Lower Ordovician (Floian) conodonts from the Western Puna Magmatic Belt in northwestern Argentina: palaeobiogeographic significance and implications

Abstract

The arc-derived volcaniclastic rocks of the Aguada de la Perdiz Formation, exposed in the Vega Pinato section, yielded the first Floian conodont fauna identified in the Western Puna Magmatic Belt, northwestern Argentina. Despite the presence of fractures, the conodont elements are sufficiently preserved for taxonomic identification. The assemblage, comprising 380 elements, is notably diverse and includes Acanthodus lineatus, Acodus sp., Aloxoconus aff. staufferi, Bergstroemognathus extensus, B. robustus, Colaptoconus quadraplicatus, Diaphorodus cf. delicatus, Drepanodus arcuatus, Drepanodus? sp., Drepanoistodus pitjanti, D. aff. pitjanti,D. cf. basiovalis, Gothodus andinus, Juanognathus jaanusoni, J. variabilis, Oelandodus? sp., Oneotodus costatus, Paroistodus sp., Periodon flabellum, Pohlerodus heligma, Protopanderodusgradatus, Pr. leonardii, Reutterodus andinus, Rhipidognathus sp., Scalpellodus cf. striatus, S. cf. tersus, Scolopodus striatus, Scolopodus sp., Tropodus australis, Zentagnathus cf. argentinensis, and gen. et sp. A. Dated to the middle–late Floian, this conodont assemblage includes severaltypical warm water taxa; this is unusual compared with contemporaneous faunas from the nearby Cordillera Oriental, and instead has stronger palaeobiogeographical affinities with the Famatinian arc. Additionally, the presence of elements commonly associated with Australasia, China, Laurentiaand the Argentine Precordillera suggests an active faunal dispersal across the Iapetus Ocean during the Early Ordovician, connecting palaeoequatorial settings to the volcanic environments developed along the southwestern margin of Gondwana.