First Middle Ordovician Conodont Record Related to Key Graptolites from the Western Puna, Argentina

Andean Geology 47 (1): 144-161. January, 2020 Andean Geology doi: 10.5027/andgeoV47n1-3261 www.andeangeology.cl

First Middle Ordovician conodont record related to key graptolites from the western Puna, Argentina: perspectives for an integrated biostratigraphy and correlation of the Central Andean Basin

Blanca A. Toro1, Susana E. Heredia2, *Nexxys C. Herrera Sánchez1, Florencia Moreno2

1 Universidad Nacional de Córdoba, Facultad de Ciencias Exactas, Físicas y Naturales, Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Centro de Investigaciones en Ciencias de la Tierra, (CICTERRA), Av. Vélez Sarsfield 1611, X5016CGA, Córdoba, Argentina. [email protected]; [email protected] 2 Laboratorio de Micropaleontología, IIM (UNSJ)-CIGEOBIO, Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Av. Libertador Gral. San Martín 1109, J5400, San Juan, Argentina. [email protected]; [email protected]

* Corresponding author: [email protected]

ABSTRACT. Recent biostratigraphic studies on the western argentine Puna recorded the Middle Ordovician conodont Baltoniodus cf. B. navis (Lindström) for first time, related to key graptolite taxa of the Central Andean Basin. The analyzed material comes from the lower and middle thirds of the turbidite succession exposed at the Huaytiquina section, Salta Province, which was previously assigned to the “Coquena” Formation. The conodont fauna was recovered from the calcareous sandstone beds intercalated in the middle portion of this unit, and it is composed by species of the genera Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus, and Protopanderodus, among others. The conodont association indicates a middle Dapingian (Dp2) age, linking the conodonts of the Argentine Puna with those from Baltoscandinavia and South China. The conodont productive levels also contain graptolites assignable to Tetragraptus bigsbyi (Hall) and Isograptus sp. They are located overlying strata bearing Azygograptus lapworthi Nicholson and underlying deposits with Xiphograptus lofuensis (Lee). The graptolite associations are indicating a Dapingian age (Dp1-Dp2) for the lower and middle portions of the “Coquena” Formation. The current findings from the western Puna, as well as the record of Azygograptus lapworthi related to the early Dapingian (Dp1) index conodont Baltoniodus triangularis in the Argentine Cordillera Oriental, are suggesting that a high-resolution correlation between both geomorphological regions is possible. This also documents that the Cordillera Oriental as well as the Puna were connected parts of the Central Andean Basin, during the interval from the Lower Ordovician (Floian) to the Middle Ordovician (Dapingian), instead of corresponding to the source and infill sectors of the basin, respectively. Furthermore, the regional and global correlations are discussed, and the potential of the Ordovician successions of the Argentine Puna for future advances on conodont-graptolite high-resolution biostratigraphy is highlighted.

Keywords: Conodonts, Graptolites, Puna, Argentina, Biostratigraphy, Correlation. Toro et al. / Andean Geology 47 (1): 144-161, 2020 145

RESUMEN. Primer registro de conodontes del Ordovícico Medio asociado a graptolitos clave de la Puna occidental, Argentina: perspectivas para una bioestratigrafía y correlación integrada de la Cuenca Andina Central. Nuevas investigaciones bioestratigráficas desarrolladas en el sector occidental de la Puna Argentina, permitieron obtener el primer registro del conodonte Baltoniodus cf. B. navis (Lindström) del Ordovícico Medio, asociado a especies características de graptolitos de la Cuenca Andina Central. El material analizado proviene de los tercios inferior y medio de la sucesión turbidítica expuesta en la sección de Huaytiquina, provincia de Salta, previamente asignada a la Formación “Coquena”. La fauna de conodontes fue recuperada de los niveles de areniscas calcáreas intercalados en la parte media de la unidad, y se encuentra compuesta por especies de los géneros Baltoniodus, Gothodus, Trapezognathus, Drepanoistodus, Drepanodus y Protopanderodus, entre otros. La asociación de conodontes indica una edad dapingiana media (Dp2), relacionando los conodontes de la Puna Argentina con aquellos de Baltoescandinavia y del Sur de China. Los niveles productivos de conodontes también contienen graptolitos asignables a Tetragraptus bigsbyi (Hall) e Isograptus sp. Se encuentran ubicados por encima de los depósitos portadores de Azygograptus lapworthi Nicholson y por debajo de niveles con Xiphograptus lofuensis (Lee). Estas asociaciones de graptolitos indican una edad dapingiana (Dp1-Dp2) para los tramos inferior y medio de la Formación “Coquena”. Tanto los presentes hallazgos en la Puna occidental, como el reciente registro de A. lapworthi, relacionado a niveles portadores del conodonte guía del Dapingiano temprano (Dp1) Baltoniodus triangularis en la Cordillera Oriental Argentina, sugieren que una correlación de alta resolución es posible entre ambas regiones morfoestructurales, a la vez que documentan que ambos sectores de la Cuenca Andina Central configuraban una cuenca marina durante el intervalo correspondiente al Ordovícico Inferior (Floiano)-Ordovícico Medio (Dapingiano), en lugar de corresponder respectivamente a las áreas de depositación y aporte de la misma. Por último, se discute la correlación regional y global de la sucesión estudiada, y se destaca el potencial de las sucesiones ordovícicas de la Puna Argentina para futuros avances bioestratigráficos de alta resolución de conodontes y graptolitos.

Palabras clave: Conodontes, Graptolitos, Puna, Argentina, Bioestratigrafía, Correlación.

1. Introduction Later on, Albanesi and Ortega (2016) summarized a graptolite biostratigraphic framework for the Conodonts and graptolites are the most important Ordovician System of Argentina, including previously groups to define global stages and correlations of postulated graptolite biozones by diverse authors for the Lower Palaeozoic sequences (Cooper et al., the Argentine northwestern Andes. They referred the 2001; Bergström et al., 2004, 2009; Wang et al., Azygograptus eivionicus Biozone (sensu Brussa et al., 2005, between others). They are widely distributed 2008) to the Lower Dp1?, based on the records of the in the thick Ordovician successions of the Central nominal taxa in the Huaytiquina area, western Puna Andean Basin, mainly in the Cordillera Oriental of (Monteros et al., 1996), and the Muñayoc section, at northwestern Argentina, where their knowledge was the Quichagua range, northeastern Puna (Martínez et significantly improved during the last decades (Toro al., 1999). More recently, Toro (2017) recorded the and Brussa, 2003; Toro et al., 2015; Voldman et al., first azygograptids from the Los Colorados and La 2016, between others). On the contrary, graptolite Quiaca areas, at the western flank of the Argentine records from the Puna highland continue scarcely Cordillera Oriental, documenting the early Dapingian studied and its knowledge includes taxonomic (Middle Ordovician) age of the bearer deposits. Toro uncertainties, biostratigraphic gaps and confusing and Lo Valvo (2017) suggested a Dapingian age for correlations; while only one conodont record, deposits carrying Isograptus cf. I. victoriae (Dp2) assigned to the Late Cambrian-Early Ordovician, from the Tafna area, close to the border between was established for the Las Vicuñas Formation at the Argentina and Bolivia; and Toro et al. (2018) described western Puna (Rao et al., 2000) prior to the newly the first record of Xiphograptus lofuensis from the report of Toro et al. (2019) at Huaytiquina section. western flank of the Cordillera Oriental of Argentina, Toro (1994, 1997) and Toro et al. (2015) proposed suggesting a probably Dapingian (Dp2) age for the a comprehensive biostratigraphic graptolite scheme bearer levels and their regional correlation with comprising the Tetragraptus phyllograptoides, deposits of Chala Mayu, southern Bolivia, in which T. akzharensis, Baltograptus cf. B. deflexus and the Isograptus victoriae Biozone was described by Didymograptellus bifidus biozones for the Floian Egenhoff et al. (2004). The last mentioned authors, deposits of the Acoite Formation exposed in the proposed a graptolite biozonation based on the Cordillera Oriental of northwestern Argentina. records from numerous stratigraphic sections located 146 First Middle Ordovician conodont record related to key graptolites from the western Puna... at the provinces of Tarija, Potosí and Chuquisaca, in 2. Geological Framework southern Bolivia. They described the Rhabdinopora flabelliformis, Adelograptus sp., Aorograptus victoriae, The Argentine Puna morpho-structural province Araneograptus murrayi, Hunnegraptus copiosus, is part of the high Andean plateau with an average Tetragraptus phyllograptoides, Expansograptus altitude above 3,500 m that embraces together with protobalticus, E. holmi, Baltograptus minutus, the Cordillera Oriental, Sierras Subandinas and Azygograptus lapworthi and Isograptus victoriae local Sierras de Santa Bárbara, from the west to the east, biozones and provided an international correlation the Argentine northwestern (Fig. 1A). This region with the Lower-Middle Ordovician graptolite biozones was developed in a continental margin at western of Scandinavia and Eastern North America. Gondwana, during the Cambrian-Ordovician times, Ordovician conodonts from northwestern Argentina as part of the Central Andean Basin (Sempère, 1995) have been studied since decades (Rao, 1994, 1999; which also includes parts of Chile, Bolivia and Peru Rao and Hünicken, 1995; Albanesi and Ortega, (Astini, 2003). 2016; Carlorosi and Heredia, 2017; Carlorosi et al., Lower Paleozoic at Argentine Puna is represented 2018, with complete references mentioned in the by sedimentary deposits and associated volcanic three last papers). These investigations produced rocks. It is widely accepted that the region comprises important results on conodont biostratigraphy from two submeridional belts corresponding to the eastern the Ordovician northwestern sedimentary deposits and western Puna (Turner, 1970) (Fig. 1B), which that have been recorded into the geological provinces were developed from a Cambrian rifting margin to of Puna, Cordillera Oriental and Sierras Subandinas a Floian back-arc basin until a Darriwilian turbidite (Carlorosi and Heredia, 2017). The main region for sequence at a foreland basin system (Astini, 2003, conodont studies is currently represented by the 2008 and references therein). Additionally, Egenhoff Cordillera Oriental (Carlorosi and Heredia, 2017), (2007) postulated that the evolution of the Central but conodonts spanding the Cambrian-Ordovician Andean Basin from an extensional basin, opening in boundary were reviewed recently by Giuliano et al. the Cambrian, to a compressional regime, in the late (2013) at Salar del Rincón area, western Puna. With Early Ordovician, triggering the basin closure in the regard to the Lower-Middle Ordovician conodont latest Ordovician, reflects the relative movements of biostratigraphy of the Central Andean Basin, the the Arequipa-Antofalla terrane alongside Gondwana. contributions carried out by Carlorosi et al. (2013), Conversely, Zimmerman (2011) refused the hypothesis Heredia et al. (2014); and Carlorosi et al. (2018) of the terrane accretion processes, proposing the recorded several biozones: Trapezognathus diprion evolution of an active continental arc with associated and Baltoniodus cf. B. triangularis as upper Floian basins and magmatic record for the proto-Andean zones, and B. triangularis (Carlorosi et al., 2013) margin of western Gondwana. According to this and B. cooperi (Carlorosi et al., 2018) as lower author, the Argentine Puna represents a retroarc Dapingian zone and subzone, respectively. The basin environment composed by three different Dapingian conodont assemblages include the species: complexes, based on distinctive facies: Puna Volcanic Baltoniodus triangularis Lindström, Baltoniodus Complex, Turbidite Complex and Shelf Complex pretriangularis (Lindström), Gothodus costulatus (sensu Zimmerman, 2011). The author also proposed Lindström, Drepanoistodus pitjanti Cooper, a correlation between the Puna shelf deposits and Erraticodon patu Cooper, Trapezognathus diprion the shallow marine sedimentary successions in the Lindström, Trapezognathus quadrangulum Lindström, Cordillera Oriental. Drepanodus sp., Oistodus sp., and Triangulodus sp. The studied Huaytiquina section is located at (Carlorosi and Heredia, 2017). Salta Province, close to the border between Argentina The aim of this contribution is to describe the first and Chile, in the western belt of the Argentine Puna conodont record from the Middle Ordovician deposits (Fig. 1B). Monteros et al. (1996) recognized two of the western Argentine Puna and stratigraphically different stratigraphic units in the area, the Aguada related graptolites, discussing the biostratigraphic de la Perdíz Formation, comprising the volcano- ranges of conodont and graptolite key species, to sedimentary lower succession, and the “Coquena” precise the age of the bearing strata and possible Formation, which includes a 1,450 m thick turbidite biostratigraphic correlations. dominated sedimentary deposits yielding graptolites. Toro et al. / Andean Geology 47 (1): 144-161, 2020 147

FIG. 1. Location map of northwestern Argentina showing the Ordovician deposits and fossiliferous localities at the Argentine Puna region and the Cordillera Oriental.

Afterwards, Zimmerman and Bahlburg (2003) and Complex, respectively. According to these authors, Zimmerman (2011) assigned a number of previously these deposits are characterized by associations of defined stratigraphic units from the western Argentine mainly volcaniclastic rocks, andesites and rhyolites, Puna, including the formations of the studied section, tuffs and pyroclastic flows, turbidites, conglomerates to the Puna Volcanic Complex and the Turbidite and fine-grained sandstones, as well as immature 148 First Middle Ordovician conodont record related to key graptolites from the western Puna... coarse-grained wackes carrying graptolites and 4. Systematic Paleontology brachiopods; and large turbidite systems and channel systems, respectively. The fossil-bearing deposits 4.1. Conodonts correspond to the Puna Turbidite Complex sensu Astini (2003). Early Dapingian conodonts from northwestern Argentina were recently studied by Carlorosi et al. 3. Materials and Methods (2013, 2018) and Voldman et al. (2013) mostly referred to the B. triangularis Zone. Baltoniodus Two conodont bearing samples were collected triangularis associated to B. cooperi Carlorosi, from calcareous sandstone beds at random intervals Sarmiento and Heredia (Carlorosi et al., 2018) was on the “Coquena” Formation at the Huaytiquina proposed by these authors representing the upper section (Fig. 2). The samples were processed by part of the B. triangularis Zone. Elements of B. formic acid technique described by Stone (1987). cooperi were previously recognized by Albanesi A total of 847 elements were obtained from HA and Vaccari (1994) and Albanesi and Ortega (2016), sample (1,03 kg) and 277 from H5 sample (0,67 kg). recovered from coquinoid beds from the upper part The faunal diversity is relatively poor, but almost of the Suri Formation, but they were assigned to all identified species are biostratigraphically Baltoniodus navis sensu Cooper. In this sense, significant. Most of the recovered specimens exhibit conodont elements with close affinity to B. navis excellent state of preservation, and different growth were not recorded until now in the northwestern stages (juvenile, adult and mature) of each species of Argentina (Fig. 5). recovered. The Color Alteration Index corresponds The great amount of the basin infilling that is to a range of 1.5-2 of the Epstein et al. (1977) table. characteristic of the northwestern Argentina offers Conodont illustrations (Fig. 3) are SEM digital the chance of recovering conodont specimens from photomicrographs obtained by scanning electron the transition between species, Carlorosi et al. (2013, microscope at the SEM Laboratory of IIM, Facultad 2018) showed transitional forms of Baltoniodus de Ingeniería, Universidad Nacional de San Juan and Trapezognathus from different intervals and (Argentina). The conodont elements are deposited locations in the Cordillera Oriental. Nevertheless, in collections of the INSUGEO- MP Collection of diversity of these studied conodont populations is Microvertebrates Lillo-Conodonts under the code low due to paleoenvironmental conditions controlled CML-C (Instituto Miguel Lillo and Universidad mostly by fine clastic input to the basin. Nacional de Tucumán, Argentina). The species Baltoniodus navis, Gothodus cf. With regard to the analyzed graptolites, we put costulatus and Traprezognathus quadrangulum emphasis in the detailed description and comparison represent an assemblage already described for of the material housed in the paleontological collection Baltoscandinavia (Bagnoli and Stouge, 1997, pag. of the Centro de Investigaciones en Ciencias de la 131). Tierra (CICTERRA), CONICET and Universidad Nacional de Córdoba, Argentina, under the prefix 4.1.1. Previous comments on taxonomy: early CEGH-UNC. This material is coming from the Baltoniodus middle levels of the Huaytiquina section, at western Lindström (1955) described for first time the Puna (Fig. 2) and was illustrated in the figure 4. The species Prioniodus triangularis and P. navis, and graptolite taxa collected from the Huaytiquina section stablished Prioniodus navis as the type species of by Monteros et al. (1996: pls. 1, 2) were stored as the genus. Later, Lindström (1971) introduced the CNS-I 119/697:1-14 in the collection of the “Cátedra generic name Baltoniodus for these species. The de Paleontología General de la Universidad Nacional revised diagnosis of B. navis was carried out by de Salta, Argentina”, but they are unfortunately Lindström (1977), and he recognized prioniodiform missing. For this reason, their revision is based on (amorphognatiform and ambaloliform), ramiform the descriptions and illustrations provided by the and oistodiform elements describing especially the authors, as well as on the geomorphometric analysis characters of the amorphognatiform element as having of the azygograptid species recently carried out by a quite distinct inner flare, posterior process longer than Herrera Sánchez et al. (2019). the other two and more than twice as long as the cusp Toro et al. / Andean Geology 47 (1): 144-161, 2020 149

FIG. 2. Stratigraphic column of the Huaytiquina section at western flank of the Argentine Puna (modificated in red from Monteros et al., 1996: fig. 2), displaying the stratigraphic ranges of the significant graptolite and conodont taxa. 150 First Middle Ordovician conodont record related to key graptolites from the western Puna...

FIG. 3. Dapingian conodonts from the Huaytiquina section, Baltoniodus navis Zone. SEM Microphotographs. A-H. Baltoniodus cf. B. navis (Lindström). A, B. Pa element, upper view and anterior view respectively, sample H5, CML-C 3500(1), 3501(1). C. sinistral Pb element, anterior-lateral view, sample H5, CML-C 3502(1). D, E. M elements, lateral views , sample H5, CML-C 3507(1,2). F. Sa element, lateral view, sample H5, CML-C 3503(1). G. Sc element, lateral view, sample H5, 3505(1). H. Sd element, lateral view, sample H5,CML-C 3506(1). I-M. Gothodus cf. G. costulatus Lindström. I. Pa element, lateral view, sample HA, CML-C 3508(1). J. Pb element, lateral view, sample HA, CML-C 3509(1). K. Sa element, lateral view, sample HA, CML-C 3510(1). L. Sb element, lateral view, sample HA, CML-C 3511(1). M. Sd element, lateral view, sample HA, CML-C 3513(1). N-P. Trapezognathus quadrangulum Lindström. N. Pb element, lateral view, sample H5, CML-C 3515(1, 2). O. Sa element, lateral view, Sample H5, CML-C 3516(1, 2). P. M element, lateral view, sample H5, CML-C 3517(1). Scale bars: 0,1 mm. Toro et al. / Andean Geology 47 (1): 144-161, 2020 151

FIG. 4. Different early Dapingian (Dp2) graptolites taxa from the Argentine Puna. A, D-G, I-J. Tetragraptus bigsbyi (Hall) associated with Baltoniodus cf. B. navis at Huaytiquina section. A. Flattened proximal end showing conspicuous sicula with nema, CEGH-UNC 24969; D. Mature specimen with strongly reclined stipes and slightly sigmoid dorsal margins, CEGH-UNC 24972; E. Enlargement of the proximal portion of the specimen illustrated in D to highlight the sub-horizontal growing of the first theca, CEGH-UNC 24972; F. Juvenile specimen exhibiting sub-horizontal first thecae and reclined proximal end, CEGH-UNC 24968; G. Flattened juvenile specimen preserving long sicula and conspicuous apertural denticles, CEGH- UNC 24971; I. Incomplete specimen showing the characteristic reclined stipes, CEGH-UNC 24970; J. Complete specimen showing the four strong reclined stipes, CEGH-UNC 24966. B, C. Isograptus sp. associated with Baltoniodus cf. B. navis at Huaytiquina section. B. Symmetric proximal end exhibiting a long sicula, CEGH-UNC 24973; C. Proximal end showing its symmetric appearance and the origin of the first theca from the long sicula, CEGH-UNC 24967. H. Isograptus cf. I. victoriae Harris from the Tafna area. Mature specimen showing the strongly reclined stipes and the symmetric appearance of the proximal end, CEGH-UNC 24974. Scale bars: 1 mm. 152 First Middle Ordovician conodont record related to key graptolites from the western Puna...

FIG. 5. Biostratigraphic conodont-graptolite framework of the Lower-Middle Ordovician (Fl1 to Dp2) proposed for the Central Andean Basin. The shaped biostratigraphic range of B. cf. B. navis corresponds to the lowermost part of the eponymous conodont biozone. is tall. Löfgren (1978) recognized six morphotypes Prioniodus Pander, but Carlorosi et al. (2013) of the apparatus such as amorphognatiform, illustrated early specimens of Baltoniodus cf. ambalodiform, belodontiform (gothodiform and B. triangularis sharing morphological characters paracordylodondiform), tetraprioniodontiform, with Trapezognathus diprion Lindström. trichonodelliform and oistodontiform and also defined Following Lindström (1977) and Bagnoli and the surface microstructure like the fine longitudinal Stouge (1997) we find difficult to support that B. navis striae that characterize all elements of this genus directly evolved from B. triangularis after there is not (Löfgren, 1978). Cooper (1981) compared elements of a precise record of this transition and there are many Baltoniodus retrieved from the Horn Valley Siltstone, morphological differences between these species. Amadeus Basin (Australia) to Baltoniodus navis Middle and late forms of B. navis are well (Lindström) from Baltoscandinavia; however the known from numerous studies throughout Middle illustrated elements resulted not coincident with the Ordovician sections in Baltoscandinavia and South Baltoniodus navis redescribed by Stouge and Bagnoli China (Löfgren, 1978; Stouge and Bagnoli, 1990, (1990). These authors recognized a septimembrate 1999; Bagnoli and Stouge, 1997; An, 1987). Only apparatus with Pa, Pb, Sa, Sb, Sc, Sd and M elements. a probable early form was proposed by Bagnoli and The origin and main characters of the early species Stouge (1997) from Sweden. of the genus Baltoniodus was carried out by Bagnoli In the descriptions, we have used the conventional and Stouge (1997) and Stouge and Bagnoli (1999). orientation terms -anterior, posterior and lateral- noting Albanesi (1998) described and illustrated one Pa that these do not relate to the anatomical orientation element from the Precordillera (Argentina) that he of elements (see Purnell et al., 2000). assigned to B. navis, mentioning that this element shows morphological intermediate characters with B. Class Conodonta Pander, 1856 triangularis; a review of the illustrated element (pl. 2, Order Prioniodontida Dzik, 1976 fig. 13) shows closer characters to B. triangularis Superfamily Prioniodontacea Bassler, 1925 than B. navis. Family Balognathidae Hass, 1959 Stouge and Bagnoli (1990) proposed that the Genus Baltoniodus Lindström, 1971 earliest specimens of Baltoniodus derived from Type species: Prioniodus navis Lindström, 1955 Toro et al. / Andean Geology 47 (1): 144-161, 2020 153

Remarks: The genus Baltoniodus has a septimembrate cusp appears as having a short or long extension apparatus with pectniform, pastinate, alate, tertiopedate, directed downward. The posterior extension is bipennate, quadriramate and geniculate elements that also long. are occupying Pa, Pb, Sa, Sb, Sc, Sd and M positions. Sa element: alate element. It has a long and thin proclined cusp with tree strong rib that extend Baltoniodus cf. B. navis (Lindström, 1955) beyond the cusp and form tree processes, two lateral Figure 3. A-H and one posterior, only the posterior process carries M element triangular denticles with similar size and height. The 1997 B. navis (Lindström), Bagnoli and Stouge, basal cavity is deep and extends into the processes pl. 1, fig. 8. (Fig. 3F). 1997 B. cf. navis (Lindström), Bagnoli and Stouge, Sb element: Is a tertiopedate element. The cusp pl. 1, fig. 9. is slightly proclined; a strong rib on the inner side of the cusp gives rise to a posterior process. Two Description. The Pa element is a pastinate element. adenticulated lateral processes are recognized, they This element is characterized by their lateral present a different angle which grants an asymmetry compressed form with sharply flanks on the cusp. to the element. Denticles on the posterior process The cusp is long, twisted and delicate. The cusp has are long with triangular shape. The basal cavity is a triangular shape in a cross section view, from the deep and runs into the processes. flanks three denticulate processes develop: anterior, Sc element bipennate: the cusp is long, with the lateral and posterior. The anterior face of the cusp external flank curved. The anterior process extends is sharp and ends in a short anterior process with beyond the basal cavity and is directed to posterior denticles. The denticles on the anterior and lateral side, this process ended in a keel; the inner flank is processes are regular and wide with triangular shape, flat and extends in a posterior process that carries but those on the anterior process are smaller and triangular and long denticles. The basal sheath separated. The denticulate posterior process develops is connecting the two processes and presents an a small lobe whose location pointed out right and undulation near the anterior one. The basal cavity left forms. The denticles on the posterior process is deep (Fig. 3G). are erect with triangular shape and larger than the Sd element quadrirramate: it has a long denticles of others processes. The basal cavity is proclined cusp, four processes are developed and elongated, open and deep. The basal sheath linking their position are two latero-anterior and two latero- processes is wide and wavy (Fig. 3A, B). posterior. The posterior process carries denticles; Pb element: pastinate with tree processes. The these are long and triangular as those exhibited by cusp is similar to those of the Pa elements but more the others S elements. The basal cavity is deep; the robust and shorter. It has triangular shape in a cross basal sheath is wide and connects the four processes section view with sharp sides from which two given a quadrangular shape to the base (Fig. 3H). processes are developed, the shortest lateral and the Remarks: Baltoniodus cf. B. navis is represented in longest posterior. From the middle part of the cusp, a our collection by many specimens, all of them have marked rib extends along the anterior process which a microstructure pattern on the element surface like is adenticulated. The lateral and posterior processes fine longitudinal striae. Compared with B. navis carry small triangular denticles, the first denticle the denticulation is larger but only the posterior of the lateral and posterior processes arise about process of the S elements has denticles. The Pa and the half of the cusp. The basal cavity is deep and Pb elements resemble to Baltoniodus cooperi (in extends to the processes; the basal sheath connects Carlorosi et al., 2018), mainly the Pb element. The the processes but is less developed than that from M elements are very similar to those of B. navis the Pa element (Fig. 3C). and B. cf. navis (illustrated by Bagnoli and Stouge, M element: is geniculate, laterally compressed 1997). The specimens at hand are interpreted as early with sharp edges. Two M elements were recognized, representatives of the species Baltoniodus navis. being the oistodiform one characterized by incipient Material: 443 elements in the HA sample: 3524(1- denticles on the anterior side (Fig. 3D, E). The cusp 212), 3525(1-162), 3526(1-69); 124 elements H5 is reclined to suberect. The anterior margin of the sample: 3500(1), 3501(1), 3502(1), 3503(1), 3504(1), 154 First Middle Ordovician conodont record related to key graptolites from the western Puna...

3505(1), 3506(1), 3507(1, 2), 3527(1-55), 3528(1- Remarks: the Gothodus cf. G. costulatus specimens 36), 3529(1-24). in our collection show many similarities to those Provenance: H5 sample, lower B. navis Zone. described by Bagnoli and Stouge (1997) except that “Coquena” Formation, Huaytiquina section, Salta the P, M and S elements develop fine striae on the Province, Argentina. cusp and few fine costae behind the keel of the cusp. Material: 318 elements in the HA sample: 3508(1), Genus Trapezognathus Lindström, 1955 3509(1), 3510(1), 3511(1), 3512(1), 3513(1), 3514(1), Type species: Trapezognathus quadrangulum 3518(1-114), 3519(1-90), 3520(1-107). 116 elements Lindström, 1955 in the H5 sample: 3521(1-58), 3522(1-36), 3523(1-22). Trapezognathus quadrangulum Lindström, 1955 Provenance: H5 and HA sample, lower B. navis Figure 3. N-P Zone. “Coquena” Formation, Huaytiquina section, 1955 Prioniodus triangularis Lindström, pp. 591, Salta Province, Argentina. 592 (partim), pl. 5, fig. 45 (only). 1955 Prioniodus navis Lindström, pp. 590, 591 4.2. Graptolites (partim), pl. 5, figs. 31, 32 (only). 1955 Trapezognathus quadrangulum Lindström, For the taxonomic classification of the studied p. 598 (partim), pl. 5, figs. 38, 39 (only). graptolites at upper level than genus we follow the 1977 Baltoniodus triangularis (Lindström), recent proposes of Maletz and Zhang (2016) and Lindström, pp. 81-82 (partim), Baltoniodus, pl. Maletz et al. (2018), and the revision of the species 2, figs. ?8, ?9. Tetragraptus bigsbyi provided by Williams and Stevens 1978 Prioniodus (Baltoniodus) triangularis (1988). The last authors emphasised that Skevington Lindström; Löfgren, pp. 81, 82, pl. 12, fig. 1. (1965) divided the original species of T. bigsbyi in 1990 Trapezognathus quadrangulum Lindström; two separated taxa based only on the stipe attitude, Stouge and Bagnoli, pp. 26, 27, pl. 10, figs. 1-5. and despite the fact of all the material coming from 1997 Trapezognathus quadrangulum Lindström; a single stratigraphical level. Consequently, they Bagnoli and Stouge, p. 160, pl. 8, figs. 1-5. consider that continuous variations observed between 2003 Icriodella n. sp. A., Moya et al., p.64, pl. 12 T. bigsbyi and T. pseudobigsbyi suggesting that both figs. 13, 15. species are synonymous.

Remarks: Pb, S and M elements were recovered. Phyllum Hemichordata Bateson 1885, This species was widely described by Carlorosi and (emend. Fowler, 1892) Heredia (2017). These elements resemble to those from the Santa Gertrudis Formation (Carlorosi et Order Graptoloidea Lapworth, 1875 in al., 2018). Hopkinson and Lapworth, 1875 Material: 5 elements, 3515 (1, 2), 3516(1, 2), 3517(1) Suborder Dichograptina Lapworth, 1873 Provenance: H5 sample, lower B. navis Zone. Family Phyllograptidae Lapworth, 1873 “Coquena” Formation, Huaytiquina section, Salta Genus Tetragraptus Salter, 1863 Province, Argentina. Type species: Tetragraptus serra (Brongniart, 1828) Family Phragmodontidae Bergström, 1981 Genus Gothodus Lindström, 1955 Diagnosis: (Maletz et al., 2018) Phyllograptid with Type species: Gothodus costulatus Lindström, 1955 four horizontal to reclined, reflexed and scandent Gothodus cf. G. costulatus Lindström, 1955 stipes; proximal end isograptid, dextral, with wide Figure 3I-M crossing canals and tetragraptid proximal end; theca P element with considerable overlap and moderate development 1997 Gothodus costulatus Lindström, Bagnoli and of rutellum. Stouge, pp. 141, pl. 2, figs. 11-13. M element Tetragraptus bigsbyi (Hall, 1865) 1997 Gothodus costulatus Lindström, Bagnoli and Figure 4A; 4D-G; 4I-J Stouge, pp. 141, pl. 2, fig. 10. 1858 Phyllograptus similis Hall, p. 40. Toro et al. / Andean Geology 47 (1): 144-161, 2020 155

1865 Graptolithus bigsbyi Hall, pp. 86-88; pl. 16, lapworthi, recently assigned to the Dapingian (Dp1) figs. 22-30. of the Central Andean Basin (Toro, 2017; Toro 1902 Tetragraptus bigsbyi, Elles and Wood, and Herrera Sánchez, 2019), and they correspond pp. 68-69; pl. 6, figs. 6d-e; figs. 42a-b. to the overlaying “Isograptus victoriae” Biozone 1988 Tetragraptus bigsbyi; Williams and Stevens, (Dapingian, Dp2, sensu Toro and Herrera Sánchez, p. 31; pl. 2, figs. 7-8; text-figs. 19C-O, non 19A?, B?. 2019, fig. 2.A). And synonymies therein. Toro and Brussa (2003) summarized the records of T. bigsbyi from the Argentine Precordillera, Material. Numerous specimens corresponding to corresponding to the Isograptus victoriae maximus, different stages of development regularly preserved Oncograptus upsilon, Cardiograptus morsus, as flattened films and internal molds. The illustrated Undulograptus austrodentatus and Undulograptus material is identified as CEGH-UNC 24966, 24968, dentatus biozones. 24969, 24970, 24971, 24972. Williams and Stevens (1988) observed that Description. Robust tubaria with four reclined stipes T. bigsbyi is a very widespread form described from a that reach a maximum of 14 mm in length (Fig. 4D). variety of stratigraphical horizons, and they assigned In juvenile specimens that preserve the sicula, it the type material from Point Levis, Canada, to the commonly varies between 1.5 to 1.7 mm long and T. akzharensis-I. victoriae lunatus biozones. The 0.4-0.6 mm of apertural diameter (Fig. 4A, E, G). species had also been recorded from Scandinavia Th11 originates at the upper part of the sicula, and the (Bulman, 1936; Skevington, 1965). two first thecae grow sub-horizontal conferring the asymmetric proximal end of the tubarium (Fig. 4F, G). Suborder Glossograptina Jaanuson, 1960 The thecae are strong curved to the distal part, Family Isograptidae Harris, 1933 developing apertural denticles, which are usually Genus Isograptus Moberg, 1892 obscured by the rock matrix (Fig. 4G, J). Dorsal- Type species: Didymograptus gibberulus Nicholson, ventral width of the stipes increases from 1.5 mm up to 1875 2.5 mm and the thecal density is 13-14 thecae in 10 mm. Dorsal margin of the stipes in mature specimens Diagnosis: (Maletz and Zhang, 2016) Reclined two- display a slightly sigmoid curvature (Fig. 4D). stiped isograptids; dextral, thecae simple with rutellate Discussion. The studied material present the general apertures, shorter and wider in earlier species, with characteristics previously described by Skevington thecal length increasing in later species; proximal (1965) and later discussed by Williams and Stevens development type isograptid, dextral, with low (1988) in T. bigsbyi. The measurements of the proximal prosicular origin of th11, rarely sinistral. end, such as the sicular length, the apertural width of the sicula, and the distance of growing of the first Isograptus sp. theca from the sicular apex, are also agreeing with Figure 4B, C those described in T. bigsbyi. The specimens here assigned to T. bigsbyi are Material. Two specimens corresponding to early associated at the same stratigraphic level with stages of development. The material is identified fragments of stronger stipes that reach 60 mm in as CEGH-UNC 24967, 24973. length and 4 mm of width, that probably correspond Description. Juvenile specimens exhibiting long to the second order stipes of the T. serra. It is also sicula with rutellum, which vary between 2.3 to important to mention another younger specimens that 2.5 mm in length and 0.7 mm of apertural width show symmetrical proximal ends, similar to those (Fig. 4B, C). Th11 originates at the upper part of the characteristics of isograptids (Fig. 4B, C). sicula, at approximately 0.3 mm from the apex and Geographic and stratigraphic provenance. The grows downwards. It develops a symmetric proximal studied material was collected for the first time in end with the sicula, conferring to the tubarium the the Argentine Puna, from the middle portion of the distinctive isograptid symmetry characteristic of the “Coquena” Formation, Salta Province (Fig. 2). Levels genus Isograptus. containing T. bigsbyi are located approximately 300 Discussion. The material assigned to Isograptus sp. meters above to the last record of Azygograptus differs considerably from the associated proximal 156 First Middle Ordovician conodont record related to key graptolites from the western Puna... ends corresponding to Tetragraptus bigsbyi, mainly 2015, 2018) (Fig. 5). The lower Dapingian conodont in the bigger dimensions of the proximal end, such as record in northwestern Argentina is well represented the sicular length and apertural width of the sicula. by the Baltoniodus triangularis Zone (Carlorosi et Forms included in the genus Isograptus exhibit al., 2013). Carlorosi et al. (2018) recently proposed remarkable pendent direction of growing of the first that the Pa elements of B. triangularis from the Alto thecae from the upper part of the sicula, in contrast del Cóndor Formation could be interpreted as early to the subhorizontal growing of the first thecae in forms of this species, and that would represent the T. bigsbyi (Fig. 4E, F). lowermost part of the biozone. On the other hand, The occurrence of Isograptus sp. in the Huaytiquina late forms of this species associated to B. cooperi section and the xiphograptids previously mention from the Santa Gertrudis Formation were proposed by Monteros et al. (1996) in the studied area, are as index conodonts for the uppermost part of this confirming that both taxa are associated in levels of biozone (Carlorosi et al., 2018). The morphological Dapingian (Dp2) age in the Central Andean Basin. similarities between the Pb elements of B. cooperi Geographic and stratigraphic provenance. and B. cf. B. navis suggest a strong evolutionary link Specimens assigned to the genus Isograptus were that deserves more studies. previously collected from equivalent levels cropping out at Tafna area (Toro and Lo Valvo, 2017) and 5.2. Graptolites Chala Mayu section, southern Bolivia (Egenhoff et al., 2004). Isograptus sp. is located for the first For biostratigraphic discussions we follow the time at the Huaytiquina section, approximately 300 graptolite biostratigraphic framework recently meters above to the last record of Azygograptus proposed by Toro et al. (2015, 2018) and Toro and lapworthi (Fig. 2). The association of this taxon Herrera Sánchez (2019), based on the first record of with the key conodont Baltoniodus cf. B. navis is the index species or the characteristic taxa associations confirming the conodont-graptolite biostratigraphic previously recognized at different levels of a certain framework proposed for the Central Andean Basin biozone in different stratigraphic sections of the (Fig. 5). northwestern Argentina and southern Bolivia. As the Early-Middle Ordovician graptolite taxa in the Central 5. Biostratigraphyc Framework and Correlations Andean Basin clearly indicate cold to temperate faunal affinities; we referred the ages and correlations 5.1. Conodonts to the global stage slices proposed by Bergström et al. (2009) to solve previous misunderstandings The B. navis Zone is an interval biozone defined related to the use of the Australian standard stages, by the first appearance of this species to the first which have been established on key species with appearance of Microzarkodina parva. In the reference warm faunal affinities. Additionally, an updated section of north of Horns Udde (Sweden) this biozone graptolite-conodont biostratigraphic framework for is represented by a measured rock sequence of the Lower Ordovician (Floian) to Middle Ordovician 1.68 m (Bagnoli and Stouge, 1997). The Hagudden (Dapingian) in the Central Andean Basin is presented section (Sweden) records part of this biozone probably in figure 5, as a complete reference for the discussion the P. (B.) triangularis-navis Zone of Löfgren (1978) of regional correlations. after measured rock sequence of ca. 0.20-0.25 m Based on the first records for Argentina of thick (Stouge and Bagnoli, 1990). Even though Azygograptus eivionicus, D. (Expansograptus) sp. we have not an extensive collection of conodonts aff. D. (E.) extensus, Dichograptus octobrachiatus, through the entire Huaytiquina section, we consider Pseudotrigonograptus minor and Tetragraptus sp. in the present record of the B. cf. B. navis as a marker the lower third of the “Coquena” Formation at the of the lower part of the eponymous zone. A more Huaytiquina section; and Xiphograptus svalbardensis detailed biostratigraphic research to accurate the (X. lofuensis, sensu Toro and Brussa, 2003) and thickness and boundaries of this biozone are under Xiphograptus sp. in the middle part of this unit, development. The conodont biostratigraphy are Monteros et al. (1996) assigned to the yielding levels currently in agreement with the graptolite framework and age corresponding to the Ca1-Ya1 interval of proposed for the Central Andean Basin (Toro et al., the Australian sequence. Toro et al. / Andean Geology 47 (1): 144-161, 2020 157

Herrera Sánchez et al. (2019) recently reviewed coming from the Tafna area, at western flank of the all the records of azygograptids from the northwest Argentine Puna. On the other hand, Toro et al. (2018) of Argentina and southern Bolivia concluding that described Xiphograptus lofuensis for the first time in all of them correspond to Azygograptus lapworthi, the Cordillera Oriental in the upper part of the Los and Toro y Herrera Sánchez (2019) proposed the Colorados section, suggesting an equivalent age for eponymous biostratigraphical interval for the Middle the bearer deposits. Newly records of Isograptus sp. Ordovician (early Dapingian Dp1) in the Central here described in association with Baltoniodus cf. B. Andean Basin. Accordingly, we assume that the navis, are documenting the “Isograptus victoriae” Azygograptus lapworthi Biozone is developing Biozone through the middle part of the “Coquena” through the lower part of the “Coquena” Formation at Formation at Huaytiquina section, and the Dapingian Huaytiquina section up to the studied levels (Fig. 2) (Dp2) age of the studied deposits (Toro and Herrera (Toro and Herrera Sánchez, 2019, fig. 2A). The Sánchez, 2019, fig. 2A). Accordingly, the correlation revision of Azygograptus lapworthi interval with the previous mentioned levels is here confirmed. from the western flank of the Quichagua range The interval of the “Isograptus victoriae” Biozone at the northeastern Puna (Herrera Sánchez et al., from the Huaytiquina section is also regionally 2019; Toro and Herrera Sánchez, 2019) allows correlated with the Isograptus victoriae Biozone of postulating a regional correlation with the studied southern Bolivia (Fig. 5), first mentioned in the Chala levels in which the mentioned species is present Mayu section by Müller (2000) and successively at Huaytiquina section. described by Egenhoff et al. (2004) and Toro and First findings of Azygograptus lapworthi at Los Maletz (2018), who furthermore of the eponymous Colorados and La Quiaca areas (Toro, 2017; Toro species mentioned Xiphograptus cf. X. lofuensis, and Herrera Sánchez, 2019) allowed extend the Pseudophyllograptus sp. and Tetragraptus sp. distribution of this biostratigraphical interval to the western flank of the Cordillera Oriental, where the 6. Conclusions related conodont records, corresponding to the early Dapingian (Dp1), confirm the regional correlation of New records of Baltoniodus cf. B. navis associated the bearing levels with the lower part of the “Coquena” with Tetragraptus bigsbyi and Isograptus sp., located Formation at Huaytiquina section. in the middle portion of the “Coquena” Formation, at A regional correlation is also possible with the the Huaytiquina section confirm a Middle Ordovician Azygograptus lapworthi Biozone, first analyzed in (Dapingian, Dp2) age for the studied levels. the Central Andean Basin at southern Bolivia in the The Azygograptus lapworthi Biozone (early Sama-Chaupi Uno and Sella areas. Maletz and Egenhoff Dapingian, Dp1, sensu Toro and Herrera Sánchez, (2003) and Egenhoff et al. (2004) described in more 2019) is developing below of the studied levels, detail the Azygograptus lapworthi Biozone, defining whereas the overlaying deposits with Xiphograptus its base at the first occurrence of the eponymous lofuensis corresponds to the “Isograptus victoriae” species and proposing an international correlation (Dapingian, Dp2, sensu Toro and Herrera Sánchez, with the Pseudophyllograptus angustifolius elongatus 2019). Biozone of Scandinavia and the Isograptus victoriae The biostratigraphic distribution of the studied lunatus of Eastern North America. conodont association is in agreement with the It is noteworthy, the similar distribution between graptolite biozonation, previously proposed for the the key conodont species Baltoniodus triangularis Lower-Middle Ordovician of the Central Andean associated with azygograptids that occurs in the Basin, and allows to precise the boundary between Huanghuachang GSSP section, across the boundary the last mentioned biostratigraphic units. interval for the formal base of the Dapingian Stage The biostratigraphic distribution of the index in Yichang, southern China (Cooper and Sadler, conodonts (Baltoniodus triangularis and B.cf. 2012; fig. 20.4 and references therein), and those B. navis), as well as the ranges of the graptolite key mentioned from the Central Andean Basin. taxa (Azygograptus lapworthi and Isograptus sp.) Toro and Lo Valvo (2017) postulated a younger document a high resolution regional correlation (Dp2) age for strata of the “Coquena” Formation that between the Ordovician successions located at the carry isograptids of the “I. victoriae group” (Fig. 4.h) Puna region, as Quichagua and Huaytiquina, and 158 First Middle Ordovician conodont record related to key graptolites from the western Puna... classical localities at the Cordillera Oriental of based on sections from Horns Udde, north Öland, Argentina and Bolivia, as Los Colorados, La Quiaca Sweden. Bollettino della Società Paleontologica and Chaupi Uno. Italiana 35: 109-163. The calibration through conodont records of Bassler, R.S. 1925. Classification and stratigraphic use remarkably complete Lower Ordovician graptolite of the conodonts. Geological Society of American succession of the Cordillera Oriental (Tetragraptus Bulletin 36: 218-220. phyllograptoides, T. akzharensis, Baltograptus cf. B. Bateson, W. 1885. The later stages in the development of deflexus and Didymograptellus bifidus), and younger Balanoglossus kowalevskii, with a suggestion as to units of the Puna region and Cordillera Oriental of the affinities of the Enteropneusta. Quarterly Journal Bolivia (Azygograptus lapworthi and Isograptus of Microscopical Science 25: 81-122. victoriae), provides new insights for global correlation Bergström, S.M. 1981. Conodonta. In Treatise on Invertebrate and solid perspectives to fill remaining gaps and Paleontology, part W, Miscellanea, suppl. 2, W1-W202 solve uncertainties. (Robison, R.A., editor). Geological Society of America and University of Kansas, Boulder. Colorado and Acknowledgements Lawrence, Kansas. This work was supported by ANPCYT, PICT 2016-0558. Bergström, S.M.; Löfgren, A.; Maletz, J. 2004. 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Manuscript received: December 18, 2018; revised/accepted: March 18, 2019; available online: September 30, 2019.