Carboniferous postglacial faunas in the late Serpukhovian–Bashkirian interval of central-western Argentina

Abstract

Typical glacial–postglacial sequences associated with the Late Palaeozoic Ice Age (LPIA) are recognized in the Calingasta-Uspallata Basin, central-western Argentina, particularly in the Hoyada Verde and El Paso formations (late Serpukhovian–Bashkirian) at Barreal Hill (San Juan province). Brachiopods and bivalves accompanied by gastropods, conulariids, nautiloids, corals and ostracods constitute the marine assemblages of the El Paso Formation. They are assigned to the Aseptella–Tuberculatella/Rhipidomella–Micraphelia (AT/RM) fauna, characterized by two fossil assemblages: Aseptella–Tuberculatella, identified in the lower fossiliferous interval, and Rhipidomella–Micraphelia in the upper. The development of the different invertebrate assemblages within the El Paso Formation, and their relationship with coeval suite in the Hoyada Verde Formation, can be explained by a complex array of abiotic factors (substrate stability, turbidity, nutrient availability, variation in oxygen levels, poor circulation and salinity variations in the water column) that were directly related to glacial retreat dynamics and coastal configuration. A restricted palaeofjord setting is proposed for the depositional environment of the El Paso Formation in contrast to an exposed open marine coast with a gently sloping shelf for the Hoyada Verde Formation. The study of the postglacial fauna of the El Paso Formation and its relationship with the Levipustula fauna in the Calingasta-Uspallata Basin, help determine the main controls on the distribution of the postglacial faunas in other late Palaeozoic South American basins, such as the Tepuel Genoa Basin in Patagonia and the Tarija Basin in Bolivia.