Pennsylvanian brachiopod faunas from the El Imperial Formation (San Rafael Basin) of central-western Argentina

Abstract

While some Upper Paleozoic basins in central-western Argentina have been extensively studied, others have poorly understood biostratigraphy. The current biozone heterogeneity between basins could be an artefact of incompletely sampled invertebrate fossil assemblages preventing precise correlations. Here, we therefore provide a taxonomic assessment of brachiopods recovered from fossil-bearing beds of the El Imperial Formation at Arroyo del Imperial, Quebrada de La Horqueta, and Cañón del Atuel. Two distinct biozones are identified: (1) a conspicuous Moscovian Tivertonia jachalensis–Streptorhynchus inaequiornatus Biozone (TS) from the Cañón del Atuel section; (2) a new early late Bashkirian Saltospirifer guevarai–Pericospira sanjuanensis Biozone (SP) from the Arroyo del Imperial and Quebrada de La Horqueta sections. The TS assemblage includes Argentiella stappenbecki, Oehlertella annae, Orbiculoidea saltensis, Coolkilella aredesi, Calytrixia piersoni, Costatumulus sp. and Septosyringothyris? sp. The SP assemblage comprises cf. Buxtonia riojana, Streptorhynchus inaequiornatus, cf. Septosyringothyris (Precosyringothyris) feruglioi, cf. Septosyringothyris (Precosyringothyris) jaguelensis, ?Spiriferellina sp., Saltospirifer guevarai and cf. Pericospira sanjuanensis. The El Imperial Formation brachiopod biozones provide a basis for accurate biocorrelation between regional lithostratigraphical units, and clarify the Upper Paleozoic biochronostratigraphical scheme for central-western Argentina during the Pennsylvanian. Cristian Adrián Pardo [pardocr22@gmail.com], Centro de Investigación Esquel de Montaña y Estepa Patagónica (CIEMEP) CONICET-UNPSJB, Roca 780, Esquel (U9200), Chubut, Argentina. Laboratorio de Investigaciones en Evolución y Biodiversidad (LIEB), Facultad de Ciencias Naturales y Ciencias de la Salud (FCNyCS), Sede Esquel, Edificio de Aulas, km 16.5, Esquel, Chubut, U9200, Argentina; César Augusto Taboada [ctaboada@mef.org.ar], Museo Paleontológico Egidio Feruglio (MEF)-CONICET, Avenida Fontana N°140, Trelew, Chubut, U9100GYO, Argentina; Arturo César Taboada [taboadaart@gmail.com], Centro de Investigación Esquel de Montaña y Estepa Patagónica (CIEMEP) CONICET-UNPSJB, Roca 780, Esquel (U9200), Chubut, Argentina. Laboratorio de Investigaciones en Evolución y Biodiversidad (LIEB), Facultad de Ciencias Naturales y Ciencias de la Salud (FCNyCS), Sede Esquel, Edificio de Aulas, km 16.5, Esquel, Chubut, U9200, Argentina; María Alejandra Pagani [apagani@mef.org.ar], Museo Paleontológico Egidio Feruglio (MEF)-CONICET, Avenida Fontana N°140, Trelew, Chubut, U9100GYO, Argentina.