Paleoenvironmental insights from a middle Pennsylvanian trace-fossil assemblage during the late Paleozoic ice age in southern Brazil

Abstract

Trace fossils play a fundamental role as biotic records in glacial deposits associated with the Late Paleozoic Ice Age, especially in the upper units of the Itararé Group in the Paraná Basin, where they are widely described and studied. The absence of ichnological studies for the lower interval of the Itararé Group, represented by the Campo do Tenente Formation, creates a significant gap in understanding the interaction between organisms and glacial environment during the middle Pennsylvanian period in the Paraná Basin. Addressing this gap provides new insights into adaptive strategies and paleoecological aspects related to extreme climatic events. Through macro and microscopic descriptions, we documented for the first time the occurrence of eight ichnotaxa in a siltstone interval of the Campo do Tenente Formation: Dimorphicnus isp., Diplichnites gouldi, Helminthoidichnites tenuis, Hormosiroidea meandrica, Irichnus saltatorius, Merostomichnites narragansettensis, Monomorphicnus lineatus, and Umfolozia sinuosa. This trace fossil association, dominated by arthropod trackways and burrows of wormlike organisms, indicates the coexistence of the Mermia and Scoyenia ichnofacies. Combined with the sedimentological data, these results reflect marginal continental conditions of shallow and restricted environments, with occasional input of glacial freshwater. These contributions not only provide new insights into the understudied ichnological content of this interval of the Itararé Group but also offer important paleoenvironmental and paleoecological perspectives on the middle Pennsylvanian during the most significant glaciation of the Phanerozoic.