An in situ shelly fauna from the lower Paleozoic Zapla diamictite of northwestern Argentina: implications for the age of glacial events across Gondwana

A shelly fauna from the upper part of the Zapla glacial diamictite includes thelingulate brachiopod Orbiculoidea radiata Troedsson, the rhynchonelliforms Dalmanella cf. testudinaria (Dalman) and Paromalomena sp., the bivalve Modiolopsis? sp., and the trilobite Dalmanitina subandina Monaldi and Boso. Both taphonomic and paleoecologic data indicate a lack of transport reflecting the original community. The assemblage is closely comparable to the widespread latest Ordovician Hirnantia-Dalmanitina fauna. The Hirnantian age of the Zapla diamictite is further corroborated by the record of the northern Gondwana chitinozoans Spinachitina cf. oulebsiri Paris and Desmochitina minor typicaEisenack. The graptolites and chitinozoans from the overlying Lipeón Formation indicate that the postglacial transgression took place in the earliest Llandovery (P. acuminatus Biozone). According to the tectonosedimentary evidence, the Early Silurian age of the Cancañiri and San Gabán diamictites of north-central Bolivia and south Peru based on their palynological record is more likely the age of posglacial gravity flows and not that of the glaciation. We support the hypothesis that the weakly lithified glacigenic deposits ofHirnantian age were reworked and redistributed by high-energy marine processes during the postglacial transgression and then transported to the adjacent deep-marine trough. Ironrich horizons have been recognized in many basins of southern South America reflecting eustatic and paleoclimatic fluctuations. Most of them formed during the early stages of the postglacial transgression at the Ordovician/Silurian transition and are associated with low sedimentation rates and condensed intervals. The mild maritime postglacial climate, the increasing atmospheric CO2, and possibly the presence of incipient vegetated areas led toextensive weathering of glacigenic sediments supplying iron into the marine system to form ferruginous deposits. The sea level fall related to the peak of glaciation is recorded by both paleovalley incision and a sharp subaerial to subglacial unconformity. The transgressive systems tract starts with fluvio-estuarine deposits within incised valleys followed by widespread deposition of subtidal to open marine organic-rich shales onlapping regionally the basement rocks. The recognition of key stratigraphic markers (e.g. sequence boundary, flooding surface, ferruginous beds), alongside reliable micro and macropaleontological evidence allow a more accurate correlation between the Central Andean Basin of Peru, Bolivia and NW Argentina, the W Puna region, the Paraguayan and Brazilian sectors of the Paraná Basin, the Precordillera Basin of W Argentina, and the Cape Basin of South Africa.Fil: Benedetto, Juan Luis Arnaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Halpern, Karen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: de la Puente, Graciela Susana. Universidad Nacional del Comahue. Facultad de Ingeniería. Departamento de Geología y Petróleo; ArgentinaFil: Monaldi, Cesar Ruben. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentin

New records of Tremadocian conodonts (Early Ordovician) from the Zenta Range, Jujuy Province, Argentina

THE study area is located nearby the Santa Ana village, province of Jujuy, in the Zenta Range of the Cordillera Oriental, northwestern Argentina. Localities can be reached by the national Route 9 to the town of Humahuaca, then continue to the East through the provincial Route 73 up to the Santa Ana village (Fig. 1). In this contribution we analyze an Ordovician conodont fauna from 15 levels of calcarenites and coquinas, along with graptolites, trilobites and associated fauna from siltstones and claystones. The studied collection of 2263 conodont elements is housed in the Museum of Paleontology at the National University of Córdoba, under repository code CORDMP 21941 to 22023.Fil: Zeballo, Fernando Javier. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; ArgentinaFil: Albanesi, Guillermo Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Voldman, Gustavo Gabriel. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Monaldi, Cesar Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; Argentin

Early Ordovician (Late Floian) conodonts from the Zenta range, Cordillera Oriental, NW Argentina

LOWER Ordovician strata from the Central Andean Basin are superbly exposed in the Zenta Range of the Cordillera Oriental, NW Argentina. At the Laguna Verde section (23°18'S, 65° 1W, 4500 MASL) the sedimentary succession is mostly siliciclastic with subordinate coquinas and calcarenites (Fig. 1). It is unconformably overlain by glacial diamictites and quartzites from the Zapla Formation (Hirnantian). Previous conodont work by Albanesi et al. (2011) recognized the Acodus deltatus – Paroistodus proteus Zone in the nearby Abra de Santa Ana. Aráoz et al. (2008) suggested a Darriwilian to Sandbian age for the strata exposed in the Laguna Verde section, based on the presence of Erismodus and Trapezognathus. In a recent revision of the section, Carlorossi and Heredia (2013) documented from one sample Trapezognathus diprion Lindström(1954) and mentioned the occurrence of Baltoniodus triangularis Lindström (1954) and B. cf. triangularis Lindström (1954) in the same sample (p. 311 and table 2), suggesting a Dapingian age for the upper exposed levels of the Acoite Formation. In order to define the age of aforementioned strata, we took 18 rock samples from the Laguna Verde section plus 2 isolated samples (ZEN17 and ZEN17.2) located 2.5 km to the SW (23°19'S, 65° 0'W), stratigraphically below, which produced a significant conodont fauna, although the diversity is low. The rock samples (24 kg in total), which were digested in 10% acetic acid following the conventional procedures, produced 608 conodont elements. The studied specimens are relatively well preserved (CAI 2, Epstein et al., 1977), with no chemical alteration but abundant fractures that truncate cusps and denticles. The faunal association includes Acodus n. sp. (see Zeballo et al., this volume), Baltoniodus cf. triangularis, Trapezognathus? argentinensis Rao et al.(1994), Trapezognathus diprion, Trapezognathus? primitivus n. sp., Scolopodus houlianzhaiensis An and Xu in An et al. (1983), Drepanodus arcuatus Pander (1856), Drepanoistodus chucaleznensis Albanesi and Aceñolaza (2005), D. costatus (Abaimova, 1971), D. basiovalis (Sergeeva, 1963) and Erraticodon patu Cooper (1981). The record of the taxon Baltoniodus cf. triangularis confirms the presence of the homonymous biozone in the host strata, which indicates the uppermost zone of the Early Ordovician (Floian). According to its age, these strata correlate with the upper part of the Acoite Formation and equivalent units such as the Capillas/Zanjón Formation from the Subandean Ranges. The conodonts are stored in the Museo de Paleontología, Universidad Nacional de Córdoba, with repository code CORD-MP.Fil: Voldman, Gustavo Gabriel. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Albanesi, Guillermo Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Zeballo, Fernando Javier. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; ArgentinaFil: Monaldi, Cesar Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; Argentin

Upper Cambrian/Lower Ordovician conodont and graptolite records in the Lari section, Salar del Rincón, Puna of Salta, Argentina

Fil: Giuliano, María Eugenia. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Ortega, Gladys del Carmen. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba; ArgentinaFil: Albanesi, Guillermo Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Ciencias de la Tierra; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba; ArgentinaFil: Monaldi, Cesar Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; Argentin

Tectonic inversion in the Santa Barbara System of the central Andean foreland thrust belt, northwestern Argentina

The Santa Barbara System (SBS) of northern Argentina is a 400 km long segment of the Subandean foreland thrust belt. It is characterized by predominantly west verging, relatively high-angle thrust faults. Many of these faults are reactivated normal faults from one branch of a complex Cretaceous to Paleogene rift system. Heteroaxial folding in parts of the SBS is probably due to a slight component of range-parallel dextral strike-slip motion acting on preexisting faults striking north and NE during inversion. Regional balanced cross sections along two transects across the northern SBS indicate that the major faults flatten into a detachment in the basement at about 10 km depth. Neogene E-W contraction in the SBS is of the order of 21-26 km. Rift extension is not very well constrained but was probably less than 10 km. The structural style of the SBS differs from the thin-skinned Subandean thrust belt to the north and from the large-wavelength Sierras Pampeanas basement uplifts to the south. The changes between the different styles are sharp and coincide with the northern and southern boundaries of the rift in the foreland, suggesting that crustal or lithospheric heterogeneities exert an overriding control on foreland structural style.Fil: Kley, Jonas. Universität Karlsruhe. Institut Geologisches; AlemaniaFil: Monaldi, Cesar Ruben. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; Argentin

Preserved extensional structures in an inverted Cretaceous rift basin, northwestern Argentina: Outcrop examples and implications for fault reactivation

During the Cretaceous-Eocene interval a system of intracontinental rift basins, the Salta group rift, evolved in northwestern Argentina. Individual segments of the rift later suffered different degrees of inversion during Cenozoic shortening. The Tres Cruces subbasin, on the west side of the Eastern Cordillera, was strongly deformed, being now part of a thick-skinned thrust belt with a predominantly N-S structural trend. On its eastern border, tilting due to folding and thrusting and subsequent erosion have produced exceptional outcrops of preserved east-trending extensional structures including half grabens, rollover anticlines, and extensional fault-propagation folds. Farther west, the synrift succession is only intermittently exposed, although the interference of north- and east-trending structures as well as peculiar, dome-shaped anticlines with spur-like extensions suggest that north-and east-trending Cretaceous faults were reactivated, particularly near their intersections. Compilation of published data and analysis of our new data focused on the Salta rift indicates three main factors favoring the contractional reactivation of normal faults: dip angles lower than approximately 60°, especially for faults striking roughly normal to contraction; strikes no closer to the contraction direction than approximately 30°; and low downdip fault curvatures. Occasional dip-slip reactivation of east-trending faults does not match the present and long-term Andean stress regimes and presents an unresolved problem.Fil: Monaldi, Cesar Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Salta; ArgentinaFil: Salfity, Jose Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Salta; ArgentinaFil: Kley, Jonas. Universitat Jena; Alemani

Geology and metal ore deposits in the Argentine Puna

This paper provides a geological overview of the Argentine Puna through a brief analysis of its sedimentary and magmatic stratigraphy, diastrophic episodes and tectonic arrangement, which allow the main mineralization events that occurred during the Cenozoic to be located in time and space. The intensive, widespread magmatic activity that took place in the region, particularly during various pulses in the Miocene, is responsible for generating various types of metal ore deposits hosted directly in the magmatic bodies, whether intrusive, flows and/or pyroclastic mantles, or in the host rock. The development of post-Inca continental sedimentary basins, their distribution areas, associated metal ore deposits and prospective possibilities are also discussed. Finally, the genesis of the metal ore deposits in the Argentine Puna is analyzed, in close relationship to the diastrophic phases and the evolution of associated magmatism. The following Metallogenic Intervals and Events are recognized: i) Late Eocene-Late Oligocene Metallogenic Interval, between the Inca and Pehuenche phases: First late Eocene- middle Oligocene Mineralizing Event. ii) Early Miocene-Middle Miocene Metallogenic Interval, between the Pehuenche and initial Quechua phases: First early Miocene Mineralizing Event; Second middle Miocene Mineralizing Event. iii) Late Miocene-Late Pliocene Metallogenic Interval, between the initial Quechua and Diaguita phases: First late Miocene Mineralizing Event; Second Pliocene Mineralizing Event. iv) Pleistocene-Holocene Metallogenic Interval, post-Diaguita phase: First Pleistocene- Holocene Mineralizing EventSe brinda un panorama geológico de la Puna argentina a través de un breve análisis de la estratigrafía sedimentaria y magmática, de los episodios diastróficos y de la disposición tectónica que permiten ubicar en el tiempo y en el espacio los principales eventos mineralizantes ocurridos durante el Cenozoico. La intensa y amplia actividad magmática que tuvo lugar en la región, especialmente a través de varios pulsos durante el Mioceno, es la responsable de la generación de diversos tipos de depósitos metalíferos que se alojan directamente en los cuerpos magmáticos, sean intrusivos, coladas y/o mantos piroclásticos, o en las rocas de caja. Se discute asimismo el desarrollo de las cuencas sedimentarias continentales posincaicas, sus áreas de distribución, los depósitos metalíferos asociados y las posibilidades prospectivas. Finalmente se realiza un análisis de la génesis de los depósitos metalíferos en estrecha relación con las fases diastróficas y la evolución del magmatismo asociado acontecidos en la Puna argentina. Se reconocen los Intervalos y Sucesos Metalogenéticos siguientes: i) Intervalo Metalogenético Eoceno Superior-Oligoceno Superior, entre las fases Incaica y Pehuenche: Primer Suceso Mineralizante Eoceno Superior-Oligoceno Medio. ii) Intervalo Metalogenético Mioceno Inferior-Mioceno Medio, entre las fases Pehuenche y Quechua inicial: Primer Suceso Mineralizante Mioceno Inferior; Segundo Suceso Mineralizante Mioceno Medio. iii) Intervalo Metalogenético Mioceno Superior-Plioceno Superior, entre las fases Quechua inicial y Diaguita: Primer Suceso Mineralizante Mioceno Superior; Segundo Suceso Mineralizante Plioceno. iv) Intervalo Metalogenético Pleistoceno-Holoceno, posfase Diaguita: Primer Suceso Mineralizante Pleistoceno-Holoceno.Fil: Gorustovich, Sergio Antonio. Comisión Nacional de Energía Atómica; ArgentinaFil: Monaldi, Cesar Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; Argentina. Universidad Nacional de Salta; ArgentinaFil: Salfity, Jose Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; Argentina. Universidad Nacional de Salta; Argentin

Seismic and field evidence for selective inversion of Cretaceous normal faults, Salta rift, northwest Argentina

Northwestern Argentina was the site of the continental Salta rift in Cretaceous to Paleogene time. The Salta rift had a complex geometry with several subbasins of different trends and subsidence patterns surrounding a central high. Fault trends in the rift were extremely variable. There is evidence of normal and/or transfer faults trending N, NE, E and SE. It is not clear if all these faults were active at the same time, indicating a poorly defined extension direction, or if they formed in different, non-coaxial extension phases. In either case, their trends were very likely influenced by preexisting fault systems. Beginning in early Eocene time, the rift basins were superseded by Andean foreland basins and later became caught in the Andean thrust deformation propagating eastward, resulting in the inversion of rift faults. Due to their different orientations, not all faults were equally prone to reactivation as thrusts. N to NNE trending faults were apparently most strongly inverted, probably often to a degree where the traces of their normal fault origin have become obliterated. We present seismic evidence of moderately inverted N trending faults in the Tres Cruces basin and field examples of preserved E trending normal faults. However, reactivation sometimes also affects faults trending approximately parallel to the main Neogene shortening direction, indicating short-term deviations from the general pattern of Neogene thrust deformation. These pulses of orogen-parallel contraction may be linked to the intermittent activity of oblique transfer zones.Fil: Kley, Jonas. Universitat Jena; AlemaniaFil: Rossello, Eduardo Antonio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Monaldi, Cesar Ruben. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Habighorst, Bjórn. Universität Karlsruhe; Alemani

An Early Ordovician conodont fauna from the Santa Rosita Formation at its type area in the Santa Victoria Range, Cordillera Oriental, Northwestern Argentina

The Cambrian - Lower Ordovician stratigraphic units from the Cordillera Oriental were originally defined in the Santa Victoria Range, Salta Province, northwestern Argentina, however, the extensive outcrops of this region lack detailed biostratigraphic studies. We describe and analyse the first reported conodont fauna from the Santa Rosita Formation at its type area, which produced significant biostratigraphic information. Over 4,500 well-preserved conodont elements were recovered from outcrops of the Santa Rosita Formation at the southern margin of the Santa Victoria River, near the homonymous locality. Collected specimens exhibit a CAI 3 and correspond to the Paltodus deltifer deltifer Subzone of the P. deltifer Zone (middle Tremadocian, Tr2). A number of species are described for the genera Acanthodus, Acodus, Decoriconus, Drepanodus, Drepanoistodus, Filodontus, Granatodontus, Hammannodus, Iapetonudus, Kallidontus, Paltodus, Paroistodus, Teridontus, Tilcarodus, Utahconus, Variabiloconus, Gen. and sp. indet., the protoconodont Phakelodus and the paraconodont Coelocerodontus. Two new conodont species, Drepanoistodus andinus Voldman, Zeballo and Albanesi and Filodontus carolinae Voldman, Albanesi and Zeballo, are diagnosed herein. The studied assemblages include conodont species of wide intercontinental distribution as well as endemic forms from the Central Andean Basin, which characterize a faunal province with a particular signature from the Shallow Water Realm.Fil: Voldman, Gustavo Gabriel. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Albanesi, Guillermo Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Monaldi, Cesar Ruben. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zeballo, Fernando Javier. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentin

Late Tremadocian (Ordovician) Conodonts and Graptolites from the Sierra de Zenta, cordillera oriental of Jujuy, Argentina

En la Sierra de Zenta, Cordillera Oriental de Jujuy, aflora una potente sucesión psamo-pelítica ordovícica con concreciones calcáreas, coquinas y calcarenitas subordinadas, portadora de una importante fauna de conodontes y graptolitos. Las localidades investigadas se ubican en el camino que une el Abra de Zenta con Santa Ana, sobre una amplia estructura anticlinal. En las inmediaciones del Abra de Santa Ana se registran pelitas grises y coquinas con una fauna de conodontes de baja diversidad compuesta por Acodus apex n. sp., Drepanoistodus chucaleznensis Albanesi y Aceñolaza, y Drepanoistodus costatus (Abaimova) referida a la parte inferior de la Zona de Acodus deltatus — Paroistodus proteus. Se enmienda la diagnosis del género Acodus. Por encima de este afloramiento se coleccionó una asociación de graptolitos integrada por Araneograptus murrayi (J. Hall), Kiaerograptus cf. K supremus Lindholm y Kiaerograptus? sp., sugiriendo la Zona de A. murrayi. Estas faunas de conodontes y graptolitos indican una edad tremadociana tardía. En otra localidad, al oeste de Santa Ana se hallaron rabdosomas de Hunnegraptus cf. H. novus (Berry), Hunnegraptus spp. y Paradelograptus sp., indicadores de la Zona de Hunnegraptus copiosus del Tremadociano tardío alto. La sucesión analizada es equivalente a la parte superior de la Formación Santa Rosita, y a la Formación Parcha, en otras áreas de la Cordillera Oriental. Las faunas estudiadas contienen formas endémicas y de distribución geográfica intercontinental. El hallazgo de concentraciones de graptolitos y lingúlidos con evidentes signos de transporte en algunos niveles, indica fondos retrabajados por episodios erosivos en la cuenca.A thick heterolithic Ordovician succession lies exposed in the Zenta Range of the Cordillera Oriental, Jujuy Province, Argentina. It is mostly siliciclastic with subordinated calcareous concretions, coquinas and calcarenites, and bears a significant conodont and graptolite fauna. The sampled localities are situated on the road running from Abra de Zenta to Santa Ana, within a wide anticline structure. Exposures of gray shales and coquinas near Abra de Santa Ana, yielded a low diversity conodont fauna that includes Acodus apex n. sp., Drepanoistodus chucaleznensis Albanesi and Aceñolaza, and Drepanoistodus costatus (Abaimova), which are referred to the lower part of the Acodus deltatus — Paroistodus proteus Zone. The diagnosis of the conodont genus Acodus is emended. The A. murrayi Zone is suggested by a graptolite assemblage including Araneograptus murrayi (J. Hall), Kiaerograptus cf. K supremus Lindholm and Kiaerograptus? sp., which was collected from strata overlying the conodont-bearing levels. These conodont and graptolite faunas indicate a late Tremadocian age. Another locality on the road to Abra de Zenta, west of Santa Ana, contains Hunnegraptus cf. H. novus (Berry), Hunnegraptus spp. and Paradelograptus sp., indicating the Hunnegraptus copiosus Zone of the latest Tremadocian. The biostratigraphic succession is equivalent to that from the upper part of the Santa Rosita Formation and to the Parcha Formation exposed in other areas of the Eastern Cordillera in northwestern Argentina. The faunas contain elements of wide intercontinental distribution as well as endemic forms. The occurrence of concentrations of graptolites and lingulids showing evidence of transport in some strata indicates bottom reworking by erosive episodes in the basin.Fil: Albanesi, Guillermo Luis. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba; ArgentinaFil: Ortega, Gladys del Carmen. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba; ArgentinaFil: Monaldi, Cesar Ruben. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta; ArgentinaFil: Zeballo, Fernando J.. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Museo de Paleontología; Argentin