanic glacial deposits, the Aquidauana Formation is unique to present Warvichnium and Monomorphichnus. This unit also reveals a relationship with freshwater influence, similar to the Mafra Formation fjords in the southern Parana Basin. Thus, the Aquidauana Formation represents invertebrate colonization of submerged glacial freshwater environments in Gondwana, followed by subaerial exposure.