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Graptolites and trilobites from the Eusebio Ayala Formation (Hirnantian?–early Llandovery), Paraná Basin, eastern Paraguay

Authors

  • M. B. Alfaro,

    1. División Geología del Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina
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  • N. J. Uriz,

    Corresponding author
    • División Geología del Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina
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  • C. A. Cingolani,

    1. División Geología del Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina
    2. CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), Buenos Aires, Argentina
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  • M. F. Tortello,

    1. CONICET (Consejo Nacional de Investigaciones Científicas y Técnicas), Buenos Aires, Argentina
    2. División Paleozoología Invertebrados del Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina
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  • A. R. Bidone,

    1. División Geología del Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina
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  • J. C. Galeano Inchausti

    1. Ministerio de Obras Públicas y Comunicaciones de Paraguay, Asunción, Paraguay
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Correspondence to: N. J. Uriz, División Geología del Museo de La Plata, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque s/nº, 1900 La Plata, Argentina. E-mail: nuriz@fcnym.unlp.edu.ar

Abstract

A low-diversity graptolite fauna from the upper part of the Eusebio Ayala Formation exposed in the intracratonic Paraná Basin of eastern Paraguay is reported herein. The sections studied are composed dominantly of red micaceous mudstones with intercalations of purple sandstones from a series of clay quarries (Santa Elena; Galeano; Western Itauguá) around Itauguá city. The graptolites Metaclimacograptus sp., Normalograptus cf. ajjeri (Legrand), and Normalograptus cf. medius (Törnquist) indicate an early Llandovery age for the upper Eusebio Ayala unit. Compared to coeval, postglacial successions in southwestern Gondwana, the graptolites studied have their closest affinities with those from the Rhuddanian lower Lipeón (Subandean Ranges, northwestern Argentina) and La Chilca (Precordillera) formations. In addition, a trilobite assemblage dominated by the genus Mucronaspis was collected from the Eusebio Ayala Formation type locality near Eusebio Ayala city. The latter represents an isolated small outcrop which seems to be latest Ordovician (Hirnantian) in age. Copyright © 2012 John Wiley & Sons, Ltd.

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