No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Hoja Geológica 4172-IV, San Carlos de Bariloche (provincias de Río Negro y Neuquén)
... Las rocas del basamento cristalino ígneo-metamórfico son denominadas Complejo Colohuincul, definido por Turner (1965), el cual está integrado por esquistos micáceos y esquistos cuarzo-micáceos, Cordillerano (Giacosa y Heredia, 2001), designado por Gordon y Ort (1993) se corresponde con granitos, granodioritas y tonalitas de hornblenda y biotita. ...
... Su génesis está relacionada al desarrollo de dos áreas englazadas principales, la región del lago Nahuel Huapi y los glaciares que provenientes desde el Norte. Estos depósitos están formados por bloques, gravas, arenas, limos y arcillas (Giacosa y Heredia, 2001). ...
... El Cuaternario está representado por depósitos glaciarios, los cuales en el sector argentino, se agruparon en dos sistemas denominados externo e interno. El primero se ubica en las márgenes del rio Pichileufú y el sistema interno está representado por el arco morénico oriental del Nahuel Huapi (Giacosa y Heredia, 2001). Los depósitos glacilacustres cuaternarios se disponen en una franja paralela a la costa del lago Nahuel Huapi, en el sector comprendido entre los arroyos Ñireco y Ñirihuau y vuelven a aparecer en una franja de menor magnitud hasta el rio Limay. ...
The frequent eruptive activity from the Southern Volcanic Zone (SVZ) directly affects the sedimentation in adjacent areas, and the dominance of the westerlies in austral latitudes allowed the dispersion of pyroclastic products over Argentinean territory. The Nahuel Huapi National Park (NHNP) and surroundings are adequate places for the study of quaternary pyroclastic sedimentation due to its geographic location and the geological setting. This has been evidenced with the recent eruptions of Cordón Caulle and Calbuco volcanoes, among others. The diversity of environments within the Park, lacustrine and superficial, offers the possibility to perform comparative studies about past pyroclastic events and its effects. Considering this, the objective of the present work is to characterize volcanic ash deposits identified in different depositional settings, both superficial and lacustrine, defining the origin volcano and comparing the sedimentation conditions and the preservation potential of pyroclastic material in the different environments. The characterization of volcanic layers included the sedimentology of the sequences, and the geochemistry, mineralogy and mineral chemistry of the volcanic components. This information allowed to identify the volcanic origin and to perform correlations between sites when it was possible.
On one hand, medial-proximal deposits from superficial environments were studied by the opening of a pit. The proximity of the sampling site to the Puyehue-Cordón Caulle Volcanic Complex, close to the Cardenal Samoré international border (Argentina-Chile border) and next to the NHNP, allowed to obtain a depositional sequence with high influence of such Complex. It was possible to identify 3 deposits which were correlated, in part, with previous bibliographic information, identifying products emitted by Puyehue-Cordón Caulle Volcanic Complex during the last 1100 years approximately.
In addition, two lacustrine sequences recovered from El Trébol lake, located in medial-distal zones from the SVZ inside the NHNP were studied, and the piroclastic layers were analyzed. Eight tephra layers were identified and the morphological, petrological, mineralochemical, and geochemical characterization of the most abundant components, named pumice, scoria, glass shards, and crystaloclast, was carried out. Each tephra layer was correlated with material of explosive origin from Cordón Caulle Complex and Calbuco volcano, mainly based on the geochemical information. The eruptive chronology was established by the dating of one sequence using 210Pb and 137Cs, the estimation of sedimentation rates, and from available information about historical eruptions. In some cases, pyroclastic layers corresponded to estimated dates older than the most ancient historical records of these volcanoes, spanning approximately 500 years before present.
The magma features that originate the pyroclasts, the atmospheric factors, the kind of depositional environment, and the geographic location regarding the different volcanic sources strongly determine the dispersion patterns, the importance, and the preservation potential. This is evidenced in the presence or absence of tephra layers and the complexity in the field correlations, as was observed in the lack of correlation of deposits between the two environments analyzed in this work. However, each kind of environment has advantages and disadvantages in the study of volcanic events, being highly important the sampling in several dispersion directions to obtain better information of the pyroclastic dispersal phenomenon in the past.
Beside these complexities, the correct characterization of a tephra layer, mainly in lacustrine
environments, gives the possibility to be applied as a valuable tephrochronological tool, very important to perform correlations and dates in areas with high eruptive frequency, in periods in which other methods result inaccurate.
... [11] The eastern slope of the Andes is formed by the eastern continuation of the Patagonian Batholith, locally intruding a Late Paleozoic basement ( Figure 2) [Pankhurst et al., 1992] that is thrust over thick Mesozoic volcaniclastic successions ( Figure 3) [Giacosa et al., 2001;Tobal et al., 2012]. This region forms the internal part of the North Patagonian fold and thrust belt, developed mainly in the eastern slope of the Andes at these latitudes (Figure 2, 3 and 4). ...
... This region forms the internal part of the North Patagonian fold and thrust belt, developed mainly in the eastern slope of the Andes at these latitudes (Figure 2, 3 and 4). Deformation in this section is characterized by east-vergent thick-skinned thrusts [Ramos and Cortés, 1984;Giacosa et al., 2001] that emplaced Jurassic, Cretaceous, and Cenozoic granitoids in the hinterland zone [Petersen and González Bonorino, 1947;Basei et al., 1999;Giacosa et al., 2001Giacosa et al., , 2005. Sparse roof pendants of Lower Jurassic volcano-sedimentary successions are engulfed in these plutonic rocks [González Bonorino, 1944;Miró, 1967;González Bonorino, 1974;Thiele et al., 1978;Lizuaín, 1980;Diez and Zubia, 1981;Giacosa et al., 2001]. ...
... This region forms the internal part of the North Patagonian fold and thrust belt, developed mainly in the eastern slope of the Andes at these latitudes (Figure 2, 3 and 4). Deformation in this section is characterized by east-vergent thick-skinned thrusts [Ramos and Cortés, 1984;Giacosa et al., 2001] that emplaced Jurassic, Cretaceous, and Cenozoic granitoids in the hinterland zone [Petersen and González Bonorino, 1947;Basei et al., 1999;Giacosa et al., 2001Giacosa et al., , 2005. Sparse roof pendants of Lower Jurassic volcano-sedimentary successions are engulfed in these plutonic rocks [González Bonorino, 1944;Miró, 1967;González Bonorino, 1974;Thiele et al., 1978;Lizuaín, 1980;Diez and Zubia, 1981;Giacosa et al., 2001]. ...
The Northern Patagonian Andes have been constructed through multiple
mechanisms that range from tectonic inversion of extensional structures
of Early to Middle Jurassic age in the Main Andes to Oligocene in the
Precordilleran region. These have acted during two distinctive orogenic
stages, first in late Early Cretaceous and later in Miocene times Late
Oligocene extension separates these two contractional periods and is
recorded by half-grabens developed in the retroarc region. The last
contractional stage coexists with an eastward foreland expansion of the
late Miocene arc whose roots are presently exposed as minor granitic
stocks and volcanic piles subordinately in the Main Andes, east of the
present arc. As a consequence of this orogenic stage a foreland basin
has developed, having progressed from 18 Ma in the main North Patagonian
Andes, where the mountain front was flooded by a marine transgression
corresponding to the base of the Ñirihuau Formation, to 11 Ma in
the foreland area. Cannibalization of this foreland basin occurred
initially in the hinterland and then progressed to the foreland zone.
Blind structures formed a broken foreland at the frontal zone inferred
from growth strata geometries. During Pliocene to Quaternary times most
of the contractional deformation was dissipated in the orogenic wedge at
the time when the arc front retracted to its present position.
... El tercer episodio (D3) se caracteriza por el desarrollo de pliegues dúctiles mesoscópicos con planos axiales de orientación N a NO, y zonas de cizalla miloníticas de orientación similar y alta inclinación (Cerredo 1997). En las cercanías de la localidad de Pilcaniyeu, Giacosa et al. (2001) y Giacosa y Heredia (2004) definieron la zona de cizalla dúctil Carhué, de rumbo NO y carácter compresivo, la cual se habría generado durante la última fase de deformación dúctil (D3). Sobreimpuestas a la foliación milonítica de la zona de cizalla se observan fajas discretas de cizalla dúctil transcurrente de rumbo N70º-80ºE. ...
... ura del basamento del sector cordillerano , Dalla Salda et al. (1991) describieron dos fases principales de deformación dúctil afectando las rocas metamórficas del Complejo Colohuincul que afloran al sur de la localidad de San Carlos de Bariloche, las cuales generaron planos de foliación con orientaciones N75ºE/31ºS y N130ºE/61ºNE, respectivamente. Giacosa et al. (2001) observaron en estas rocas una foliación de rumbo predominante NO en los alrededores de San Carlos de Bariloche, y E-O en las cercanías de la localidad de El Bolsón. Por otra parte, en afloramientos del Complejo Colohuincul ubicados en la costa norte del lago Nahuel Huapi se observa una estructura gnéisica subvertical de rumbo N14ºO, la ...
... Las segundas estructuras se generan cuando la extensión diferencial supera un cierto umbral o cuando existen estructuras preexistentes subparalelas a la dirección de extensión (Acocella et al. 2005). En el caso de la cuenca de Ñirihuau, la presencia de zonas de cizalla discretas de rumbo NE en el sector occidental del Macizo Nordpatagónico (Giacosa et al. 2001, Giacosa y Heredia 2004) y de rocas metamórficas con foliación de orientación N75ºE en el basamento de la región cordillerana (Dalla Salda et al. 1991 ) sugiere que las fallas de transferencia se generaron a partir de reactivaciones de las fracturas previas del basamento. ...
Introducción La zona abarcada en este estudio se encuentra ubicada en el borde oriental de la Cordillera Patagónica Septentrional (Fig. 1). El área está comprendida entre los paralelos 41°09 41°28, y entre los meridianos 70°56 71°20, al sureste de la localidad de San Carlos de Bariloche, provincia de Río Negro. Entre los 41 y 43º S, la Cordillera Patagónica Septentrional se caracteriza por la presencia de una faja ple-gada y corrida de edad andina y estilo estructural predomi-nante de piel gruesa (Ramos y Cortés 1984, Giacosa y Heredia 2004). En la zona de estudio, la estructuración de la faja plegada y corrida expone en superficie rocas volcánicas y sedimentarias terciarias que conforman parte del relleno de la cuenca oligo-miocena de Ñirihuau (Cazau et al. 1989). Numerosos investigadores estudiaron el área; sin embargo, no existe un consenso generalizado acerca del origen de la cuenca de Ñirihuau. Las primeras interpretaciones tectónicas la mencionaban como una típica cuenca de antepaís asocia-da al levantamiento de los Andes a estas latitudes (Ramos y Cortés 1984), teoría que fue adoptada por posteriores inves-tigadores (Giacosa et al. 2001). Por otro lado, Dalla Salda y Franzese (1987) y Spalletti y Dalla Salda (1996) interpreta-ron a la cuenca como de tipo "pull-apart", mientras que Mancini y Serna (1989) propusieron un origen extensional. El objetivo del presente trabajo es el de realizar un estudio Inflexiones en estructuras del sector norte de la faja plegada y corrida de Ñirihuau, provincia de Río Negro
... The most relevant topics on the genesis of the El Mait� en magmatism involve changes in the composition of the magma source, melting mechanisms, differentiation processes, and the interaction with the upper plate, as evidenced by the changes in its geochemical signature in relation to potential tectonic controls. Echaurren et al. (2016), Giacosa and Heredia (2002), Lizuain and Viera (2010), Sernageomin (2003), and Turner (1982). Main localities and morphostructural elements of North Patagonia are indicated in black. ...
... Contrastingly with the restricted Eocene record, Oligocene ages are the most frequent along the belt. Oligocene volcanic rocks crop out more to the east (Fig. 3), distributed along the north of Esquel, El Mait� en, El Bols� on, Bariloche and Junín de los Andes localities (Fern� andez Paz et al., 2019;Giacosa and Heredia, 2002;Rapela et al., 1988). Oligocene ages of the Ventana Formation range from 33 to 24 Ma, though they are concentrated mostly in the 33-30 Ma interval (Fig. 3). ...
During Mid-Cenozoic times, voluminous and genetically heterogeneous volcanism took place across North Patagonia in response to a period of plate tectonic reorganization. One of these volcanic associations is represented by the El Maitén Belt, located to the east of the main Andes for over ∼300 km. This volcanic belt reflects the evolution of a continental arc in an extensional setting with remarkable compositional variations between the late Eocene and the early Miocene. We present new field and isotopic data that, together with lithological, geochronological and geochemical data compilations, suggest significant changes in the nature and location of magmatic sources. This evolution may be summarized in three stages: i) incipient arc magmatism, with a tholeiitic basaltic-basaltic andesitic composition, which evolved to ii) a mature arc, characterized by calc-alkaline andesitic-dacitic associations, and a final stage characterized by iii) a late Oligocene-early Miocene juvenile, tholeiitic basaltic volcanism, interpreted as the result of a westward arc migration and extension in the back-arc. Therefore, considering the mid-Cenozoic tectonic configuration given by the eastward subduction of the Farallon and Nazca plates, we evaluate slab dynamics within a petrological framework that can reproduce the geochemical-geochronological characteristics of this belt. In this sense, rollback of the Nazca plate is the most suitable scenario to explain the El Maitén Belt behavior during this protracted extensional regime of Andean evolution.
... Los sedimentos que se observaron allí están formados por conglomerados matriz sostén intercalados con distintos bancos limo-arcillosos bien laminados o con laminación convoluta. Para su estudio y caracterización, se optó por discriminar dentro del llamado drift glaciario (-till-estratificado y no estratificado) (Flint y Fidalgo 1964, 1969, Diez y Zubia 1981) entre sedimentos glacifluviales y glacilacustres, till del dominio subglacial y till del dominio supraglacial, siguiendo las ideas de Giacosa et al. 2001, Colavitto 2014). Se destacan además las principales crestasmorénicas, entre las que sobresalen aquellas frente al cerro Perito Moreno, en el centro del mapa. ...
... El valle se encuentra limitado al este por una serie de cordones formados por complejos ígneos e ígneo-metamórficos neopaleozoicos y jurásicos, y al oeste por el cordón del Hielo Azul, donde afloran rocas plutónicas y volcánicas jurásico-cretácicas. El sinclinal de El Bolsón constituye una zona triangular, limitada por corrimientos con vergencia oriental que estructuran la Cordillera Principal (cerros Hielo Azul, Perito Moreno, Ventisquero, etc.) y corrimientos retrovergentes que estructuran las sierras del Serrucho y Piltriquitrón (Ramos y Cortés 1984, Giacosa et al. 2001 ). Así, dado el control estructural, este valle se extiende en dirección sur-norte, desde el lago Puelo hasta su intersección con el valle del río Manso, dónde comienzan a aparecer una serie de serranías más bajas entre las que se halla el cerro Negro (Fig. 1) Negro, se ha identificado un afloramiento de sedimentos glaciarios de aproximadamente 400 m de largo. ...
Sobre el faldeo nororiental del cerro Negro, en el extremo norte del valle de El Bolsón, en la Cordillera Patagónica de Río Negro, un corte de ruta expone un afloramiento de depósitos glaciarios de aproximadamente 400 metros de longitud. En dicha localidad se observaron una serie de rasgos deformacionales cuya descripción y análisis son objeto de este trabajo. A través de la confección de una serie de secciones y perfiles sedimentarios se interpretaron los depósitos y las estructuras como glaciotectónicas, producto de los esfuerzos que produce el movimiento glaciar, restando una investigación más exhaustiva para descartar su eventual conexión con procesos neotectónicos. Siendo así, la vergencia de las fallas y de los plegamientos observados permitió definir un avance de la masa glaciar desde el norte, siendo un aporte más para estudiar la dirección del flujo de hielo en este sector de los Andes durante el Último Máximo Glaciar. Además, se reconocieron dos pulsos de avance de los glaciares, el primero de los cuales puede no haber guardado expresión geomorfológica tras haber sido sobre cabalgado por el pulso posterior.
\n
Deformation evidences on the glacier sediments from the northernmost El Bolsón valley, Northpatagonian Andes
On the northeast face of Cerro Negro, in the northern extreme of the El Bolsón valley in the Patagonian Cordillera of Río Negro, a road cut left an outcrop of around 400-meters length of glacigenic deposits. In thislocation, some deformational features were observed, whose description and analysis are objects of this work. Through the development of a series of sedimentary sections and profiles, the observed structures were interpreted as glaciotectonic in origin, resulting from the stresses applied from the movement of glaciers. However, still remain further research to be done in order to discard their potential connection with
neotectonic processes. The folding direction indicates an advance from north to south, providing useful information on the study of ice flow direction in this Andean region during the Last Glacial Maximum. Moreover, two glacial advances were recognized, the first one having probably no geomorphological expression as it was overthr usted by a latter glacial advance.
... The North Patagonian Cordillera is characterized by the presence of the Quaternary volcanic arc of the Southern Andes Volcanic Zone including large stratovolcanoes that correspond to the highest elevations at these latitudes (see Stern 2004). A conspicuous feature of this region is Giacosa et al. 2001Giacosa et al. , 2005Bechis and Cristallini 2006;Bechis et al. 2014;Orts et al. 2012Orts et al. , 2015. Location of the performed structural cross sections and seismic lines interpreted in this study are shown. ...
... In this study, we present an integration of the structure and the geology of the retroarc zone between 40°and 43°30′S from the hinterland to the foreland area (Fig. 2). This was made through the compilation of previously published and our own data (e.g., Giacosa et al. 2001;Bechis and Cristallini 2006;Ramos et al. 2011;Tobal et al. 2012;Orts et al. 2012Orts et al. , 2015. The regional data integration has allowed the construction of five cross sections (Fig. 3) perpendicular to the strike of the main structures. ...
The Cenozoic tectonic evolution of the North Patagonian Andes is analyzed linking geological and geophysical data in order to decipher the deformational processes that acted through time and relate them to basin formation. Field observations and seismic reflection profiles reveal the shallow structure of the retroarc area where contractional structures, associated with Oligocene to early Miocene inverted extensional sections, are partially onlapped by early to late Miocene synorogenic deposits. From the construction of five structural cross sections along the retroarc area between 40° and 43° 30′S, constrained by surface, gravity, and seismic data, a shortening gradient is observed along Andean strike. The highest shortening of 18.7 km (15.34 %) is determined near to 41° 30′S where basement blocks were uplifted in the orogenic front area, and the deepest and broadest synorogenic depocenters were formed toward the foreland. Additionally, eastward shifting of Miocene calc-alkaline arc rocks occurred at these latitudes, which is interpreted as indicative of a significant change in the subduction parameters at this time. Deep crustal retroarc structure is evaluated through inversion of gravity models that made also possible to infer Moho attenuated zones. These coincide with the occurrence of younger than 5 Ma within-plate volcanics as well as with crustal thermal anomalies suggested by shallowing of the Curie isotherm calculated from magnetic data.
... Asimismo, en la Cordillera Norpatagónica no está aún del todo clara en las rocas de basamento, su evolución geológica integral para el Paleozoico . Según las recientes contribuciones de Giacosa y Heredia (2001 Heredia ( , 2004), Giacosa et al. (2005 Giacosa et al. ( , 2014b), Varela et al. (2005a), Pankhurst et al. (2006), GarcíaSansegundo et al. (2009) y Martínez et al. (2011 esta evolución es compleja con, al menos, tres eventos tectono-metamórficos y magmáticos. El más antiguo es del Devónico, luego otro del ciclo Gondwánico (Carbonífero -Pérmico) y finalmente el evento tectónico y magmático más joven es del ciclo Andino. ...
... El evento Devónico es compartido con el borde occidental del Macizo Norpatagónico . Se caracteriza por un magmatismo de arco (Ramos 1983, Varela et al. 2005a, Pankhurst et al. 2006, Gregori et al. 2011, Hervé et al. 2013) con un eje esbozado con rumbo ~N-S, metamorfismo regional (Vattuone 1988, 1990, Dalla Salda et al. 1991a y b, Urraza et al. 2006, Martínez et al. 2011 ) y procesos de deformación dúctil compresiva que lo acompañan (Giacosa y Heredia 2001, Giacosa et al. 2005, 2014b, García-Sansegundo et al. 2009). Tanto en el borde occidental del Macizo Norpatagónico como en la Cordillera Norpatagónica, las edades de los protolitos sedimentarios de las rocas metamórficas son anteriores o groseramente contemporáneas al evento Devónico. ...
Based on 23 whole rock chemical analyses of the igneous basement rocks from the Northwest Patagonia, Neuquén, Río Negro and Chubut provinces, we characterize the magmatism and tectonic setting for the region between 40º and 42º S, further west of 70º W. The analysed rocks are mainly granitoids (with one migmatite and another meta-basite), with ductile deformation. Previously, all these rocks have been isotopically dated by U-Pb, K-Ar and Sm-Nd methods, and then the crystallization and metamorphism-deformation ages, and extraction time from the mantle are known. According to their geological ages, they have been separated into Chanic (Devonian) and Gondwanic Groups (Carboniferous-Permian). In both cases, the granitoids are subalkaline, normal calc-alkaline, I- type, peraluminous, and related to their respective magmatic arcs, developed on continental margin. The Gondwanic granitoids were also compared with the granitoids of the same age ranging from Northpatagonian Massif, Cordillera Norpatagónica, and Cordillera Frontal from Mendoza (Argentina) and Chile.
... Los antecedentes específicos del área incluyen los tra- bajos de Volkheimer (1964), Volkheimer y Lage (1981), Franzese et al. (1992), Duhart et al. (2002) y Márquez et al. (2002. Se pretende que esta caracterización sirva para comparar con los resultados de los estudios petrológicos y geocronológicos realizados en la Formación Cushamen al norte del área tipo, particularmente los de), Cerredo (1997, Cerredo y López de Luchi (1999), Cerredo et al. (2000), Dalla Salda et al. (1990 Salda et al. ( , 1994), Giacosa et al. (2001, López de Luchi (1994), López de Luchi y Cerredo (1996) y López de Luchi et al. (2002) entre otros. Volkheimer (1964) y Volkheimer y Lage (1981), denominaron y mapearon como Formación Cushamen a un miembro mayoritario de rocas ectiníticas, que incluía micacitas, filitas cuarzosas y metacuarcitas filíticas y micáceas, y afloramientos de un miembro de migmatitas. ...
... Cerredo (1997) asignó las rocas pelíticas del cañadón La Angostura, ubicadas al oeste de la localidad de Río Chico, a la zona de la clorita y hasta la zona del granate con un clímax metamórfico con anatexis y emplazamiento de cuerpos graníticos tabulares. Al norte de Pilcaniyeu Viejo, Giacosa et al. (2001) vincularon el metamorfismo con la deformación asociada a una zona de cizalla dúctil compresiva vergente al NE en facies de anfibolitas (zona de cizalla dúctil Carhué). En las rocas esquistosas que afloran aisladamente en la sierra del Me- dio, Llambías et al. (1984) describieron rocas con cuarzo, biotita, sillimanita, moscovita y cianita como indicativas de la facies de anfibolitas, subfacies sillimanita- almandino-ortosa. ...
The pre-Triassic igneous-metamorphic basement of the SW border of the North-Patagonian Massif in Cushamen region is composed of metasedimentites, orthogneisses, foliated tonalites, foliated alkaline granites, leucogranites and diorites. Leucogranites and diorites present weak ductile deformation which allows us to considerer them as late to post-kinematics intrusions (post-regional foliation). The mineral metamorphic associations correspond to medium grade metamorphism (high grade amphibolitic facies) and a more extended low grade metamorphism (greenschist facies, biotite zone). Discrete sector associated to late deformations has low to very low grade. Metasedimentary rocks and orthogneisses have a penetrative foliation regionally crenulated. Two orthogonal directions of boudinage and folds axis indicate a strong flattening during ductile progressive syn-metamorphic deformation. NW to W-NW dominant regional foliation had an important control on the late-kinematics intrusions in the basement and on the Paleogene intrusions of the Huitrera Formation. The ductile and ductile-fragile basement structures and fabrics were formed in a stress field in which the plane that contain the maximum shortening axes (Z) has a 035°-215° strike.
... (Griffin et al. 2004) proveniente de las márgenes del Río Foyel, localidad tipo de la formación homónima. Asimismo, la datación K/Ar de un dique andesítico, que intruye a los depósitos marinos terciarios aflorantes en el cordón del Piltriquitrón (Giacosa et al. 2001), arrojó una edad de 31 Ma situándola en el Oligoceno temprano (Gradstein et al. 2004). Conexiones y brazos marinos han sido propuestos de antiguo (cf. ...
... Las dataciones de la unidad compilados en el trabajo de síntesis de Cazau et al. (1989) señala que el rango geocronológico se halla entre los 31 y los 16 Ma. Actualmente se reconoce que la Forma-ción Ventana, interpretada de modo clásico como unidad basal del relleno sedimentario de la cuenca de Ñirihuau, en realidad estaría precedida por los depósitos terciarios ubicados en la porción más occidental de la cubeta (Giacosa et al. 2001, Cazau et al. 2005 1984), y abarcaría las etapas iniciales de configuración y relleno de la cuenca, previos a la intrusión de las volcanitas de la Forma-ción Ventana. Consecuentemente, el Grupo El Foyel podría alcanzar los 3000 metros de potencia (Fig. 3). ...
The strong extensive tectonics caused by the negative roll-back of the subduction zone between the Farallón and Southamerican plates due to their relative velocity of convergence, from the Eocene until the early Oligocene, generated diverse marine depocenters connected with the Pacific Ocean, originating marine deposits of dominant deep facies. The restricted circulation and the dysoxic and even anoxic prevailing conditions were a consequence of the morphology of these depocenters; these conditions are inferred for the Río Foyel Formation. Crystalline gypsum internal moulds, of both specimens and isolated chambers of the foraminifera Transversigerina cf. transversa, from apparent basal samples of this formation; suggest a Pacific connection and deep water settings. Palynomorphs are scarce in the basal levels; in the upper levels, the abundance and diversity of dinocysts and the predominance of amorphous organic matter with abundant framboidal pyrite suggest anoxic marine environments relatively distal from the continental source area. The sporomorphs indicate the presence of template-humid forest with subordinate open areas and a remarkable input from the coastal environment.
... Asimismo, en la Cordillera Norpatagónica no está aún del todo clara en las rocas de basamento, su evolución geológica integral para el Paleozoico . Según las recientes contribuciones de Giacosa y Heredia (2001 Heredia ( , 2004), Giacosa et al. (2005 Giacosa et al. ( , 2014b), Varela et al. (2005a), Pankhurst et al. (2006), GarcíaSansegundo et al. (2009) y Martínez et al. (2011 esta evolución es compleja con, al menos, tres eventos tectono-metamórficos y magmáticos. El más antiguo es del Devónico, luego otro del ciclo Gondwánico (Carbonífero -Pérmico) y finalmente el evento tectónico y magmático más joven es del ciclo Andino. ...
... El evento Devónico es compartido con el borde occidental del Macizo Norpatagónico . Se caracteriza por un magmatismo de arco (Ramos 1983, Varela et al. 2005a, Pankhurst et al. 2006, Gregori et al. 2011, Hervé et al. 2013) con un eje esbozado con rumbo ~N-S, metamorfismo regional (Vattuone 1988, 1990, Dalla Salda et al. 1991a y b, Urraza et al. 2006, Martínez et al. 2011 ) y procesos de deformación dúctil compresiva que lo acompañan (Giacosa y Heredia 2001, Giacosa et al. 2005, 2014b, García-Sansegundo et al. 2009). Tanto en el borde occidental del Macizo Norpatagónico como en la Cordillera Norpatagónica, las edades de los protolitos sedimentarios de las rocas metamórficas son anteriores o groseramente contemporáneas al evento Devónico. ...
Based on 23 whole rock chemical analyses of the igneous basement rocks from the Northwest Patagonia, Neuquén, Río Negro and Chubut provinces, we characterize the magmatism and tectonic setting for the region between 40º and 42º S, further west of 70º W. The analysed rocks are mainly granitoids (with one migmatite and another meta-basite), with ductile deformation. Previously, all these rocks have been isotopically dated by U-Pb, K-Ar and Sm-Nd methods, and then the crystallization and metamorphism-deformation ages, and extraction time from the mantle are known. According to their geological ages, they have been separated into Chanic (Devonian) and Gondwanic Groups (Carboniferous-Permian). In both cases, the granitoids are subalkaline, normal calc-alkaline, I- type, peraluminous, and related to their respective magmatic arcs, developed on continental margin. The Gondwanic granitoids were also compared with the granitoids of the same age ranging from Northpatagonian Massif, Cordillera Norpatagónica, and Cordillera Frontal from Mendoza (Argentina) and Chile.
... This area is characterised by a strong precipitation gradient due to the rain shadow produced by the westerly winds from the Pacific Ocean as they pass over the southern Andes (Paruelo et al. 1998). The study area comprised different landscape types, mostly erosive relief over vulcanites, lava plains, and landforms created by glacio-fluvial and glaciolacustrine deposits (Giacosa and Heredia 2001). These differences resulted in a heterogeneous environment with a rich and diverse flora (Anchorena and Cingolani 2002;Speziale and Ezcurra 2012). ...
... This formation is characterised by a granitic facies formed by biotitic granites. The furthest one to the south-east corresponded to the Campana formation, characterised by olivinic basalts, whereas the one further east belonged to Estratos de Comallo, the oldest formation of the studied outcrops (Triassic -Lower Jurassic), composed by ignimbrites, andesites and basalts (Giacosa and Heredia 2001;Speziale and Ezcurra 2012). The elevation of the outcrops ranged from 737 to 1440 m a.s.l. ...
Background: Under climate-change scenarios, rock outcrops, by providing microclimatically diverse habitats, different
from those of surrounding zonal vegetation matrix, may serve as climatic refugia and thereby facilitate the persistence of
specialist species.
Aim: We tested whether rock outcrops of southern temperate latitudes could act as local refugia for a cold-adapted flora in
the face of global warming.
Methods: We related species composition of 50 outcrops and that of their surrounding vegetation to climatic data at local
and regional scales to establish whether species distributions reflected differences that could indicate the existence of
climatic refugia.
Results: While at a regional scale, species composition of the outcrops across the study area was related to mean annual
precipitation and mean annual maximum temperature, locally, southern faces of outcrops had different species and lower
maximum temperatures than insolated north faces and surrounding vegetation plots.
Conclusions: South faces of outcrops by providing cool microhabitats, and currently harbouring species not found in the
surrounding zonal vegetation matrix, could serve as local refugia for heat-intolerant plants and other microthermic organism.
The degree of ‘stability’ of these refugia will depend on the degree of future change in climate. Therefore, it is important to
plan protected area networks that maximise local environmental heterogeneity, including the protection of rock outcrops
both as refugia for cold-adapted species and as potential stepping stones that would allow dispersal of these species between
supportive environments through unfavourable ones.
Keywords: climate change; microclimate; refugia; rock outcrops; species composition
... En base a relaciones estratigráficas Asensio et al. (2005) (Griffin et al., 2004) que arrojó 30,65 Ma. Ésta coincide con la edad K/Ar de 31 Ma, obtenida sobre un dique andesítico, que intruye a la sección en el cordón del Piltriquitrón (Giacosa et al., 2001). Cornou (2012) y Quattrocchio et al. (2012) proponen una edad oligocena para la sección inferior de la Formación Río Foyel, la cual estaría avalada por la similitud de la presente asociación palinológica con otras de igual edad en Patagonia. ...
... subscabratus), Rutaceae (Rhoipites (Archangelsky, 1972;Romero, 1977;Romero y Zamaloa, 1985;Romero y Castro, 1986) Además de estos taxa la asociación derivada de la Formación Cerro Bororó (Archangelsky, 1973;Archangelsky y Zamaloa, 1986;Volkheimer et al., 2007;Scafati et al., 2009) y Spinizonocolpites hialinus con registro Daniano-Oligoceno y el mayor índice de similitud (0,71) obtenido con la Formación San Julián, Oligoceno (Barreda, 1997c;Náñez et al., 2009;Heredia et al., 2012) de Cuenca Austral. Teniendo en cuenta que sobre los niveles estudiados yacen, en contacto neto, depósitos marinos de la Formación Río Foyel (sección inferior) cuya edad fue establecida, en base a dataciones radimétricas, como Oligoceno temprano (Giacosa et al., 2001;Griffin et al., 2004), se sugiere en este trabajo una edad Eoceno medio-Oligoceno temprano para la Formación Salto del Macho. ...
556
AMEGHINIANA - 2014 - Tomo 51 (6): 556 – 571 ISSN 0002-7014
AMGHB2-0002-7014/12$00.00+.50
PALINOESTRATIGRAFÍA DE LA FORMACIÓN
SALTO DEL MACHO, PALEÓGENO DE LA
CUENCA DE ÑIRIHUAU, ARGENTINA
M. ELINA CORNOU1,2, MIRTA E. QUATTROCCHIO1 AND MARCELO A. MARTÍNEZ1,2
1Instituto Geológico del Sur–Consejo Nacional de Investigaciones Científicas y Técnicas, San Juan 670, B8000ICN Bahía Blanca, Buenos Aires, Argentina.
elina.cornou@uns.edu.ar; mquattro@criba.edu.ar; martinez@criba.edu.ar
2Universidad Nacional del Sur, Departamento de Geología, San Juan 670, B8000ICN Bahía Blanca, Buenos Aires, Argentina.
Resumen. Se da a conocer el registro completo de palinomorfos de la Formación Salto del Macho (Paleógeno) en su localidad tipo, sección
Río Foyel, sector andino de la Cuenca de Ñirihuau, Argentina. Se identificaron elementos de origen continental y marino. En total 109 especies
correspondientes a esporas de Bryophyta, Lycopodiophyta y Polypodiopsida, granos de polen de Gymnospermophyta y Magnoliophyta
(Angiospermae), algas continentales y microplancton marino de pared orgánica. Se presenta la distribución estratigráfica de los esporomorfos
reconocidos en la Formación Salto del Macho, en otras cuencas del Paleógeno–Neógeno Temprano (Mioceno) de Patagonia argentina,
Chile y Antártida. La presencia de Echitriporites trianguliformis forma A Müller et al., Psilatricolpites minutus González Guzmán y Myrtaceidites
parvus forma nesus Cookson y Pike en la Formación Salto del Macho, constituye la primera mención de estas especies en Argentina. Una
edad comprendida entre el Eoceno medio y el Oligoceno temprano es aquí propuesta para esta unidad a partir del registro de marcadores
palinoestratigráficos y del resultado de los análisis palinoestratigráfico y multivariado.
Palabras clave. Palinoestratigrafía. Paleógeno. Formación Salto del Macho. Cuenca de Ñirihuau. Argentina.
... (Griffin et al. 2004) proveniente de las márgenes del Río Foyel, localidad tipo de la formación homónima. Asimismo, la datación K/Ar de un dique andesítico, que intruye a los depósitos marinos terciarios aflorantes en el cordón del Piltriquitrón (Giacosa et al. 2001), arrojó una edad de 31 Ma situándola en el Oligoceno temprano (Gradstein et al. 2004). Conexiones y brazos marinos han sido propuestos de antiguo (cf. ...
... Las dataciones de la unidad compilados en el trabajo de síntesis de Cazau et al. (1989) señala que el rango geocronológico se halla entre los 31 y los 16 Ma. Actualmente se reconoce que la Forma-ción Ventana, interpretada de modo clásico como unidad basal del relleno sedimentario de la cuenca de Ñirihuau, en realidad estaría precedida por los depósitos terciarios ubicados en la porción más occidental de la cubeta (Giacosa et al. 2001, Cazau et al. 2005 1984), y abarcaría las etapas iniciales de configuración y relleno de la cuenca, previos a la intrusión de las volcanitas de la Forma-ción Ventana. Consecuentemente, el Grupo El Foyel podría alcanzar los 3000 metros de potencia (Fig. 3). ...
La fuerte tectónica extensional producida por el roll-back negativo de la zona de subducción entre las placas Farallón y Sudamericana, desde el Eoceno hasta el Oligoceno temprano, generó diversos depocentros que fueron inundados por el océano Pacífico, originando depósitos marinos con predominio de facies profundas. Las condiciones de circulación marina restringida, anóxicas hasta disóxicas, inferidas para la Formación Río Foyel serían consecuencia de la morfología de los mencionados depocentros. Moldes de yeso cristalino de ejemplares y de cámaras aisladas de Transversigerina cf. transversa en las muestras aparentemente basales de esta formación indicarían una conexión pacífica y profunda. Los niveles basales preservan escasos palinomorfos, pero en los niveles superiores la diversidad y abundancia de dinoquistes y el predominio de materia orgánica amorfa con abundante pirita framboidal sugieren ambientes marinos anóxicos, relativamente distales al área de aporte continental. Los esporomorfos denotan la presencia de bosques templado-húmedos con áreas abiertas subordinadas y gran aporte del ambiente costero.
... The study area comprises different types of landscapes, mostly erosive relief over vulcanites, lava plains, and landforms originated by glacio-fluvial and glacio-lacustrine deposits (Giacosa and Heredia, 2001). These differences determine a heterogeneous environment with a rich flora (Anchorena and Cingolani, 2002). ...
... This formation is characterized by a granitic facies formed by biotitic granites. The furthest one to the southeast corresponds to Campana formation characterized by olivinic basalts, whereas the one further east belongs to Estratos de Comallo, the oldest formation of the studied outcrops (Triassic -Lower Jurassic), composed by ignimbrites, andesites and basalts (Giacosa and Heredia, 2001). Even though their origins differ, most outcrops are similar in that most of them are of volcanic origin and predominantly composed of porphyry and andesitic lavas and basalts. ...
Outcrops around the world enhance biodiversity as they provide heterogeneous environments and varied habitats for species with different requirements than those living in the surroundings, and in this way they increase alpha and beta diversity. We studied the floristic composition of the vegetation of rock outcrops in northwestern Patagonia, Argentina, and compared them to the surrounding matrix of shrubland and steppe. For this we sampled 50 outcrops and 50 matrix plots close to them, identified all the species present, and analyzed their floristic composition with Detrended Correspondence Analysis (DCA). We also analyzed the floras of the north and south faces of the outcrops. The resulting ordinations were related to geographic gradients of the region. The proportions of alien to native species, different life forms, and phylogenetic groups of the outcrop floras were compared to the matrix with G-tests. Our results showed similar dominant families, life form proportions and percentage of alien species in the outcrops and the surrounding matrix. However, species composition of the outcrops was markedly different. North Patagonian outcrops present several taxa not found in the matrix, especially in their southern, less insolated walls. The previously recorded distribution of most of these exclusive species is found in colder areas further south. Thus, we hypothesize that outcrops could be acting as relicts of cold-adapted glacial paleofloras that were probably more extended during glacial times and retreated south after the last glacial maximum.
... Geochronological data is available at Supplementary material (Table S2). Geological data modified from Giacosa et al. (2001); González et al. (1999); Remesal et al. (2001); Franchi et al. (2001); Ardolino et al. (2001); Anselmi et al. (2004); Sacomani et al. (2007); Silva Nieto (2005); Haller et al. (2010) and Pezzuchi (2011). NPM: North Patagonian Massif, DM: Deseado Massif. ...
... En sus nacientes atraviesa rocas volcánicas (de basaltos a riolitas), piroclásticas (incluyen ignimbritas, tobas y vitrófiros) y también rocas sedimentarias marinas y continentales. Luego pasa a recorrer un ambiente de rocas sedimentarias continentales de edad miocena inferior que constituyen la Formación Ñirihuau y hacia el norte, afloran los elementos de la Formación Huitrera del Paleógeno, integrados por ignimbritas y tobas dacíticas y riolíticas , andesitas, traquitas y basaltos, areniscas y conglomerados continentales (Giacosa y Heredia, 2001). En el tramo inferior atraviesa granitoides paleozoicos y facies clásticas de la Formación Collón Cura (Nullo, 1979). ...
Las investigaciones arqueológicas en América Latina han aportado una visión del pasado que nos permite conocer los procesos a través de los cuales se fue construyendo el desarrollo humano. No obstante, constituye un denominador común acercarnos al conocimiento de nuestra región a través de miradas externas, como consecuencia del imperialismo cultural y el financiamiento de los denominados “países centrales” a sus respectivos investigadores. En ocasiones, las narrativas propias nos son ajenas, precisamente por esa carencia de dar a conocer lo que producimos en un ámbito más amplio. Esta obra cumple ese cometido, en pos de generar nuevas iniciativas que integren y difundan las investigaciones que se llevan a cabo en América Latina, con especial interés, en esta ocasión, en Cuba y Argentina, a partir de diversos intercambios académicos entre ambos países que han estrechado los lazos de cooperación.
... El contacto con la infrayacente Formación Troncoso es claramente disconforme, y se encuentra muy bien expuesto en las márgenes del Río Foyel aguas arriba del Puesto Troncoso, donde se ubica su estratotipo. En contacto neto, sobreyace la Formación Río Foyel con edades Oligoceno temprano (Giacosa et al., 2001;Griffin et al., 2004) y Oligoceno tardío-Mioceno (Barreda et al., 2003). Por lo cual la edad de la Formación Salto del Macho abarcaría un lapso de tiempo que va desde el Eoceno medio hasta el Oligoceno temprano. ...
The first palynological data from the type locality of the Salto del Macho Formation, at the Rio Foyel section, Nirihuau Basin, Argentina, is here presented. Nineteen taxa of trilete and monolete spores of Bryophyta and Tracheophyta (Lycopsida and Polypodiopsida) belonging to the following genera were recorded: Anthocerisporis, Azolla, Baculatisporites, Biretisporites, Cingutriletes, Cyatheacidites, Cyathidites, kchyosporites, Laevigatosporites, Matonisporites, Muricingulisporis, Peromonolites, Polypodiisporites, Reboulisporites, Retitriletes, Trilites and Tuberculatosporites. The palynoflora is dominated by representatives of the Class Polypodiopsida, with predominant Cyatheaceae and Dicksoniaceae, in asociation whith Osmundaceae and Blechnaceae. The comparison of the record of spores with that of other Paleogene/early Neogene basins from Argentinian Patagonia, Chile and Antartica, made through the PAST program, shows remarkable palynofloristic similarities between Salto del Macho Formation with the spore associations recorded in the Rio Foyel, Chenque and San Julian formations. The accompanying palynoflora (Nothofagaceae, Podocarpaceae, Araucariaceae, Myrtaceae, Botryococcus braunii and low diversity of dinocysts) suggests a marginal-marine enviroment, in conditions of sub-normal salinity and temperate-warm water temperature.
... Éste ejerce actualmente una fuerte influencia en los cursos de los ríos Manso y Azul, los cuales muestran en algunos tramos un marcado comportamiento subsecuente. Durante el Plioceno y el Cuaternario, este valle fue ensanchado y profundizado por la acción glaciar, evidenciada por un relleno de más de 200 metros de depósitos de drift glaciario (Giacosa y Heredia 2002) y por diversas geoformas glaciarias, como los cordones morénicos que se ven en el mapa de la figura 1 y aquellos ubicados al frente del cerro Perito Moreno, al sur de la zona de este trabajo. En el área de estudio se realizaron una serie de perfiles de estos depósitos glaciarios a los 41º34'30 " S y 71º30'25 " O, sobre el corte del camino que bordea el río Manso en el cerro Negro y sobre la ruta 40 (Fig. 1). ...
... El contacto con la infrayacente Formación Troncoso es claramente disconforme, y se encuentra muy bien expuesto en las márgenes del Río Foyel aguas arriba del Puesto Troncoso, donde se ubica su estratotipo. En contacto neto, sobreyace la Formación Río Foyel con edades Oligoceno temprano (Giacosa et al., 2001;Griffin et al., 2004) y Oligoceno tardío-Mioceno (Barreda et al., 2003). Por lo cual la edad de la Formación Salto del Macho abarcaría un lapso de tiempo que va desde el Eoceno medio hasta el Oligoceno temprano. ...
PALYNOLOGICAL STUDY OF SPORES FROM SALTO DEL MACHO FORMATION, PALEOGENE OF THE ÑIRIHUAU BASIN, ARGENTINA. The first palynological data from the type locality of the Salto del Macho Formation, at the Río Foyel section, Ñirihuau Basin, Argentina, is here presented. Nineteen taxa of trilete and monolete spores of Bryophyta and Tracheophyta (Lycopsida and Polypodiopsida) belonging to the following genera were recorded: Anthocerisporis, Azolla, Baculatisporites, Biretisporites, Cingutriletes, Cyatheacidites, Cyathidites, Ischyosporites, Laevigatosporites, Matonisporites, Muricingulisporis, Peromonolites, Polypodiisporites, Reboulisporites, Retitriletes, Trilites and Tuberculatosporites. The palynoflora is dominated by representatives of the Class Polypodiopsida, with predominant Cyatheaceae and Dicksoniaceae, in asociation whith Osmundaceae and Blechnaceae. The comparison of the record of spores with that of other Paleogene/early Neogene basins from Argentinian Patagonia, Chile and Antartica, made through the PAST program, shows remarkable palynofloristic similarities between Salto del Macho Formation with the spore associations recorded in the Río Foyel, Chenque and San Julián formations. The accompanying palynoflora (Nothofagaceae, Podocarpaceae, Araucariaceae, Myrtaceae, Botryococcus braunii and low diversity of dinocysts) suggests a marginal-marine enviroment, in conditions of sub-normal salinity and temperate-warm water temperature.
... To the west, the dotted yellow line represents the emergent deformational front. Giacosa et al., 2001Giacosa et al., , 2005Bechis and Cristallini, 2006;Bechis et al., 2014;Orts et al., 2012, and new data). Location of the performed structural cross sections and seismic lines interpreted in this study are shown. ...
The Oligocene to present evolution of the North Patagonian Andes is analyzed linking geological and geophysical data in order to decipher the deformational processes that acted through time and relate them to basin formation processes. Seismic reflection profiles reveal the shallow structure of the retroarc area where contractional structures, associated with Oligocene to early Miocene inverted extensional depocenters, are partially onlapped by early to late Miocene synorogenic deposits. From the construction of five structural cross sections along the retroarc area between 40 • and 43 • 30 S, constrained by surface, gravity and seismic data, a shortening gradient is observed along Andean strike. The highest shortening of 18.7 km (15.34%) is determined near 41 • 30 S coincidentally with maximum mean topographic values on the eastern Andean slope, where basement blocks were uplifted in the orogenic front area, and the deepest and broadest synorogenic depocenters were formed towards the foreland. Additionally, eastward shifting of Miocene calc-alkaline rocks occurred at these latitudes, which is interpreted as indicative of a change in the subduction parameters at this time. Deep crustal retroarc structure is evaluated through inversion of gravity models that made possible to infer Moho attenuated zones. These coincide with the occurrence of younger than 5 Ma within-plate volcanics as well as with crustal thermal anomalies suggested by shallowing of the Curie isotherm calculated from magnetic data. Younger volcanism and thermal anomalies are explained by slab steepening since early Pliocene, after a mild-shallow subduction setting in the middle to late Miocene, age of the main compressive event.
... Posteriormente, surgieron trabajos tales como la descripción geológica de la Hoja 40a, Monte Tronador (Greco, 1975) y el estudio de la cuenca del río Manso (González Bonorino, 1976), que incorporó un mapa geológico de detalle. Más recientemente, Giacosa y Heredia (2001) elaboraron la Hoja Geológica San Carlos de Bariloche. ...
A petrological study, combined with field and microstructural evaluation of metapelites, metabasites and a tonalitic to quartz-dioritic rock of Cerro Catedral, North Patagonian Andes of Argentina, reveals the protracted polyphase deformational and metamorphic evolution of the area during the Late Paleozoic to Mesozoic. The 11-component system Si–Ti–Al–Fe–Mn–Mg–Ca–Na–K–O–H was used to model the bulk-rock composition of a mylonitic garnet- and andalusite-bearing micaschist. For this purpose, a P-T pseudosection was calculated using the GeoPs software and contoured with isopleths and mineral isomodes of interest. Refractory zoned garnet typically exhibits a prograde bell-shaped compositional zoning. Its core (gros+andr0.29, spes0.13, pyr0.02, alm0.55) to rim (gros+andr0.22, spes0.05, pyr0.04, alm0.69) compositions yield a prograde path from initial conditions of ∼9 kbar and 490-500 °C to ∼12 kbars and 510 °C. The remnant compositions (Si: 3.10-3.18 apfu) of K-white mica of the dominant S2m-foliation support these physical conditions. The, thus, calculated low geothermal gradient of 11-14°Ckm-1 suggests that the studied rocks were transported to a maximum depth of ∼45 km in a shallow paleosubduction zone. Microstructures of coalescent quartz ribbons might indicate a peak temperature around 650 °C after peak pressure conditions. These quartz-ribbons of S2m-mylonitic foliation are slightly wrapped around sigmoidal syn-kinematic plagioclase (Ab76-Ab83) containing a Si-foliation. The outermost garnet rim (gros+andr0.08, spes0.07, pyr0.05, alm0.80) also grew syn-kinematically with the S2m, and indicates a dominant tectonic exhumation into the middle crust (5.5 kbar ≈ 20 km) with a subsequent cooling to 550°C. A randomly oriented mineral assemblage of andalusite and biotite indicates a subsequent low-pressure (< 3 kbar) thermal overprint between 627 ± 24 °C and 664 ± 50 °C, calculated by Ti-in-biotite geothermometers, near the ductile-deformed tonalite pluton. High Y2O3 (> 1.5 wt.%) homogeneous monazite yielded a Middle Jurassic age (170 ± 4 Ma). Subsequent cooling produced large muscovite laths (Si: ∼3.0 apfu) in metapelites prior to the generation of upward open folds and a S3-crenulation cleavage below 500 °C and late low-grade S-C mylonites. Microstructures in minerals indicate high- to low-temperatures solid-state deformation in the igneous and country rocks during the cooling phase. A final retrogression by chlorite and sericite overprinted the metapelites and the intrusive at < 400 °C. The deciphered ẞ-shaped P-T-d path provide constraints on the geotectonic evolution of this particular sector of the North Patagonian Andes, from a Gondwanan subduction setting, followed by exhumation with intense shearing and ending with a contact metamorphism in the Jurassic, prior to Andean orogeny.
With only four species, Pteridium is one of the most-known fern genera for its role as pioneer in ecological succession and for being an aggressive weed. Despite its current wide distribution that extends to almost the entire world, there is a relatively small number of fossil records of macrofossils and palynological assemblages
related to or compared with this genus. The majority of these belong to Oligocene ─ Pliocene deposits from the United States, Europe, Asia and New Zealand and only one has been described for South America, in upper Pliocene? – Quaternary deposits from Brazil. In this contribution, we describe the oldest and southernmost record
of Pteridium for South America, based on frond impressions from Miocene deposits of the Ñirihuau Formation, exposed in the North Patagonian Andes (Argentina) and interpreted as deposited in alluvial, lacustrine, deltaic, and fluvial environments. We illustrate the finding and compare it with previous records of Pteridium and Pteris
and with the current Neotropical species Pteridium esculentum. Additionally, we characterise the palaeoenvironmental framework in which the palaeoflora developed and we discuss the association of the fossil with other taxa fossils found in the same deposits, and of Pteridium with other species in current floras.
Yarquen dolgopolae gen. et sp. nov. is described from fragmentary fossil bones (humerus and phalanges) found in the Middle Miocene Collón Curá Formation (Río Negro Province, Argentina). Fossil owls in Argentina are limited to occasional fragments as old as the Early Miocene to Late Pleistocene. Here, an extinct species is described. The humerus (MLP 92-V-10-86) is similar in size to that of the Short-eared Owl but differs mainly by the depth and arrangement of the fossa m brachialis, the fossa olecrani is shallow and rimless, the sulcus scapulotricipitalis is shallow, a pneumatic foramen located on a scar proximal to the condylus ventralis, the incisura intercondilaris is narrow and the condylus ventralis is rounded with a conspicuous groove running caudoventrally. The ungual phalanx of digit 1 shows a strongly curved corpus, lateral grooves on both sides, a processus extensorius dorsally directed, a flexor tubercle wide and robust and a crista slightly protruding that separates both cotylae. Aves recovered from the Collón Curá Formation correspond to diurnal hunters (Phorusrhacidae and Falconidae) to which is added this large owl that, like other Strigidae, presumably was nocturnal or crepuscular hunters.
An approximately 3500 m thick stratigraphic section was detailed surveyed in order to study the tectono-sedimentary evolution of the Ñirihuau Formation along the Arroyo Las Bayas, in the northern sector of the Ñirihuau basin, North Patagonian Andes. A total amount of 29 lithofacies were recognized and used to define facies, grouped into six facies associations (FA) that reflect different paleoenvironments: FA1 (Gray to brownish conglomerates), FA2 (Conglomerates and sandstones), FA3 (Tabular mudstones), FA4 (Brownish sandstones and conglomerates with large scale foresets), FA5 (White tuffaceous sandstones) and FA6 (Sandstones and conglomerates with mudstones). The lower section of the unit was interpreted as deposited in a medium to distal alluvial fan or an axial fluvial system developed in the most distal zone of an alluvial fan (FA1 and FA2). The middle section of the unit is characterized by a Gilbert-type delta developed between two lacustrine sequences (FA3 and FA4). In the upper section of the unit, higher energy deposits corresponding to fluvial systems are registered (FA5 and FA6). Deposits from synchronic volcanic events are recorded along the stratigraphic section. Also, a provenance analysis was carried out by using sedimentary petrography and U–Pb zircon geochronology data. The main identified sediment source corresponds to the contemporaneous Miocene volcanic arc. A secondary detrital provenance from older Cenozoic volcanic rocks of the El Maitén Volcanic Belt was also identified, as well as minor contributions from pre-Cenozoic igneous and metamorphic units. U–Pb geochronological data constrain deposition of the middle and upper sections of the Ñirihuau Formation in the Arroyo Las Bayas section to the middle to late Miocene, between 15 and 11.4 Ma (Langhian to Tortonian). Also, a possible middle Miocene age was discussed for the lower section. An integrated tectono-stratigraphic model was finally proposed, with contrasting extensional and synorogenic tectonic stages registered in the lower and upper sections of the Ñirihuau Formation, respectively.
Quartz segregations in paragneisses from the Paleozoic basement of the North Patagonian Andes contain highly saline multiphase fluid inclusions with the rare daughter mineral ferropyrosmalite detected by Raman analysis, besides halite, sylvite, hematite, and/or magnetite. During heating experiments, L-V homogenization occurs (256–515 °C), followed by halite dissolution (287–556 °C) and the dissolution of ferropyrosmalite at 550–581 °C. The latter phase transition triggers the growth of clinoamphibole crystals according to the following idealized reactions, written for potential end-members:
4 F e 8 S i 6 O 15 [ ( O H ) 6 C l 4 ] + 6 C a 2 + ( a q ) Ferropyrosmalite ↔ 3 C a 2 F e 5 S i 8 ↔ O 22 ( O H ) 2 + 17 F e 2 + ( a q ) + 16 C l − ( a q ) + 12 O H − + 3 H 2 Ferro-actinolite F e 8 S i 6 O 15 [ ( O H ) 6 C l 4 ] + 2 C a 2 + ( a q ) Ferropyrosmalite + Fe 3 + ( aq ) + 2Al 3 + ( aq ) + Na + ( aq ) + H 2 O ↔ Na C a 2 ( Fe 4 2 + F e 3 + ) ( Al 2 Si 6 ) ↔ O 22 Cl 2 + 4 F e 2 + ( a q ) + 2 C l − ( a q ) + 4 H 2 Chloro-hastingsite
Ferropyrosmalite ↔ Chloro-hastingsite The amphibole resembles the composition of ferro-actinolite but also has striking similarities with chloro-hastingsite, as indicated by Raman spectroscopy. During the heating experiment, hematite (when present) transforms to magnetite by the uptake of H2, whereas inclusions without Fe-oxides contain traces of H2 after the reaction. This mineral transformation shows that ferropyrosmalite might result from the retrograde re-equilibration of amphibole with the brine, implying the uptake of Fe2+, Cl–, and H2O and the enrichment of Ca2+ in the brine. Pervasive fluid flow and fluid-assisted diffusion are recorded by channel way microstructures, healed microfractures, and dissolution-reprecipitation phenomena, as demonstrated by cathodoluminescence microscopy. These alkali- and FeCl2-rich brines, derived from magmatic sources and of possible Mesozoic age, were related to regional metasomatism, coeval with widespread granitoid activity.
Evidence is growing that a belt of Devonian plutonism is present in the Northern Patagonian segment of the present-day Andes. This plutonism formed along the paleo-Pacific margin of the Gondwana supercontinent. New whole rock chemistry and SHRIMP U–Pb zircon data for plutonic rocks of the San Martín de los Andes batholith (southwestern Argentina) provide insights into the magmatic and tectonic evolution of the southwestern Gondwana margin during the middle Palaeozoic. The San Martín de los Andes batholith was formed between 390 and 374 Ma and intruded into a Lower Paleozoic metamorphic basement that had been previously affected by Late Ordovician-middle Silurian deformation. Most of the batholith is composed of metaluminous, calc-alkaline tonalites and granodiorites, with subordinate volume of peraluminous garnet-bearing granites. Discrete and disperse gabbroic and dioritic rocks hosted in tonalites and granodiorites occur as either microgranular enclaves or syn-magmatic dykes. Tonalitic, granodioritic and granitic rocks develop transitional contacts among them revealing coetaneous building up throughout the plutonic suite, but when interpreting their chemical variability, they are not strictly comagmatic rocks. Collectively, field, petrographic, and geochemical data of the San Martín de los Andes batholith are interpreted to reflect concurrence of crystal fractionation, crustal assimilation and magma mixing in driving petrological diversification. Yet, gabbroic and dioritic rocks in the San Martín de los Andes batholith display geochemical characteristics of calc-alkaline primitive basalts that concur with what is being hypothesized to be a magmatic arc zone for the Devonian period. This study discusses how to interpret the evolution of the San Martín de Los Andes batholith together with other geodynamic models such as the Chaitenia magmatic arc.
We recall here recent developments concerning the filling and paleogeography of the Neogene Collón Curá basin in the foothill of the North Patagonian Andes. To better constrain its evolution, we bring two new ⁴⁰Ar/³⁹Ar on biotite datings of two ignimbrites that allow bracketing of the filling between 19.04 ± 0.72 and 5.06 ± 0.69 Ma. Like the other intramontane basins of the North Patagonian foothill, the Collón Curá basin initiated around 18 Ma at the time of the Quéchua phase. This corresponds in the area neither to an increase of the convergence rate of the Nazca and South America plates, nor to a significant change in the angle of convergence. We propose to look at this profound alteration of the regional stress regime in the light of the recent results of analog and numerical modeling of subduction. Folding of the slab above the mantle discontinuity at 660 km depth leads to the development of geometries that we retrieve in seismic tomography images in the region. Modeling shows that the overriding plate is coupled to this folding in depth. It suffers from changes in stress (from extensive to compressive stress regime) and topography. It is assumed that a more compressive stress regime will favor the reactivation of border faults of the basin and a regional uplift, hence agradation in basins. On the contrary, subsidence associated with a decrease in shortening will favor the backward erosion that will cannibalize these basins. The life duration of basins will be modulated by efficiency of earth surface processes proper to each watershed (catchment area, river slopes, lithology …). This internal cyclicity of subduction due to slab folding is freed from the kinematics of convergence. It is now necessary to look for the expression of this process in the sequential filling of the basins.
The El Foyel Group is defined in the western section (Andean) of the Ñirihuau Basin, Argentina (41°44′S-71°30′W). It consists of three units: the Troncoso, Salto del Macho and Río Foyel formations. The age of the group and of the formations is still controversial. We studied the fungal remains recovered from 14 palynological samples from outcrops in the group with the intention of providing data to solve this problem. The fungal assemblage found is highly diverse and it is mostly composed of spores of different affinities (mainly ascomycetes). We identified 38 species from 18 genera (Anatolinites, Dictyosporites, Didymoporisporonites, Diporicellaesporites, Diporisporites, Dyadosporites, Exesisporites, Foveodiporites, Hypoxylonites, Inapertisporites, Lacrimasporonites, Monoporisporites, Multicellites, Papulosporonites, Pluricellaesporites, Polycellaesporonites, Staphlosporonites and one indet.). Moreover, we propose two new species (Hypoxylonites foyelensis sp. nov. and Pluricellaesporites patagonicus sp. nov.) and a new combination (Dyadosporites annulatus comb. nov.). Most of the species were recovered from samples from the Troncoso Formation (21), while the Salto del Macho and Río Foyel formations showed lesser diversity. Anatolinites subcapsilaris, Dyadosporites subovalis, Inapertisporites subovoideus, Monoporisporites singularovalis and Multicellites ellipticus, biomarkers from the Middle Eocene appeared in the Troncoso and Salto del Salto del Macho formations; whereas indicators of the Eocene-Oligocene, such as Dyadosporites elsikii, Didymoporisporonites panshanensis, Foveodiporites elegans, Lacrimasporonites fusoides and Multicellites leptaleus, were mainly recorded in the Río Foyel Formation. The appearance of the biomarkers mentioned above reinforces the Palaeogene age proposed for the El Foyel Group in previous palynological studies. The record of Hypoxylonites ater (Miocene) in the Salto del Macho formation would expand its range as far back as the Palaeogene.
The Tronador Volcanic Group (TVG) is located in the transition between the central and southern segment of the Andean Southern Volcanic Zone (SVZ), =50 km to the east of the current volcanic front. The TVG includes, from older to younger, the deeply eroded Early Pleistocene Garganta de Diablo unit (GDU; ≈1.3 Ma) and Steffen volcanic complex (SVC), the Middle Pleistocene Tronador Volcanic Complex (TVC; <1.0 Ma to ≈300 ka), as well as the post-glacial Fonck monogenic volcanic cone. Temporal petrochemical variations observed for older compared to younger samples from the TVG are similar to differences occurring across the active southern SVZ arc, from the current volcanic front to centers east of the front, and consistent with decreasing input of slab-derived fluids, and consequently decreasing percent of partial melting of the mantle source of the TVG. Relatively depleted (K2O<0.96 wt %; Rb<26 ppm; La<14.6 ppm) Group I basalts and basaltic andesites, and medium-K more differentiated rocks, were erupted to form the GDU and SVC during the Early Pleistocene. These have Ba/La>20 similar to the current volcanic front, but higher La/Yb and lower Yb, consistent with their genesis by 10% partial melting of subarc garnet-peridotite mantle, followed by 20% fractional crystallization involving olivine, clinopyroxene and plagioclase. Younger TVC Group I basic rocks have similar Ba/La, but higher Yb, and were generated by slightly lower degrees (7%) of partial melting in shallower garnet-free mantle. Beginning in the Middle Pleistocene (≈500-300 ka, Tronador II and III units of the TVC) relatively enriched (K2O>0.96 wt %; Rb>31 ppm; La>20 ppm) Group II basalts, with geochemical characteristics similar to volcanic centers east of the current volcanic front (Ba/La<20), were erupted together with Group I basalts. The generation of Group II rocks are consistent with 5% partial mantle melting in drier and shallower plagioclase-bearing mantle modified by less fluids derived from the subducted slab than involved in the generation of Group I rocks. Although these petrochemical changes were gradual, the relative volume of magma erupted across this region of the SVZ arc changed in the late Middle Pleistocene, after ≈300 ka, with the nearly complete termination of volcanic activity in the TVG and growth of Osorno and Calbuco volcanoes along the current volcanic front at this latitude.
The Late Cenozoic mineral resources of Argentine Patagonia represent a group of deposits of varied characteristics, intimately related to the geology of the existing morphostructural units and to the sequence of geological, geomorphological, and paleoclimatic processes that took place during the Late Cenozoic times. The prevailing climatic conditions during the last 10 Ma in this region have played a significant role in the genesis of some of the mineral concentrations discussed in this chapter. The mineral deposits have been subdivided into three main groups according to the geological environment in which they have been formed: (1) detritic, (2) evaporitic, and (3) volcanic. The Quaternary gold-bearing detritic deposits are found both along the Atlantic coast and in the fluvial drainage systems at the Andean foothills. Their importance is related to their probable economic use and as a prospective tool in the search for older primary mineralization areas. The detritic iron-titaniferous deposits in the southern coast of Buenos Aires Province are the sole titanium resources of Argentina. However, their actual economic importance is still unknown. Evaporitic deposits are the most important economic Holocene mineral resources of Argentine Patagonia and show a wide regional distribution.
The Cenozoic structure of the North Patagonian Andes of Argentina (41°-42° S) is characterised by an E-verging imbricated fold and thrust belt with some important back-thrusts. The western sector (west of 71° 15′ W) exhibits back-thrust systems that interact with the E-verging thrusts conforming triangular areas. There are two important back-thrust systems that have deformed both the Piltriquitrón (2,284 m) and Serrucho ranges (2,120 m). The first is composed of three W-verging thrusts with belts of intense deformation; the second system consists of at least two N-trending faults that form the great western scarp of the mountain range. As a consequence of the interaction with the E-verging thrusts, the Paleogene deposits of the El Bolsón valley have been deformed into a large N-trending drag-syncline. From a stratigraphical point of view, the back-thrust systems expose igneous and metamorphic rocks of the pre-Mesozoic basement. Their cartographic pattern suggests that both are branches of the Ventana - Catedral thrust, a main structure that is the boundary between the western and the eastern sectors of the fold and thrust belt. It is proposed that the surface structure might represent a subsurface thick-skinned triangular zone, whose location is related to the Cenozoic tectonic inversion of normal faults formed during Mesozoic extensional regime, which controlled the palaeogeographic distribution of the Jurassic volcano-sedimentary deposits.
Gas emissions discovered on the Brazo Rincon sector of Lake Nahuel Huapi in Patagonia, are described and characterized through analysis of hydroacoustic targets rising from the bottom. Echograms target analysis allowed for the identification of two possible sources. The first one corresponding to multiple gas vents in a seep field in 30 m to 100 m water depths. The second consisting of gas, fluids, resuspended bottom debris, and sediments in near-shore shallow waters. The hydroacoustic characteristics of these plumes are described, and possible origins of gas emissions are considered in relation to geological characteristics associated to local volcanism and/or biological phenomena.
This chapter reviews the Late Cenozoic Quaternary Volcanism in Patagonia and Tierra del Fuego. Patagonia has a vast and significant volcanic history, which started in the Triassic and developed mainly during the Jurassic with the emplacement of extended ignimbritic–rhyolitic plateaus covering the major part of the present area and of the Atlantic continental platform. With the break-up of Gondwana and the beginning of the migration of South America toward the west, during most of the Cretaceous, arc magmatism developed at the western margin of South America. To describe and better understand the evolution of the Late Cenozoic volcanic processes and their relationship with the geodynamic setting, a more extended period from the Late Miocene to the Holocene has been considered in this chapter. However, mostly Pliocene to Holocene volcanic centers and sequences are emphasized as a part of major volcanic provinces. Quaternary volcanism in Patagonia has been strongly influenced by tectonic processes involved in both arc and backarc domains. Tectonic evolution in Patagonia has been characterized by subsequent episodes of compression and transpression–transtension along the volcanic front with localized extension in the backarc region.
Although the Neuquén basin in Argentina forms a key transitional domain between the south-central Andes and the Patagonian Andes, its Cenozoic history is poorly documented. We focus on the sedimentologic and tectonic evolution of the southern part of this basin, at 39-40°30’ S, based on study of 14 sedimentary sections. We provide evidence that this basin underwent alternating erosion and deposition of reworked volcaniclastic material in continental and fluvial settings during the Neogene. In particular, basement uplift of the Sañico Massif, due to Late Miocene–Pliocene intensification of tectonic activity, led to sediment partitioning in the basin. During this interval, sedimentation was restricted to the internal domain and the Collon Cura basin evolved toward an endorheic intermontane basin. From stratigraphic interpretation, this basin remained isolated 7 to11 Myr. Nevertheless, ephemeral gateways seem to have existed, because we observe a thin succession downstream of the Sañico Massif contemporaneous with the Collon Cura basin-fill sequence. Comparisons of stratigraphic, paleoenvironmental and tectonic features of the southern Neuquén basin with other foreland basins of South America allow us to classify it as a broken foreland with the development of an intermontane basin from Late Miocene to Late Pliocene. This implies a thick-skinned structural style for this basin,with reactivation of basement faults responsible for exhumation of the Sañico Massif. Comparison of several broken forelands of South America allows us to propose two categories of intermontane basins according to their structural setting: subsiding or uplifted basins, which has strong implications on their excavation histories.This article is protected by copyright. All rights reserved.
Gas emissions discovered on the Brazo Rincon sector of Lake Nahuel Huapi in Patagonia, are described and characterized through analysis of hydroacoustic targets rising from the bottom. Echograms target analysis allowed for the identification of two possible sources. The first one corresponding to multiple gas vents in a seep field in 30 m to 100 m water depths. The second consisting of gas, fluids, resuspended bottom debris, and sediments in near-shore shallow waters. The hydroacoustic characteristics of these plumes are described, and possible origins of gas emissions are considered in relation to geological characteristics associated to local volcanism and/or biological phenomena.
The Tronador Volcanic Group (TVG) is located in the transition between the central and southern segment of the Andean Southern Volcanic Zone (SVZ), »50 km to the east of the current volcanic front. The TVG includes, from older to younger, the deeply eroded Early Pleistocene Garganta de Diablo unit (GDU; »1.3 Ma) and Steffen volcanic complex (SVC), the Middle Pleistocene Tronador Volcanic Complex (TVC;
The sub-Andean region of the North Patagonian Andes is located between the north Patagonian foreland and the highest elevations of the Andean Cordillera. Its Tertiary contractional structure, active since the upper Late Oligocene and through the upper Late Miocene, corresponds to the external sector of the North Patagonian Andes fold-and-thrust belt, which is characterized by east-vergent thrusts that affect stratified Cenozoic rocks. The units involved in the deformation correspond to El Maiten Oligocene volcanic belt, deformed between east-vergent thrusts and backthrusts, and Oligocene-Miocene sedimentary rocks of the (N) over tilde irihuau-Collon Cura Basin. The northern sector of the basin was structured as a thin-skinned fold belt that comprises the (N) over tilde irihuau fold belt and a frontal sedimentary wedge. To the south, sedimentary depocenters are confined between medium- to high-angle reverse faults with evidence of basement structural control. In both cases, the general tectonosedimentary framework shows the youngest units toward the east, in agreement with the advance of the orogenic wedge. Most of the (N) over tilde irihuau-Collon Cura Basin infill fits a foreland basin system model. Some sectors of the basin show evidence of structural control by normal faults in the initial sedimentation stages. This early extensional regime might be associated with late phases of Oligocene volcanism. Extensional structures probably were partially reactivated during the upper Late Oligocene, as suggested by seismic data. (c) 2005 Elsevier Ltd. All rights reserved.
The sedimentary evolution of the Ñirihuau Formation (late Oligocene-middle Miocene) was studied along the southern margin of the Ñirihuau River, in the North Patagonian Andes. The 1300-m-thick section includes 15 epiclastic and volcaniclastic lithofacies which are grouped into five lithofacies associations: deep lacustrine, shallow lacustrine, fluvial channels, subaerial floodplains and volcaniclastic flows (lahar). Syn-eruptive and inter-eruptive stages are recorded along the Ñirihuau River section. The former consist of highly aggradational packages several tens of meters thick of ash-fall beds and lahar deposits. During inter-eruptive periods sedimentation took place mostly in shallow and deep lacustrine environments, with four cycles of lake expansion and contraction, and a minor proportion of fluvial deposits. Sedimentary supply originated from the northeast and northwest in the lower part of the unit through low to moderate sinuosity fluvial systems, flowing into a lake with high-gradient margins, and forming Gilbert-type deltas. The younger sections were sourced from the northeast, east and southeast, indicating changes in the basin morphology. Basic and intermediate volcanic rocks similar to those of the Ventana Formation (Oligocene) are interstratified at the beginning of the sedimentation. The syn-orogenic nature of the Ñirihuau Formation is evidenced by the changes in the basin shape, but mainly by the differences in styles and intensities of deformation between the Ñirihuau River section and the overlying outcrops of La Buitrera Hill, both separated by a folded unconformity.
The structure of the southern sector of the central Andes in the North Patagonian Andes of the Argentinean slope (41°-42°S) is characterized by a Tertiary fold-and-thrust belt formed by an E-vergent imbricate thrust structure and a retrovergent thrust system. The paleogeographic distribution of Jurassic rocks suggests that some of the W-vergent thrusts may have been part of a Mesozoic extensional fault system inverted during Andean compression. On the basis of the structures and rocks involved in the deformation, we distinguish a western and an eastern sector. The western sector developed on pre-Tertiary basement rocks with E-vergent thrusts and an associated backthrust system that forms a triangle zone that exposes Mesozoic and pre-Mesozoic rocks. In the eastern sector, thrusting that formed the Ñirihuau foldbelt involved Cenozoic volcanic and sedimentary rocks and affected a subsurface synorogenic wedge. The boundary between the two sectors is probably a normal fault that was active during the middle Mesozoic. The regional cartography and microtectonic observations suggest predominant dip-slip movements of the thrust sheets. However, there is no evidence of major N-S strike-slip movements as has been proposed for the forearc region (Chilean Andes) and northwestern Patagonia on the basis of fault slip data analysis. A Tertiary sedimentary basin was developed in relation to the eastward migration of the orogenic front toward the foreland.
Morphological, molecular and biogeographical information bearing on early evolution of the sunflower alliance of families suggests that the clade containing the extant daisy family (Asteraceae) differentiated in South America during the Eocene, although palaeontological studies on this continent failed to reveal conclusive support for this hypothesis. Here we describe in detail Raiguenrayun cura gen. & sp. nov., an exceptionally well preserved capitulescence of Asteraceae recovered from Eocene deposits of northwestern Patagonia, Argentina.
The fossil was collected from the 47·5 million-year-old Huitrera Formation at the Estancia Don Hipólito locality, Río Negro Province, Argentina.
The arrangement of the capitula in a cymose capitulescence, the many-flowered capitula with multiseriate-imbricate involucral bracts and the pappus-like structures indicate a close morphological relationship with Asteraceae. Raiguenrayun cura and the associated pollen Mutisiapollis telleriae do not match exactly any living member of the family, and clearly represent extinct taxa. They share a mosaic of morphological features today recognized in taxa phylogenetically close to the root of Asteraceae, such as Stifftieae, Wunderlichioideae and Gochnatieae (Mutisioideae sensu lato) and Dicomeae and Oldenburgieae (Carduoideae), today endemic to or mainly distributed in South America and Africa, respectively.
This is the first fossil genus of Asteraceae based on an outstandingly preserved capitulescence that might represent the ancestor of Mutisioideae-Carduoideae. It might have evolved in southern South America some time during the early Palaeogene and subsequently entered Africa, before the biogeographical isolation of these continents became much more pronounced. The new fossil represents the first reliable point for calibration, favouring an earlier date to the split between Barnadesioideae and the rest of Asteraceae than previously thought, which can be traced back at least 47·5 million years. This is the oldest well dated member of Asteraceae and perhaps the earliest indirect evidence for bird pollination in the family.
ResearchGate has not been able to resolve any references for this publication.