The large scale structure of the Internet
Barrat, Alain; Dall'Asta, Luca; Alvarez Hamelin, José Ignacio; Vespigna, Alessandro
The Internet is a prototypical example of info-structure that has grown following a self-organized dynamics. Even though governments are waking up to the reality that the Internet is a critical infrastructure that has dramatically changed our way to access information, exploit social relations, and run commerce, nobody has ever run the Internet growth or drawn a blueprint for its development. The dynamics of Internet is indeed defined by the interplay between cooperation (the network has to work efficiently) and competition (providers wish to earn money). These evolutionary prin- ciples have shaped an intrinsically heterogenous system ruled by different administrative policies whose complicate structure cannot be found in any repository or “official” map. For these reasons, in the last years, several research groups have started to deploy technologies and infrastructures in order to obtain a more global picture of the Internet. Several studies aiming at tracking and visualizing the Internet large scale topology and/or performance are now providing Internet maps at different resolution scales. These projects typically collect data on Internet nodes (routers, domains, etc.) and links in order to create a graph-like representation of large parts of the Internet. The obtained Internet graphs exhibit most of the features characterizing large scale complex networks and in the present chapter we provide a review of the results obtained in the characterization of their structure. We also present a critical discussion of the eventual experimental biases that might lead to erroneous conclusions on the actual topological properties of the Internet network. Finally we discuss some novel measurements aimed at uncovering the hierarchical and ordering principles underlying the Internet structure.
Aquatic Biodiversity in Latin America: Neotropical Ceratopogonidae (Diptera: Insecta)
Borkent, Art; Spinelli, Gustavo Ricardo
This book brings together, for the first time, all known information on the 51 genera and 1095 described Neotropical species of biting midges. An overview of the group includes a discussion of bionomics, adaptations of the various life stages, habitats, their ecological roles (including disease transmission), collecting and preparation techniques, zoogeography and classification. A key to adults (including males) provides the first key to all the genera of this region. Limited keys to eggs and larvae are presented. Keys are written in both English and Spanish. A table of all previous descriptions of immatures and a catalog of all Neotropical species is included.
La provincia flotante: Historia de los exiliados argentinos de la última dictadura militar en Cataluña (1976-2006)
Jensen, Silvina Inés
Este libro es una historia del exilio argentino de la última dictadura militar construida con las voces de aquellos que recalaron en Cataluña a mediados de la década del ´70. Sin embargo, esta pesquisa anclada en la historia social y política catalana, es a vez un "caso" o mejor dicho opera como un laboratorio para entender cómo esa experiencia de destierro fue vivida y pensada y luego recordada desde la contemporaneidad del fenómeno (1976-1983) hasta el presente y tanto por sus protagonistas como por aquellos que de una u otra forma han interactuado con ellos desde la sociedad de origen (Argentina) y desde la de destierro (Cataluña). A lo largo de sus páginas se reconstruye la historia de los protagonistas de la diáspora del ´76, desde su salida abrupta desde Argentina, pasando por sus descubrimientos y aprendizajes en Cataluña, la evaluación o la concreción del retorno tras el final de la dictadura, su reencuentro con la Argentina de adentro y hasta el presente. Este libro intenta por un lado reconocer las marcas que permiten individualizar al exilio dictatorial de Cataluña de otros exilios nacionales contemporáneos. Y, por el otro, pensar desde la experiencia de los argentinos que vivieron su destierro en Cataluña, cómo la sociedad argentina en su conjunto ha recordado/recuerda el exilio dictatorial y cuáles son las razones de lo que a mi juicio es una "memoria silenciosa" o discreta sobre aquel acontecimiento traumático.
Antibacterial and Cytotoxic Activity of Extracts and Secondary Metabolites Obtained from Plants and Lichens of Patagonia Austral
Enriz, Ricardo Daniel; Freile, Monica Liliana; Correché, María Susana; Gomez-Lechon, María José
In medicinal chemistry, the discovery of a new lead structure substance represents the most uncertain stage in a drug development program. In the past, the discovery of lead compounds depended essentially upon random occurrences such as accidental observations, fortuitous findings, hearsay or laborious screening of a large number of molecules. More recently, more rational approaches have become available, based on the knowledge of structures of the endogenous metabolites and receptors or on the nature of the biochemical disorder implied in the disease at molecular level. Nowadays there are different strategies to obtain lead structure candidates. These methods may consist of more or less intuitive approaches, such as the synthesis of analogues, isomers and bioisosters or they may be based on computer-assisted design, such as identifying pharmacophores by molecular modeling, Structure-Activity Relationship (SAR) or Quantitative SAR (QSAR) studies.
Patrón espacial del paisaje serrano (Córdoba, Argentina)
Menghi, Mirta Melva Mercedes; del Sueldo, Ruben Arturo
Se analiza el paisaje rural de una área (31°50’S/64°50’W) de las Sierras de Córdoba (Argentina central) objeto de la mayor extensión de plantaciones de Pinus spp. «pino» realizadas en los últimos 30 años. Se describen la estructura y diversidad del patrón espacial actual del paisaje entre 650 y 2.400 m snm., y su relación con factores físicos y con plantaciones de pino. Se realizó la clasificación supervisada de una imagen Landsat TM (30 x) (Envi 3.5, CONAE) de septiembre de 2002, considerando unidades de vegetación y usos del suelo nativas y antrópicas. Se analizó en forma exploratoria toda la cuenca (77.622 Ha) y, con mayor detalle, 21.000 Ha que concentran plantaciones, considerando la estructura del paisaje total, de cada hábitat o unidad de paisaje, y de parche (Fragstats 3.3). La matriz del paisaje actual (77% de la cuenca) es un mosaico de comunidades nativas en distinto estado de conservación con límites irregulares entre ellas, en el cual los bosques nativos representan hoy una superficie menor. El bosque de Lithraea ternifolia («molle») cubre actualmente 3.148 Ha (19% de su área potencial) repartidas en numerosos parches menores a 1 Ha; la mayor parte fue degradado a arbustales compuestos por Acacia spp. y otras especies del sotobosque original, y está invadido por leñosas exóticas. Los bosques y arbustales de Polylepis australis («tabaquillo») representan cerca de 300 Ha, están muy fragmentados en pequeños parches confinados a quebradas; tanto factores antrópicos como físicos explicarían ese patrón. Los bosques nativos mostraron relación espacial escasa (L. ternifolia, «molle») a nula (P. australis, «tabaquillo») con las plantaciones de «pino». La mayor extensión de bosque de «pino» (7.670 Ha) cubre áreas originales del matorral serrano de Hetherotalamus alienus («romerillo») y, en menor grado, de pastizales de altura. La variedad y extensión de hábitat artificiales y exóticos aumentan hacia las zonas media y baja; tienen en común fronteras bruscas y rectas, muy contrastantes con su entorno. Los valores de diversidad (H’ 1,85), de equidad (E’ 0,80) y de dominancia (0,34) de unidades de paisaje indicarían que el patrón espacial es heterogéneo a escala regional, y más diverso hacia los extremos alto (2.43 bits) y bajo (2.20 bits) respecto del sector medio (1.53 bits) de la cuenca. La interacción entre la complejidad y accesibilidad del relieve a lo largo del gradiente altitudinal explicaría esa tendencia por mayor variabilidad espacial de elementos naturales hacia las cumbres, y de origen antrópico hacia zonas bajas. La estructura espacial detectada no es estática y de ella emergen hipótesis para investigación futura. Son de particular interés temas relacionados a la calidad del hábitat, la dirección y dinamismo de las transiciones bióticas en diferentes tipos de fronteras, la percolación de la estructura para organismos y procesos ecosistémicos, entre otros.; Traditional land-uses involving burnt, grazing and/or wood cutting of native plant cover, and more recently its complete replacement by agriculture and urban landuses have all promoted plant cover alteration, retraction and/or fragmentation, with particular impact on native forests. Based on remote sensing (Landsat TM 30 x) (Envi 3.5) the current spatial pattern of a landscape mosaic of 77.622 Ha (31o2’S / 64o30’W) was described taking into account the following cover types: native or exotic forests, agriculture, urban, artificial lake, shrub-land, grassland. The spatial structure was analyzed at mosaic, habitat, and patch levels. The habitat diversity of spatial pattern was also measured. From present analysis emerged a matrix composed by different types of native plant cover still well connected by gradual transitions among them. At the same time, significant degrees of native forests retraction and fragmentation were detected. The Polylepis australis («tabaquillo») (over 1500 m a.s.l) and of Lithraea ternifolia («molle») (from 900 to 1100 m a.s.l.) woods, currently represent from 10 to 19% of their potential areas at the analyzed water-basin. The larger part has been replaced by tall sized and spiny shrub-lands dominated by Acacia («espinillo») in the case of Lithraea, or by grasslands the Polylepis one. The Pinus plantation has replaced 40% of native short sized shrub-lands of Hetherotalamus alienus («romerillo») related to areas with moderated relief, and has involved new boundary types, straight and sharp, related to different cover types all over the basin. Present landscape is dynamic and from its spatial structure hypothesis for future research have emerged. Topics related to forest ecosystem services, to habitat quality, to biotic transitions associated to different boundary types, as well as the spatial structure percolation for organisms and ecosystem processes, among others, are of particular interest.
Fundamentals of supercritical fluid technology
Pereda, Selva; Bottini, Susana Beatriz; Brignole, Esteban Alberto
This chapter deals with fundamentals of supercritical fluid extraction. Considering first the typical phase diagrams of high pressure systems. Thereafter the application of supercritical fluids to separations is illustrated with alcohol extraction and dehydration with hot propane, extraction of vegetable oils with non flammable solvents and fractionation of fish oils and essential oils with carbon dioxide. Also the removal of chemicals using supercritical fluids is considered. Finally the subject of phase equilibrium engineering of supercritical reactors is developed.
Flavoparmelia amplexa and F. springtonesis (Parmeliaceae) new to the Americas and additions to the lichen flora of Argentina
Adler, Monica Teresa; Calvelo, Susana
The world distribution of nine species of the Parmeliaceae is presented including new localities in Argentina. Flavoparmelia amplexa (Stirt.) Hale, formerly known exclusively from Africa, is cited for the first time for the American continent, and is therefore categorized as a South American-African species, whereas F. springtonensis (Elix) Hale, until now known as an Australasian endemic, is reported for the first time for America as well and consequently categorized as a South American-Australasian species. World distribution maps of each species are included.
Development and implementation of advanced training course for diabetes educators in Argentina
Gagliardino, Juan Jose; Malbran, Maria del Carmen; Clark, Carmen
Preliminary report on the development and evaluation of a university-based master's degree program in diabetes education in Latin America. The program, based on reported international standards, was developed through the Department of Postgraduate Studies of the National University of La Plata, Argentina, with funds provided by the American Association of Diabetes Educators. This highly interactive program combines pedagogical, psychological, and communication-based education specifically related to diabetes. Consequently, its graduates will be prepared to communicate effectively with their patients about their self-care needs and work with them to overcome the day-to-day barriers that prevent them from integrating self-care effectively into their lives.
Stereoselective synthesis of 4-oxo-2,5-dienes and conjugated dienes by Stille cross coupling reactions of vinylstannanes
Fidelibus, Pablo Martin; Gerbino, Darío César; Mandolesi, Sandra Delia; Podestá, Julio Cesar
The palladium-catalyzed cross coupling reactions between trineophylstannylvinyl esters and unsaturated acyl chlorides lead mostly to 4-oxo-2,5-dienes in good yields (60-77%). In some cases homocoupling products are also formed. On the other hand, the Stille reaction of Z-di- and trisubstituted vinyl iodides with trineophylvinylstannanes enables the synthesis of polysubstituted butadienes in moderate to good yields (40-60%).
Deglycerolization of biodiesel streams by adsorption over silica beds
Yori, Juan Carlos; D'ippolito, Silvana Andrea; Pieck, Carlos Luis; Vera, Carlos Roman
A simple method for the almost complete removal of glycerol from methanol-free biodiesel streams coming out from industrial transesterification reactors is presented. The method is posed as a "dry" alternative to the conventional "wet" methods involving water washing. It is based on the use of silica beds and relies on the adsorption at room temperature to retain the small amounts of glycerol dissolved in the solutions of fatty acid methyl esters and adjust their content to the quality standards for biodiesel fuel. Fresh silica has a great processing capacity and the breakthrough of the bed depends mainly on the feed rate, the concentration of glycerol, and the mass of adsorbent. In the case of the silica gel used, the saturation capacity was found to be 0.13 g of glycerol per gram of silica. If the particle diameter is 1-1.5 mm, the breakthrough and saturation point almost coincide and the full capacity of the bed is used. However, industrial adsorption units with 1/8 in silica beads suffer from mass-transfer limitations inside the pellet pores, and for this particle size, the breakthrough point (C/C0 = 0.01) is located at about one-half of the time of full saturation. For a glycerol concentration of 0.11-0.25% typical of biodiesel streams issuing from gravity settling tanks and an entrance velocity of 11 cm min-1, a 2 m high silica bed with 1/8 in. beads has a breakthrough point of 8 h and a net processing capacity of 0.01-0.02 m3 biodiesel, kgsilica -1. The breakthrough curves were studied using approximate solutions to the set of differential equations. Assuming a linear isotherm gives erroneous results; fitting the experimental breakthrough curves produces underestimated values of the Henry's adsorption constant and of the mass-transfer resistances. Modeling the high dilution regime with the UNIFAC method gives more realistic values of the Henry's constant (1.1 m3 kg-1). The experimentally measured saturation capacity is close to the monolayer capacity (13-15% w/w). These values give a Langmuir isotherm which can be fairly well approximated by a square irreversible isotherm. Accordingly, breakthrough curves were fairly well predicted using an irreversible isotherm, a shrinking-core adsorption model, and common correlations for the mass-transfer coefficients. The silica bed was succesfully regenerated eluting 4 bed volumes of methanol and drying in a nitrogen stream for 1 h. Temperature programmed oxidation tests of fresh, regenerated, and glycerol impregnated silica pellets indicated that desorption of glycerol was practically complete. In the industrial practice, the eluted volume can be recycled to the transesterification reactors with no waste of products or reactants. Evaporation of the adsorbed methanol during drying of the bed produced a decrease of the bed temperature and about 200 kJ kgsilica -1 should be provided in order to maintain the temperature.
Multiple mechanisms of growth hormone-regulated gene transcription
Ceseña, Teresa I.; Cui, Tracy Xiao; Piwien Pilipuk, Graciela; Kaplani, Julianne; Calinescu, Anda Alexandra; Huo, Jeffrey S.; Iñiguez Lluhí, Jorge A.; Kwok, Roland; Schwartz, Jessica
Diverse physiological actions of growth hormone (GH) are mediated by changes in gene transcription. Transcription can be regulated at several levels, including post-translational modification of transcription factors, and formation of multiprotein complexes involving transcription factors, co-regulators and additional nuclear proteins; these serve as targets for regulation by hormones and signaling pathways. Evidence that GH regulates transcription at multiple levels is exemplified by analysis of the proto-oncogene c-fos. Among the GH-regulated transcription factors on c-fos, C/EBPbeta appears to be key, since depletion of C/EBPbeta by RNA interference blocks the stimulation of c-fos by GH. The phosphorylation state of C/EBPbeta and its ability to activate transcription are regulated by GH through MAPK and PI3K/Akt-mediated signaling cascades. The acetylation of C/EBPbeta also contributes to its ability to activate c-fos transcription. These and other post-translational modifications of C/EBPbeta appear to be integrated for regulation of transcription by GH. The formation of nuclear proteins into complexes associated with DNA-bound transcription factors is also regulated by GH. Both C/EBPbeta and the co-activator p300 are recruited to c-fos in response to GH, altering c-fos promoter activation. In addition, GH rapidly induces spatio-temporal re-localization of C/EBPbeta within the nucleus. Thus, GH-regulated gene transcription mediated by C/EBPbeta reflects the integration of diverse mechanisms including post-translational modifications, modulation of protein complexes associated with DNA and re-localization of gene regulatory proteins. Similar integration involving other transcription factors, including Stats, appears to be a feature of regulation by GH of other gene targets.
A fast fluorimetric flow injection method to determine ibuprofen
Lista, Adriana Guillermina; Palomeque, Miriam Edid; Fernández Band, Beatriz Susana
The native fluorescence of ibuprofen was enhanced when a host-guest complex of the analyte with b cyclodextrin (b-CD) was formed. So, based on this fact, a flow injection method to determine ibuprofen in different pharmaceutical preparations with fluorescence detection (lem 287 nm, lexc 223 nm) was developed. The calibration curve was linear over the range 6.00 – 60.0 mg L-1 of ibuprofen and the detection limit (LOD) for S/N=3 was 4.5 mg L-1. The relative standard deviation was 1.2% and the sample throughput 240 h-1. The method was validated by comparing the proposed and the official method to commercial preparation samples.; A fluorescência natural da ibuprofeína foi melhorada quando foi formado um complexo convidado-hospedeiro com a beta-ciclodextrina (beta-CD). A partir disso, foi desenvolvido um método por injeção em fluxo para a determinação de ibuprofeína em diferentes preparações farmacêuticas, com detecção fluorescente (lem 287 nm, lex 233 nm). A curva de calibração foi linear no intervalo entre 6,00 a 60,0 mg L-1 de ibuprofeína, com limite de detecção (LOD para S/N=3) de 4,5 mg L-1. O desvio padrão relativo foi de 1,2% e a velocidade de determinação de 240 amostras por hora. O método foi validado pela comparação do método proposto, e do usado oficialmente, em amostras comerciais preparadas.
Identification of Families Among Highly Inclined Asteroids
Gil Hutton, Ricardo Alfredo
A dataset of 3652 high-inclination numbered asteroids was analyzed to search for dynamical families. A fully automated multivariate data analysis technique was applied to identify the groupings. Thirteen dynamical families and twenty-two clumps were found. When taxonomic information is available, the families show cosmochemical consistency and support an interpretation based on a common origin from a single parent body. Four families and three clumps found in this work show a size distribution which is compatible with a formation due to a cratering event on the largest member of the family, and also three families have B- or related taxonomic types members, which represents a 14% of the B-types classified by Bus and Binzel [2002. Icarus 158, 146-177].
The strange polarimetric behavior of Asteroid (234) Barbara
Cellino, Alberto; Belskaya, I. N.; Bendjoya, P. H.; Di Martino, M.; Gil Hutton, Ricardo Alfredo; Muinonen, K.; Tedesco, E. F.
We have discovered that the Asteroid (234) Barbara exhibits very anomalous polarimetric properties. The phase-polarization curve of this asteroid is unique and is not matched by any other known atmosphereless body of our Solar System. Although a few preliminary conjectures can be made, for the moment the reasons of the peculiar polarimetric properties of this asteroid remain essentially unknown.
Preparation and characterization of polymeric microspheres for Cr(VI) extraction
Ochoa, Nelio Ariel; Illanes, Cristian Omar; Marchese, Jose; Basualto, C.; Valenzuela, Fernando R.
Microspheres (MS) from different polymers were prepared using two routes. Route A: process of phase inversion with solutions of polysulfone (PSf) in dichloromethane (DCM) and polyvinylpyrrolidone (PVP) as additive. Different weight ratios of PSf-PVP were used in the MS preparation. Route B: MS were obtained by cross-linking in emulsion using a commercial silicone as raw material. The obtained MS were analysed according to their morphological-structural characteristics and in relation to their Cr(VI) extraction capacity using impregnated MS with Aliquat 336. The results obtained showed that MS prepared with PSf-PVP have both less specific surfaces and relative porosities when the proportion of PVP in the mixture is increased. Extraction tests of ion Cr(VI) indicated that synthesized MS have adequate structural characteristics and interesting adsorptive properties which give rise to impregnating selective extractants. Impregnated microspheres with Aliquat 336 prepared from 2:1 PSf-PVP ratio achieved the highest Cr(VI) extractive performance (92% of Cr extraction for contact time of 60 min) and the best breakthrough point in column tests (up to 10 h in the first cycle).
¿Teorías científicas fuera de lugar? Algunas derivas del evolucionismo en el positivismo argentino
Fernandez, Cristina Beatriz
El propósito de este trabajo es estudiar comparativamente dos textos escritos en la Argentina a comienzos del siglo XX: "La simulación en la lucha por la vida" de José Ingenieros y "Los simuladores del talento" de José María Ramos Mejía. En ambos casos se estudia la relación de los textos con el léxico y los conceptos heredados de las teorías evolucionistas, los cuales se transforman, en estos textos, en claves de interpretación del proceso cultural y político local. El artículo concluye con una reflexión sobre la dialéctica de apropiación y transformación de las teorías científicas de origen europeo en el ámbito latinoamericano.; The aim of this paper is to study in a comparative way two works written in Argentina, at the beginning of the twentieth century: "La simulación en la lucha por la vida" by José Ingenieros and "Los simuladores del talento" by José María Ramos Mejía. The focus of the analyses is on the relationship between the terms and the concepts inherited from the evolutionary theories, which are transformed, in Ingenieros and Ramos’ texts, into clues for interpreting the cultural and political local processes. The paper ends with some considerations about the dialectis of the appropriation of the scientific theories borned in Europe and their transformation in Latin American.
Seguidor del punto de máxima potencia para sistemas fotovoltaicos basado en convertidor CC/CC elevador de tensión
Molina, Marcelo Gustavo; Pontoriero, Domingo Hector; Gandolfo, Daniel; León, Eugenio; Mercado, Pedro Enrique
Este trabajo presenta el modelado, simulación e implementación experimental de un seguidor del punto de máxima potencia (SPMP) para sistemas fotovoltaicos (FV), el cual utiliza un convertidor CC–CC elevador de tensión operando en modo de conducción continua (MCC). El convertidor es capaz de extraer la máxima potencia del panel fotovoltaico para niveles de radiación solar y temperatura ambiental dados, ajustando periódicamente el ciclo de trabajo del convertidor. La técnica de control propuesta se basa en el método de Perturbación y Observación (P&O) y utiliza un algoritmo simple y eficaz de seguimiento del punto de máxima potencia (PMP) del panel FV ante cambios en la carga y en las condiciones ambientales. La implementación del sistema de control se realiza mediante un procesador digital de señales (PDS) TMS320F2812. Los resultados experimentales obtenidos permiten comprobar el muy buen desempeño del SPMP propuesto.; This work presents the modelling, simulation and experimental implementation of a maximum power point tracker (MPPT) for photovoltaic systems (PV), which uses a dc-dc boost converter operating in continuous conduction mode (CCM). The converter is able to draw the maximum power from the photovoltaic panel for a given solar radiation level and environment temperature by periodically adjusting the duty cycle of the converter. The proposed control technique is based on the Perturbation and Observation (P&O) method and utilizes a simple and effective algorithm for tracking the maximum power point (MPP) of the PV panel in cases that changes occur in the load and in environmental conditions. The implementation of the control system is carried out by means of a TMS320F2812 digital signal processor (DSP). The obtained experimental results allow proving the very good performance of the proposed MPPT.
Existencialismo y humanismo ante la crisis de la psicoterapia: Una revisión
González, Eliana Noemí
A la largo de la historia en el campo de la psicología y de la psicoterapia se han percibido diferentes crisis, dadas por motivos muy diversos. En este artículo se analiza la crisis de la psicoterapia entendida como una crisis enraizada en su objeto de estudio, es decir en el hombre mismo, como sujeto de continuos cambios y devenires. Asimismo esta crisis del hombre reclama una psicoterapia capaz de dar respuesta a los planteos existenciales, esenciales de todo hombre. En tal sentido, se analiza la filosofía existencial y humanista y los posteriores planteos existenciales y humanistas dentro de la psicoterapia como una respuesta a este hombre en crisis.; Historically, psychology and psychotherapy fields have gone through several crisis due to different reasons. The present paper analyzes the crisis of psychotherapy in relation to its object of study, i.e. man as a subject who undergoes continuous changes and experiences. The crisis of man claims for a psychotherapy able to answer existencial questions which are esential to his nature. Hence, existencial and humanist philosophy and the subsecuent psychotherapy approaches are analyzed as an answer to man in crisis
Revisión estratigráfica de la Formación Ponón Trehué (Ordovícico), Bloque de San Rafael, Mendoza; Stratigraphic revision of the Ponon Trehue Formation (Ordovician), San Rafael Block, Mendoza
Heredia, Susana Emma
This paper provides new descriptions and interpretations of the Ordovician rocks cropping out to the south of the Arroyo de Ponón Trehué, in the San Rafael Block, Mendoza Province. These data allow a new stratigraphic interpretation for the Ordovician rocks which leads to a formal redefinition of the Ponón Trehué Formation. These rocks are mainly siliciclastics (Darriwilian to lower Upper Ordovician), and two members are defined. The lower one is a siliciclastic/ carbonate sequence from the upper Middle Ordovician (upper Darriwilian) to the lower Upper Ordovician and the upper one is an olistostrome deposits that is correlated with the lower Upper Ordovician. The stratigraphic succession is interpreted in terms of the following geologic history: 1) Early to early Mid Ordovician: deposition on shallow marine carbonate platform. 2) Mid Ordovician (pre-P. serra zone): exposure and erosion of basement as result of a gentle uplift, which is thought to be a local, but not a regional, event because it is not recorded in other parts of the San Rafael Block nor in the Precordillera. 3) Mid to early Late Ordovician (P. serra to P. anserinus Zones): gentle subsidence and extensive flooding surface, and siliciclastic deposition in gradually deepening marine environment. 4) Early Late Ordovician: rapid increase in rate of deepening (basin subsidence) to create steep basin margin and collapse of carbonate blocks into basin. In order to create accommodation space for the thick olistostrome sequence including large olistoliths and to create steep basin margin necessary to generate gravity slide process, basin subsidence must have been rapid and tectonically driven.; Nuevas descripciones y análisis de las rocas ordovícicas aflorantes al sur de Arroyo Ponón Trehué, en el ámbito del Bloque de San Rafael, permiten establecer una reinterpretación estratigráfica de las mismas. La redefinición formal de la Formación Ponón Trehué contempla que estas rocas de edad ordovícica media y superior, mayormente siliciclásticas, conforman una sucesión estratigráfica que permite diferenciar dos miembros: una secuencia basal siliciclástica/carbonática darriwiliana depositada en una plataforma con evidentes signos de exhondación al tope, y otra unidad conformada por depósitos olistostrómicos asignados al Ordovícico Superior que sobreyace a la anterior.
