"Levipustula Fauna" in central-western Argentina and its relationships with the Carboniferous glacial event in the southwestern Gondwanan margin

Abstract

The Levipustula Fauna (included in the Levipustula levis Zone) is a relatively diversified fossil assemblage composed of brachiopods, bivalves, bryozoans, gastropods, and crinoids. This fauna usually is associated with glaciomarine sequences related to the Carboniferous glacial event that affected the southwestern Gondwanan margin. The Levipustula Fauna has been identified in different units (e.g., Hoyada Verde, La Capilla, Leoncito, and Yalguaraz Formations) exposed in the Calingasta-Uspallata Basin. The Hoyada Verde Formation, herein proposed as a key section, contains the most complete record of the Levipustula Fauna. A detailed compositional, taphonomic, and paleoecological study of this section allows us to propose two associations within the so-called Levipustula Zone: the "Intraglacial Levipustula Fauna," present in the diamictite-dominated lower part, and the "Postglacial Levipustula Fauna," dominant in the upper part of section. The fossils of the "Intraglacial Levipustula Fauna" are scarce and poorly diversified. These two features suggest environmentally stressed conditions, probably related to low temperatures in areas close to glaciers. In comparison, the "Postglacial Levipustula Fauna," relatively more abundant and diverse, exhibits compositional variations that could be explained by paleoenvironmental changes associated with fluctuations in substratum and food supply, such as those identified in modern ecosystems. The identification of the "Intraglacial Levipustula Fauna" and the "Postglacial Levipustula Fauna" may constitute a new tool for understanding the particular relationship between faunal assemblages and climatic variations linked to the Gondwanan glaciation in the Calingasta-Uspallata Basin. Also, the new "Intraglacial Levipustula Fauna" identified in the Hoyada Verde Formation would have biostratigraphical and paleogeographical implications in intra-and interbasinal correlations.