Upper Carboniferous - Lower Permian fishes and conodonts from Peru: biofacies and stratigraphy of the Madre de Dios Basin

The Late Palaeozoic Ice Age (LPIA) is characterized by glacioeustatic transgressive–regressive cycles, whose signatures are commonly recorded in stratigraphic sequences and associated environmental parameters. Although these glacioeustatic cycles have been documented in Late Carboniferous–Early Permian successions from the Amazonian basins of Brazil, equivalent deposits remain poorly known in the Andean region. This region, particularly Bolivia and Peru, preserves extensive carbonate outcrops from this interval that provide valuable insights into paleoenvironments and faunal assemblages. The Copacabana Formation is composed by warm-water carbonates, evaporites, and open-marine facies. Its broad distribution and cyclicity reflect pronounced climatic and eustatic fluctuations during the LPIA. Studies carry on Puerto Arturo section (Puno, Peru) have revealed abundant early chondrichthyans remains, including Protacrodus, Denaea, Stethacanthus, and Cooleyella amazonensis—preserved as teeth and scales. The relative abundance of these taxa suggests shallow-water conditions (Protacrodus biofacies). In addition, a diverse conodont assemblage, including Idiognathodus, Streptognathodus, Sweetognathodus, and Gondolella, has also been identified. Conodont biostratigraphy and biofacies distributions, based on taxonomic composition and relative abundance per bed, indicate mid-ramp environments characterized by Idiognathodus–Streptognathodus biofacies and outer-ramp settings dominated by Gondolella biofacies. This integrated approach combining sequence-stratigraphic, microfacies, and paleontological analyses provides the first robust paleoenvironmental reconstruction for this interval in Peru, significantly improving regional correlations and revealing new aspects of Palaeozoic diversity in western Gondwana.

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