ABSTRACT The city of Bahía Blanca, located in the southwest of the province of Buenos Aires, has sustained for several decades a strong process of territorial expansion towards urban peripheral sectors. The use of land in the east and southeast of the city is currently manifested as an important element in the urban structure, sometimes without an adequate geotechnical study to know their response to the loads they can bear when used as physical support for engineering structures. With the aim of characterizing and classifying the soils of the outcropping and subsoil units of the sector, standardized in situ tests were carried out: resistance to penetration to estimate the compactness of the soil in its natural state and density of the soil in situ by the cone of sand method. In the laboratory, the granulometry determination method was applied by wet sieving and the Atterberg limits were determined. Based on the established parameters, the Unified Soil Classification System (USCS) was carried out. The preliminary studies carried out allowed us to define that, in the study area, the soils vary in depth from fine soils, clays of medium to high plasticity and silts of low plasticity, which grade to clayey sands / silty sands. The soils studied are mainly made up of: soils type CH and Cl on the surface that grade to SC and

RESUMEN La ciudad de Bahía Blanca, ubicada en el sudoeste de la provincia de Buenos Aires, sostiene desde hace varias décadas un fuerte proceso de expansión territorial hacia sectores periféricos urbanos. El uso de las tierras en el este y sudeste de la ciudad, se manifiesta actualmente como un elemento importante en la estructura urbana, en ocasiones sin un adecuado estudio geotécnico para estudiar su respuesta ante las cargas que puedan soportar cuando son utilizados como soporte físico de estructuras ingenieriles. Con el objetivo de caracterizar y clasificar los suelos de las unidades aflorantes y del subsuelo del sector, se realizaron ensayos normalizados in situ: resistencia a la penetración para estimar la compacidad del suelo en estado natural y densidad del suelo in situ por el método de cono de arena. En laboratorio se aplicó método de determinación de la granulometría mediante tamizado por vía húmeda y se determinaron los límites de Atterberg. En función a los parámetros establecidos se realizó la Clasificación Unificada de Suelos (Unified Soil Classification System, USCS). Los estudios preliminares realizados permitieron definir que, en el área de estudio los suelos varían en profundidad desde suelos finos, arcillas de plasticidad media a alta y limos de baja plasticidad, que gradan a arenas arcillosas / arenas limosas. Los suelos estudiados están constituidos principalmente por: suelos tipo CH y Cl en superficie que gradan a SC y SM.

Resumen El presente artículo muestra el uso de la vinaza de Saccharum officinarum en la estabilización de suelos cohesivos. Estos suelos en mención son aquellos que presentan propiedades de resistencia muy pobres, lo cual impide que el suelo trabaje de una forma adecuada como parte de una subrasante en una vía. El objetivo de la investigación fue determinar la estabilización de suelos cohesivos con la incorporación de vinaza de Saccharum officinarum. El tipo de investigación es experimental, la técnica utilizada es la observación y ficha de recolección de datos, mediante en la cual se pudo obtener valores de los ensayos realizados en laboratorio con el suelo natural y suelo estabilizado con vinaza de Saccharum officinarum. Los resultados indican que el suelo en estudio son limos y arcillas inorgánicas de baja plasticidad. Con la aplicación de vinaza de Saccharum officinarum se identificó que la densidad del suelo aumenta con los diferentes porcentajes utilizados. Luego al realizar los ensayos de resistencia mecánica del suelo estabilizado se logró incrementar la resistencia respecto a la del suelo natural, siendo el 25% de vinaza de Saccharum officinarum la que obtuvo los valores más altos. La investigación concluye que la incorporación de vinaza de Saccharum officinarum aumenta las propiedades de resistencia de un suelo cohesivo.

Abstract This article shows the use of Saccharum officinarum stillage in stabilizing cohesive soils. These soils in mention are those that present very poor resistance properties, which prevents the soil from working properly as part of a subgrade on a road. The objective of the research was to determine the stabilization of cohesive soils with the incorporation of vinasse from Saccharum officinarum. The type of research is experimental, the technique used is observation and data collection sheet, through which it was possible to obtain values from the tests carried out in the laboratory with natural soil and soil stabilized with Saccharum officinarum vinasse. The results indicate that the soil under study is low plasticity inorganic silts and clays. With the application of Saccharum officinarum vinasse, it was identified that the density of the soil increases with the different percentages used. Then, when carrying out the mechanical resistance tests of the stabilized soil, it was possible to increase the resistance with respect to that of the natural soil, being 25% of Saccharum officinarum vinasse the one that obtained the highest values. Research concludes that the incorporation of Saccharum officinarum stillage increases the strength properties of a cohesive soil.

Resumen: Para analizar la dinámica del carbono orgánico de los suelos (COS) asociada a su cambio de uso, de vegetación y prácticas de manejo, es necesario desarrollar modelos para usarse en forma predictiva. Un enfoque de modelación es la distribución del COS presente en los complejos organominerales primarios (arcillas, limos y arenas) ligado a las fracciones físicas. Para la separación de las fracciones físicas se emplea la dispersión del suelo por ultrasonido, paso que requiere optimizar las energías de sonicación para lograr la completa dispersión del suelo. En este trabajo se discute el modelo COLPOS y su hipótesis, así como sus posibles extensiones que consideran las masas y los enriquecimientos de las fracciones físicas del suelo, adicionalmente al análisis de las relaciones entre esas fracciones. Para analizar los patrones asociados al modelo COLPOS y sus extensiones, se analizan resultados disponibles de fraccionamientos de suelos mexicanos realizados con ultrasonido, además de tres bases de datos de fraccionamientos similares publicados en la literatura. Éstos muestran que el modelo COLPOS puede ser parametrizado en función del tamaño y masa de las partículas del suelo; aunque para el caso de las masas algunos resultados son inconsistentes. Del análisis de los cocientes del carbono orgánico entre fracciones para dos cinéticas lineales diferentes (organomineral y organomineral más partícula) las relaciones muestran mayor dispersión que para el caso de solo considerar fracciones de una cinética.

Summary: In order to analyze the dynamics of soil organic carbon (SOC) associated with changes in land use / vegetation and management practices, it is necessary to develop models that can be used predictively. A modeling approach is the distribution of SOC by physical fractions of the primary organomineral complexes (clays, silts and sands), using ultrasound soil dispersion techniques, where it is necessary to optimize the sonication energies to achieve complete soil dispersion. Under this consideration of complete dispersion, the COLPOS model and its hypothesis are discussed, as well as its possible extensions when considering the masses and enrichments of the physical fractions of the soil, in addition to the analysis of the relationships between these fractions. To analyze the patterns associated with the COLPOS model and its extensions, the available Mexican soil fractionations using ultrasound are analyzed, in addition to three databases of similar fractionations published in the literature. The results show that the COLPOS model can be parameterized according to the size and mass of the soil particles; although for the case of the masses some results are inconsistent. From the analysis of the organic carbon ratios between fractions for two different kinetics, the relationships show greater dispersion than for the case of only kinetic fractions.

Abstract: From the typological analysis of adobe, rammed earth, and bahareque constructions of 50 properties located in the provinces of Pichincha, Cotopaxi, Tungurahua, Chimborazo, and Bolívar, the physical, mechanical, chemical-biological, and anthropic damages produced by atmospheric agents and by the soil have been analyzed, which affect raw earth buildings in the Ecuadorian Andean area and subsequently the physical characteristics, mechanical resistance, and chemical mineralogical composition. The results determined that water mainly affects 40% of the buildings due to construction defects, such as the lack of footings over foundations that facilitate dampness in the lower parts or small eaves that do not protect from rainwater, deteriorating the mud coatings, especially of the bahareque and that is accentuated by the isolated location of the buildings. In addition, the empirical earth mixture used with a maximum gravel size of 15-18mm plus sands is in the proportion of less than 30% and a little more than 70% of clays and silts in the adobe and rammed earth samples; proportions that vary in the bahareque, with almost 55% of gravel-sand and 45% of fines; with compressive strengths less than 3MPa. The wood species, reeds, and fibers used in the manufacture of roof trusses, frameworks, and masonry have been collected. The age of the rural buildings exceeds 50 years and 82% of those studied are in a state of abandonment.

Resumen: A partir del análisis tipológico de las construcciones de adobe, tapial y bahareque de 50 inmuebles situados en las provincias de Pichincha, Cotopaxi, Tungurahua, Chimborazo y Bolívar, se han analizado las lesiones físicas, mecánicas, químico-biológicas y antrópicas producidas por los agentes atmosféricos y por el suelo, que afectan a las edificaciones en tierra cruda del área andina ecuatoriana y posteriormente las características físicas, resistencia mecánica y composición químico-mineralógica. Los resultados determinan que el agua afecta principalmente al 40% de los inmuebles por defectos constructivos, como la falta de sobrecimientos que facilitan las humedades en las partes bajas o de aleros pequeños que no protegen del agua de lluvia deteriorando los recubrimientos de barro, sobre todo de los bahareques y que se acentúa por el emplazamiento aislado de las edificaciones. Además, la dosificación empírica de la tierra utilizada con tamaño máximo de grava de 15-18mm más arenas está en la proporción de menos de 30% y poco más de 70% de arcillas y limos en las muestras de adobe y tapial; proporciones que varían en el bahareque con casi 55% de gravas -arenas y 45% de finos; con resistencias a compresión menores a 3MPa. Se han recogido las especies madereras, cañas y fibras utilizadas en la confección de las armaduras de cubiertas, entramados y mampuestos. La antigüedad de las edificaciones rurales sobrepasa los 50 años y el 82% de las estudiadas se encuentran en estado de abandono.

EXTENDED ABSTRACT A sedimentological study of the prograding area of the Paraná River delta (PRD) is here presented with the aim of characterizing the deposits related to the last ~100 yr. of paleoenvironmental evolution and to contribute to facies models of bayhead deltas. Delta deposits are the result of the interaction of various processes and factors (principally hydrological characteristics, waves, tidal action, type and volume of sedimentary discharge, water depth, sea level, climate) that disperse the sediments transported to the river mouth (Wright, 1977). The Paraná River, together with the contribution of the Uruguay River, develops a bayhead delta into the Río de la Plata (RdP) estuary (Fig. 1a). The delta constitutes an extensive plain with a very low gradient, lined by numerous fluvial channels of diverse hierarchy, and a series of distributary mouth bars with a lobate morphology (Figs. 1c, 2). It is a fluvial-dominated delta, regulated by the hydrological regime of its drainage basin and modulated by the estuary dynamics (Iriondo, 2004; Cavallotto et al., 2005). This bayhead delta has a drainage area of 3.000.000 km2. The Paraná river supplies 160 million tons of sediment per year to the delta mouth, with ~145 million tons of suspended sediments (30% clays, 60-65% silts and 5-10% sands) and 15 million tons of sands as bottom load (Sarubbiet al., 2004). In the Uruguay River, the suspended load reaches 7 million tons per year of sediments, with a higher contribution of sandy bottom sediments (Urien, 1972). Several studies revealed a high-constructive dynamic for the Paraná river delta during the last decades, with progradation rates of 30 to 70 m per year since AD 1818 (Soldano, 1947; Codignotto and Marcomini, 1993; Pittau et al., 2007; Leal, 2011; Medina and Codignotto, 2013). In particular, the study area grew an average of 42-45 m per year between AD 1933-2016 (Marcomini et al., 2018; Fig. 3). The PRD is placed at a temperate zone of southern South America, under a subhumid, mesothermal climate (periods 1981-1990 and 1991-2000; National Meteorological Service, 1992, 2003). Winds are mainly from the northeast and the southeast quadrants (Simionato and Vera, 2002), and are the main forcing of the RdP estuary circulation (Moreira et al., 2016). The estuary experiences a microtidal regime and the wave energy in the inner estuary is low (in average lower than 0.6 m high) and local (Moreira, 2016). Strong southeasterly wind (sudestada), that can last several days, triggers storm surges in the estuary and extensive floods in coastal areas (Seluchi, 1995). On the opposite, when ebb tides are accompanied by intense northeasterly winds, a very low water level happens (Simionato et al., 2004). Fitogeographically, the PRD belongs to the Neotropical region, and the vegetation is strongly influenced by the landscape and the hydrologic regime (Kandus et al., 2006). At the subaerial deltaic plain, plant communities are characterized by riparian forest along the levees and graminoid type plants in the interior, while bulrush colonizes the proximal subaqueous delta (Fig. 4d). Materials and methods include a geomorphologic-temporal evaluation, in-situ survey and sampling of surficial sediments and sediment cores in the lower subaerial and proximal subaqueous delta plains (34° 26’S, 58° 30’ W; Fig. 3), accompanied by lab determinations and then facies analysis. Surficial sediments were sampled with a Snapper dredge and the sediment cores were extracted using 2.5 inches PVC tubes. Grain size was measured with a Malvern Mastersizer Hydro 2000 laser analyzer, after pretreatment to eliminate organic content by soaking samples in hydrogen peroxide solution (H2O2) and rinsed with distilled water. The textural results were statistically processed and evaluated following the Folk and Ward (1957) protocols (Table 1). Due to the common presence of heterolithic sediments and in order to obtain an improved interpretation of the relationship between grain size distribution and sedimentary processes, extreme member (EM) analysis (after Paterson and Heslop, 2015) was applied to identify subpopulations (parametric curve-fitting applying the Weibull distribution; Fig. 5). EM modelling of the studied deposits was guided by geologic criteria and examined in terms of sediment availability and transport-deposition processes, including particle trapping due to bulrush vegetation (a common process in the PRD). The textural characterization by means of ME results a convenient technique to interpret mixed sediments like the here studied. Particularly, it can be useful when the sediment sample are acquired with dredges or augers, methods that produce the loss of sedimentary structures but demand less time and logistics than to extract cores. Sediment cores were described in terms of grain-size, sedimentary structures, color (Munsell, 2000), biological remains, mass magnetic susceptibility (SM, using a Bartington MS2B sensor) and percentage of LOI550 and LOI950. The time constrain for the core successions (ca. 1915-2017) was inferred by means of two main elements: correlation with a sediment core extracted about 15 km to the north of our study area and dated using radionuclide dating (210Pb and 137Cs) by (Schuerch et al., 2016) and the presence and depth of shells of Corbícula fluminea (Table 2), invader bivalve first recorded in the RdP estuary by ca. 1970 (Ituarte, 1981). The vertical growth rate of 1.52 cm per year (since year 1960) estimated for that core, that shows a comparable thickness and grain-size trend and represents a similar subaqueous delta subenvironment (Schuerch et al., 2016), was used in the here study sediment cores (Table 3). In a couple of studied cores there is some inconsistency between the two elements, possibly due to a higher rate of sedimentation. Besides, it is important to notice these estimations are relative age that have a degree of uncertainty due to these organisms not necessary may appear in all the sampled sites. The inferred relationships of grain-size subpopulations and sediment transport-deposition, the analysis of the sediment cores (Figs. 6,7) and the evaluation of the geomorphological setting of surficial and core samples, allow proposing a series of lithofacies (Table 2) and facies associations (Table 4). Core location in a time series of aerial photograph and Google Earth® images (Fig. 3) and previous delta models and concepts (mainly those by Wright and Coleman, 1973; Coleman and Wright, 1975; Wright, 1977; Orton and Reading, 1993) were applied in the facies analysis. Principally, the theoretical model of friction-dominated effluents proposed by Wright (1977) can be applied to the PRD, developed in a shallow basin (inner estuary is less than 4 m deep; Urien, 1972; Fig. 2) that promotes turbulent bed friction. The distributary mouth bars are laterally extensive (several km2), with very low slope (Fig. 4a-c) and crossed by shallow tidal channels. Bars are made up of massive or horizontal laminated beds forming heterolithic beds (sandy and muddy silt) and few fine-very fine sand and silty sand (bar crest) (Facies association F1, Table 4; Figs. 6, 7). This is interpreted as quick accumulation of tractive sediments, due to friction at the shallow river mouth, and then reworked by semidiurnal tidal currents and exceptional storm surges and accompanied by settling of fines from suspension. Once these shoals are stabilized by bulrush vegetation the sedimentation is dominated by suspension and particle trapping by vegetation (Fig. 4d), with eventual very low currents. Finally, the bar becomes an island of the lower subaerial delta plain, dominated by accumulation from flooding events. During this final stage clayey silt and silty clay, with the largest values of LOI550 of all core sediments, are deposited by flooding from the distributary channels (Facies association F5). Facies association F2 represents high energy deposition of sand and silty sand, usually with shells, due to exceptional storm surges or fluvial flooding. Deposits of interdistributary bays (Fig. 4e), included in facies association F4, are dominated by horizontal and heterolithic laminated, clayed silt with low LOI550 (Figs. 6,7). Deposits of subaqueous distributary channel (Fig. 4f) are fine-very fine sand and silty sand interlayered with silt and muddy silts with heterolithic laminations (Facies association F3a, Figs. 6,7). In core D11-T2 a succession with interbedded fine-very fine sand and sandy silt-silt with inclined heterolithic stratification (HIS) was identified (Facies association F3b, Fig. 7), and interpreted as subaqueous channel deposits, developed next to distributary bars (Fig. 3e). The textural characterization by means of ME proves to be a convenient technique to interpret mixed sediments like the here studied. Particularly, it can be useful when the sediment sample are acquired with dredges or augers, methods that produce the loss of sedimentary structures but demand less time and logistics than to extract cores. The proposed lithofacies and facies association will allow to systematize the sedimentological studies of the DRP and research of prograding deposits of bayhead deltas fed by big rivers with a sandy silt load.

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RESUMEN El modulo cortante a pequeñas deformaciones juega un rol fundamental en la evaluación de parámetros de respuesta en sitio. El Ensayo de Penetración Estándar (SPT) y el Ensayo de Penetración de Cono Sísmico (SCPTU), los cuales pueden rápidamente obtener la densidad y la velocidad de la onda de corte (Vs), se han utilizado poco en la estimación del módulo cortante a pequeñas deformaciones. En este estudio se realiza un acercamiento para desarrollar la relación de regresión entre los valores N del Ensayo de Penetración Estándar y el módulo cortante a pequeñas deformaciones (G max ). Con este objetivo se utilizó la información de las investigaciones de campo del SPT y del SCPTU en las ubicaciones de la autovía Su-Xin de China, que también se usaron en el proyecto de mejoramiento del terreno. La densidad in-situ de la capa de suelo se estimó a través de muestras inalteradas tomadas por perforación. Los perfiles Vs con profundidad se obtuvieron de ubicaciones cercanas a las perforaciones. Los valores del módulo cortante a pequeñas deformaciones fueron calculados por la medición de los valores Vs y la densidad del suelo in-situ. Cerca de 50 acoples de valores SPT-N y G max se utilizaron en el análisis de regresión. Además, se analizaron las diferencias entre los valores medidos y los valores corregidos que fueron usados en las relaciones de regresión ajustadas. Gran parte de las correlaciones se desarrollaron con base en estudios realizados en Japón e India, donde los valores N se midieron con martillo eléctrico de 78 %, que no sería directamente aplicable para otras regiones debido a que la variación en el Ensayo de Penetración Estándar del martillo eléctrico en China es del 55 %. Una nueva correlación se ha generado a través de valores medidos en sedimentos en China. En este estudio se encontró que los valores N no corregidos y del módulo proporcionan las relaciones de regresión más adaptables cuando se comparan con los valores N corregidos y del módulo. Con las ecuaciones usadas para la arena y la arcilla, las relaciones de regresión entre los valores N corregidos y del módulo proporcionan la ecuación de sedimentos en China.

ABSTRACT Small strain shear modulus plays a fundamental role in the evaluation of site response parameters. The Standard penetration test (SPT) and Seismic Piezocone Penetration Test (SCPTU), which can quickly get the density and shear wave velocity (Vs), were rarely used in small strain shear modulus estimating. In this study, an attempt has been made to develop the regression relationship between standard penetration test (SPT) N values and the small strain shear modulus (G). For this purpose, field investigations SPT and seismic piezocone penetration test (SCPTU) data from locations in Su-Xin Expressway of China have been used, which were also used for ground improvement project. The in-situ density of soil layer was estimated using undisturbed soil samples from the boreholes. The Vs profiles with depth were obtained for the locations close to the boreholes. The values for small strain shear modulus have been calculated by measured Vs and in situ soil density. About 50 pairs of SPT-N and G max values were used for regression analysis. The differences between measured and corrected values which were used in fitted regression relations were analyzed. Most of the existing correlations were developed based on the studies carried out in Japan and in India, where N values are measured with hammer energy of 78%, which may not be directly applicable for other regions because of the variation in SPT hammer energy which in China is about 55%. A new correlation has been generated using the measured values in silts of China. From this study, it is found that uncorrected values of N and modulus give the best fit regression relations when compared to corrected N and corrected modulus values. With most equation was used for sand and clay, the regression relations between corrected values of N and modulu gives the equation of silts in China.

The hydrochemical and sedimentary features of water bodies are directly linked to climate conditions during genesis and evolution (Williamson et al., 2008). Lacustrine deposits record climatic signals spatially and temporally, so their study allows the reconstruction of these environmental conditions and their evolution (Lapridaet al., 2014). The high resolution of the lake sedimentary record has a key role in paleoenvironmental and paleoclimate understanding (Gierlowski-Kordesch and Kelts, 1994; Bohacs et al., 2000). Hence, paleolimnology is an interdisciplinary science developed from chemical, physical and biological information of sedimentary records of aquatic bodies that allows paleo-environmental reconstruction (García-Rodríguez, 2002). In particular, these studies are performed in current lakes by drilling and core extraction, which limits the interpretation of macro structures given that many cores are required to perform a comprehensive analysis of past environmental and climatic conditions. In this work we analyze the sedimentary sequence of the exposed profile of a paleolake where remains of an equine belonging to the Hippidion devillei species were found (Cerdeño et at., 2008). These remains correspond to dental material consisting in premolars and molars that constitute the first fossil record of a Pleistocene horse found in the province of Mendoza (Argentina) (32º S). The objective of our work is to understand the sedimentary regime and evolution of this high altitude-paleolake (2680 m) associated with the megafauna of South America. This paleolake, named as DL3, is preserved along the Arroyo Minero located in the northwest of Mendoza province, specifically in the north extreme of the El Plata range (Central Andes) (Fig. 1). This paleolake was naturally dammed by the PB3 rock avalanche (Fig. 2). The chronology of this collapse was established by terrestrial cosmogenic nuclides (TCN) dating, performed on surficial big boulders on the top of rock avalanche deposits. 36Cl isotope was used because of the volcanic composition of these blocks. An~ 115±23 Ka age (Moreiras et al., 2015) was determined after discarding a younger result from 4 dated samples (PB4.01 in Table 1). The total lake succession reaches 29 m in thickness, for this reason several profiles were analyzed considering the abrupt topography (Fig. 3). Each level was described considering grain size, sedimentary structures, and main facies according to the lithofacies code of Miall, (1978) (Table 3). Color of layers was determined with field humidity and was described according to the Munsell chart. Descriptions were documented by pictures taken with a digital camera (Sony DSC, zoom 15X). Three sections were a priori established in the whole lake sequence profile. A Lower section corresponding to the lowest 9 m.; the Medium section comprehends the following 10 m up, and the Upper section involves the last 10 m of the sequence. Data of the revealed profiles were used to draw the lacustrine stratigraphic sequence (Fig. 4). Sedimentary analysis shows a thick succession of alternating levels of sands and silts with thicker subordinate boulders and gravels in the profile base. The facies association a is composed by matrix supported gravels, stratified sands and laminated silt-clays (Gm-Sh-Fl) (Table 2) representing the lower 10 meters of the profile. It consists of the interbedding of clays and silts layers of 50-70 mm (Fig. 5a) with 60 mm - thick sand layers. The clays and silts are laminated (facies Fl), with reddish, light brown and green sheets of 0.5 to 1 mm in thickness (Fig. 5b and c); they can be massive (Fm) and present organic matter (OM) content. Sand levels are medium to fine in grain with yellow color. They can be massive (Sm facies) or show planar lamination (Sh facies) within 1-2 cm thick layers. The Sm facies can present CaCO3 nodules (Fig. 5e), associated with oxidized levels showing rain drop marks. The Sh facies presents lags of rhyolitic angular clasts of 5-30 cm in diameter (Fig. 5d), from local outcrops. Towards the top of the lower section we can observe matrix supported gravels (Gm facies) with angular to subangular blocks of 0.07 m in diameter of rhyolitic porphyries and vulcanites within a sabulitic matrix of coarse sand of equal composition, its base is erosive. The facies b association is composed by stratified sands and laminated silt-clays (facies Sh-Sr-Sp-Fl-Fr) that extend over 9 m of the exposed profile (Fig. 6a). The Sh facies is characterized in this case by lentiform levels (Fig. 6b) that may have superimposed load structures and silt cracks (Fig. 6e and f). The Sr facies have ripples of 2 cm in width and 1 cm in height (Fig. 6c). The Sp facies are characterized by 7 cm planar cross-bedding structures forming 0.5-1 cm sets and 2 cm cosets containing the found remains of the Hippidion devillei (Fig. 6d). Silts and clays (facies Fl) contain sand dikes (Fig. 6g) and mud drapes with cracks drying out at the tops. They can form ripples of 0.5 mm in height on inclined surfaces between 10-15°. We identified rework, cut and fill structures supported by silts in diffuse contact. In certain strata, the presence of a reverse fault is observed towards the top of this section. Concerning interpretation of the facies associations, the alternation of facies Sh-Sm with facies Fl suggests a zone of interaction of tractive flows probably sheet flood with processes of deposition by suspension (Young et al., 2003, Fisher et al., 2008). The presence of massive sandstones arranged in coarsening-thickening upward pattern and covered by levels rich in carbonate nodules indicates alteration of the fabric by pedogenetic processes (Retallack, 1994). This indirectly raises the possibility of a system with low sediment input. The deposit of clasts, possibly dealing with a hyper-concentrated flow without lamination, came from the outside or edge of this level. It is ruled out that it is a local fall since no deformation is observed at the base of said level. The angular blocks originating from the Choiyoi Group reinforce the hypothesis of sediment supply from the basin margin. Taking into account the described facies, and the scarce presence of organic matter, one can deduce a sub-environment of ephemeral sandy plain (Smoot and Lowenstein, 1991). While, interpretation of the facies b association with an alternation of facies Sh and Fl with greater contribution of fine sediments allows inferring a more central position in the system with greater dominion of decantation processes and lower contribution of coarse sediments from the margin of the basin through tractive processes (Gierlowski-Kordesch and Rust, 1994). The presence of Sr suggests tractive processes associated with sheet flood flows. The Fr facies suggest ripple formation by wave action in possible bodies of water seasonally generated (Gierlowski-Kordesch, 1998). Loading structures are interpreted as a result of alternating sediments of different densities and with different degrees of water saturation (Van Loon, 2009). The presence of wafers suggests the development of a thin sediment cover during the cessation of water and sediment supply (mud drapes) and subsequent erosion (wafers) during the subsequent flood event of the system (Fisher et al., 2008). The thin covering added to the presence of desiccation cracks is a robust evidence of the system's ephemeral regime (Smoot and Lowenstein, 1991). Sand dams are associated with possible seismites (Obermeier, 1996, Rodríguez-Pascua et al., 2000, Alfaro et al., 2010). The reverse type fault corresponds to the most central area of the playa (Fig. 4i) to which sliding structures (slumps) could have been extended. The dominion of the facies Fl towards the top of the succession allows inferring an ephemeral muddy plain (Smoot and Lowenstein, 1991). Facies associations correspond to two sub-environments: sandy and muddy plains that conform an ephemeral playa lake. The normal gradation trend of layers with presence of thick sediments (Gm) at the base and finer layers (Fl) towards the top of the succession suggest a decrease in the sedimentary contribution over time and a more central position in the basin. These findings are significant for Quaternary paleo environment record of the Central Andes. The predominance of arid climate conditions restricts development and preservation of organic matter. Thus, the use of commonly used techniques such as pollen determination or radiocarbon dating in Quaternary records is practically unfeasible in this region. For this reason, the study of paleolakes if they show well preserved successions, may be a response to this limitation in paleoclimate reconstruction in the Arid Andes.

En este trabajo se estudia el régimen sedimentario de un paleolago donde fueron encontrados restos que constituyen el primer registro fósil de un équido perteneciente a la especie Hippidion devillei, en la provincia de Mendoza (Argentina). Los niveles lacustres donde se encontró el material dentario compuesto por premolares y molares fueron analizados en detalle mediante perfiles estratigráfico-sedimentológicos realizados a distintos niveles en la comarca de Uspallata al pie del Cordón del Plata. En esta sucesión principalmente limo-arenosa de 29 m de espesor total se describieron las estructuras sedimentarias, la granulometría de los depósitos y las facies principales. Este paleolago, represado por una avalancha de rocas pleistocena (~115Ka) permite reconstruir parcialmente el paleoambiente donde vivió el equino. Se trató de un sistema efímero de tipo barreal con períodos de llenado y secado.

The Neogene to Quaternary continental sedimentary record of the southern Buenos Aires province has been the object of numerous stratigraphic and biostratigraphic studies. However, much has to be done concerning the evolution and sedimentary dynamics of this area. To this end, the Claromecó creek basin (CCB) was chosen as a case study. The aim of this work is to analyze the Neogene to Quaternary sedimentary record to understand the geological evolution of the basin. To reach this objective, a preliminary geomorphological study was carried out. Then, facies and associations of facies were defined in order to identify the sedimentary environment and to establish the ratio between accommodation space and sediment supply. This information was subsequently used to interpret the main controls on the sedimentation of the CCB. The CCB is located in the center of the southern Buenos Aires province. It covers an area of 3017.18 km2, from the northwestern flank of the Tandilia range to the Atlantic coastline (Fig. 1). The basin can be divided in three parts (upper, middle and lower) depending on slope, drainage and main geomorphologic characteristics (Fig. 2). Its infill is dominated by Neogene to Quaternary sediments lying over Palaeozoic shales and sandstones (Zárate and Rabassa, 2005; Ramos, 2005). The few sedimentological, stratigraphical and paleoenviromental studies are located close to the Atlantic coastline (Frenguelli, 1928; Isla et al., 1996; Isla et al., 2000; Prieto et al., 2014). A three step methodology was adopted. Firstly, a preliminary geomorphological study was carried out to understand the main geomorphological units and their relations with the landscape. The geomorphological setting was established with field observations and supported by SRTM. Secondly, eight sedimentological logs were made (Fig. 3). Facies and facies associations were defined according to Miall’s scheme (1985, 2014) (Table 1). Postdepositional processes were analysed and relative facies defined based on Mack et al. (1993) (Table 1). Finally, the interpretation of the depositional environments was performed considering the facies associations within the geomorphological units (Table 2). Accommodation space, sediment supply and controls were then defined and considered in a regional context. Two main geomorphological units were defined. The plain and elevations unit (U1) covers the upper and middle part of the basin. In the upper basin, the U1 is composed by an elevated plain in which the springs of the Claromecó creek are located. This plain evolves in a series of hills and elevations that cover discontinuously the middle part of the basin. U1 is characterized by reddish silty to conglomeratic calcretized fluvial sediments, which represent the substrate of the basin. In the middle and lower basin, this unit is eroded and forms large valleys, which represent the second geomorphological unit (U2). This unit is filled in by Late Pleistocene fluvial sediments that make up the present day floodplain. A total of eleven sedimentary facies and two postdepositional facies were defined (Table 1). These facies were grouped into six facies associations (FA) according to the geometry of the bodies and the interpreted depositional environments. These were subsequently grouped in accordance to the geomorphological units (Table 2). In this sense, U1 is composed by sheet flows (AF-A) forming mantles of matrix-supported conglomerates and sands (Gm and Sm facies) (Fig. 4a). Sheet-flow deposits are capped by amalgamated channel deposits of AF-B, composed of laminated and trough cross-stratified poorly sorted sands (Gm, Sh and St) (Fig. 4b). Both facies associations are capped by calcisols (AFP-C) (Fig. 4c, d). U2 is composed of sandy sheets (AF-C), floodplain deposits (AF-D), vegetated silty dunes (loess, AF-E) and marshy deposits (AF-F) (Fig. 5a). The sheet-like deposits are interpreted as unconfined channels filled by bars and locally preserved ripples (Ss, St and Sh). Floodplain deposits are broadly distributed in the basin and comprise massive to laminated silty sands with heterolithic lenses associated to secondary courses (Hl, Fl, Fm and Fr). Large and flat patchy dunes are present in the lower basin, composed of massive coarse silts (Fme and Fl) associated to eolian processes (loess). Close to the Atlantic coastline, whitish and laminated clayey silts are present, and are characterized by the presence of fresh and salty water gastropods (Hl, Fl y Fcf). U2 sedimentary successions are generally capped by hydromorphic paleosols (AFP-H) which are characterized by Fe-Mn rich nodules and rhizoliths (Fig. 6). The sedimentological succession can be divided in two subcycles (sensu Zarate, 2005) (Fig. 7). The first subcycle was developed between the late Miocene and middle-late Pliocene and is associated to the U1; the second subcycle was deposited between the late Pleistocene and the present and is linked to the U2 (Fig. 8). Both subcycles are followed by a stabilization stage (paleosols) that is related to a decrease of the accommodation space. For the Mio-Pliocene subcycle, this period can also be characterized as an erosional, no-depositional stage. This behavior is probably associated to a tectonic reactivation that occurred at some time after the middle-late Pliocene and that resulted in the formation of terrace and hills (U1) and the partial capture of the drainage of the CCB and nearby drainage basins (e.g., Quequén Grande and Quequén Salado rivers). In this context, the upper basin represents an elevated plain not affected by erosion and constituting a no-depositional surface. A regional discontinuous dynamic subsidence occurred during the Neogene and probably controlled the sedimentation and accommodation space in this area (Folguera et al., 2015). The late Pleistocene-Present subcycle responded to controls (changes in sea level and base level of continental systems) that did not significantly affect topography but rather resulted in facies variations. The development of eolian inland deposits (loess type), as well as marshy deposits restricted to the coastline, are probably related to the glacial/ interglacial stages that characterized the late Pleistocene-Holocene.

El registro sedimentario continental del Neógeno y Cuaternario de la cuenca interserrana bonaerense ha sido objeto de numerosos trabajos estratigráficos y bioestratigráficos. Sin embargo, aún mucho se desconoce sobre la evolución y la dinámica sedimentaria dentro de este área. A tal fin, se tomó como caso de estudio la cuenca del arroyo Claromecó, ubicada en el centro de la llanura interserrana y se realizó por primera vez un estudio que integra los aspectos geomorfológicos y sedimentológicos de las unidades aflorantes. Se establecieron así dos subciclos depositacionales. El primero, que tuvo su desarrollo entre el Mioceno tardío y el Plioceno medio-tardío, está compuesto por depósitos loéssicos y por depósitos fluviales asociados a flujos en manto y canales gravosos amalgamados. El segundo subciclo se habría desarrollado a partir del Pleistoceno tardío hasta la actualidad y está integrado por facies de canales arenosos mantiformes y facies de llanura de inundación que culminan en depósitos eólicos tipo loess asociados a las últimas glaciaciones del Cuaternario. Los dos subciclos finalizan con una etapa de estabilización (paleosuelos) que se relaciona con una disminución del espacio de acomodación. Sin embargo, es luego del primer subciclo cuando tiene lugar una etapa de erosión y no depositación cuya duración estimada sería no menor a 500 ka. Estos resultados muestran diferencias en la jerarquía y en los factores de control de cada uno de los subciclos sedimentarios.

The presence of a significant thickness of soft silts beneath the site of a proposed new road bridge caused concerns over the suitability of shallow foundations. Despite extensive conventional ground investigations, it was not possible to obtain reliable stiffness data, and so a full-scale, fully instrumented load test was undertaken to better determine ground stiffness. The data obtained was used in conjunction with sophisticated numerical analysis to demonstrate that the settlement of shallow foundations would be acceptable. Following completion of the bridge construction, Continuous Surface Wave testing was undertaken and a range of simple non-linear elastic settlement analyses conducted to model the behaviour of the load test. Through these analyses this paper demonstrates the benefit of using continuous surface wave ground stiffness testing in conjunction with simple analysis methods. It underlines the importance of obtaining high-quality stiffness data to accurately predict settlement of shallow foundations.

Al desarrollar el proyecto «Limos Cuaternarios» se encontró que dentro de la Formación Libertad se incluían dos lodolitas diferentes: una, derivada de la meteorización de un loess finiplioceno, sin gravilla, con menos de 20 % de arena y con illita como mineral arcilloso dominante, a la que se propone mantener como Formación Libertad. A la otra lodolita, derivada de rocas básicas con alto porcentaje de arena, minerales ferromagnesianos en esa fracción, abundante gravilla (30-50 %) y montmorillonita como mineral arcilloso dominante, se propone denominarla Formación La Carolina. En realidad se trata de unidades edafoestratigráficas. Las diferencias mineralógicas sugieren una concentración diferente en oligoelementos que podría resultar en un comportamiento disímil de la fertilidad natural. La distribución actual puede definirse a partir de las asociaciones de suelos relevados en la Carta de Suelos a escala 1/1.000.000 de Uruguay.

As a result of the «Quaternary Silts» project, two different mudstones were found included in the Libertad Formation: one, derived from Finipliocene loess, without gravel, with less than 20 % of sand, and illite as the dominant clay mineral, which is proposed to maintain as Libertad Formation. The other mudstone, derived from basic rocks with high sand percentage, ferromagnesian minerals in the sand fraction, abundant gravel (30-50 %), and montmorillonite as dominant clay mineral, is proposed to be defined as La Carolina Formation. The two formations are actually soil stratigraphic units. The mineralogical differences suggest a different concentration of trace elements, which might result in dissimilar natural fertility behavior. The current distribution can be defined from soil associations surveyed in the soil chart of Uruguay at 1/1.000.000 scale.

The main purpose of this contribution is to present an updated vision of the knowledge of the Quaternary sedimentary successions and the first morphostratigraphic mapping of the central-west of San Luis province, at the distal eastern piedmont plain of the Cordillera de los Andes. These sequences are composed of deposits of fluvial, fluvial-lacustrine and alluvial-aeolian origin and their main outcrops are exposed in the central-western region of the San Luis province and the central-east sector of Mendoza province, in the Desaguadero River valley and the Bebedero depression (Fig. 1). The main geomorphological units of the area are the tectonic depressions known as depresión longitudinal central and depresión occidental, and the serranías occidentales hills (González Díaz, 1981), represented in the study area by the Cabras hill. The Desaguadero River valley is a notorious north-south elongated feature on the depresión occidental unit, with a main channel incised approximately between 3 and 11 meters into an older fluvial plain. The Bebedero depression is a subunit in the southern part of the depresión longitudinal central, interpreted as a fault-block basin (González, 1994) and structured at the east of the Desaguadero block (Ortiz et al., 1977) from the Diaguita tectonic event (late Pliocene). It contains the present day saline of Bebedero surface and paleoshores linked to the remarkable Late Pleistocene-Holocene expansion of an approximately 650 km2 paleolake, when the Desaguadero River and the Bebedero depression were connected from the south with the Bebedero Arroyo. The Bebedero depression and the Desaguadero River are separated by the Cabras hill and its underground continuity to the south in the Pencoso-Donado structural high, through a broad and very low slope piedmont covered by a mixed of alluvial and aeolian deposits. The Arco del Desaguadero Formation (Rodríguez y Barton, 1993) is the only Quaternary unit defined in the region and its typical sedimentary profile outcrops at the confluence of Jarilla Arroyo in the middle basin of the Desaguadero River. Here, the base of the Arco del Desaguadero Formation overlies an erosional unconformity carved on deposits which we attribute to lower to middle Pleistocene (Fig. 3). On the other hand, the sedimentary sequences present in the Bebedero depression have been linked to climatic events and piedmont deposits in the Cordillera de los Andes (González, 1981), but they have not been referred to any lithostratigraphic unit in particular. Considering stratigraphy, regional geomorphology, paleontological records of gastropods and charophytes, and new radiocarbon ages, we propose three lower-level units composing the Arco del Desaguadero Formation, namely: Salina del Bebedero Member (late Pleistocene), Río Desaguadero Member (early to middle Holocene) and Dos Anclas Member (late Holocene) (Table 1; Fig. 2). The Salina del Bebedero Member is a fluvial succession dominated by sandy gravels (high-energy environment) as in saline of Bebedero paleoshores (Figs. 4, 5) and silty sands (moderate-energy environment) as the ones at the basal strata on the Desaguadero River banks (Figs. 6-8). They present gray to brown yellowish-reddish colors and, at the saline of Bebedero paleoshores, have radiocarbon dates of 20.140 ± 170 y 14C BP (23.963-24.368 cal yr BP) and 15.280 ± 200 y 14C BP (18.283-18.723 cal yr BP). The Río Desaguadero Member is characterized by a cyclicity of fluvial and lacustrine deposits outcropping in the arroyo Jarilla banks (Fig. 9), as well as identified in the core taken from the borehole drilled at the center of saline of Bebedero (Fig. 10). These deposits are dominated by silty sands with reddish brown, yellowish and greenish colors and isolated layers containing high concentrations of carbonate and gypsum of white and gray colors, whose radiocarbon ages are in the range between 10.700 ± 170 y 14C BP (12.180-12.743 cal yr BP) and 6.519 ± 54 y 14C BP (7.324-7.433 cal yr BP). The Dos Anclas Member represents a set of relatively thin outcropping deposits (less than 3 meters), but widely distributed in the region and with high variability of sediments, which suggest different depositional conditions (Fig. 11) such as the fluvial silts of the Tunuyán River paleochannel (Figs. 12-14), the evaporites of Bebedero depression, and the sandy silt of paleosoil and silty sands of floodplain units (Table 4). The radiocarbon ages range from 3.444 ± 54 y 14C BP (3.570-3.718 cal yr BP) to 930 ± 60 y 14C BP (731-904 cal yr BP). Paleontological record includes the presence of shells restricted to certain levels of the external paleoshore in the saline of Bebedero, Desaguadero River and paleochannels of Tunuyán River, from which radiocarbon datings were possible. We report the presence of the shells of the gastropods: Chilina mendozana, Heleobia parchappii, Biomphalaria peregrina, Succinea meridionalis (Fig. 15), the family Ancylidae, Lymnaeidae, Physidae and Pupillidae, as well as few specimens of the bivalves Pisidium chiquitanum and Musculium aff. patagonicum (Fig. 16). The gyrogonites of charophyta have their greatest representation in the strata of arroyo Jarilla and are recognized as Chara contraria, Chara cf. papillosa, Chara halina and Chara hornemannii (Fig. 17). The evolution of these sedimentary basins responds to climatic stages linked to the Last Glacial Maximum and the Holocene Postglacial, under the influence of a paleo-landscape generated by the effects of neotectonics. In this context, the Desaguadero regional fault in the depresión occidental and local faults southward of the Bebedero depression are the main structures (González, 1994). High-energy fluvial regimes during late Pleistocene in the region are expressed through the incision of early to middle Pleistocene deposits in the Desaguadero River basin and the expansion of the Bebedero paleolake. This fluvial erosion originated the paleosurface where the Salina del Bebedero Member was deposited. During the early Holocene, probably related to the fluctuations of the Hypsithermal, sedimentary deposits in conditions of lower fluvial energy and local lacustrine bodies were developed (Río Desaguadero Member). The marked variability of late Holocene climatic conditions is manifested by restricted fluvial deposits, alluvial soil development, and aeolian sediments, all of them being encompassed by the Dos Anclas Member. Finally, during the last centuries, the region has suffered a climate crisis that characterizes the South American Arid Diagonal (Piovano et al., 2009), while the relationship between seismic events and strong river discharges has caused the retreat of headers and the incision of the Desaguadero River channel, as well as the desiccation of the lake and the development of the Bebedero saline.

Se presenta la descripción de los sedimentos cuaternarios y primer mapeo morfoestratigráfico de detalle de las sucesiones aflorantes en el sector centro-occidental de la provincia de San Luis, correspondientes al valle del río Desaguadero y la depresión del Bebedero. La Formación Arco del Desaguadero (Rodríguez y Barton, 1993) constituye la única unidad definida en la región y dichos autores la vincularon al intervalo temporal correspondiente al “Lujanense” (Pleistoceno tardío) sugiriendo su perfil tipo en el área de confluencia del arroyo Jarilla y el río Desaguadero. Se propone la integración de la Formación Arco del Desaguadero en tres unidades de menor categoría, Miembro Salina del Bebedero (Pleistoceno tardío), Miembro Río Desaguadero (Holoceno temprano a medio) y Miembro Dos Anclas (Holoceno tardío). El Miembro Salina del Bebedero constituye una sucesión fluvial dominada por gravas arenosas de alta energía (paleocosta de salina del Bebedero) y areniscas limosas de moderada energía (base del río Desaguadero), de tonos castaño amarillentos a rojizos, con fechados radiocarbónicos de 20.140 ± 170 a 14C AP (23.963-24.368 años cal. AP) y 15.280 ± 200 a 14C AP (18.283-18.723 años cal. AP) en la depresión del Bebedero. El Miembro Río Desaguadero presenta una ciclicidad de depósitos fluviales y lacustres considerando los afloramientos del arroyo Jarilla y una perforación del centro de salina del Bebedero. En su evolución dominan las areniscas limosas, de tonos castaño rojizas, amarillentas y verdosas, aislados estratos de tonos blanco y gris con altas concentraciones de carbonato y yeso, y edades radiocarbónicas entre 10.700 ± 170 a 14C AP (12.180-12.743 años cal. AP) y 6.519 ± 54 a 14C AP (7.324- 7.433 años cal. AP). El Miembro Dos Anclas, representa un conjunto de depósitos de escasa potencia aflorante, variada litología y amplia distribución areal. Corresponden a las limolitas fluviales del paleocanal de río Tunuyán, las limolitas y evaporitas de la salina del Bebedero, las limolitas arenosas del paleosuelo y las areniscas limosas de la planicie aluvial, con edades radiocarbónicas entre 3.444 ± 54 a 14C AP (3.570- 3.718 años cal. AP) y 930 ± 60 a 14C AP (731-904 años cal. AP). Los aspectos geomorfológicos destacados involucran a la planicie aluvial pedemontana de la cerrillada de las Cabras (serranías occidentales), la profunda incisión fluvial que representan las barrancas en el valle del río Desaguadero (depresión occidental), la notable expansión del paleolago en la salina del Bebedero (depresión longitudinal central), y la llanura de inundación del arroyo Bebedero. La diversidad y abundancia de los moluscos es relativamente escasa, así, la paleocosta externa en salina del Bebedero, los estratos cuspidales del río Desaguadero y los niveles del paleocanal de río Tunuyán constituyen las sucesiones destacadas y vinculadas con los fechados radiocarbónicos. Los girogonitos de las carófitas tienen su mayor representatividad en los estratos del arroyo Jarilla. Considerando las descripciones estratigráficas, características geomorfológicas zonales, nuevas edades radiocarbónicas y evidencias paleontológicas de gasterópodos y caráceas se logró proponer la evolución de las cuencas en respuesta a los estadios climáticos vinculados al Último Máximo Glacial y postglacial Holoceno (MIS 2 y 1).

The Claromecó Basin is located between the horst of Tandil and Ventania. The Irene formation is defined to the west of the Interserrana ("between ranges") Plain, Buenos Aires Province, for light-coloured carbonatic siltstones with joints that sums 7 m thick at the locality close to Irene Railway Station. These rocks comprising the Araucanense are underlying reddish sandy silts assigned to the Pampian sediments of La Toma Formation. According to the fossiliferous and escoria content, these sediments were similar to those outcropping as Monte Hermoso and Chapadmalal formations. It is therefore assumed a Pliocene age for the upper levels of the Irene Formation, as well as to the La Toma Formation. The hilly landscape is crowned by silt with calcretes.

La cuenca de Claromecó se ubica entre los positivos de Tandil y Ventania. La Formación Irene fue definida para el ámbito del sudoeste de esta Pampa Interserrana, Buenos Aires, para margas claras diaclasadas y lajadas que alcanzan 7 m de espesor en la Estación Irene del Ferrocarril General Roca. Estas rocas que comprenden lo que fue denominado "Araucanense" están subyaciendo limos arenosos carbonáticos rojizos que corresponden a sedimentos pampeanos de la Formación La Toma. De acuerdo a los contenidos fosilíferos y la presencia de escorias, estos sedimentos que coronan las lomas han sido equiparados a las Formaciones Monte Hermoso y Chapadmalal. Se postula entonces una edad pliocena para la porción aflorante (superior) de la Formación Irene y para la formación La Toma. El paisaje es de lomas coronadas por limos entoscados.

In this paper the biosedimentation and mineralogy of intertidal sediments of two sites of the Bahía Blanca estuary, and its relation to plant species and population dynamics of Neohelice granulata was analyzed. Two transects perpendicular to the subtidal were placed; A transect in Puerto Cuatreros and B in Villa del Mar. Sampling was conducted from March to June 2013. Two stations at each transect were selected, where surface sediments (control) and sediments removed by crabs were analyzed through environmental, textural and mineralogical studies. Density of burrows, vegetation cover and environmental data were also recorded. For the granulometric and mineralogical studies, loose grain method under the microscope and X-ray diffraction were done using standardized laboratory methods. The XRD results revealed that in both study sites, intertidal sediments were represented by minerals like quartz, feldspar and halite, and in lesser proportions were found clays such as illite and montmorillonite. The clay fraction prevailed in intertidal sediments of Puerto Cuatreros (50-45%) over samples of Villa del Mar, where quartz was predominant (42-35%). In the grain size analysis, Puerto Cuatreros was characterized by the dominant presence of the fine size fraction; sandy silts and clayey silts (<0.05 mm) and Villa del Mar for the medium size; medium sands and fine sands (0.05-1mm). Sediments removed by biological activity in both study sites were similar in mineralogical composition than control sediments, but they were enriched with clay material and abundant organic vegetal material, mainly due to bioturbation work of crabs. The mean density of burrows of Neohelice granulata in Puerto Cuatreros was higher than Villa del Mar. The hardest minerals (such as quartz and feldspar) were in greater proportion in places not removed by crabs; so we can predict that they select sectors to mobilize and build burrows in substrates with lower hardness, which they can easily dig. These combinations of features were reflected in Puerto Cuatreros. The generic distribution of sedimentary materials is a direct consequence of the dynamics of the environment. In Bahía Blanca estuary, vegetation dissipates the energy of the water entering and bioturbator species, like Neohelice granulata, contribute to increase fine particles in the intertidal.

En el presente trabajo se analizó la biosedimentación y la mineralogía de los sedimentos intermareales de dos sitios del estuario de Bahía Blanca, y su relación con las especies vegetales y la dinámica poblacional de Neohelice granulata. Se trazaron dos transectas perpendiculares al submareal; la trasecta A en Puerto Cuatreros y la B en Villa del Mar. Los muestreos se realizaron de marzo a junio de 2013. En cada transecta se seleccionaron dos estaciones, en las cuales se recolectaron sedimentos superficiales (control) y sedimentos removidos por cangrejos que fueron examinados teniendo en cuenta un enfoque ambiental, textural y mineralógico. Se estimó la densidad de cuevas, la cobertura vegetal y paralelamente se registraron datos ambientales. Para la caracterización granulométrica y mineralógica de arcillas se efectuaron estudios con el método de grano suelto bajo lupa y de difracción por rayos X, empleando métodos estandarizados de laboratorio. Los resultados de los difractogramas revelaron que en ambos sitios de estudio los sedimentos intermareales estuvieron representados por los minerales cuarzo, feldespato y halita, y en menor proporción se encontraron las arcillas, como illita y montmorillonita. La fracción arcillosa prevaleció en el sedimento del intermareal de Puerto Cuatreros (50-45%) por sobre las muestras de Villa del Mar, donde predomino el cuarzo (42- 35%). En cuanto a la granulometría, Puerto Cuatreros se caracterizó por la presencia dominante de la fracción de tamaño fino; limos arenosos y arcillosos (<0,05mm) y Villa del Mar por el tamaño mediano; arenas medianas y finas (0,05-1mm). Los sedimentos removidos por la actividad biológica en ambos sitios de estudio tuvieron una composición mineralógica similar a los sedimentos control, pero enriquecidos con material arcilloso y abundante material orgánico vegetal, debido principalmente al trabajo bioturbador de los cangrejos. La densidad media de cuevas de Neohelice granulata en Puerto Cuatreros fue mayor que en Villa del Mar. Esta característica sumada a la presencia en mayor proporción de minerales con mayor dureza (cuarzo y el feldespato) en lugares no removidos por los cangrejos; nos permite señalar que ésta especie bioturbadora selecciona sectores para movilizarse y construir sus cuevas en sustratos con menor dureza; pudiendo remover y escavar con facilidad el sustrato. Esta conjunción de características se vio reflejada en la zona de Puerto Cuatreros. La distribución genérica de los materiales sedimentarios es una consecuencia directa de la dinámica del ambiente. En el estuario de Bahía Blanca las especies vegetales actúan en la disipación de la energía del agua que ingresa y las especies bioturbadoras, como Neohelice granulata, contribuyen en a la acumulación de partículas finas en el intermareal.

Mudanças no uso e ocupação do solo representam um importante impacto antrópico sobre a qualidade de habitats e a diversidade biológica. Os efeitos do uso do solo sobre a qualidade de habitats e a granulometria do sedimento em um rio tropical impactado por urbanização e agricultura fora m investigados. Foram selecionados 15 trechos de amostragem representativos da bacia do Rio das Mortes, sendo 12 localizados no leito principal, desde a cabeceira até a foz, e os restantes em três dos principais tributários. Um levantamento de habitat foi realizado nestes trechos durante a estação seca de 2010 e amostras de sedimento foram coletadas para análise granulométrica. A cobertura da bacia nos trechos estudados foi dominada por vegetação natural (41.6 a 60.2%), seguida por agricultura (38.4 a 56.9%) e urbanização (1.4 a 5.6%). Os sedimentos foram dominados por silte e areia, pouco favoráveis à diversidade biológica. De acordo com o levantamento de habitat, todos os trechos apresentaram integridade moderada ou totalmente perturbada, devido a diversos impactos frequentes, tais como remoção de mata ciliar, captação de água, extração de areia e cascalho e erosão. Apenas um dos trechos estudados apresentou largura de corredor ripário em concordância com o exigido pelo Código Florestal Brasileiro. Os resultados indicam que a integridade de habitat e a qualidade do sedimento riverinos dependem principalmente das condições presentes na vizinhança imediata dos trechos estudados. Assim, a restauração custo-efetiva dos habitats aquáticos poderia ser alcançada por medidas simples de restauração do canal e a proteção da vegetação ripária neste rio tropical.

Land-use change, i.e., the transformation of natural land into agricultural and urban area is among the most important human impacts on habitat quality and species diversity. In this study, we investigated the effects of land use on river habitat quality and sediment granulometry in a larger tropical river, affected by urbanization and agricultural land use. We selected 15 representative sampling reaches in the Rio das Mortes basin, 12 of them along the main river from its headwater to its mouth, and 3 in major tributaries. A habitat survey was conducted in these reaches in the dry season 2010 and sediment samples were taken for granulometry analyses. Sub-basin land cover of reaches was dominated by natural vegetation (41.6 to 60.2% of total land cover), followed by agricultural land cover (38.4% to 56.9%) and urban land cover (1.4% to 5.6%). Sediments were dominated by poorly to moderately sorted silts to sands, little conducive to diverse biological communities. According to the river habitat survey, all investigated river reaches exhibited moderately to totally disturbed habitat integrity, due to diverse and often co-occurring human impacts, such as riparian deforestation, water abstraction, sand and gravel extraction, and margin erosion. Only one of the investigated sampling reaches exhibited the minimum riparian forest corridor width demanded by the Brazilian Forest Code. Our results indicated that river habitat and sediment quality mainly depended on conditions in the direct vicinity of river reaches. Accordingly, initial cost-effective restoration of aquatic habitats could be achieved by relatively simple channel restoration measures and the protection of the riparian corridor in the investigated tropical river.

In the distal foreland region of central Argentina the Mio-Pliocene continental record is widely distributed (Fig. 1a, Folguera and Zárate, 2009). In La Pampa province it is represented by the Cerro Azul Formation (Fm) (Linares et al., 1980; Visconti, 2007) that involves the lapse between ca. 12-11? Ma and 5.8 Ma (Verzi and Montalvo, 2008; Folguera and Zárate, 2009). This lithostratigraphical unit crops out along the walls and floors of the transversal valleys (Calmels, 1996) situated in the central-eastern sector of La Pampa province. The deposits are blanketed by aeolian silty sands and sandy silts mantles which together with the sand dunes systems usually located along the transversal valleys are considered of Late Pleistocene-Holocene age (Zárate y Tripaldi, 2012). According to Visconti (2007) the outcrops of the Cerro Azul Fm consist of lacustrine, aeolian and fluvial facies. The lacustrine facies, made up of laminated claystones and sandy siltstones to very fine sandstones, have been stratigraphically placed at the base of the Formation. However, field work allowed recognizing the existence of similar deposits making up comparable geoforms at different absolute altitudes in several transversal valleys. This paper is focused on the sedimentological characteristics of these deposits and questions their stratigraphic position. Based on the observations and previous work, three working hypothesis are considered: the deposits are the oldest exposed stratigraphic sections of the Cerro Azul Fm as already stated; the deposits post date the valleys formation, hence they were accumulated within the valleys; the deposits represent similar and diachronic sedimentary settings during the accumulation of the Cerro Azul Formation. The study consisted of a sedimentological-pedological description and sampling coupled with the geomorphological analysis of the deposits at several localities in different transversal valleys of La Pampa (Fig. 1b). Textural, mineralogical (X-Ray difractometry) and micromorphological analyses of thin sections were carried at selected samples. A lithofacies approach was used to describe the deposits resulting in the identification lithofacies (Table 1) and facies associations following Miall's (2006) proposal, with a partially modified lithofacies code. Interpretations were made following Miall (2006), Reading (1996) and Nichols (2009). Two main geomorphic systems (SE1 and SE2) of different altitude are identified in the Nerecó, Hucal, Quehué and Chapalcó valleys (Figs. 1b, 2a) resulting in a characteristic stepped topography. The deposits under study compose the SE2 with a relative height between 2 and 5 m above the valley floor, surrounding the deepest part of them; the lower stratigraphic contact remains unexposed. They are made up of unconsolidated sandy silt, silt and, secondarily, silty fine sand, either massive or with rare planar laminar bedding at some localities, while a dominant angular blocky structure is present at exposed sections. In some exposures, the deposits under study are featured by the occurrence of cutans and slickensides. Calcium carbonate is commonly present as powdery accumulations, nodules and concretions. The organic matter content varies from 0.03 to 1.17 %. At some levels the deposits exhibit layers of darker colors and higher concentration of organic matter with subprismatic secondary structure when dried. According to the grain-size and primary and secondary structures several lithofacies have been identified: Afm(f), Afb, Lab(c), Lab(mf), Lam(i), Lb(fc), Lal, Lab(cP), Afb(mfP) (Table 1), which were grouped into two main facies, A and B. Facies A represents abandoned channels of low relief and nonchannelized areas linked to low energy ephemeral streams/flows transporting sediments to the deepest part of the landscape. Facies B is interpreted as a paludal-like setting corresponding to poorly drained low energy aggradational environments. Both facies are gathered into facies association 1 (FA1), recognized in all the studied localities. It is interpreted as the record of low energy ephemeral fluvial and paludal-like environments, including episodes of higher water inputs linked to heavy rain events. This together with the geomorphological setting of the deposits suggests the occurrence of an aggradational process of low energy during the late Miocene in the interior of the valleys once they were already formed.

En la región centro-oriental de la provincia de La Pampa, comprendida en el ámbito del Bloque de La Pampa Central, los depósitos de la Formación (Fm.) Cerro Azul constituyen el registro de la sedimentación continental neógena de antepaís (Mio-Plioceno). La unidad aflora en los márgenes y pisos del sistema de valles transversales que domina el paisaje del área analizada. En el interior de los valles aparecen comúnmente depósitos dominantemente limosos, no consolidados, descriptos como facies lacustres basales de la Fm. Cerro Azul. Conforman, en general, lomadas de hasta 5 m de altura relativa que en varias localidades marginan los sectores más deprimidos de los valles. El análisis de estos depósitos ha permitido plantear interrogantes respecto a su posición estratigráfica y ambiente de sedimentación. Entre ellos, ¿los depósitos corresponden a las secciones estratigráficas más antiguas de la Fm. Cerro Azul? ¿o representan unidades de agradación desarrolladas en el interior de los valles transversales, en forma posterior a su incisión, en algún momento del Mioceno tardío? ¿Corresponderían a ambientes de sedimentación que se han repetido en el Mioceno tardío, dando lugar a depósitos de características litológicas similares en distintas posiciones estratigráficas de la sucesión de la Fm. Cerro Azul?. Para dilucidarlo se llevó a cabo un estudio sedimentológico-pedológico, estratigráfico y geomorfológico sobre dichas facies limosas. Éstas registran ambientes sedimentarios de tipo fluvial efímero, de baja energía, y de tipo palustre, donde habrían ocurrido procesos de sedimentación y pedogénesis. Estos últimos habrían sido particularmente dominantes durante algunos lapsos de la evolución de estos sistemas. La posición y expresión geomorfológica que exhiben permite plantear que son parte de un ciclo de agradación acontecido en el interior de los valles transversales en algún momento de su evolución durante el Mioceno tardío.