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Moreiras S.M.,CONICET | Hermanns R.L.,Norges Geologiske Undersokelse | Fauque L.,Servicio Geologico Minero Argentino
Quaternary Science Reviews | Year: 2015

This paper provides a comprehensive review of the chronostratigraphy of six rock avalanches clustered in the northern extreme of the Cordon del Plata range. These rock avalanches are stratigraphically related to Pleistocene glacial drifts and valley-fill deposits documenting the regional neotectonic activity. We used cosmogenic dating (TCN) to directly date block surfaces of rock-avalanche deposits, as well as optically stimulated luminescence dating (OSL) of paleo-lakes dammed by these rock avalanches. Our new direct dates (17 TCN and 4 OSL) determine the Middle-to-Late Pleistocene age of these collapses. These are in contrast to the previously established chronostratigraphy based on relative dating techniques, paleontological context, and tephrochronology. These new data help to redefine the geomorphological evolution of the Mendoza River valley. Especially, the new data indicate that the glacial stratigraphy earlier proposed must be reconsidered. We redefine this stratigraphy as far as possible with our data and discuss the data in relation with other recently published results. However, it becomes clear that the glacial history of the Mendoza valley has to be studied anew by using modern dating techniques. In addition, our data suggest that the Carrera Fault system bounding the valleys of the Cordillera del Plata has been active more recently than proposed earlier. © 2015 Elsevier Ltd.


Bonadonna C.,University of Geneva | Pistolesi M.,University of Florence | Cioni R.,University of Florence | Degruyter W.,Georgia Institute of Technology | And 2 more authors.
Journal of Geophysical Research B: Solid Earth | Year: 2015

The 2011 Cordón Caulle eruption represents an ideal case study for the characterization of long-lasting plumes that are strongly affected by wind. The climactic phase lasted for about 1 day and was classified as subplinian with plumes between ∼9 and 12 km above the vent and mass flow rate (MFR) on the order of ∼107 kg s-1. Eruption intensity fluctuated during the first 11 days with MFR values between 106 and 107 kg s-1. This activity was followed by several months of low-intensity plumes with MFR < 106 kg s-1. Plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation. The plumes that developed on 4-6 and 20-22 June can be described as transitional, i.e., plumes showing transitional behavior between strong and weak dynamics, while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes. Individual phases of the eruption range between Volcanic Explosivity Indices (VEIs) 3 and 4, while the cumulative deposit related to 4-7 June 2011 is associated with VEIs 4 and 5. Crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion, with velocities between 1 and 10 m s-1. Downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection, with velocities between 17 and 45 m s-1. Results show how gravitational spreading can be significant even for subplinian and small-moderate eruptions strongly advected by wind and with low Richardson number and low MFR. ©2015. American Geophysical Union. All Rights Reserved.


Bonadonna C.,University of Geneva | Cioni R.,University of Florence | Pistolesi M.,University of Florence | Elissondo M.,Servicio Geologico Minero Argentino | Baumann V.,Servicio Geologico Minero Argentino
Bulletin of Volcanology | Year: 2015

Sedimentation processes and fragmentation mechanisms during explosive volcanic eruptions can be constrained based on detailed analysis of grain-size variations of tephra deposits with distance from vent and total grain-size distribution (TGSD). Grain-size studies strongly rely on deposit exposure and, in case of long-lasting eruptions, can be complicated by the intricate interplay between eruptive style, atmospheric conditions, particle accumulation, and deposit erosion. The 2011 Cordón Caulle eruption, Chile, represents an ideals laboratory for the study of long-lasting eruptions thanks to the good deposit accessibility in medial to distal area. All layers analyzed are mostly characterized by bimodal grain-size distributions, with both the modes and the fraction of the coarse subpopulation decreasing rapidly with distance from vent and those of the fine subpopulation being mostly stable. Due to gradually changing wind direction, the two subpopulations characterizing the deposit of the first 2 days of the eruption are asymmetrically distributed with respect to the dispersal axis. The TGSD of the climactic phase is also bimodal, with the coarse subpopulation representing 90 wt% of the whole distribution. Polymodality of individual samples is related to size-selective sedimentation processes, while polymodality of the TGSD is mostly related to the complex internal texture (e.g., size and shape of vesicles) of the most abundant juvenile clasts. The most representative TGSD could be derived based on a combination of the Voronoi tessellation with a detailed analysis of the thinning trend of individual size categories. Finally, preferential breakage of coarse pumices on ground impact was inferred from the study of particle terminal velocity. © Springer-Verlag Berlin Heidelberg 2015.


Violante R.,Servicio de Hidrografia Naval | Osella A.,University of Buenos Aires | Vega M.D.L.,University of Buenos Aires | Rovere E.,Servicio Geologico Minero Argentino | Osterrieth M.,University of the Sea
Journal of South American Earth Sciences | Year: 2010

Lakes are key sites for studying paleoclimates. Llancanelo Lake (southern Mendoza Province, western Argentina) is an endoreic, highly saline water body located in the southern extreme of a tectonic basin, the Central or Huarpes Depression. The lake is located between the Andean Cordillera, San Rafael Block and Payenia Volcanic Field. The lake evolved as a major regional depocenter during the Pliocene-Quaternary, hence it contains important thicknesses of intra and extra basinal clastic and evaporitic sediments mainly dominated by volcaniclastic products. The main conditioning factors in the lake evolution were arc and back-arc volcanism as well as climatic changes. Geomorphological and sedimentary evidence supports the hypothesis that the lake was in past times larger than in present days. This paper estimates the lake's former extension on the western lacustrine plain using electromagnetic induction (EMI) and geoelectricity (Multielectrode Resistivity Meter) surveys, as well as shallow wells, along an 8. km long transect perpendicular to the lake's western shoreline. The geophysical and sedimentological information, as well as microfaunal studies, lab analysis and petrographic/EDAX determinations, support the presence, in the subsoil, of a lacustrine sequence at least 30. m thick composed mainly of volcaniclastic sediments. Volcanic eruptions and climatic changes influenced the evolution of the lake, producing intercalations in the lacustrine sedimentary sequences of ash layers, evaporites, soils, and eolian and swamp deposits. © 2009 Elsevier Ltd.


Foix N.,National University of Patagonia San Juan Bosco | Foix N.,CONICET | Paredes J.M.,National University of Patagonia San Juan Bosco | Giacosa R.E.,Servicio Geologico Minero Argentino | And 2 more authors.
Sedimentary Geology | Year: 2013

The Upper Paleocene Río Chico Formation is a 50-180. m thick fluvial succession developed in a passive-margin setting, Golfo San Jorge basin, Central Patagonia, Argentina. A detailed description and interpretation of outcrops was carried out, analyzing exposures from the northern basin margin to the most complete successions at the southern depocenter. The unit is characterized by a regional fluvial system that flowed to the south-east. Five main lithofacies associations were defined: (I) active fluvial channels, with three sub-types: braided, meandering and low-sinuosity, (II) sheet-flood deposits, (III) proximal floodplain (natural levee and crevasse-splay), (IV) distal floodplain, and (V) abandoned channels.Lateral/vertical changes in fluvial architecture of the Río Chico Formation were recognized by variations in preserved thickness, fluvial styles, geometry of fluvial channels, regional paleoflow directions, and channel/floodplain ratios. Close to the northern basin margin, the fluvial succession is 50-60. m thick, composed of braided channels, sheet-flow deposits, and high channel/floodplain ratio. In a basinward direction, the alluvial succession increases to 180. m in thickness, the dominant fluvial styles change to low-sinuosity and meandering channels and channel/floodplain ratio reduces.The fluvial architecture of the Río Chico Formation shows two main depositional trends that resulted from changes in accommodation space across the basin. The interpreted break-point coincides with the underlying Cretaceous basin-boundary, thus the synsedimentary extensional reactivation of the pre-existing tectonic lineament generated differential subsidence, delimiting two different accommodation settings. © 2013 Elsevier B.V.


The succession of microfossil assemblages in the almost complete marine Late Cretaceous- Miocene stratigraphic column found in the Fuegian Andes, the orogenic margin of the Austral Basin, reveals a close relationship with the local tectonic events, the Atlantic transgressions-regressions on the Patagonian Platform, and the most relevant paleoceanographic global events. The Fuegian upper Campanian-lower Eocene sequence, dominated by flysch-type assemblages of agglutinated foraminifers and poorly oxygenated waters of fairly limited depth, is coherent with silled basins in a recently proposed cortical stretching period. The Maastrichtian (Policarpo Formation) has a cosmopolitan agglutinated foraminiferal assemblage contrasting with the coeval austral endemic calcareous assemblages of Patagonia. In the Paleocene/Eocene transition the assemblages of calcareous microfossils, of restricted distribution, exhibit the greatest Cenozoic turnover from a cosmopolitan Midway-type assemblage (La Barca Formation) to a strongly endemic Early Eocene assemblage (Punta Noguera Formation), with the oldest records of the Fuegian-Patagonian Cenozoic most typical genera. The Early Paleogene has no record of philothermic taxa such as larger foraminifera or morozovelids planktonic foraminifera, and only a short-lived bryozoan limestone (Río Bueno Formation) and the low percentage of the ostracod family Hemicytheridae insinuated a warm period. The upper middle-uppermost Eocene sequence (La Despedida Group) starts with a transgression recorded in the Austral Basin (Leticia, Man Aike, Río Turbio formations and Boltovskoyella beds), and in the Colorado Basin. This transgression is coeval with a temperature peak of 42 Ma, bringing a Fuegian retrograde fauna and a foraminiferal assemblage with large-sized nodosarids, which were replaced throughout the Late Eocene (Cerro Colorado Formation) by typical Antarctic genera that reflect the falling global temperature, culminating in the Tenuitella insolita Zone with abundant Chiloguembelina, a local effect of the global environmental fluctuations. The Eocene/Oligocene boundary and the Oi-1 seem to be represented by an unconformity and/or the Tchat Chii Conglomerate. In the earliest Oligocene (Maria Cristina beds) foredeep environments below the LCC and deep water foraminifer indicators appear, contrasting with coeval global high δ18O values and a Late Eocene-Early Oligocene withdrawal in the Patagonian Platform, which suggest that the coeval deepening recorded in the Fuegian Andes is due only to tectonic causes that facilitated the incursion of Antarctic waters into the basin. The latest Oligocene-Early Miocene global warm anomaly corresponds to a constriction period of the Drake Passage; in the Fuegian Andes lysocline conditions dominate, and a generalized transgression occurs including an Antarctic corrosive water current, which penetrates in the Patagonian Platform; on both regions, there are minor discontinuities coincident with the Mi-1, and an extended unconformity is found prior to the mid Miocene transgressive pulse coeval with the Neogene optimum.


Vizan H.,University of Buenos Aires | Geuna S.,University of Buenos Aires | Melchor R.,National University of La Pampa | Bellosi E.S.,CONICET | And 5 more authors.
Tectonophysics | Year: 2013

The red bed succession cropping out in the Quebrada Santo Domingo in northwestern Argentina had been for long considered as Upper Triassic-Lower Jurassic in age based on weak radiometric and paleontological evidence. Preliminary paleomagnetic data confirmed the age and opened questions about the nature of fossil footprints with avian features discovered in the section. Recently the stratigraphic scheme was reviewed with the identification of previously unrecognized discontinuities, and a radiometric dating obtained in a tuff, indicated an Eocene age for the Laguna Brava Formation and the fossil bird footprints, much younger than the previously assigned. We present a detailed paleomagnetic study interpreted within a regional tectonic and stratigraphic framework, looking for an explanation for the misinterpretation of the preliminary paleomagnetic data.The characteristic remanent magnetizations pass a tilt test and a reversal test. The main magnetic carrier is interpreted to be low Ti titanomagnetites and to a lesser extent hematite. The characteristic remanent magnetization would be essentially detrital. The obtained paleomagnetic pole (PP) for the Laguna Brava Formation has the following geographic coordinates and statistical parameters: N=29, Lon.=184.5° E, Lat.=75.0° S, A95=5.6° and K=23.7. When this PP is compared with another one with similar age obtained in an undeformed area, a declination anomaly is recognized. This anomaly can be interpreted as Laguna Brava Formation belonging to a structural block that rotated about 16° clockwise along a vertical axis after about 34Ma. This block rotation is consistent with the regional tectonic framework, and would have caused the fortuitous coincidence of the PP with Early Jurassic poles. According to the interpreted magnetostratigraphic correlation, the Laguna Brava Formation would have been deposited during the Late Eocene with a mean sedimentation rate of about 1.4cm per thousand years, probably in relation to the onset of the Andean deformation. © 2012 Elsevier B.V.


Suarez M.,Andrés Bello University | Marquez M.,Servicio Geologico Minero Argentino | De La Cruz R.,Servicio Nacional de Geologia y Mineria | Navarrete C.,National University of Patagonia San Juan Bosco | Fanning M.,Australian National University
Journal of South American Earth Sciences | Year: 2014

Four new SHRIMP U-Pb zircon ages older than 93 Ma from samples of the two uppermost formations accumulated in two different depocenters (Golfo de San Jorge and Cañadón Asfalto basins) of the Chubut Group in central Argentinean Patagonia, establish a pre-late Cenomanian-? early Turonian age for the group. It also confirms a coeval and comparable evolution of the two depocenters, where distal pyroclastic material was deposited together with fluvial and lacustrine facies. © 2013 Elsevier Ltd.


In this paper new basaltic outcrops from Ramírez de Velasco ranger (Santiago del Estero province) are described. They are basaltic dikes that vary from few meters to two kilometers long across the igneous basement. All these rocks show dark colors with aphyric (S9 sample) to porphyritic (S17 and S20 samples) textures. When these basalts present phenocrysts, they are composed of lagioclase within a groundmass of subophitic texture. The low alteration of the groundmass allows to recognise microliths of labradorite, augite and opaque minerals of about 0.2 and 0.5 mm. These sizes suggest a hypabisal emplacement of the biggest dikes. Sericite, chlorite, epidote, sphene and opaque minerals compose the alteration assemblage on these rocks. Quartz and carbonates mainly fill small cavities. The geochemical compositions of all analyzed samples support the petrographic classification. They have negative slopes of their trace elements and evidence affiliation with calc-alkaline basalts from magmatic arcs. Their similar textures, mineralogy and chemical compositions suggest that all these basalts where crystallized from the same source and due to the same magmatic process. On the basis of all these data and the features of the basalts that crops out in the surrounding of the study area, this volcanism is attributed to the post-orogenic stage of the Pampean orogeny and therefore it is correlated with the Balbuena Formation (Sierra Norte of Córdoba).


Garcia V.H.,National University of Rio Negro | Casa A.L.,Servicio Geologico Minero Argentino
Geological Society Special Publication | Year: 2015

The Andean retrowedge, located between 33°S and 34°S, lies in the transition region of the Pampean flat-slab subduction zone to the north and a normal subduction zone to the south. Neotectonic structures and shallow seismicity are very common north of this segment and become progressively less frequent southwards. The Frontal Cordillera and the Cerrilladas Pedemontanas are the main morphostructures involved in the Quaternary deformation of this region. The Frontal Cordillera is a thick-skinned fold-and-thrust belt uplifted since Late Miocene time. The Cerrilladas Pedemontanas are low-relief hills that represent the mild inversion of the Cuyo Triassic rift depocentre since Pliocene time. Middle Miocene-Holocene synorogenic strata cover the Cuyo basin and surrounding foreland areas. The Quaternary tectonic evolution of this area has been established through integration of new data from fieldwork in the Frontal Cordillera piedmont with subsurface information and previously published data. Mean Late Pleistocene uplift rates ranging between 0.21 and 0.92 mm a-1 and earthquake minimum moment magnitudes (Mw) of c. 6.4-6.7 have been estimated for the morphostructural units analysed in this manuscript. © 2015 The Geological Society of London.

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