La historia de la sífilis o ¿la sífilis en la historia?

Fil: Comerio, Carlos

Moritz Kaposi (1837-1902)

Fil: Comerio, Carlos. Hospital Luis Lagomaggiore (Mendoza, Argentina). Servicio de DermatologíaFil: Parra, Viviana Gladys. Universidad Nacional de Cuyo. Facultad de Ciencias Médicas. Cátedra de Dermatologí

Endometriosis vulvar : presentación de un caso clínico

Fil: Comerio, Carlos. Hospital Luis Lagomaggiore (Mendoza, Argentina). Servicio de DermatologíaFil: Sánchez, Cecilia. Hospital Luis Lagomaggiore (Mendoza, Argentina). Servicio de GinecologíaFil: Parra, Viviana Gladys. Hospital Luis Lagomaggiore (Mendoza, Argentina). Servicio de DermatologíaFil: Innocenti, Carolina. Hospital Luis Lagomaggiore (Mendoza, Argentina). Servicio de Dermatologí

The origin of gley colors in hydromorphic vertisols: the study case of the coastal plain of the Río de la Plata estuary

This work aims to contribute to the interpretation of soil colors; mainly to identify the pigments that generate the greenish colors in hydromorphic conditions (gley colors) in vertisols of the coastal plain of the Río de la Plata estuary. These colors are of cold hues, generally greenish (olive-gray), and occur in poorly drained soils with prolonged water accumulation. For this purpose, samples of Bssg horizons of hydromorphic vertisols from the coastal plain of the Río de la Plata estuary were analyzed using routine and chemical analyses, Mössbauer spectroscopy, determination of rocks magnetic parameters, X-ray diffraction, thermogravimetric and differential thermal analysis and petrographic-electronic microscopy. The pigments associated with the gley colors of these soils are mainly due to ferric iron content, corresponding to minerals such as ferric iron-rich smectites (nontronite/Fe-rich beidellite) and oxy-hydroxides like goethite, which colors range from green to yellow. These minerals, combined with gray or black components, e.g., manganese compounds and/or organic matter, contribute to the generation of the usual gley colors in the analyzed soils of the Pampean plain. The obtained data allows us to state that it is a mistake to assing the olive color in hydromorphic soils to the presence of ferrous iron compounds, as it is traditionally done. The oxidizing condition of iron is dominant in all the analyzed samples, integrating the composition of ferric iron-rich clay minerals and oxy-hydroxides (goethite).Fil: Gómez Samus, Mauro Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tierra del Fuego, Antártida e Islas del Atlántico Sur. Instituto de Ciencias Polares, Ambientales y Recursos Naturales; ArgentinaFil: Comerio, Marcos. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Montes, María Luciana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Boff, Laura Daniela. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Geomorfología y Suelos; ArgentinaFil: Loffler, Julia. Universidad Nacional de La Plata; ArgentinaFil: Mercader, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Bidegain, Juan Carlos. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentin

Iron oxidation status and mineralogy of gley soils in the coastal plain of the Río de la Plata

Se estudian los agentes cromógenos (pigmentos) que originan los colores gley de los suelos. Estos colores son de matices fríos, generalmente verdosos (gris oliva). Se dan en suelos con drenaje deficiente, con acumulación prolongada de agua. Para este fin, se analizaron muestras de horizontes Bssg de vertisoles hidromórficos de la llanura costera del estuario del Río de la Plata. Se efectuaron análisis de rutina, químicos, espectroscopia Mössbauer, parámetros magnéticos, difracción de rayos X, análisis térmico diferencial-termogravimétrico y microscopía de barrido electrónico. Esto permitió comprobar que en los pigmentos que determinan los colores gley de estos suelos domina el hierro férrico, conformando minerales como esmectitas ricas en hierro (nontronita/Fe-beidellita), de color verde a amarillo, y goethita muy fina, de color amarillo. Estos minerales, combinados con componentes grises/negros (ej. compuestos de manganeso y/o materia orgánica), contribuyen a la generación de los típicos matices verdosos.Centro de Investigaciones Geológica

Iron oxidation status and mineralogy of gley soils in the coastal plain of the Río de la Plata

Se estudian los agentes cromógenos (pigmentos) que originan los colores gley de los suelos. Estos colores son de matices fríos, generalmente verdosos (gris oliva). Se dan en suelos con drenaje deficiente, con acumulación prolongada de agua. Para este fin, se analizaron muestras de horizontes Bssg de vertisoles hidromórficos de la llanura costera del estuario del Río de la Plata. Se efectuaron análisis de rutina, químicos, espectroscopia Mössbauer, parámetros magnéticos, difracción de rayos X, análisis térmico diferencial-termogravimétrico y microscopía de barrido electrónico. Esto permitió comprobar que en los pigmentos que determinan los colores gley de estos suelos domina el hierro férrico, conformando minerales como esmectitas ricas en hierro (nontronita/Fe-beidellita), de color verde a amarillo, y goethita muy fina, de color amarillo. Estos minerales, combinados con componentes grises/negros (ej. compuestos de manganeso y/o materia orgánica), contribuyen a la generación de los típicos matices verdosos.Centro de Investigaciones Geológica

Iron-bearing minerals in clays related to the Holocene marine ingression in the coastal plain of the Río de la Plata estuary (Argentina): paleoenvironmental implications

En este trabajo se efectúa la caracterización de los minerales portadores de hierro en arcillas de la llanura costera del estuario del Río de la Plata, incluidas en la Facies Villa Elisa de la Formación Las Escobas (MIS1), con el principal objetivo de contribuir a su interpretación paleoambiental. Además, los resultados permiten hacer inferencias que se estiman de interés para la Pedología y para las Ciencias Ambientales. El trabajo abarca el uso de diversas técnicas (análisis químicos, determinación de propiedades magnéticas, análisis térmico diferencial-termogravimétrico, difractometría de rayos X y espectroscopia Mössbauer). Los materiales analizados presentan tonalidades gris-oliva y se clasifican como arcillas. Presentan una asociación mineralógica compleja, resultado de la combinación de múltiples factores, que incluyen procesos vinculados a su procedencia, al ambiente de depositación y a los efectos de la pedogénesis. Dominan los argilominerales (aproximadamente 60%), representados principalmente por esmectitas, illita y secundariamente por caolinita e interestratificados illita/esmectita con elevado contenido de capas expansivas. Se identificó también la presencia de cuarzo, plagioclasas, feldespatos alcalinos y en menor medida calcita y óxi-hidróxidos de hierro. El contenido de hierro total es considerable (alrededor del 10%), con un claro predominio de Fe3⁺ sobre el Fe2⁺ (92% y 8%, respectivamente). Los óxi-hidróxidos de hierro presentes (goethita y eventualmente ferrihidrita) no constituyen los principales portadores de hierro. De esta manera se concluye que el Fe3⁺ se encuentra principalmente en los argilominerales, en particular en esmectitas ricas en hierro (Fe-esmectitas), del tipo nontronita/Fe-beidellita. La asociación mineral determinada tiene importantes implicancias para la interpretación paleoambiental. Se concluye que un ambiente de marisma recibió argilominerales a partir de la erosión de suelos loessicos (principalmente esmectitas e illita) y por corrientes mareales (más ricos en esmectitas y caolinita). Mecanismos propios del ambiente depositacional, vinculados a ciclos de humedecimiento-secado con oscilaciones de Eh en un medio levemente alcalino permitieron la incorporación de hierro en la estructura de las esmectitas. Un aspecto a destacar es que estos materiales presentan colores glei originados por minerales con Fe3⁺ (Fe-esmectitas y goethita), lo cual contradice el tradicional supuesto en Pedología, que asocia este patrón de color a minerales de Fe2⁺. Finalmente, se destaca que la elevada participación de Fe-esmectitas en asociación con óxi-hidróxidos de hierro, contribuye a la adsorción de metales pesados y otros contaminantes de la región, dándole a la Facies Villa Elisa un importante valor ambiental.Iron in sediments can be part of a wide variety of minerals which characteristics are heavily dependent upon the environmental conditions. Hence, their knowledge is useful for paleoenvironmental interpretations. The aim of this work is to contribute to the understanding of iron-bearing minerals in clay deposits associated whit the Holocene hypsthermal sea-level fall, in the coastal plain of the Río de la Plata estuary, at Ensenada, Berisso and La Plata localities (Figs. 1, 2a). The studied unit corresponds to the Villa Elisa Facies of the Las Escobas Formation (Cavallotto, 1995 , Fig. 2b). The aforementioned author indicated that the analyzed deposits reflected sedimentation in a marine-continental transition linked to a saltmarsh environment, developed when the Holocene sea flooded the coastal plain. Cavallotto (1995) also indicated that this low-energy environment would have received suspended material from different origins (such as creeks and tidal currents), which flocculated as result of a high salinity. An important aspect to emphasize is that these deposits comprise the parent materials of the soils of the region that has been classified as Vertisols (see Imbellone and Mormeneo, 2011). The present study includes the use of several techniques of proven effectiveness for mineralogical characterization, especially related to iron-bearing minerals in order to contribute to the paleoenvironmental interpretation of this unit. In addition, the results allow performing inferences that may interest to Soil and Environmental Sciences. Sampling was performed in eight excavations (Figs. 2a, 3) where eleven samples were obtained at depths ranging from 20 to 110 cm. The most affected levels by the current pedogenetic cycle (A horizons) were not taken into account. Routine analyses such as color, grain size, organic matter and swelling were performed (Table 1), in addition to chemical analysis (Table 2), Mössbauer spectroscopy (Fig. 4; Table 3), magnetic properties (Figs. 6, 7; Table 4,), X-ray diffraction (Fig. 8; Table 5) and differential thermal-thermogravimetric analysis (Fig. 9). The analyzed samples are gray-olive in color (commonly known in Soil Science as gley colors) and show a clear predominance of clay fraction. From a textural point of view, the materials are classified as clays (Fig. 4). Samples are composed of a mineralogical complex association, although considering the wide area of sampling, the composition (e.g., texture, magnetic parameters, chemical elements) are similar in all samples. This association results from the combination of multiple factors, including processes related to the source area, the depositional environment at a saltmarsh, and also the current pedogenetic environment. The clay minerals (approximately 60% of total) are dominant over the other mineral phases, represented mainly by smectites and illite, and secondarily by kaolinite and interstratified I/S (Table 5; Fig. 8). Also quartz, plagioclase, alkaline feldspar, and to a lesser extent calcite and iron oxy-hydroxides (goethite and probably ferrihydrite), are present. The presence of goethite is consistent with the magnetic and differential thermal-thermogravimetric results (Table 4; Figs. 6, 9), which also evidenced a low concentration of this mineral (less than 3%). Samples have shown a considerable total iron content (about 10%; Table 2) and according to the Mössbauer spectroscopy the ferric iron (Fe3⁺) predominates over the ferrous (Fe2⁺), being the relative percent of Fe3⁺ phase approximately 92% and Fe2⁺ phase only around 8% (Table 3; Fig. 5). In view of these results the iron oxy-hydroxides do not constitute a dominant mineral phase, and therefore do not represent the main iron-bearing minerals. On the basis of the obtained results, it is concluded that Fe3⁺ is mainly within the clay minerals structure, in particular in iron-rich smectites, of the nontronite/Fe-beidellite type. The mineral association presented here has important implications for paleoenvironmental interpretations. Taking into account the previous models that considered the Villa Elisa saltmarshes Facies of Las Escobas Formation, we concluded that this environment received clay minerals, coming from the erosion of loessic soils (mainly smectites and illite) in addition to a tidal input (more rich in smectites and kaolinite). Once deposited, those materials were subjected to the environmental conditions, including repeated wetting-drying cycles and their respective Eh fluctuations under slightly alkaline pH conditions. Such conditions gave rise to complex mechanisms, which allowed the incorporation of iron into the smectites structure. One interesting aspect to emphasize is that the gley colors of these materials were originated by Fe3⁺ bearing minerals as Fe-smectites, which contradicts the traditional assignation of this color pattern to Fe2⁺ iron minerals. Besides, it is highlighted that the participation of Fe-smectites in association with iron oxy-hydroxides, contributes to the adsorption of heavy metals and other contaminants of the region. This aspect gives to the Villa Elisa Facies a great environmental importance.Facultad de Ciencias Naturales y MuseoLaboratorio de Entrenamiento Multidisciplinario para la Investigación TecnológicaCentro de Tecnología de Recursos Minerales y CerámicaInstituto de Física La Plat

Iron-bearing minerals in clays related to the Holocene marine ingression in the coastal plain of the Río de la Plata estuary (Argentina): paleoenvironmental implications

En este trabajo se efectúa la caracterización de los minerales portadores de hierro en arcillas de la llanura costera del estuario del Río de la Plata, incluidas en la Facies Villa Elisa de la Formación Las Escobas (MIS1), con el principal objetivo de contribuir a su interpretación paleoambiental. Además, los resultados permiten hacer inferencias que se estiman de interés para la Pedología y para las Ciencias Ambientales. El trabajo abarca el uso de diversas técnicas (análisis químicos, determinación de propiedades magnéticas, análisis térmico diferencial-termogravimétrico, difractometría de rayos X y espectroscopia Mössbauer). Los materiales analizados presentan tonalidades gris-oliva y se clasifican como arcillas. Presentan una asociación mineralógica compleja, resultado de la combinación de múltiples factores, que incluyen procesos vinculados a su procedencia, al ambiente de depositación y a los efectos de la pedogénesis. Dominan los argilominerales (aproximadamente 60%), representados principalmente por esmectitas, illita y secundariamente por caolinita e interestratificados illita/esmectita con elevado contenido de capas expansivas. Se identificó también la presencia de cuarzo, plagioclasas, feldespatos alcalinos y en menor medida calcita y óxi-hidróxidos de hierro. El contenido de hierro total es considerable (alrededor del 10%), con un claro predominio de Fe3⁺ sobre el Fe2⁺ (92% y 8%, respectivamente). Los óxi-hidróxidos de hierro presentes (goethita y eventualmente ferrihidrita) no constituyen los principales portadores de hierro. De esta manera se concluye que el Fe3⁺ se encuentra principalmente en los argilominerales, en particular en esmectitas ricas en hierro (Fe-esmectitas), del tipo nontronita/Fe-beidellita. La asociación mineral determinada tiene importantes implicancias para la interpretación paleoambiental. Se concluye que un ambiente de marisma recibió argilominerales a partir de la erosión de suelos loessicos (principalmente esmectitas e illita) y por corrientes mareales (más ricos en esmectitas y caolinita). Mecanismos propios del ambiente depositacional, vinculados a ciclos de humedecimiento-secado con oscilaciones de Eh en un medio levemente alcalino permitieron la incorporación de hierro en la estructura de las esmectitas. Un aspecto a destacar es que estos materiales presentan colores glei originados por minerales con Fe3⁺ (Fe-esmectitas y goethita), lo cual contradice el tradicional supuesto en Pedología, que asocia este patrón de color a minerales de Fe2⁺. Finalmente, se destaca que la elevada participación de Fe-esmectitas en asociación con óxi-hidróxidos de hierro, contribuye a la adsorción de metales pesados y otros contaminantes de la región, dándole a la Facies Villa Elisa un importante valor ambiental.Iron in sediments can be part of a wide variety of minerals which characteristics are heavily dependent upon the environmental conditions. Hence, their knowledge is useful for paleoenvironmental interpretations. The aim of this work is to contribute to the understanding of iron-bearing minerals in clay deposits associated whit the Holocene hypsthermal sea-level fall, in the coastal plain of the Río de la Plata estuary, at Ensenada, Berisso and La Plata localities (Figs. 1, 2a). The studied unit corresponds to the Villa Elisa Facies of the Las Escobas Formation (Cavallotto, 1995 , Fig. 2b). The aforementioned author indicated that the analyzed deposits reflected sedimentation in a marine-continental transition linked to a saltmarsh environment, developed when the Holocene sea flooded the coastal plain. Cavallotto (1995) also indicated that this low-energy environment would have received suspended material from different origins (such as creeks and tidal currents), which flocculated as result of a high salinity. An important aspect to emphasize is that these deposits comprise the parent materials of the soils of the region that has been classified as Vertisols (see Imbellone and Mormeneo, 2011). The present study includes the use of several techniques of proven effectiveness for mineralogical characterization, especially related to iron-bearing minerals in order to contribute to the paleoenvironmental interpretation of this unit. In addition, the results allow performing inferences that may interest to Soil and Environmental Sciences. Sampling was performed in eight excavations (Figs. 2a, 3) where eleven samples were obtained at depths ranging from 20 to 110 cm. The most affected levels by the current pedogenetic cycle (A horizons) were not taken into account. Routine analyses such as color, grain size, organic matter and swelling were performed (Table 1), in addition to chemical analysis (Table 2), Mössbauer spectroscopy (Fig. 4; Table 3), magnetic properties (Figs. 6, 7; Table 4,), X-ray diffraction (Fig. 8; Table 5) and differential thermal-thermogravimetric analysis (Fig. 9). The analyzed samples are gray-olive in color (commonly known in Soil Science as gley colors) and show a clear predominance of clay fraction. From a textural point of view, the materials are classified as clays (Fig. 4). Samples are composed of a mineralogical complex association, although considering the wide area of sampling, the composition (e.g., texture, magnetic parameters, chemical elements) are similar in all samples. This association results from the combination of multiple factors, including processes related to the source area, the depositional environment at a saltmarsh, and also the current pedogenetic environment. The clay minerals (approximately 60% of total) are dominant over the other mineral phases, represented mainly by smectites and illite, and secondarily by kaolinite and interstratified I/S (Table 5; Fig. 8). Also quartz, plagioclase, alkaline feldspar, and to a lesser extent calcite and iron oxy-hydroxides (goethite and probably ferrihydrite), are present. The presence of goethite is consistent with the magnetic and differential thermal-thermogravimetric results (Table 4; Figs. 6, 9), which also evidenced a low concentration of this mineral (less than 3%). Samples have shown a considerable total iron content (about 10%; Table 2) and according to the Mössbauer spectroscopy the ferric iron (Fe3⁺) predominates over the ferrous (Fe2⁺), being the relative percent of Fe3⁺ phase approximately 92% and Fe2⁺ phase only around 8% (Table 3; Fig. 5). In view of these results the iron oxy-hydroxides do not constitute a dominant mineral phase, and therefore do not represent the main iron-bearing minerals. On the basis of the obtained results, it is concluded that Fe3⁺ is mainly within the clay minerals structure, in particular in iron-rich smectites, of the nontronite/Fe-beidellite type. The mineral association presented here has important implications for paleoenvironmental interpretations. Taking into account the previous models that considered the Villa Elisa saltmarshes Facies of Las Escobas Formation, we concluded that this environment received clay minerals, coming from the erosion of loessic soils (mainly smectites and illite) in addition to a tidal input (more rich in smectites and kaolinite). Once deposited, those materials were subjected to the environmental conditions, including repeated wetting-drying cycles and their respective Eh fluctuations under slightly alkaline pH conditions. Such conditions gave rise to complex mechanisms, which allowed the incorporation of iron into the smectites structure. One interesting aspect to emphasize is that the gley colors of these materials were originated by Fe3⁺ bearing minerals as Fe-smectites, which contradicts the traditional assignation of this color pattern to Fe2⁺ iron minerals. Besides, it is highlighted that the participation of Fe-smectites in association with iron oxy-hydroxides, contributes to the adsorption of heavy metals and other contaminants of the region. This aspect gives to the Villa Elisa Facies a great environmental importance.Facultad de Ciencias Naturales y MuseoLaboratorio de Entrenamiento Multidisciplinario para la Investigación TecnológicaCentro de Tecnología de Recursos Minerales y CerámicaInstituto de Física La Plat

Iron-bearing minerals in clays related to the Holocene marine ingression in the coastal plain of the Río de la Plata estuary (Argentina): paleoenvironmental implications

En este trabajo se efectúa la caracterización de los minerales portadores de hierro en arcillas de la llanura costera del estuario del Río de la Plata, incluidas en la Facies Villa Elisa de la Formación Las Escobas (MIS1), con el principal objetivo de contribuir a su interpretación paleoambiental. Además, los resultados permiten hacer inferencias que se estiman de interés para la Pedología y para las Ciencias Ambientales. El trabajo abarca el uso de diversas técnicas (análisis químicos, determinación de propiedades magnéticas, análisis térmico diferencial-termogravimétrico, difractometría de rayos X y espectroscopia Mössbauer). Los materiales analizados presentan tonalidades gris-oliva y se clasifican como arcillas. Presentan una asociación mineralógica compleja, resultado de la combinación de múltiples factores, que incluyen procesos vinculados a su procedencia, al ambiente de depositación y a los efectos de la pedogénesis. Dominan los argilominerales (aproximadamente 60%), representados principalmente por esmectitas, illita y secundariamente por caolinita e interestratificados illita/esmectita con elevado contenido de capas expansivas. Se identificó también la presencia de cuarzo, plagioclasas, feldespatos alcalinos y en menor medida calcita y óxi-hidróxidos de hierro. El contenido de hierro total es considerable (alrededor del 10%), con un claro predominio de Fe3⁺ sobre el Fe2⁺ (92% y 8%, respectivamente). Los óxi-hidróxidos de hierro presentes (goethita y eventualmente ferrihidrita) no constituyen los principales portadores de hierro. De esta manera se concluye que el Fe3⁺ se encuentra principalmente en los argilominerales, en particular en esmectitas ricas en hierro (Fe-esmectitas), del tipo nontronita/Fe-beidellita. La asociación mineral determinada tiene importantes implicancias para la interpretación paleoambiental. Se concluye que un ambiente de marisma recibió argilominerales a partir de la erosión de suelos loessicos (principalmente esmectitas e illita) y por corrientes mareales (más ricos en esmectitas y caolinita). Mecanismos propios del ambiente depositacional, vinculados a ciclos de humedecimiento-secado con oscilaciones de Eh en un medio levemente alcalino permitieron la incorporación de hierro en la estructura de las esmectitas. Un aspecto a destacar es que estos materiales presentan colores glei originados por minerales con Fe3⁺ (Fe-esmectitas y goethita), lo cual contradice el tradicional supuesto en Pedología, que asocia este patrón de color a minerales de Fe2⁺. Finalmente, se destaca que la elevada participación de Fe-esmectitas en asociación con óxi-hidróxidos de hierro, contribuye a la adsorción de metales pesados y otros contaminantes de la región, dándole a la Facies Villa Elisa un importante valor ambiental.Iron in sediments can be part of a wide variety of minerals which characteristics are heavily dependent upon the environmental conditions. Hence, their knowledge is useful for paleoenvironmental interpretations. The aim of this work is to contribute to the understanding of iron-bearing minerals in clay deposits associated whit the Holocene hypsthermal sea-level fall, in the coastal plain of the Río de la Plata estuary, at Ensenada, Berisso and La Plata localities (Figs. 1, 2a). The studied unit corresponds to the Villa Elisa Facies of the Las Escobas Formation (Cavallotto, 1995 , Fig. 2b). The aforementioned author indicated that the analyzed deposits reflected sedimentation in a marine-continental transition linked to a saltmarsh environment, developed when the Holocene sea flooded the coastal plain. Cavallotto (1995) also indicated that this low-energy environment would have received suspended material from different origins (such as creeks and tidal currents), which flocculated as result of a high salinity. An important aspect to emphasize is that these deposits comprise the parent materials of the soils of the region that has been classified as Vertisols (see Imbellone and Mormeneo, 2011). The present study includes the use of several techniques of proven effectiveness for mineralogical characterization, especially related to iron-bearing minerals in order to contribute to the paleoenvironmental interpretation of this unit. In addition, the results allow performing inferences that may interest to Soil and Environmental Sciences. Sampling was performed in eight excavations (Figs. 2a, 3) where eleven samples were obtained at depths ranging from 20 to 110 cm. The most affected levels by the current pedogenetic cycle (A horizons) were not taken into account. Routine analyses such as color, grain size, organic matter and swelling were performed (Table 1), in addition to chemical analysis (Table 2), Mössbauer spectroscopy (Fig. 4; Table 3), magnetic properties (Figs. 6, 7; Table 4,), X-ray diffraction (Fig. 8; Table 5) and differential thermal-thermogravimetric analysis (Fig. 9). The analyzed samples are gray-olive in color (commonly known in Soil Science as gley colors) and show a clear predominance of clay fraction. From a textural point of view, the materials are classified as clays (Fig. 4). Samples are composed of a mineralogical complex association, although considering the wide area of sampling, the composition (e.g., texture, magnetic parameters, chemical elements) are similar in all samples. This association results from the combination of multiple factors, including processes related to the source area, the depositional environment at a saltmarsh, and also the current pedogenetic environment. The clay minerals (approximately 60% of total) are dominant over the other mineral phases, represented mainly by smectites and illite, and secondarily by kaolinite and interstratified I/S (Table 5; Fig. 8). Also quartz, plagioclase, alkaline feldspar, and to a lesser extent calcite and iron oxy-hydroxides (goethite and probably ferrihydrite), are present. The presence of goethite is consistent with the magnetic and differential thermal-thermogravimetric results (Table 4; Figs. 6, 9), which also evidenced a low concentration of this mineral (less than 3%). Samples have shown a considerable total iron content (about 10%; Table 2) and according to the Mössbauer spectroscopy the ferric iron (Fe3⁺) predominates over the ferrous (Fe2⁺), being the relative percent of Fe3⁺ phase approximately 92% and Fe2⁺ phase only around 8% (Table 3; Fig. 5). In view of these results the iron oxy-hydroxides do not constitute a dominant mineral phase, and therefore do not represent the main iron-bearing minerals. On the basis of the obtained results, it is concluded that Fe3⁺ is mainly within the clay minerals structure, in particular in iron-rich smectites, of the nontronite/Fe-beidellite type. The mineral association presented here has important implications for paleoenvironmental interpretations. Taking into account the previous models that considered the Villa Elisa saltmarshes Facies of Las Escobas Formation, we concluded that this environment received clay minerals, coming from the erosion of loessic soils (mainly smectites and illite) in addition to a tidal input (more rich in smectites and kaolinite). Once deposited, those materials were subjected to the environmental conditions, including repeated wetting-drying cycles and their respective Eh fluctuations under slightly alkaline pH conditions. Such conditions gave rise to complex mechanisms, which allowed the incorporation of iron into the smectites structure. One interesting aspect to emphasize is that the gley colors of these materials were originated by Fe3⁺ bearing minerals as Fe-smectites, which contradicts the traditional assignation of this color pattern to Fe2⁺ iron minerals. Besides, it is highlighted that the participation of Fe-smectites in association with iron oxy-hydroxides, contributes to the adsorption of heavy metals and other contaminants of the region. This aspect gives to the Villa Elisa Facies a great environmental importance.Facultad de Ciencias Naturales y MuseoLaboratorio de Entrenamiento Multidisciplinario para la Investigación TecnológicaCentro de Tecnología de Recursos Minerales y CerámicaInstituto de Física La Plat

The origin of gley colors in hydromorphic vertisols : The study case of the coastal plain of the Río de la Plata estuary

This work aims to contribute to the interpretation of soil colors; mainly to identify the pigments that generate the greenish colors in hydromorphic conditions (gley colors) in vertisols of the coastal plain of the Rio de la Plata estuary. These colors are of cold hues, generally greenish (olive-gray), and occur in poorly drained soils with prolonged water accumulation. For this purpose, samples of Bssg horizons of hydromorphic vertisols from the coastal plain of the Rio de la Plata estuary were analyzed using routine and chemical analyses, Mossbauer spectroscopy, determination of rocks magnetic parameters, X-ray diffraction, thermogravimetric and differential thermal analysis and petrographic-electronic microscopy. The pigments associated with the gley colors of these soils are mainly due to ferric iron content, corresponding to minerals such as ferric iron-rich smectites (nontronite/Fe-rich beidellite) and oxy-hydroxides like goethite, which colors range from green to yellow. These minerals, combined with gray or black components, e.g., manganese compounds and/or organic matter, contribute to the generation of the usual gley colors in the analyzed soils of the Pampean plain. The obtained data allows us to state that it is a mistake to assing the olive color in hydromorphic soils to the presence of ferrous iron compounds, as it is traditionally done. The oxidizing condition of iron is dominant in all the analyzed samples, integrating the composition of ferric iron-rich clay minerals and oxy-hydroxides (goethite).Instituto de Física La PlataLaboratorio de Entrenamiento Multidisciplinario para la Investigación Tecnológic