The Normalograptus persculptus Biozone in the Eusebio Ayala Formation, Paraná Basin, Eastern Paraguay

Abstract

In this contribution we report a low diversity graptolite-trilobite fauna from the Eusebio Ayala Formation (Itacurubí Group) exposed at the intracratonic Paraná Basin of eastern Paraguay. Analyzed sections are composed dominantly of red micaceous mudstones with intercalations of purple sandstones located about 60 km east of Asunción City. Shelly faunas such as brachiopods, bivalves, gastropods and cephalopods are abundant at many exposures. The graptolites Normalograptus persculptus (Elles and Wood), Normalograptus normalis (Lapworth) and Normalograptus medius (Törnquist), and the dalmanitid trilobite Mucronaspis sp. are described herein. Since these taxa are characteristic elements of the N. persculptus Biozone, the successions studied are assigned to the Hirnantian-Llandovery transition. The Eusebio Ayala Formation is correlated with coeval, postglacial units of South America and Africa in southwestern Gondwana, and the palaeobiogeographical implications of its faunas are discussed.