Postglacial Ichnofaunas of Western Gondwana: An example from the upper Carboniferous Hoyada Verde Formation of Argentina

PABLO JOAQUIN ALONSO MURUAGA; LUIS A. BUATOIS; CARLOS O. LIMARINO

St. John´s

Congreso; The 3rd International Congress on Ichnology; 2012

Memorial University

The Upper Carboniferous Hoyada Verde Formation of the Calingasta-Uspallata Basin of Argentina provides an opportunity to document postglacial ichnofaunas. Lingulichnus verticalis, Lockeia isp., Palaeophycus isp., Protovirgularia isp., Psammichnites plummeri, Psammichnites implexus, Ptychoplasma vagans, Treptichnus bifurcus, scarce arthropod trackways and a short bilobate structure are present in these progradational deposits that occur above the maximum flooding interval that marks the culmination of the postglacial transgression. This ichnofauna is characterized by the dominance of horizontal trace fossils and subordinate presence of vertical and inclined structures, which represent different ethological categories. It is dominated by simple and small forms restricted to bedding planes, whereas shallow vertical structures are scarce and only locally present. The Hoyada Verde ichnofauna shows affinities with the Cruziana Ichnofacies, although the low to moderate ichnodiversity, relative small size, sporadic distribution of trace fossils with localized high abundance, impoverishment of suspension-feeding trophic types and very low bioturbation intensities suggest a stressed expression, which is consistent with a deltaic context. In addition, postglacial biotas may have been influenced to some degree by the salinity gradient triggered by freshwater release near to melting ice masses stored in adjacent highlands. Distinction between normal-marine and brackish-water settings in glacially influenced environments using trace fossils may not be as straightforward as in non-glacial settings.