Ichnology of the latest Carboniferous–earliest Permian transgression in the Paganzo Basin of western Argentina: The interplay of ecology, sea-level rise, and paleogeography during postglacial times in Gondwana
Patricio R. Desjardins, Luis A. Buatois, M. Gabriela Mángano, Carlos O. Limarino, 2010. "Ichnology of the latest Carboniferous–earliest Permian transgression in the Paganzo Basin of western Argentina: The interplay of ecology, sea-level rise, and paleogeography during postglacial times in Gondwana", Late Paleozoic Glacial Events and Postglacial Transgressions in Gondwana, Oscar R. López-Gamundí, Luis A. Buatois
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The late Paleozoic climatic evolution of Gondwana can be traced by analyzing the benthic ecology of its coastal environments as revealed by their ichnologic content. Latest Carboniferous–earliest Permian transgressive deposits occur in the lower member of the Tupe Formation, Paganzo Group, western Argentina. Three different trace-fossil assemblages are present as part of two complete depositional sequences. Trace-Fossil Assemblage 1 consists of Treptichnus pollardi and Helminthopsis abeli , which occur in fine-grained heterolithic facies. This assemblage characterizes a subaqueous freshwater substrate in a flood-plain environment. Trace-Fossil Assemblage 2, consisting of Halopoa isp., Palaeophycus crenulatus and Planolites montanus , occurs in thin-bedded, tabular sandstone. The tracemakers inhabited a low-energy distal-bay environment dominated by background sedimentation with sporadic storm episodes. The trace fossils represent the activity of post-storm colonizers. Trace-Fossil Assemblage 3 is monospecific, comprising only Rhizocorallium commune preserved at the interface between a sandstone bed and the overlying mudstone. The tracemakers inhabited the overlying muddy substrate in a low-energy distal-bay environment and burrowed down into the sediment, expanding laterally at the top of the underlying sandstone layer. Trace-Fossil Assemblages 2 and 3 do not resemble typical marine ichnocoenoses and can be considered a depauperate Cruziana ichnofacies, suggesting brackish-water conditions in a restricted marine embayment. The ichnofauna associated with the latest Carboniferous–earliest Permian transgression of the Tupe Formation is compared with that in the older (early Late Carboniferous) postglacial transgression recorded in the underlying Guandacol Formation. The latter reflects freshwater conditions related to an extreme meltwater influx coming from retreating glaciers in fjord environments. In contrast, the latest Carboniferous–earliest Permian transgression in the Paganzo Basin occurred in a confined, brackish-water embayment, but away from the direct influence of meltwater discharges.