New conodont taxa and biozones from the Lower Ordovician of the Cordillera Oriental, NW Argentina

Abstract

The upper strata of the Santa Rosita and the Acoite formations (Lower Ordovician) exposed at Chulpíos Creek in the Santa Victoria study area of the Cordillera Oriental, NW Argentina, are analysed by means of conodont biostratigraphy. Four conodont zones are analysed for the referred formations, i.e. the Acodus apex, Acodus triangularis, Gothodus vetus and Gothodus andinus zones, on the basis of a collection with ca. 2800 conodont specimens that includes new conodont taxa. Acodus apex Albanesi and Zeballo, Acodus triangularis (Ding), Acodus zeballus n. sp., Gothodus andinus (Rao et al.), Gothodus vetus n. sp., and Paltodus cf. inaequalis (Pander) are described herein. The conodont genus Zentagnathus is diagnosed including two previously known species: Zentagnathus argentinensis (Rao et al.) and Zentagnathus primitivus (Voldman et al.). The Tetragraptus akzharensis and Baltograptus cf. deflexus graptolite zones were identified as well in the ∼1800‐m‐thick stratigraphic section. The incertae sedis Phosphannulus universalis Müller et al. is discussed for the Cordillera Oriental for the first time. The lower part of the Chulpíos section that involves the contact between the Santa Rosita and the Acoite formations is not able to be dated with precision either as upper Tremadocian or lower Floian because the ranges of the index taxa recorded in that interval of the study section span the stage boundary. Copyright © 2016 John Wiley & Sons, Ltd.

Outlining the thermal posdepositional evolution of the Ordovician successions of northwestern Argentina by clay mineral analysis, chlorite geothermometry and Kübler index.

“…The temperatures estimated through inorganic indices for the eastern flank of Sierra de Santa Victoria coincide with those indicated by conodonts from the Rupasca Formation at Nazareno (Manca et al, 1995;Giuliano et al, 2013a) and the Santa Rosita (Voldman et al, 2013) and Acoite formations (Voldman et al, 2016) at Santa Victoria, with CAI 3 (110-200 °C, Epstein et al, 1977). Moreover, conodonts have no traces of deformation or metamorphic alteration, according to the illustrations of Rejebian et al (1987) and later authors.…”

“…The Mesón Group is, in turn, unconformably covered by the upper Cambrian-Lower Ordovician rock succession. We will adopt the widely accepted stratigraphic nomenclature that assigned the upper Cambrian-Ordovician strata from Cordillera Oriental and the siliciclastic levels from the northeastern Puna to the Santa Victoria Group (Turner, 1964), which consists of the Santa Rosita (upper Cambrian-Tremadocian) and the Acoite (upper Tremadocian?-Floian) formations (Rubiolo et al, 2001;Astini, 2003;Buatois and Mángano, 2003;Voldman et al, 2016). In the Puna region, the fossiliferous siliciclastic marine sediments assignable to Upper Cambrian, Tremadocian to Floian interdigitate with synsedimentary lavas and subvolcanic intrusives of the Eastern Puna Eruptive Belt (Méndez et al, 1973;Giuliano et al, 2013b) that were grouped into the Magmatic-Sedimentary Cochinoca-Escaya Complex (Coira et al, 1999;Coira et al, 2001).…”

“…In the last decades this rocks series has been the subject of many paleontological, sedimentological, structural and geochronological studies (e.g., Mon and Hongn, 1991;Bahlburg and Breitkreuz, 1991;Coira et al, 2001;Moya, 1999;Astini, 2003;Buatois et al, 2006;Moya, 2003;Zimmermann and Bahlburg, 2003;Ortega and Albanesi, 2005;Buatois et al, 2006;Astini, 2008;Albanesi et al, 2008;Voldman et al, 2013Voldman et al, , 2016Zeballo and Albanesi, 2013;Giuliano et al, 2013a;Albanesi et al, 2015;Toro et al, 2015). On the contrary, its burial/metamorphic evolution has only been briefly mentioned (Mon and Hongn, 1991;Zimmermann, 1999;Do Campo et al, 2013), lacking specific studies.…”

“…The aim of this paper is to constrain the thermal post depositional evolution of the lower Paleozoic successions of northwestern Argentina integrating several inorganic indices, including determination of clay mineral assemblages by XRD, Kübler Index (KI), SEM study of selected samples by backscattered electron images (BSE) and energy dispersive X ray (EDS) and chlorite geothermometry, coupled with previously published data on conodont Color Alteration Index (CAI) (Giuliano et al, 2013a, b;Voldman et al, 2013;Voldman et al, 2016). This study concentrates on five representative areas of Lower Palaeozoic rocks exposures in the northeastern Puna and Cordillera Oriental, namely at Sierra de Santa Victoria (Nazareno and Santa Victoria river areas), Cordón de los Siete Hermanos (Yavi), Sierra de Rinconada and Sierra de Cochinoca-Escaya.…”

Conodonts in Ordovician biostratigraphy

“…() and Voldman et al . (). Although the faunas tend to be dominated by Baltoscandian taxa, there are also species best known from North America which provide useful links between provincial zone classifications.…”