CONICET | Buscador de Institutos y Recursos Humanos

The postglacial interval of the Upper Carboniferous Hoyada Verde Formation of western Argentina contains an ichnofauna dominated by Psammichnites plummeri and Psammichnites implexus , with minor occurrences of Ptychoplasma vagans , Treptichnus bifurcus , Lingulichnus verticalis , Protovirgularia isp., Lockeia isp., Palaeophycus isp., scarce arthropod trackways and some bilobate structures. The particular features of this association indicate a depauperateexpressionofthe Cruziana Ichnofacies, and suggest a contextthat differsfrom the expectedinnor- mal shallow-marine settings (i.e. archetypal Cruziana Ichnofacies). Integration of sedimentologic, ichnologic, sequence-stratigraphic and paleontologic data points to a prograding deltaic system in fl uenced by wave action. Trace fossils have been extensively used to recognize stressed brackish-water environments in the late Paleozoic of Gondwana. However, the recognition of stressed settings needs to take into consideration the speci fi c paleo- geographic context of glacially in fl uenced Gondwanan settings. A postglacial open sea adjacent to a paleotopographic high isconsideredasa possible scenariofor the Hoyada Verde Formation. In this particular set- ting,coastalbiotascouldhavebeenin fl uencedtosomedegreeby thesalinitygradienttriggeredbyfreshwaterre- lease near to melting ice masses stored in highlands and also by freshwater plumes due to longshore currents. Regional factors (e.g. proximity to highlands and climate) may have played an important role in controlling the characteristics of Gondwanan ichnofaunas. This suggests that the distinction between normal-marine and brackish-water settings in glacially in fl uenced environments using trace fossils may not be as straightforwardas in non-glacial settings