The intermontane San Antonio de los Cobres basin (SAC), is located in the Eastern border of the Puna, near the limit with the Eastern Cordillera (Ramos, 2017). This basin preserves the stratigraphic record of the Salta Group (Cretaceous-Eocene) and the Andean foreland (Eocene -Pliocene). This basin has been the subject of numerous investigations mainly focused on structural and volcanic aspects (e.g. Viramonte et al., 1994; Petrinovic et al., 1999; Riller et al., 2001; Petrinovic et al., 2005; Norini et al., 2013; Seggiaro et al., 2016). However, there are few works concerning to the sedimentary sequences, which have led to a lack of consensus on the stratigraphic record. Nevertheless, this basin is of special interest since it is located in a singular position at the limit of the Puna and the Eastern Cordillera, so that the sedimentary record archives the moment and the way in which this area evolved. In this contribution we present an integrated stratigraphic column for the San Antonio de los Cobres basin based on detailed cartography, stratigraphic relationships, sedimentological characterization and available ages. Likewise, and in accordance with the norms and recommendations of the Argentine Stratigraphy Code (1992), we propose a new lithostratigraphic unit, which allows organizing the stratigraphy of the Miocene record. The basement of this basin is composed mainly of metamorphic and metasedimentary rocks of Lower Proterozoic - Lower Paleozoic age (e.g. Puscovicana Formation - Ramos (1973), Donato and Vergani (1988), Guayoc Chico Group - Ramos (1970), Parcha Formation - Harrington y Leanza, (1957)) and intrusive igneous rocks (granodiorites and rhyodacitic porphyries) corresponding to the Oire Eruptive Complex (Middle - Upper Ordovician) (Turner, 1960). These units are exposed, in general, in ranges-limiting the basin. The sedimentary succession of the Cretaceous - Eocene age corresponding to the Salta Group rift related basin lies unconformably on the basement rocks (Turner, 1959). These units maintain the lithological characteristics described for the rest of the basin, in particular with the deposits of the Alemanía and Tres Cruces sub-basins (Salfity and Marquillas, 1994). The foreland basin is characterized by sandy to conglomeratic rocks, which have been deposited in different continental depositional systems, intercalated with volcanic deposits. The oldest unit that is recognized is the Geste Formation (Turner, 1960; Alonso, 1992). It is identified by the up-wards coarsening pattern and light gray-pink colors. Main outcrops can be found in the area of Corte Blanco and Quebrada Los Patos (Fig. 1d), in the southeastern sector of the basin at the foot of the Muñano mountain range (Fig. 1b - Quebrada Fundiciones), and in the Piscuno area (Fig. 1c). Based on differences in facies associations, three informal sections were distinguished: a) the lower section is characterized by a succession of reddish pelitic layers with sporadic intercalations of tabular banks composed of carbonate pisolites (Fig. 3c). Upwards it passes to tabular layers of claystones, silty claystones and silty sandstones with calcareous nodules and rhizoconcretions; alternating with tabular to lenticular sandy to conglomeratic layers. This section is limited in its top by a hardened calcareous horizon, approximately six meters thick (Fig. 3e); b) the middle section is composed mainly of sandy to conglomeratic facies to the bottom (Fig. 3f) and pebbly to cobbly conglomerates at the top (Fig. 3g) with lenticular geometry, which intercalate with tabular strata of clayey siltstones and silty sandstones facies. The presence of greenish-yellow limestone clasts is highlighted, which suggest the uplift and exhumation of the Yacoraite Formation (Fig. 3h); c) the upper section is made up of tabular to slightly lenticular, pebbly to bouldery, clast-supported and imbricated conglomerates (Fig. 3i). At the moment, this Formation lacks absolute age determination in the study area. By similarity and correlation with the exposed outcrops in the adjacent Pastos Grandes basin, we assume ages between 37 - 35 Ma (DeCelles et al., 2007). The Conglomerado Los Patos lies on angular unconformity over different units of the Santa Bárbara Subgroup (Fig. 3j, k) and/or on the Geste Formation (Fig. 3d). It is composed by cobbly to bouldery, matrix-supported conglomerates, clast-supported conglomerates and conglomerates with imbricated clasts. A maximum depositional age of 14.5 ± 0.5 Ma is constrained by U-Pb zircon dating in a volcanic clast contained in the base of the unit (del Papa and Petrinovic, 2017) while the top is limited at 13 Ma of the Viscachayoc Ignimbrite (Petrinovic et al., 1999). The sedimentary succession above the Vizcachayoc Ignimbrite and below the Pleistocene - Holocene deposits has been named San Antonio de los Cobres Formation by Pingel et al., (2019). In the present work, we proposed the formal assignation complemented by stratigraphic details and sedimentological descriptions. Based on distinctive sedimentary facies associations, this Formation is divided into two formal members: a) Corte Blanco Member (Nom. Nov.): it lies unconformably on the Conglomerado Los Patos (Fig. 3k), on the Vizcachayoc Ignimbrite, or on the Geste Formation. It is characterized by a basal eruptive unit known as “Corte Blanco Ignimbrite” (Nom. Nov. for Toba I of Viramonte et al., 1984). Above, it develops an aeolian and fluvio-aeolian succession (Figs. 4, 5b) composed of sets of sandstones, with tabular cross-stratification and large-scale trough/ tabular cross-stratification. The top is defined by the eruptive unit “Ignimbrita Ramadas” (Nom. Nov. for Tufita Corte Blanco - Viramonte et al., 1984) (Figs. 4, 5a). U-Pb zircon dating in both eruptive units allows us to constraint the age of this Member between 6.4 and 7.8 Ma (Late Miocene); b) Muñano Member (Nom. Nov.): it lies in sharp and concordant relation on Corte Blanco Member. It is characterized by a coarsening upward sequence. It begins with a succession of well-channelized sandstone bodies, intercalated with fine to medium conglomeratic beds. In the medium section predominates levels of multi-layering conglomerates intercalated with medium to coarse sandy beds; while the uppermost section consists of medium to coarse-grained sandy levels with erosive bases (concave) and thin lenses of pebbly conglomerate, and thick bodies of clast-supported, pebbly to bouldery conglomerates towards the top. U-Pb zircon dating yielded an age of 5.5 Ma in volcanic ash fall contained at the upper section (Pingel et al., 2019), so a Late Miocene - Pliocene? age could be assigned to this Member.

La cuenca de San Antonio de los Cobres, de tipo intermontana, ubicada sobre el límite oriental de la Puna conserva el registro estratigráfico del rift del Grupo Salta (Cretácico-Eoceno) y del antepaís andino (Eoceno?-Plioceno). El relleno de antepaís, muy poco conocido, está formado por unidades clásticas originalmente asignadas a las Formaciones Río Grande y Pisungo. A partir de trabajos de relevamiento estratigráfico y cartografía geológica de detalle se identificaron unidades litoestratigráficas que difieren de la columna originalmente propuesta para esta cuenca. Asimismo y en base a la identificación de discontinuidades estratigráficas, reconocimiento de superficies de distinta jerarquía y análisis de facies sedimentarias, se reconocieron las siguientes unidades litoestratigráficas correspondientes a la etapa de antepaís: Formación Geste (Grupo Pastos Grandes), Formación Conglomerado Los Patos y Unidad Eruptiva Ignimbrita Vizcachayoc. Asimismo, en la presente contribución se propone a la Formación Geste como la unidad más antigua de la fase de antepaís. Además, se propone formalmente a la Formación San Antonio de los Cobres, la que en base a sus características sedimentológicas se la divide en dos miembros formales: Miembro Corte Blanco, de edad acotada al mioceno tardío (7,8 - 6,3 Ma), el cual se caracteriza por depósitos de origen eólico, fluvio-eólico y volcánico, y el Miembro Muñano, de edad miocena tardía - pliocena?, de origen fluvial.

This paper focuses on the sedimentological characteristics of the basal mudstone-dominated deposits of the upper Lumbrera Formation, the uppermost unit of the Salta Group (Turner, 1959) (Fig. 1a) exposed in the El Simbolar and Juramento River sites, in the Salta province (Fig. 1b). At El Simbolar, a rich vertebrate fauna and a dated volcanic tuff (i.e., 39.9 Ma, U/Pb method) (Fig. 2) constrain a middle Eocene age for this unit (del Papa et al., 2010). On the bases of macro and microfacies descriptions, combined with petrographic, grain-size, and mineralogical studies, we interpret depositional processes and discuss a possible eolian origin for the fine-grained sediments and the paleogeographic scenario. The upper Lumbrera Formation is a thick unit (100-270 m) with blanket-like geometry dominated by reddish siltstones and sandy siltstones (Fig. 3a). The dominant sedimentary features are bioturbation, decolorized halos, desiccation cracks, carbonate nodules and pedological structures (Fig. 3 b-d). In the lower part of the unit there is a 2-3 m thick interval of fine-grained laminated sandstones and heterolithic deposits, consisting of wavy and lenticular bedding (Fig. 3c,e). Five sedimentary facies were identified: 1) Bioturbated siltstone, 2) Calcareous siltstone, 3) White fine-grained sandstone, 4) Heterolithic facies and 5) Volcanic tuff. 1) Bioturbated siltstone facies: this is a fine- to coarse-grained siltstones with subordinate percentage of clay, micro spar and hematite (Fig. 4a); some levels present volcanic shard fragments (Fig. 4b). This facies presents clay and hematite coating pores, cracks and grains. In some parts, it is possible to observe the preferential orientation of clays, interpreted as microslickensides (Fig. 4c) and delineating aggregates with low to moderate birefringence of the micro-mass. Ferric oxides minerals form nodules, concretions (Fig. 4d), and pendant cements. Also, pisolites structures floating in the fined-grained matrix are observed (Fig. 4e). The presence of chambers and tubes with open pores or filled with spar cement (Fig. 4f) are common structures. 2) Calcareous siltstone facies is characterized by the relative increment in the calcite content (Fig. 4g,h), and the moderate to high birefringence of the micro-mass (Fig. 4g). 3) White fine-grained sandstone facies: consists of fine- to very fine-grained feldspathic arenite. The beds are tabular, with internal horizontal lamination and wave ripple cross-lamination capped by mudstone drapes (Fig. 3c). 4) Heterolithic facies: consists of alternation of fine-grained sandstones and mudstones levels showing wavy and lenticular bedding (Fig. 3c,e). Vertical burrows and ferruginous nodules are also observed. 5) Volcanic tuff facies: consists of whitish, 25 cm thick beds composed of crystal tuff. The sedimentary features described in the upper Lumbrera Formation allow to reconstruct vegetated plain paleoenvironments dominated by fine-grained sedimentation from setting and sporadic low-energy water flows that temporally flooded some topographic depression. The presence of micro-fabric, microstructures and features such as birefringence, aggregates, cutans, glaebules, pisolites, crystalarias, root traces, and bioturbation are all indicative of paleosols development. Grain-size analysis show silt as the main fraction (3.9 - 63 μm) with up to a 50% of volume in weight, following by fine-grained sand (63 - 500 μm) (ranging 5.7 and 43.22%) and with 20% of clay fraction (< 3.9 μm) (Table 1). The grain-size curves (Fig. 5a) display a bimodal distribution pattern where the main mode is fine silt (7.8 - 15.6 μm), while in only three samples the modes are very fine sand (63 - 125 μm). The secondary observed mode is variable but in all cases is represented by very fine sand. The median of the analyzed samples are medium silt fraction (15.6 - 31 μm) and fine silt (7.8 - 15.6 μm) (Table 2). The samples are sandy siltstones and siltstones (Fig. 5b) according to Folk´s (1974) textural classification. Moreover, the DRX diagrams (Fig. 6) performed on whole rock remark the mineralogical homogeneity along the studied section. Two mineralogical groups are identified: 1) detrital or allogenic, composed of quartz, plagioclase and illite/muscovite, and 2) autigenic, including calcite, analcime and hematite. One of the key features to identify the loess is the dominant presence of silt particles (Pye, 1987, 1995). Although a "typical loess" is characterized by more than 80% of silt (Pye, 1987), this percentage is variable, and sometimes samples are classified as loess deposits with more than 50% of silt and important percentages of sand (sandy loess) and clay (clayey loess) fractions (Pye, 1995). On the base of the sedimentological studies presented here we interpret the deposits of upper Lumbrera Formation as sandy loess. Our results are compared with similar deposits from Quaternary loess (Pampean loess, Córdoba province) and modern dust (Marco Juarez, Córdoba province) (Gaiero et al., 2013). Figure 7 shows the existence of similarities between the mean grain-size distributions of the studied materials. We interpret that the source of loess particles is associated with the proto-Andes that was under uplift during the Eocene-Oligocene, contemporaneously with the upper Lumbrera sedimentation. Furthermore, we consider the existence of a secondary source probably linked to material derived from the volcanic arc, active in Chile at that time.

Este estudio comprende el análisis de los depósitos limolíticos basales de la Formación Lumbrera superior (unidad cuspidal del Grupo Salta), de edad Eoceno medio, los cuales se encuentran ubicados en la localidad de El Simbolar y Río Juramento, provincia de Salta. Los resultados de los análisis petrográficos, macro y microfaciales, granulométricos y mineralógicos se exponen en este trabajo con la finalidad de discutir el posible origen eólico y el escenario paleogeográfico que pudo haber contribuido a su formación. La Formación Lumbrera superior está formada por espesas sucesiones de material mayormente limolítico de intenso color rojizo, de distribución mantiforme, y groseramente estratificado en la cual se reconocieron cinco litofacies sedimentarias: Limolita bioturbada, Limolita calcárea, Arenisca fina blanca, Heterolítica y Ceniza volcánica; con evidencias de desarrollo de rasgos pedogenéticos en todas las litofacies. Las características sedimentarias sugieren un paleoambiente de llanuras vegetadas con áreas topográficamente más bajas que quedaban temporalmente inundadas. Los estudios granulométricos y mineralógicos de la fracción fina muestran una participación de más del 50% de la fracción limo y un patrón de distribución de tamaño de grano predominantemente bimodal, donde la moda principal se encuentra en el rango de limo fino (7,8 a 15,6 μm) en la mayoría de las muestras analizadas y la moda secundaria es inferior a la fracción arena muy fina (63 a 125 μm). La mediana de este conjunto de muestras está representada por la fracción limo medio (15,6 a 31 μm) y limo fino (7,8 a 15,6 μm). La distribución granulométrica de estas muestras es similar a la mostrada por el loess pampeano cuaternario y el polvo atmosférico actual. Asimismo, la mineralogía de la Formación Lumbrera es homogénea y no presenta cambios sustanciales a lo largo de la columna estratigráfica analizada, reconociéndose dos grupos de minerales: componentes detríticos (cuarzo, plagioclasa, illita/moscovita) y componentes autigénicos (calcita, analcima, hematita). Las características sedimentológicas permiten reconocer a estos depósitos como paleoloess, siendo una posible fuente del detrito el inicio del levantamiento, en forma contemporánea, de la Cordillera de los Andes. Además se atribuye como fuente secundaria del material, a la actividad del arco volcánico durante el Eoceno - Oligoceno temprano en la región oriental de Chile (20°S - 25°S).

The sedimentary record of the Andean orogenic basins in the Calchaquies Valleys (Fig. 1), consists of nearly 6000 m of an overall coarsening and thickening upward clastic succession (Díaz and Malizzia, 1983) known as the Payogastilla Group. The Payogatilla Group is composed of the Quebrada de los Colorados, Angastaco, Palo Pintado and San Felipe Formations (Díaz and Malizzia, 1983; Díaz et al., 1987 - see Fig. 2). Our investigation and previous research in the Quebrada de los Colorados Formation (e.g. Galli and Hernández, 1999; Coutand et al., 2006; Carrapa et al., 2011a,b; Galli et al., 2011) allowed the identification of several unconformity surfaces, including an angular relationship between the Quebrada de los Colorados Formation and the underlying Salta Group. Moreover, the identification of an intra-formational unconformity led us to the reconsideration of the stratigraphic scheme of the Payogastilla Group. Here, we address the regional stratigraphic relations of the Quebrada de los Colorados Formation, the lower unit of the Payogastilla Group, in order to update the knowledge and to discuss the validity of the present stratigraphic framework. Along the Calchaquies Valleys, the Quebrada de los Colorados Formation rests on different units of the Salta Group. The more frequent relation is with the uppermost unit, the Lumbrera Formation (Fig. 3), but in some areas, for example at Saladillo, the Quebrada de los Colorados Formation rests in angular relationship on the Maíz Gordo Formation (del Papa et al., 2004), as in the Esquina Azul locality (Fig. 4). In the cerro Bayo site, the Quebrada de los Colorados Formation lies also upon the Maíz Gordo Formation but few meters laterally directly overlays the Mealla Formation (Figs. 2 and 4). In other places, like in the Pucará valley (Fig. 1), the Quebrada de los Colorados overlays the Pirgua Subgroup (Villanueva García, 1992; Sabino, 2004). These variable stratigraphic relationships are key features that document the tectonic inversion of the Salta Group contemporaneous with the Quebrada de los Colorados sedimentation. The Quebrada de los Colorados Formation consists of red fine-grained floodplain facies and sandy to gravelly clastic fluvial channels facies (Fig. 6). The original description of this unit includes an eolian succession in the upper section (Díaz and Malizzia, 1983). In some localities, like at Tin Tin and Tonco (Fig. 1), the eolian and fluvio-eolian successions have thicknesses ranging from 450 to 600 m (Starck and Vergani, 1996; del Papa et al., 2013) representing a very distinctive erg record. The contact with the underlying fluvial deposits is sharp and a calcrete paleosol (Fig. 5) is locally recognized suggesting the presence of an unconformity within the Quebrada de los Colorados Formation. Moreover, this fluvio-eolian succession has a transitional contact with the overlying fluvial conglomeratic facies of the Angastaco Formation. This stratigraphic relation suggests that the former could be formally included within the Angastaco Formation. Thus we propose a redefinition of the Angastaco Formation (Díaz and Malizzia, 1983; nom. transl. Díaz et al., 1987); including the fluvio-eolian succession as the basal Tin Tin Member and to return to the previously defined Las Flechas Member. We propose the Tin Tin area (25º13'51.6'' Lat. S and 66º00'58.5'' Log. W - 25°16'12'' Lat. S and 66°2'39.45'' Log. W) as stratotype area (Fig. 7). In this locality, pale red silty sandstones to siltstones overlie coarse conglomeratic strata (Figs. 5 and 6) and are overlain by white eolian sandstones that grade to gray conglomeratic strata of the Angastaco Formation sensu Díaz and Malizzia (1983). The age of the Tin Tin Member is considered late Oligocene to early Miocene according to the 21 Ma U/Pb zircon datings (Carrapa et al., 2011a; del Papa et al., 2013). Finally we propose the Quebrada Grande locality (25º12'59.1'' Lat. S and 66º01'33.1'' Log. W), along state route Nº 42, Tin Tin area, Calchaquí Valley (Fig. 7) as hypostratotype of the Quebrada de los Colorados Formation. In this locality, this unit rests unconformably, and locally through an angular unconformity, on the Lumbrera Formation (Salta Group, Figs. 2, 3 and 4). In this area the formation is 792 m thick and is characterized by two coarsening upward successions of red siltstone, lenticular to shallow lenticular coarse sandstones and horizontally stratified conglomerates (Fig. 5). Based on mammalian biostratigraphy recorded at sites in Cerro Bayo, Tin Tin and Luracatao (Fig. 1) the age of the Quebrada de los Colorados Formation is Casamayoran (sub-age Barrancan), SALMA, suggesting a Middle Eocene age for the basal levels (Powell et al., 2011). In summary, we propose that the fluvio-eolian section of the Quebrada de los Colorados Formation should be incorporated into the Angastaco Formation, as the Tin Tin Member. This modification will simplify recognition in the field, mapping, and genetic interpretation of these foreland basin deposits.

El Grupo Payogastilla representa el registro sedimentario de la cuenca de antepaís andina en los Valles Calchaquíes. La Formación Quebrada de los Colorados, unidad basal, es de singular importancia debido a que preserva evidencias de los primeros episodios de contracción con deformación intracuencal, cambios en las áreas de aporte y asociaciones de fósiles que la datan paleógena pre-oligocena, hecho que llevó a replantear el modelo de cuenca de antepaís propuesto para el Noroeste argentino. Asimismo, la suprayacente Formación Angastaco, además de contener similar registro tectono-sedimentario, documenta el inicio del magmatismo en el borde oriental de la Puna. Los recientes trabajos de investigación llevados a cabo en estas unidades han permitido identificar y mapear superficies de discontinuidad sedimentaria, incluso de discordancias que obligan a modificar el cuadro estratigráfico existente. En la presente contribución se describen las relaciones estratigráficas de la Formación Quebrada de los Colorados con el objetivo de actualizar el conocimiento sobre la misma y discutir el esquema estratigráfico actualmente vigente. Esta formación se asienta en relación de discordancia y de disconformidad sobre las Formaciones Lumbrera, Maíz Gordo y Mealla (Subgrupo Santa Bárbara) y sobre el Subgrupo Pirgua, del Grupo Salta. Asimismo, se describe y discute el alcance de la identificación de una discontinuidad sedimentaria intra-Quebrada de los Colorados, señalada por el cambio abrupto de facies sedimentarias y la presencia de una superficie de meteorización con desarrollo de una calcreta. Esta superficie separa una sucesión netamente fluvial de otra fluvio-eólica con características sedimentarias distintivas. Por último, se describen las relaciones de transición y de concordancia entre la sucesión fluvio-eólica con la suprayacente Formación Angastaco. En base a estas relaciones se propone redefinir la Formación Angastaco con la incorporación de la sucesión fluvio-eólica con el rango de Miembro Tin Tin y retomar la definición original del Miembro Las Flechas. Finalmente y en base la nueva información disponible se propone a la quebrada Grande (área de cerro Tin Tin) como hipoestratotipo para la Formación Quebrada de los Colorados, localidad que servirá como complemento de las descripciones originales.

During Lower Cretaceous-Eocene the Salta Group rift basin was developed in northwest Argentine, showing well-defined synrift (Pirgua Subgroup) and postrift (Balbuena and Santa Barbara Subgroups) stages. Then and superimposed to the rift, broad foreland basin was generated. The Payogastilla Group represents the Andean synorogenic filling in the Calchaquí Valley; its base records the Paleogene deformation and inversion tectonics of this zone of the Eastern Cordillera. The Luracatao valley (western branch of the Calchaquí Valley) preserves a thick sedimentary sequence designed as the Luracatao Formation of possible Oligocene age in previous regional maps. This paper presents a redefinition of the stratigraphy of the Luracatao valley based on field works of regional scale, stratigraphic logs and detailed structural mapping. The analyses of sedimentary facies and facies association and the identification of stratigraphic unconformities allow identifying the units of the Santa Bárbara Subgroup (Mealla Formation, Maíz Gordo Formation and Lumbrera Formation) and of the Payogastilla Group (Quebrada de los Colorados Formation) among the levels previously assigned to the Luracatao Formation. Special importance has the identification of an unconformity between Santa Bárbara Subgroup and Quebrada de los Colorados Formation that integrated to paleontological data allow us interpret this unconformity as the record of the first Cenozoic deformation events. Based on the redefinition of the Luracatao Valley stratigraphic column, this paper proposes to replace the Luracatao Formation by the respective units identified.

Durante el Cretácico Inferior-Eoceno se desarrolló la cuenca de rift del Grupo Salta en el noroeste argentino, con un relleno constituido por depósitos sinrift del Subgrupo Pirgua y postrift de los Subgrupos Balbuena y Santa Bárbara. Posteriormente y sobreimpuesta a la primera, se generó una extensa cuenca de antepaís. En el valle Calchaquí, el Grupo Payogastilla representa el relleno sinorogénico andino (cuenca de antepaís) y guarda el registro de los episodios de deformación y de inversión tectónica cenozoica en esta parte de la Cordillera Oriental. El valle de Luracatao (ramificación occidental del valle Calchaquí) presenta una sucesión sedimentaria designada originalmente como Formación Luracatao y atribuida tentativamente al Oligoceno. A partir de trabajos de relevamiento a escala regional, perfiles estratigráficos y mapeo estructural de detalle se redefinió la columna estratigráfica del valle de Luracatao. En base a las características de las facies sedimentarias y asociaciones de facies y la identificación de discontinuidades estratigráficas se reconocieron las siguientes unidades litoestratigráficas: Formación Mealla, Formación Maíz Gordo y Formación Lumbrera (Subgrupo Santa Bárbara-Grupo Salta); y una sucesión sedimentaria rojiza asignada a la Formación Quebrada de los Colorados (Grupo Payogastilla). Se identificó una discordancia entre el Subgrupo Santa Bárbara y la Formación Quebrada de los Colorados, lo que integrado a la información paleontológica, permite interpretar esta discordancia como el registro de las primeras fases de deformación andina. En base a la redefinición de la columna estratigráfica del valle de Luracatao, en este trabajo se propone el abandono de la Formación Luracatao y su reemplazo por las respectivas unidades identificadas.

The Neoproterozoic-Lower Paleozoic basement structural features have influenced in different ways the development of later both extensional Cretaceous and contractional Cenozoic structures. Tectonic inversion of normal faults related to the Cretaceous rift has been frequently addressed as the main mechanism for explaining double-vergent and retrovergent structures in the hinterland of the Andean orogen in northwestern Argentina. This paper proposes that basement structures played a primary role in the nucleation of both Cretaceous normal faults showing Cenozoic tectonic inversion and Cenozoic reverse faults. A regional section between the Domeyko Cordillera (Chile) and the Santa Bárbara System (nearly at 24º-25ºSL) shows portions with opposite Cenozoic vergence, each one related to different controls made by previous structures. The inversion of Mesozoic rift-related faults mainly influenced the geometry and vergence of the Cenozoic structures linked to Andean shortening in the Domeyko Cordillera, in the Calchaquí Valleys region and in the Santa Bárbara System. Reactivation of structures and heterogeneities formed during the Neoproterozoic-lower Paleozoic tectonic evolution of the basement controlled the Andean contractional structures in the Puna. Reactivation of Neoproterozoic-lower Paleozoic basement heterogeneities not only contributes to changes in attitude and vergence but also to the irregular time distribution showed by the Andean shortening since many of the reactivated or inverted (positive and negative inversion) structures record superposed movements from the Cretaceous up to the Quaternary.

Los rasgos estructurales del basamento neoproterozoico-paleozoico inferior (Cámbrico- Ordovícico) del noroeste argentino han controlado en diferentes grados el desarrollo de las estructuras posteriores, principalmente las vinculadas con la extensión cretácica y el acortamiento andino. La inversión tectónica de fallas normales relacionadas con el rift cretácico ha sido frecuentemente invocada entre los mecanismos que influyen en la definición de las zonas de doble vergencia y retrovergencia que muestra el orógeno andino en el noroeste argentino. En esta contribución proponemos que las estructuras del basamento jugaron un papel primario en la localización tanto de las fallas normales cretácicas posteriormente reactivadas como de las fallas inversas andinas. Una sección estructural regional entre la Cordillera de Domeyko (Chile) y el Sistema de Santa Bárbara (aproximadamente 24º-25ºLS) muestra segmentos con vergencias cenozoicas opuestas, en la que cada porción responde a diferentes controles ejercidos por estructuras previas. La inversión de fallas normales asociadas a sistemas de rift fue el principal control de la geometría y vergencia de las estructuras cenozoicas vinculadas al acortamiento andino en la Cordillera de Domeyko, en los Valles Calchaquíes y en el Sistema de Santa Bárbara. La reactivación de las estructuras y heterogeneidades originadas durante la evolución neoproterozoico-paleozoica del basamento controlaron el desarrollo de las estructuras cenozoicas en la Puna. La reactivación de las heterogeneidades no sólo influyó en los cambios de orientación y vergencia, sino también en la distribución temporal compleja que muestra el acortamiento andino. La reactivación múltiple de algunas estructuras del basamento neoproterozoico-paleozoico inferior ocurrió en diferentes etapas de su historia incluyendo inversiones positivas y negativas entre el Cretácico y el Cuaternario.

A Formação Lumbrera é a unidade do topo do Grupo Salta, aflorante na região noroeste da Argentina. O paleoambiente da Formação Lumbrera tem sido interpretado como um lago perene depositado sob um clima temperado durante o início do Eoceno. Seu conteúdo fóssil é formado por palinomorfos, insetos, crocodilos, tartarugas, lagartos, mamíferos, além de uma ictiofauna que inclui ciclídeos, poeciliídeos e dipnóicos. †Plesioheros chauliodus é descrito com base em um único indivíduo coletado nesta formação, preservado como impressão em vista lateral (faltando as nadadeiras anal e caudal). Ele pode ser distinguido de outros ciclídeos por um corpo moderadamente alto, dentes anteriores do dentário aumentados e portando uma cúspide lingual subapical, uma baixa contagem de vértebras abdominais, cinco aberturas do canal sensorial no dentário, e XI + 12 raios na dorsal. Na análise filogenética, usando a matriz apresentada por Kullander (1998), †Plesioheros resultou dentro da Tribo Heroini mais relacionado a Australoheros e aos heroinis de corpo alto sul-americanos. A ocorrência de um heroini fóssil desta idade, bem como das outras linhagens de ciclídeos no mesmo nível estratigráfico, é uma evidência da diversificação inicial da família, corroborando fortemente a hipótese de que os Cichlidae se originaram no Gondwana ainda durante o Cretáceo.

The Lumbrera Formation is the uppermost unit of the Salta Group, which crops out in northwestern Argentina. The paleoenvironment of the Lumbrera Formation is interpreted as a perennial lake deposited under temperate climatic conditions during the early to middle Eocene. Its fossil content is made up of palynomorphs, insects, crocodiles, turtles, lizards, and mammals, besides an ichthyofauna formed by cichlids, poeciliids and dipnoans. †Plesioheros chauliodus is described based on a single individual from this formation, which was fossilized as a lateral view impression (missing anal and caudal fins). It can be distinguished from other cichlids by a moderately deep body, enlarged anterior dentary teeth bearing subapical cusp, a low abdominal vertebral count (10), five canal openings in the dentary, and XI + 12 dorsal-fin rays. A phylogenetic analysis, using the matrix by Kullander (1998), recovered †Plesioheros within Heroini. This species was recovered most closely related to Australoheros and to the deep-bodied South American heroins. The occurrence of an Eocene Heroini, as well as of other cichlid lineages in the same stratigraphical level, is evidence of an ancient diversification in this family. This ancient age supports the hypothesis that the Cichlidae originated on Gondwana.

The Tarija Formation (Macharetí Group) is mainly composed by gray diamictites which have been deposited under the glacial sedimentation that took place during the Upper Carboniferous Period in Gondwanaland. This paper describes the facies and facies associations of Itacuamí and Tarija Formations of five section located in the Aguaragüe Range, Sub-Andean Belt of Salta province, Argentina (Fig. 1). The Tarija Formation outcrops almost completely (620m thick) and consist of gray diamictites, interbedded with fine sandstone levels and laminated mudstones. The basal contact is transitional with the Itacuamí Formation and the upper contact is an erosive unconformity with Las Peñas Formation (Mandiyutí Group). The Itacuamí-Tarija cycle can be divided into three sections, according to the facies associations considered. The lowermost section is formed by the Facies Association I (FAI of Fig. 2), composed by laminated mudstones (Fl and Fm) and thin bedded sandstones (St and Sm). Towards the top of the basal section, 34 m of white coarse and thickening upward sandstones (St, Sh, Sr and Fl) intercalate. These also show a gentle downstream accretion structure (Figs. 2 and 3-A). The middle section is formed by the facies association II (Fig. 2), which is composed by different levels of stratified and massive sandy muddy diamictites (Dms and Dmm) and mudstones (Fld). In these diamictite, it is quite common to find scattered faceted and striated clasts (Fig. 3-F and 4-C). There are two kinds of interbedded sandstones, coarsening - upward succesions and fining upward ones, both showing deformed, folded and dewatering structures (Figs. 3-D and 3-E). The Fl facies, composed by shale and siltstones have plenty of outsized clasts, which have been interpreted as dropstones (facies Fld). The upper section (FA III, Fig. 2) is made up of massive diamictites (Dmm, Figs. 4-C and D) and stratified ones with frequent traction current structures (Sr). In this section, levels of lenticular sandstones with slumps structured interbedded. Two striated boulder pavements have also been found in Zanja Honda section. They cover paleosurfaces carved in diamictites and are overlain by fluvial sandstones (Fig.2). The clasts are in a single layer with flattened and striated surfaces (Fig. 4-E). In order of occurrence, the clast composition is as follows: granites, sandstones, quartz, schists and vulcanites. The local paleoflows directions measurements in tabular cross-stratification and ripples structures indicates west, south, and southeast source area. The permanent ice-rafting and slumping processes and the association of massive and resedimented diamictites indicate subaqueous sedimentation. The basal section (FAI) represents the progradation of constructive Gilbert type delta over mudstones of inner basin, from distal prodelta towards a delta front and upper delta. The glacial influence in this section was indirect and sporadic (Fig. 5). From the middle section upwards (FAII), the sedimentary facies and facies association shows a gradual increase of glacial influence in the sedimentary processes (Fig. 5). The abundance of Dms and Dmm facies indicate the constant supply of detritus of glacial origin, owed both to downslope resedimentation by debris flow and rain-out from ice masses. The sandstone levels represent subaqueous delta progradation and distributary channels fill. Towards the upper section (FA III), the presence of boulder pavements suggest a grounding process by ice mass. The Dms and Dmm are the dominant facies and indicates the large volume of glacial sediment input due to ice retreat (Fig. 5). As far as the facies and facies associations are concerned, the Tarija Formation in Aguaragüe Range was formed in a confine environment. The lacustrine system was a distal glacial fed lake type but it was at times an ice contact lake.

La Formación Tarija (Grupo Macharetí) en la sierra de Aguaragüe (Sierras Subandinas orientales) es producto de la sedimentación glacial ocurrida durante el Carbonífero Superior en el paleocontinente de Gondwana y está formada principalmente por diamictitas grises. Se la ha dividido en tres secciones en función de las características y ocurrencia de las asociaciones de facies identificadas. La sección basal está caracterizada por pelitas laminadas y areniscas blancas, en arreglo grano y estratocrecientes. En la sección media predominan los niveles de diamictitas areno-limosas estratificadas y macizas con clastos líticos dispersos facetados y estriados. Intercalan en las diamictitas areniscas canalizadas, granodecrecientes, con estructuras de deformación, escapes de agua y deslizamientos y niveles limo-arcilíticos que presentan clastos fuera de tamaño interpretados como dropstones a partir de balsaje. El tramo cuspidal está formado por diamictitas macizas y estratificadas con frecuentes estructuras de retrabajo por corrientes, interestratificadas con lentes discontinuos de areniscas con estructuras de deslizamientos. En esta sección se ha observado pavimentos de bloques estriados residuales que cubren paleosurcos labrados en diamictitas. Se interpreta que la Formación Tarija expuesta en la sierra de Aguaragüe representa depósitos lacustres con influencia glacial indirecta a lacustre en contacto con el hielo. La base de esta unidad constituye un sistema lacustre asociado con deltas, con influencia glacial esporádica e indirecta; mientras que a partir de la sección media las facies sedimentarias indican paulatino incremento del régimen glacial en la dinámica sedimentaria. La permanente evidencia de procesos de balsaje y la asociación de diamictitas macizas y resedimentadas indican condiciones subácueas. La presencia de pavimentos de bloques residuales sugeriría erosión por encallamiento del glaciar, que se transformó en forma temporaria en un lago en contacto con el hielo.