Abstract During the neoliberal regime, food policy in Mexico focused on the paradigm of ensuring physical and economic access to safe and cheap food; However, the measures to meet this objective caused, among other things, a trade deficit in basic foods such as corn, orientation of production towards export crops, environmental and people’s health deterioration. In response to this problem, in the mid-1990s, the concept of food sovereignty gained strength. This paradigm contributed to making visible the problems faced by small family productive units and the importance of including in public policy actions that respect the diversity of cultivated seeds, traditional agricultural practices, the care of resources and the reproduction of culturally accepted foods. In this context, the objective of this work is to characterize corn production in three lake regions of Michoacán (Mexico) from the perspective of food sovereignty and, based on this, raise considerations for its strengthening. A comparative analysis was carried out on the approaches of the food sovereignty paradigm based on own information obtained through a survey applied to corn producers from three lake regions of the state of Michoacán. The results show the coexistence of diverse production systems ranging from traditional to intensive production in each region, with manifest experiences of food sovereignty in the Pátzcuaro region and silent in the Cuitzeo region.

Resumen Durante el régimen neoliberal, la política alimentaria en México se centró en el paradigma de asegurar el acceso físico y económico a alimentos inocuos y baratos; sin embargo, las medidas para atender este objetivo provocaron, entre otras consecuencias, un creciente déficit en la balanza comercial de alimentos básicos como el maíz, la orientación de la producción hacia cultivos de exportación, y el paulatino deterioro de la calidad ambiental y de la salud de las personas. Frente a esta compleja problemática, a mediados de la década de los años noventa, surge con fuerza el paradigma de soberanía alimentaria, cuyo concepto contribuyó a visibilizar los problemas que enfrentan las pequeñas unidades productivas familiares y la importancia de incluir en la política pública acciones que respeten la diversidad de las semillas cultivadas, las prácticas agrícolas tradicionales, el cuidado de los recursos y la reproducción de alimentos culturalmente aceptados. En este contexto, el presente trabajo tiene como objetivo caracterizar la producción de maíz de tres regiones lacustres de Michoacán desde la perspectiva de la soberanía alimentaria y, a partir de ello, delinear algunas consideraciones de política pública para su fortalecimiento. Para ello, se realizó un análisis comparado sobre los planteamientos del paradigma de soberanía alimentaria a partir de información propia obtenida mediante una encuesta aplicada a productores de maíz de tres regiones lacustres del estado de Michoacán. Los resultados muestran la coexistencia de diversos sistemas productivos que van desde los tradicionales hasta la producción intensiva en cada región, observando experiencias de soberanía alimentaria manifiestas en la región Pátzcuaro y silenciosas en la región Cuitzeo.

ABSTRACT The last three millennia have been characterized by global temperature oscillations of around one Celsius degree, and high frequency variability on precipitation. Two main temperature anomalies have been reported worldwide, the Medieval Warm Period (ÏVIWP) and the Little Ice Age (LIA), characterized by higher and lower than average temperatures, respectively. Precipitation variability has been mostly associated with El Niño anomalies in the Equatorial Pacific. These global variability modes have been modulated by regional factors such as sea surface temperatures and their interaction with continental landmasses. Understanding regional responses to these anomalies would shed light on ecosystem response to environmental variability, a paramount tool for conservation purposes on the light of modern climate change. Here we present a 3,000-year sedimentary record from Lake Metztitlán, located in a Biosphere Reserve under the rain shadow of the Sierra Madre Oriental. Cladoceran and geo-chemical analyses were used to reconstruct lacustrine dynamics through the time period encompassed by the record. Our record points to highly dynamic lacustrine systems, coupled with global and regional climatic variability. In Metztitlán, the MWP was associated with low lake levels and a high torrentiality of the precipitation reflected in high-frequency peaks of detrital material. The LIA was associated with an enlarged water body, probably as a result of lower evapotranspiration. Overall, global climatic variability resulted in high variability of regional precipitation and detrital input in the Metztitlán region, in turn associated with changes in lake morphometry and depth. Our record highlights the vulnerability of the area to changes in sea surface temperature of the Gulf of Mexico, and to changes in the frequency of El Niño events. Although the effects of global climate change in the region are inescapable, our results emphasize the importance of controlling anthropogenic activities as an additional source of pressure on the regional ecosystems.

RESUMEN Los últimos tres milenios se han caracterizado por oscilaciones en la temperatura global alrededor de un grado Celsius, y una variabilidad de alta frecuencia de la precipitación. Dos principales anomalias de temperatura han sido reportadas mundialmente, el Periodo Cálido Medieval (PCM) y la Pequeña Edad de Hielo (PER), caracterizadas por temperaturas más cálidas y más frías que el promedio, respectivamente. La variabilidad de la precipitación ha estado estrechamente relacionada con las anomalías de El Niño en el Pacifico Ecuatorial. A nivel regional, estos modos de variabilidad han sido modulados por factores como la temperatura superficial de los océanos y .su interacción con las masas continentales. El entendimiento de las respuestas regionales a estas anomalias ayuda a comprender la respuesta de los ecosistemas a la variabilidad global, un elemento critico para la conservación en vista del cambio climático moderno. En este trabajo se presenta un registro sedimentario de 3000 años del lago Metztitlán, ubicado en la Reserva de la Biosfera en la Sierra Aladre Oriental. Se empleo un análisis geoquimico y cladócero para reconstruir dinámicas lacustre en el periodo de tiempo que abarca el informe. Nuestro registro apunta a sistemas dinámicos lacustres, asociados con la variabilidad climática global y regional. En Metztitlán, el PCM estuvo asociado con bajos niveles lacustres y una alta torrencialidad de la lluvia, reflejada en picos de alta frecuencia en los indicadores de aporte detritico. La PEH estuvo asociada con un cuerpo lacustre más extenso, probablemente resultado de una menor evapotranspiración. En general, los efectos de la variabilidad climática global se reflejaron en una alta variabilidad de la precipitación y entrada de detriticos (detrital input) en la región de Metztitlán, a su vez asociada con cambios en la morfometria y la profundidad del lago. En nuestro registro resalta la vulnerabilidad del área a cambios en la temperatura superficial de mar en el Golfo de México, y a cambios en la frecuencia de los eventos El Niño. Aunque los efectos del cambio climático en el área son inevitables, nuestros resultados enfatizan la importancia de controlar las actividades antropogénicas como una fuente adicional de presión sobre los ecosistemas regionales.

RESUMO Trata do levantamento taxonômico das Mesotaeniaceae (Zygnemaphyceae, Zygnemales) de ambientes lacustres do PEFI, Parque Estadual das Fontes do Ipiranga. O material examinado proveio de coletas de material perifítico e planctônico em diferentes sistemas aquáticos do PEFI, além da revisão de todo material citado para o Parque e depositado no Herbário Científico do Estado “Maria Eneyda P. Kauffmann Fidalgo” (SP). Foram identificadas cinco espécies distribuídas em três gêneros (Cylindrocystis, Mesotaenium e Netrium). O Lago do IAG foi o ambiente que apresentou a maior riqueza específica (três táxons), provavelmente devido à característica oligotrófica do sistema.

ABSTRACT Paper is the taxonomic survey of the Mesotaeniaceae (Zygnemaphyceae, Zygnemales) present in the PEFI, Parque Estadual das Fontes do Ipiranga lacustrine systems. The examined material included periphyton and plankton from different aquatic systems within the PEFI, and the revision of all material cited for the Park deposited in the Scientific State Herbarium “Maria Eneyda P. Kauffmann Fidalgo” (SP). Five species were identified, which are distributed in three genera (Cylindrocystis, Mesotaenium, and Netrium). IAG Pond was the system presenting the highest species richness (three taxa) probably due to its oligotrophic characteristics.

ABSTRACT Mining operations in the south of Ecuador have increased their activity in the last decades due to the great auriferous wealth of the region. Nevertheless, gold extraction involves processes that cause dangerous impacts to the environment, such as the release of metal ions and inorganic compounds, which are discharged into aquatic systems or to the earth’s surface, interacting adversely with various organisms. Due to this problem, the aim of this research was to evaluate the removal efficiency of mercury, phosphates, sulfates, and nitrates from the gold mining wastewater through a phytoremediation process. The study collected and applied microalgae species of the Andes and the Ecuadorian Amazon such as Pleurococcus sp., Scenedesmus sp., and Chlorella sp. The adaptation of the microalgae was evaluated, as well as the absorption capacity of the pollutants of the wastewater collected from one of the gold processing plants located on the riverside of the Calera River, province of El Oro. The microalgae strains were cultivated individually and as a consortium in photobioreactors for the treatment. The physical and chemical parameters of the wastewater and the treated water were characterized. The results determined that all the treatments were efficient, since the concentration of contaminants was considerably reduced. Pleurococcus was the genus of microalgae with the highest percentage of mercury removal, with 86 %, while in the removal of sulfates, phosphates, and nitrates, the microalgae consortium achieved results greater than 76 %, 93 % and 97 %, respectively. Thus, the use of isolated microalgae on the lacustrine systems of the Andes and the Ecuadorian Amazonia represents a promising source of germplasm for environmental bioremediation applications.

RESUMEN La explotación minera en el sur del Ecuador ha incrementado su actividad en las últimas décadas debido a la gran riqueza aurífera de la región. No obstante, la extracción de oro involucra procesos que causan impactos perjudiciales al ambiente, tales como la liberación de iones metálicos y compuestos inorgánicos, mismos que son vertidos a sistemas acuáticos o a la superficie terrestre, interactuando de manera adversa con diversos organismos. Debido a esta problemática, el objetivo de esta investigación fue evaluar la eficiencia de remoción de mercurio, fosfatos, sulfatos y nitratos del agua residual provenientes de la actividad minera a través de un proceso de ficorremediación mediante el uso de las microalgas Pleurococcus sp., Chlorella sp. y Scenedesmus sp., cepas aisladas de los Andes y la Amazonía ecuatoriana. Se valoró la adaptación de las microalgas, así como la capacidad de biosorción de los contaminantes del agua residual recolectada del punto de descarga de una de las plantas de beneficio, ubicada a orillas del río Calera, provincia de El Oro, Ecuador. Las microalgas fueron cultivadas para el tratamiento del agua de forma individual y como consorcio en fotobiorreactores. Se caracterizaron los parámetros físicos y químicos del agua residual y del agua tratada, determinándose que todos los tratamientos fueron eficientes, ya que se redujo considerablemente la concentración de contaminantes. El género de microalga con el que mayor porcentaje de remoción de mercurio se obtuvo fue Pleurococcus con el 86 %; mientras que, en la remoción de sulfatos, fosfatos, y nitratos, el consorcio de microalgas alcanzó resultados de remoción de contaminantes mayores al 76 %, 93 % y 97 %, respectivamente. Por lo tanto, el uso de microalgas aisladas en los sistemas lacustres de los Andes y la Amazonía del Ecuador representa una fuente de germoplasma promisorio para aplicaciones de biorremediación ambiental.

Abstract: Mountain lake environments are highly sensitive to climatic and anthropogenic changes, Lake Laja in central Chile has undergone severe modifications in recent years, impacting its entire basin. Through the diachronic analysis of multi-temporal satellite images Landsat (1986-2016) with supervised classification (ENVI) and evaluated the changes (Idrisi Andes). We define the main factors that would explain the changes in this lacustrine system through analysis of land cover, distribution of water rights and climate data. A reduction of rainfall of 1500-2000 mm is observed to 970-780 mm annually and a sustained increase of the temperature between 1.3-1.6 ° C., also was recognized fluctuations of the flooded surface cover of the lake of9.994,63 Ha (1985) to 5.135,6 Ha (2013), i.e. a reduction in the period of 48.6%. Then the systematic retreat of Lake Laja is not explained by the climatic variations analyzed, which leads us to infer that the main external cause of this process is the anthropic action, expressed in the pressure and competition for the use of the water resource between actors with unequal relations of power: hydropower plants, small-medium farmers, inhabitants of the sector and entrepreneurs of tourism.

Resumen: Los ambientes lacustres de montaña son altamente sensibles a modificaciones climáticas y antrópicas, el lago Laja en Chile central presenta modificaciones severas en los últimos años, impactando toda su cuenca. Mediante el análisis diacrónico de imágenes satelitales multitemporales Landsat (1986-2016), con clasificación supervisada (ENVI) y evaluados los cambios (Idrisi Andes), buscamos definir los principales factores que explicarían los cambios en este sistema lacustre, mediante el análisis de las coberturas de suelo, la distribución de los derechos de agua y los datos climáticos. Se observa una reducción de precipitaciones de 1500-2000 mm a 970-780 mm anuales y un aumento sostenido de la temperatura entre 1,3-1,6 °C, además se reconocieron fluctuaciones de la cobertura de superficie inundada del lago de 9.994,63 ha (1985) a 5.135,6 ha (2013), es decir, una reducción en el período de 48,6%. Entonces el retroceso sistemático del lago Laja no se explica por las variaciones climáticas analizadas, lo que nos lleva a inferir que el causante externo principal de este proceso es la acción antrópica, expresada en la presión y competencia por el uso del recurso hídrico entre actores con desiguales relaciones de poder: centrales hidroeléctricas, pequeños-medianos agricultores, habitantes del sector y empresarios del turismo.

Abstract: The discrimination/characterization of depositional systems recorded in formal lithostratigraphic, Cenozoic, continental, epiclastic units of Mexico, is largely a pending task, notwithstanding its great academic and economic importance. Contributing to fill this gap, we present a first approach to discriminate and characterize the depositional systems of the late Eocene Yolomécatl Formation, which fills the namesake, triangle-shaped tectonic basin, and carries the southernmost Paleogene vertebrate fauna of North America. The study area lies between 17°25’-17°30’ North Latitude and 97°29’-97°36’ West Longitude, and between 2000-2500 m a.s.l.; the federal highway 125 traverses it; Santiago Yolomécatl is the main town. The Yolomécatl Formation is at least 650 m thick, although the continuous thickness measured in the principal reference section is much less (~250 m); it includes fluvial and lake depositional systems sparsely interbedded by tuff sheets (a system per se). The fluvial system consists of 1) Gmm, Gmg, Gcm lithofacies: alluvial fans and related deposits; 2) Gm, Gh, Gp, Gt, St, Sp lithofacies: channel lag deposits; 3) Sr, Sh, Sl, Fl lithofacies: floodplain deposits. The (clastic) lacustrine system includes: 1) Ll, Lsm, Lm lithofacies: offshore deposits; 2) Ll, Lsm lithofacies: playa lake and mud flats deposits. This large thickness of this unit indicates superposition of fluvial/lacustrine systems, and sparse pyroclastic emplacements that took place in a basin gradually subsiding with sedimentation, under humid to subhumid conditions, probably interrupted by seasonal dryness. Finally, the tectonic setting of the Yolomécatl Basin, indicates that its genesis and development are related to the dynamics of the regional, left-lateral strike-slip Tamazulapam fault, which is also regarded as the boundary between the Mixteca (west) and Oaxaca (east) terranes.

Resumen: La discriminación/caracterización de los sistemas de depósito registrados en unidades litoestratigráficas formales, cenozoicas, epiclásticas, continentales de México, es en gran parte una labor pendiente, a pesar de su enorme importancia académica y práctica. Para contribuir a llenar este vacío, presentamos un primer acercamiento para discriminar y caracterizar los sistemas de depósito de Formación Yolomécatl del Eoceno tardío, la cual rellena totalmente la cuenca triangular homónima delimitada por fallas normales, e incluye la fauna de vertebrados más meridional de Norteamérica para esa época. El área de estudio se encuentra entre 17°25’-17°30’ Latitud Norte y 97°29’-97°36’ Longitud Oeste, y entre 2000 y 2500 m s.n.m.; la carretera federal 125 atraviesa la cuenca, y Santiago Yolomécatl es el poblado principal. Se estima que la Formación Yolomécatl tiene un espesor mínimo de 650 m, aunque el espesor contínuo medido es mucho menor (~250 m); esta formación incluye sistemas fluviales y lacustres intercalados con depósitos piroclásticos (un sistema por sí mismo). El sistema fluvial consiste de: 1) las litofacies Gmm, Gmg, Gcm: abanicos aluviales y depósitos relacionados; 2) las litofacies Gm, Gh, Gp, Gt, St, Sp: depósitos de arrastre en canal; 3) las litofacies Sr, Sl, Sh, Fl: depósitos de planicie de inundación. El sistema lacustre (clástico) incluye: 1) las litofacies Ll, Lsm, Lm: depósitos lago adentro; 2) las litofacies Ll, Lsm: depósitos de ribera. El gran espesor de esta unidad indica sobreposición de los sistemas fluvial/lacustre y la intercalación espaciada de piroclásticos en una cuenca que se hundía gradualmente con la sedimentación, bajo condiciones subhúmedas, interrumpidas por otras de aridez, tal vez estacional. Finalmente, el marco tectónico de la Cuenca Yolomécatl, indica que su origen y desarrollo están relacionados con la dinámica de la falla regional sinistral Tamazulapam, la cual también se considera como la frontera entre los terrenos Mixteca, al oeste y Oaxaca, al este.

Abstract: Annually laminated sediments (varves) frequently form in lakes with contrasting seasonal environments, and are better preserved in deep water bodies, with low oxygen content at the water/sediment interface. We characterized deposits in a laminated section within the sedimentary record from Lake Chalco, Basin of Mexico. The laminated sediments are intercalated with massive sediments, volcaniclastic material and 13 micritic mud layers. This laminated sequence corresponds to the depth interval 122.5 to 106 m and has an age >130 ka, corresponding with the end of the penultimate glacial stage or Marine Isotopic Stage 6 (MIS 6). Dark and light lamina, as well as the micritic mud components, were identified by microscopic observation of sediment smear slides; some sediment in the dark laminae, light laminae and micritic mud layers was also analyzed using a scanning electron microscope. X-ray fluorescence was used to determine Ti content and Si/Ti and Ca/Ti ratios. These analyses enabled us to determine that the light laminae have high Si/Ti values, are formed mostly by diatom valves (Stephanodiscus niagarae and S. oregonicus), and represent a biogenic diatom ooze. Dark laminae have high Ti values and are formed mainly by clastic sediments including plagioclases and amphiboles. We propose an annual depositional model in which light laminae correspond to winter diatom blooms, whereas dark laminae were deposited by allochthonous inwash during the summer rainy season, thus forming a biogenic-clastic varve. Diatom ecology suggests the laminated sequence corresponds to a relatively deep, eutrophic to hypertrophic lake with cool to cold waters. This inference is consistent with the age of the deposits, which corresponds with the penultimate glacial maximum or MIS 6, for which we infer cooler and moistier conditions than for the last glacial maximum i.e. MIS 2. Sedimentation rates estimated by varve counts suggest that the laminated sequence was deposited during a ~5000 yr interval. The micritic mud layers have high Ca/Ti and Si/Ti ratios and are formed mainly by authigenic carbonates, sponge spicules, diatoms and ostracode valves. We propose that these chemical facies were deposited during periods of higher evaporation and water concentration and also lower lake level and high biological productivity. The recurrence of these events must be further studied, but based on the mean sedimentation rate of 2.9 mm/yr, calculated from varve counting we suggest that they have a 140-yr to 280-yr recurrence interval.

Resumen: En los sistemas lacustres relativamente profundos y con un bajo contenido de oxígeno en la interfaz agua-sedimento es común la preservación de sedimentos anualmente laminados (varvas), los cuales indican una estacionalidad marcada en los procesos de depósito. El objetivo de este trabajo es caracterizar una sección laminada del registro sedimentario del Lago de Chalco, cuenca de México, que se presenta intercalada con sedimentos masivos, material volcaniclástico y 13 capas de lodo micrítico. Esta secuencia laminada se ubica entre los 122.5 y los 106 m de profundidad y se le ha asignado una edad mayor a 130 ka, periodo que coincide con el final del penúltimo máximo glacial, o Estadio Isotópico 6 (EI 6). La caracterización de los sedimentos se realizó mediante la observación al microscopio estereoscópico, compuesto y petrográfico de preparaciones frotis para identificar los componentes de las láminas claras, láminas oscuras y capas de lodo micrítico; algunas láminas claras, oscuras y capas de lodo micrítico fueron observadas con un microscopio electrónico de barrido. También se reportan datos de contenido de Ti y relaciones Si/Ti y Ca/Ti obtenidos mediante fluorescencia de rayos-X. Estos análisis permitieron identificar que las láminas claras tienen altos valores de Si/Ti y están formadas mayoritariamente por valvas de diatomeas (Stephanodiscus niagarae y S. oregonicus), por lo que se definen como una facies biogénica de lodo (ooze) de diatomeas. Las láminas oscuras tienen elevados valores de Ti y están formadas mayoritariamente por material clástico que incluye plagioclasas y anfíboles. Se propone un modelo de deposición de láminas anuales, en el cual la lámina clara corresponde con un florecimiento invernal de diatomeas mientras que la oscura corresponde con el depósito de material detrítico durante la estación de lluvias de verano, formando un par de láminas anuales biogénica-clástica o varva. La ecología de las especies dominantes indica que el depósito de la secuencia laminada corresponde con un lago relativamente profundo, eutrófico a hipertrófico de aguas dulces, templadas a frías. Esto es consistente con un escenario donde el depósito laminado correlaciona con el final del EI 6, durante el cual se interpretan condiciones más frías y húmedas que durante el EI 2 (último máximo glacial). La tasa de sedimentación calculada mediante el conteo de varvas arroja un promedio de 2.9 mm/año y permite estimar que el depósito de este tipo de sedimentos ocurrió a lo largo de un intervalo de −5000 años. Las capas de lodo micrítico tienen altas relaciones de Ca/Ti y Si/Ti y están formadas principalmente por carbonatos autigénicos y por valvas de diatomeas, espículas de esponjas y valvas de ostrácodos. Estas capas representan facies químicas que se propone se depositaron durante momentos de mayor evaporación y mayor concentración química del agua, asociados con niveles lacustres más bajos y una alta productividad biológica. Dichas capas representan eventos climáticos recurrentes cuya periodicidad deberá ser estudiada más a fondo pero que considerando su espaciamiento en la secuencia y la tasa de sedimentación de 2.9 mm/año pudiera corresponder con un rango de 140 a 280 años.

Resumo A dimensão do impacto que a transposição do rio São Francisco provocará na ictiofauna das bacias receptoras ainda é imprecisa, entretanto, é provável que haja alterações na riqueza e abundância da comunidade de peixes. Levantamentos e registros prévios da fauna íctica em sistemas chaves das bacias receptoras são ações prioritárias para a conservação da diversidade aquática. Este estudo realizou o levantamento taxonômico da ictiofauna dos reservatórios Epitácio Pessoa (município de Boqueirão), e Argemiro de Figueiredo (município Itatuba), ambos pertencentes a bacia hidrográfica do rio Paraíba do Norte, estado da Paraíba, importantes sistemas sócioeconômicos e ambientais para o projeto da transposição. Assim, foram realizadas amostragens mensais de Outubro/2014 a Setembro/2015 nas zonas lacustres e a jusante dos reservatórios. Os espécimes foram coletados com redes de espera, tarrafa, arrasto, peneiras e puçás, em seguida acondicionados em gelo no campo, posteriormente no laboratório, transferidos para o formol a 10% e conservados em álcool 70%. Foram coletados um total de 2328 espécimes distribuídas em 31 espécies, 14 famílias e cinco ordens nos dois sistemas. Nas zonas lacustres foram coletados 2057 espécimes distribuídos em 17 espécies e nas áreas a jusantes foram coletados 271 indivíduos, distribuídos em 24 espécies. Das 31 espécies registradas, 13 são endêmicas das bacias hidrográficas que drenam rios do semiárido brasileiro, destas, sete (Apareiodon davisi, Characidium bimaculatum, Hypostomus pusarum, Parotocinclus jumbo, P. spilosoma, Pimelodella enochi e Prochilodus brevis) são endêmicas do Nordeste Médio Oriental. Dentre estas últimas, P. spilosoma e Pimelodella enochi são endêmicas do rio Paraíba do Norte. Apareiodon davisi é classificada como Em Perigo de acordo com a atual lista oficial de espécies ameaçadas de peixes e invertebrados aquáticos no Brasil. Este levantamento ictiofaunístico pré-transposição servirá de base para análises futuras pós-transposição, considerando que esta ação acarretará mudanças no âmbito de diversidade dos ecossistemas em questão.

Abstract The scale of impact that the São Francisco River transposition project will have on the drainage basins ichthyofauna is still unclear, however, changes in the fish community diversity and abundance is probable. Surveys and registries of the fish fauna within key systems of the catchment basins are priority actions for the conservation of the aquatic diversity. This study conducted a taxonomic survey of the Epitácio Pessoa (Boqueirão municipality) and Argemiro de Figueiredo (Itatuba municipality), reservoirs ichthyofauna, both belonging to the Paraíba do Norte River basin, important socioeconomic and environmental systems for the transposition project. Monthly sampling was carried out between October/2014 to September/2015 in the upstream and downstream zones of the reservoirs. The specimens were collected using dip nets, drag nets, and sieves, and placed on ice in the field. Later in the laboratory, they were transferred to 10% formaldehyde and then preserved in 70% alcohol. A total of 2,328 specimens were collected representing five orders, 14 families, and 31 species in both systems. At the upstream zones 2057 specimens were collected representing 17 species, and at the downstream zones 271 specimens were collected representing 24 species. Of the 31 species recorded, 13 species are endemic to watersheds that drain rivers from the Brazilian semi-arid region, and seven species (Apareiodon davisi, Characidium bimaculatum, Hypostomus pusarum, Parotocinclus jumbo, P. spilosoma, Pimelodella enochi, and Prochilodus brevis) are endemic to the Mid-Northeastern Caatinga Ecoregion (MNCE). Among the latter, Parotocinclus spilosoma and Pimelodella enochi are endemic to the Paraíba do Norte River. Apareiodon davisi is classified as Endangered according to the current published Brazil’s official list of endangered species of fish and aquatic invertebrates. This pre-transposition ichthyofaunistic survey will serve as a basis for future post-transposition analyzes, considering this action will change the scope of the ecosystems diversity.

We propose a synthesis of current state of the paleo-hydrological changes in Antofagasta de la Sierra, to design a paleoenvironmental evolution model based on environmental heterogeneity, and assess its usefulness to analyse human occupations of the past 7200 years cal. BP. Previous research in six river systems and three lakes, included geomorphological surveys and various sedimentological analyses, soil, diatoms and ostracods, which allowed infer that during the last 7200 years cal. BP water resources have always been available, but with different magnitude and distribution spatio-temporal, creating favorable local conditions for human occupation in specific spaces. Between ca. 7200-3500 years cal. BP, would have prevailed arid conditions with a high mosaic distribution of the water recourses in intra- and inter-basin scale. Between ca. 3500-1600 years cal. BP, with wet conditions with greater development and stability of wetlands in all sectors, there have been less spatial heterogeneity in water availability. Subsequently, ca. 1600 years cal. BP, they would predominate again arid conditions with different distribution of water resource. This model of paleoenvironmental heterogeneity is suitable as scale analysis to explore the various strategies of the use of space by pre-Hispanic societies.

Se realiza una síntesis de los cambios paleohidrológicos en Antofagasta de la Sierra para generar un modelo de evolución paleoambiental que considera la heterogeneidad ambiental y permite evaluar su utilidad en relación con el análisis de las ocupaciones humanas desde el Holoceno medio. Las investigaciones previas en sistemas fluviales y lacustres (que incluyen relevamientos geomorfológicos y diversos análisis sedimentológicos, edafológicos, de diatomeas y ostrácodos) permitieron inferir que durante los últimos 7200 años cal AP existió disponibilidad de recursos hídricos aunque de variada magnitud y distribución espacio-temporal, que generaron condiciones locales favorables para la ocupación humana en espacios específicos. Entre ca. 7200-3500 años cal AP, predominaron condiciones áridas con una distribución de los recursos hídricos de forma mosaico en escala intra- e intercuencal. Entre ca. 3500-1600 años cal AP, se evidencian condiciones relativamente más húmedas con mayor desarrollo y estabilidad de humedales en todos los sectores, que implicó una disminución de la heterogeneidad espacial de la disponibilidad hídrica. Posteriormente, ca. 1600 años cal AP, predominarían nuevamente condiciones áridas con disponibilidad de recursos hídricos altamente variada. Este modelo de heterogeneidad paleoambiental resulta adecuado como escala de análisis para explorar las diversas estrategias del uso del espacio de las sociedades prehispánicas.

Resumo Este estudo avaliou a assembléia de peixes do reservatório de Nova Ponte (rio Araguari, bacia do Alto Paraná, Brasil), em termos de estrutura e composição. Foram observadas diferenças significativas na abundância (p = 0.0003), riqueza (p = 0.0005) e diversidade (p = 0.02) entre as zonas lacustres e fluviais do reservatório. Nove espécies foram mais abundantes na região fluvial: Astyanax altiparanae, Astyanax gr. fasciatus, Galeocharax knerii, Hoplias intermedius, Hypostomus sp., Leporinus friderici, Leporinus obtusidens, Pimelodus maculatus and Schizodon nasutus. Os resultados indicaram a existência de um gradiente longitudinal na composição e abundância de peixes no reservatório de Nova Ponte. Estes padrões reforçam a importância de trechos fluviais livres de barramentos para a conservação da ictiofauna neotropical nativa e refletem a forte adaptação dessas espécies aos sistemas fluviais.

Abstract We assessed the fish assemblage structure and composition of Nova Ponte Reservoir (Araguari River, Upper Paraná Basin, Brazil). We observed significant differences in abundance (p = 0.0003), richness (p = 0.0005) and diversity (p = 0.02) between lacustrine and riverine zones of the reservoir. Nine species were significantly more abundant in the riverine region: Astyanax altiparanae, Astyanax gr. fasciatus, Galeocharax knerii, Hoplias intermedius, Hypostomus sp., Leporinus friderici, Leporinus obtusidens, Pimelodus maculatus and Schizodon nasutus. The results indicated a longitudinal gradient in the composition and abundance of fishes in Nova Ponte Reservoir, reinforcing the importance of freely flowing riverine reaches for conserving native neotropical ichthyofauna and reflecting the strong adaptation of these species to riverine systems.

RESUMO Trata do levantamento taxonômico das Oocystaceae (Chlorophyceae, Chlorococcales) dos ambientes lacustres do PEFI, Parque Estadual das Fontes do Ipiranga. O material examinado proveio de coletas de material perifítico e planctônico em diferentes sistemas aquáticos do PEFI, além da revisão de todo material citado para o Parque e depositado no Herbário Científico do Estado "Maria Eneyda P. Kauffmann Fidalgo" (SP). Foram identificadas 15 espécies distribuídas em sete gêneros (Franceia, Granulocystis, Lagerheimia, Nephrochlamys, Nephrocytium, Oocystis e Rhombocystis). As citações de Lagerheimia longiseta (Lemmermann) Printz, L. citriformis (Snow) Collins e Oocystis marssonii Lemmermann são pioneiras para o PEFI. O Lago das Garças foi o ambiente que apresentou a maior riqueza específica (nove táxons), provavelmente devido ao maior esforço de coleta realizado neste sistema.

ABSTRACT Taxonomic survey of the Oocystaceae (Chlorophyceae, Chlorococcales) present in the PEFI, Parque Estadual das Fontes do Ipiranga lacustrine systems. Material examined included periphyton and plankton from different aquatic systems within the PEFI, and revision of all material cited for the Parque area and deposited in the Herbário Científico do Estado "Maria Eneyda P. Kauffmann Fidalgo" (SP). Fifteen species were identified, which are distributed in 7 genera (Franceia, Granulocystis, Lagerheimia, Nephrochlamys, Nephrocytium, Oocystis, and Rhombocystis). Citations of Lagerheimia longiseta (Lemmermann) Printz, L. citriformis (Snow) Collins, and Oocystis marssonii Lemmermann are pioneer for the PEFI. Garças Pond was the system presenting the highest species richness (nine taxa) probably due to the greater sampling effort devoted to that system.

The environment of the Andean Puna Plateau is mostly characterized by the dominance of evaporative processes due to aridity. Since the intermittent runoff lacks the morphodynamic competence to generate the present day landscape, authors have usually considered that the Puna landscape is a remnant feature of the Miocene arid-climate persistence. Then, a Quaternary-sensu lato-age was assigned to salars, alluvial fans and other geomorphologies. We present evidences from the endorheic depression of Guayatayoc-Salinas Grandes (GSG) located at 3,400 m a.s.l. in the eastern border of northen Puna. The basin includes a saline playa domain in the north (Guayatayoc Playa Lake) and a salt pan in the southern part (Salinas Grandes). We have identified two dissimilar processes originating the subdivision of the GSG depression. The characterization of those processes included sedimentological and geomorphological observations, as well as chronologies using luminescence and radiocarbon. Evidences reveal the development of a saline-lacustrine water body that is associated with the Last Glacial Maximum. During the Late Pleistocene and until ~13.8 cal kyr BP, lake shores were modelled in the front of distal-alluvial fans, the sedimentary aggradation was widespread, and associated with kaolinitic-clay accumulation, inyoite, and the formation of peat-deposits. An environmental change towards aridity occurred after 13.8 cal kyr BP, and wetter conditions returned during the early to middle Holocene, around 9 cal kyr BP. Then, incisive river dynamics accompanied the establishment of a playa lake, with montmorillonitic-fine sediments and ulexite generation during later Holocene. The subdivision of the GSG depression onset by the two following processes: 1. the topographic decoupling, that is associated with Las Burras's alluvial fan aggradation during Pleistocene; 2. the lacustrine regression phase at 13.8 cal kyr BP. Therefore, Guayatayoc and Salinas Grandes are saline systems functioning as a playa lake and a salt pan, respectively, since the Holocene, due to environmental constraints.

Las condiciones ambientales de la Puna andina se caracterizan por la aridez y el dominio de procesos evaporativos. Debido a que las escorrentías intermitentes carecen de competencia morfodinámica para la generación del paisaje actual, los autores generalmente han considerado que el paisaje puneno es una característica remanente de la persistencia de la aridez miocena y asignaron una antiguedad cuaternaria sensu lato a los salares, abanicos aluviales y otras geoformas. Presentamos evidencias obtenidas en la depresión endorreica Guayatayoc-Salinas Grandes (GSG), situada a 3.400 m s.n.m., en el borde oriental de la Puna Norte de Argentina. La cuenca incluye un dominio de barreal salino al norte ('playa lake' Guayatayoc) y un salar al sur (Salinas Grandes), relacionados con procesos que generaron la subdivisión de la depresión GSG. La caracterización de tales procesos incluye observaciones sedimentológicas y geomorfológicas, así como cronologías mediante luminiscencia y radiocarbono. Las evidencias revelan la existencia de desarrollos lacustres asociados al Ultimo Máximo Glacial. Durante la última parte del Pleistoceno y hasta hace unos 13,8 cal ka AP, las riberas lacustres se modelaron en los frentes distales de los abanicos aluviales y la agradación sedimentaria fue generalizada, asociada con la acumulación de arcillas caoliníticas, inyoita y depósitos turbosos. Un cambio ambiental hacia condiciones de aridez fue registrado después de 13,8 cal ka AP, pero las condiciones de humedad se establecieron nuevamente durante el Holoceno inferior a medio, desde 9 cal ka AP. La dinámica incisiva fluvial acompanó el establecimiento del ambiente de playa lake en el cual se generaron sedimentos montmorilloníticos y ulexita durante el Holoceno superior. La subdivisión de la depresión GSG se dio mediante dos procesos: 1. la desvinculación topográfica, asociada a la agradación del abanico Las Burras durante el Pleistoceno; 2. la retracción lacustre alrededor de 13,8 cal ka BP. En consecuencia, Guayatayoc y Salinas Grandes son sistemas salinos que funcionan como un 'playa lake' y un salar, respectivamente, desde el Holoceno y cuya génesis obedeció a condicionantes ambientales.

Environmental magnetism and paleomagnetism methods are useful tools for climate-related and environmental changes studies, as well as for age dating. In particular, they may be applied in magnetic monitoring and to investigate the behavior, response, and history of environments like rivers, lakes, soils, etc. Although the usefulness of magnetic susceptibility in such applications is well known, in this contribution the potential and the need of using additional parameters obtained from measurements of remanent magnetization (natural, anhysteretic, isothermal), magnetic hysteresis and thermomagnetic studies are discussed. Magnetic signals from sediments and soils are often dominated by ferromagnetic minerals sensu lato: ferrimagnetic (titano)-magnetite and/or antiferromagnetic hematite. These minerals are often not detected with standard analytical techniques due to their low concentrations (<1% wt). However, rock magnetic measurements are sensitive enough to detect and identify such minerals, with concentrations that are several orders of magnitude smaller. One important phenomenon to be taken into account is “magnetic enhancement” (Le Borgne 1955, Tite and Linington, 1975), which is caused by the in situ conversion of paramagnetic to ferrimagnetic materials. New formation of ferrimagnetic materials may occur by fermentation, heating, fire, biological activity and chemical processes (Mullins, 1977; Maher, 1986), and thus also be the result of pollutants and magnetized particles of anthropogenic origin (Chaparro et al., 2006, 2013a,b; Bucko et al., 2010; Marié et al., 2010; Zhang et al., 2011). Natural systems are complex and their behavior depends on the interaction of several independent forcing factors like climate variations and human activity affecting the environment. Parameters describing indirectly a system are called “proxies” and may be derived from physical, chemical or biological properties. Magnetic proxies have the advantage to be determined with high sensitivity combined with fast laboratory processing; sample preparation is easy, laboratory instruments are of relatively low cost, and most measurements are non-destructive. Magnetic properties are well suited as proxies of: a) magnetic mineral concentration; b) magnetic grain size; c) correlation of sediment cores and soil profiles; d) geomagnetic field records; e) climatic changes records; f) pollution records; and g) environmental processes records (Maher et al., 1999; Kravchinsky et al., 2003; Chaparro et al. 2006, 2007, 2013a,b, 2015; Irurzun et al., 2006, 2014a; Blundell et al., 2009; Bidegain et al., 2009; Torrent et al., 2010; Lascu and Plank 2013; Oldfield et al. 2014; Quijano et al., 2014). In this work, preliminary results from James Ross Archipelago lakes (NE Antarctic Peninsula) are presented. Sediment cores and water samples were taken from lake systems located on James Ross, Vega and Marambio islands (JRI, VI, MI, respectively, Fig. 1). Lake water’s pH and total dissolved solids exhibit a wide range of variation (<7 to 10 and <50 to 5000 mg/L, respectively), differentiating MI from JRI and VI in these aspects, due to the evaporation processes and a deficit of biological activity on MI. Organic and inorganic carbon contents in sediments are low and points to the dominance of siliciclastic materials. Thermomagnetic studies reveals in both JRI and VI the dominance of magnetite (Tc= 580°C) and subordinated titanomagnetite and/or iron sulfur (Tc= 290°C), goethite and hematite (Tc= 110°C and 680°C, Fig. 2). Lake Esmeralda (Fig. 1) shows a strong increase of magnetization after heating (sample ESM7-24, Fig. 2), maybe due to the initial presence of hematite or goethite and paramagnetic minerals, and their conversion to ferrimagnetic minerals. Magnetic measurements of both JRI and VI sediments, suggest the presence of very fine ferrimagnetic minerals (magnetite, <0.1 μm), while Esmeralda is characterized by larger particles (1-5 μm); and MI by fine ferrimagnetic and paramagnetic minerals (0.2-1 μm, Fig. 3). Magnetic hysteresis shows that magnetites tend to be of single domain size (SD) for JRI and Anónima (in Vega island) and of pseudo-single domain size (PSD) for Esmeralda (Fig. 4). The relation between a magnetic concentration dependent parameter (χ) and a magnetic grain size dependent parameter (κARM/κ) is shown in figure 5. MI and Esmeralda exhibits a trend of increasing χ and decreasing κARM/κ, that is, higher magnetic particle concentration is accompanied by coarser magnetic grain size. In contrast, JRI and Anónima show a linear relationship between parameters χ and κARM/κ, indicating a correlation of magnetic mineral concentration with decreasing grain size. A multivariate statistical analysis of magnetic concentration, magnetic grain size, physic-chemical, and geochemical characteristics shows an inverse relationship between magnetic and physic-chemical variables. Moreover, statistically significant differences between lakes from each studied island are observed. These differences may be due to individual basin and lake environment characteristics and the processes (diagenetic, biological, geochemical, etc.) occurring in them. Finally, Lake Anónima was selected to determine a curve of relative paleointensity (RPI) of high quality, and to calibrate these Antarctic lake sediments through its correlation with a dated RPI curve from Lake Esmeralda (Fig. 9). Five cores were correlated using χ and κARM/κ variations and they were converted to a common sedimentary depth, using one core as the master core. For RPI normalization, sediments must satisfy requirements proposed e.g. by Tauxe (1998): NRM/k, NRM/ARM and NRM/SIRM ratios should only depend on the intensity of the geomagnetic field. Those ratios were normalized to the unity for comparison with records from other lakes. The NRM15mT/k results (NRM15mT is the remanence left after demagnetization with 15 mT) for the Anónima cores are shown in Figure 9 and compared to the corresponding Esmeralda mean curve (Irurzun et al., 2013). Both curves show a similar behavior, with at least three possible lines of correlation. The minimum ratio NRM15mT/k at 68 cm for Anónima is clearly correlated with Esmeralda minimum ratio at the age of 7,700 cal. years. This suggests that sediments recovered from Anónima may have recorded changes of the Earth magnetic field during the last 6,000-7,000 years. We conclude that the magnetic proxies, besides being useful environmental indicators, allow the discrimination between study areas and also to select target region for future studies (e.g. paleomagnetism, environmental changes, etc.). The RPI technique is a very promising tool for dating sediments in Antarctic lakes. This study contributed to a better understanding of Antarctic lake systems from a multidisciplinary approach.

En esta contribución se describen las distintas técnicas y mediciones magnéticas utilizadas en Magnetismo Ambiental y Paleomagnetismo. Tales mediciones ofrecen útiles indicadores para realizar estudios relacionados con cambios climáticos y ambientales, así como herramientas de datación. Si bien es ampliamente conocida la utilidad de la susceptibilidad magnética, en primer lugar se discute el potencial y necesidad del uso de parámetros adicionales obtenidos a partir de mediciones de magnetizaciones remanentes (natural, anhistérica e isotérmica), histéresis magnética y estudios termomagnéticos. A continuación se presentan resultados magnéticos obtenidos en sedimentos lacustres del Archipiélago James Ross (NE de la Península Antártica) como un caso de estudio. Se complementa con estudios sedimentológicos, hidroquímicos, geoquímicos y de estadística multivariada, pero se pone énfasis en los parámetros magnéticos y su relación con los distintos procesos que ocurren en los sistemas lacustres antárticos. Se analiza además el uso de las paleointensidades relativas como herramienta de datación en lagunas antárticas.

This paper provides a review of the hydroclimatic variability reconstructions along the subtropical Argentinean region based on paleolimnological records from Laguna Mar Chiquita (Córdoba; Piovano et al., 2002, 2004, 2009), Laguna Melincué (Santa Fe; Guerra, 2015; Guerra et al., 2015) to Lagunas Encadenadas del Oeste (LEO; Buenos Aires; Córdoba, 2012; Fig. 1). Lake records span two climatologically interesting periods, the so-called Little Ice Age (LIA; Grove, 2001; Wanner et al., 2008) and the 20th century. Regional climate in the studied area is mainly defined by the South American Monsoon System that rules the precipitation regime and is one of the major atmospheric features driving seasonal climatic variability in southeastern South America (Vera et al., 2006; Garreaud et al., 2009; Carvalho et al., 2011; Fig. 1). The need for an integral analysis of the high (1-101 years) and low (>102 years) frequency hydroclimatic variability associated with the South American Monsoon System activity becomes relevant when considering the significant “hydroclimatic jump” occurred during mid-1970s in the southeast of South America (Castañeda and Barros, 1994; Boulanger et al., 2005; Piovano et al., 2009; Carvalho et al., 2011; Jacques-Coper and Garreaud, 2014). This “jump” toward humid conditions (Figs. 2, 3) has been recorded as one of the largest instrumentally recorded hydrological changes occurred globally in continental environments (Giorgi, 2002). Because some climate variability patterns are characterized by long periods, it is difficult to distinguish whether the observed environmental variability is natural or corresponds to a climatic change with multiple forcing factors (natural plus anthropogenic). In this sense hydroclimatic reconstructions based on multiple proxies (sedimentology, geochemistry, biomarkers, stable isotopes) provide insight into how was environmental variability during a longer period than that perceived by the people of an affected region. Results of instrumental data blended with multiproxy studies on sedimentary cores from Laguna Mar Chiquita (Fig. 5), Laguna Melincué (Fig. 6) and Lagunas Encadenadas del Oeste (Fig. 7) indicate that Pampean lake systems have clearly recorded hydrological variations around the end of the LIA (since AD 1770) to the present. Sedimentological, geochemical and isotopic data (Figs. 5, 6 and 7) combined with robust chronologies based on 210Pb profiles (Fig. 4) and historical data (Piovano et al., 2002, 2004; Guerra, 2015; Guerra et al., 2015; Córdoba, 2012; Córdoba et al., en revisión) provide the framework for building a sedimentary model for Pampean shallow lakes with highly variable water depth and salinity (Fig. 8). Intervals with either negative or positive hydrological balances control lake water levels, salinity and primary productivity, and also the isotopic composition of both authigenic carbonate (d18Ocarb and d13Ccarb) and sedimentary organic matter (d13Com). Extensive evaporation during lowstand stages results in an enrichment of 18O and 13C in the lake waters, and is recorded in the sediments as the most positive d18Ocarb and d13Ccarb compositions. Conversely, more negative d18Ocarb and d13Ccarb values are the result of increasing freshwater input into the lake system. Relatively low d13Com values correspond with high lake levels, low salinity, low alkalinity and high lake productivity. High water salinity during lowstands diminishes the amount of primary production and the d13Com value is correspondingly high. Lake water level drops and concurrent increases in salinity promoted the development of evaporitic layers and a marked decrease in primary productivity. The deposits of these dry stages are evaporite-bearing sediments with a low organic matter content. Conversely, highstands are recorded as organic matter-rich muds. These results show that Pampean lakes are good sensors of high- and low-frequency changes in the recent hydrological budget and, therefore, document climatic changes at middle latitudes in south-eastern South America. The paleohydrological reconstructions based on these Pampean lacustrine sedimentary sequences (Figs. 5, 6 and 7) allowed identifying three major environmental periods (Fig. 9). The paleolimnological records indicate that during the end of the LIA arid conditions prevailed along the Pampean region, reflected by low to extremely shallow-water depths, with shorter intermediate lake-level phases (Period III; Fig. 9). The LIA would have extended until AD 1870/1880, as indicated by the passage from ephemeral to perennial lake systems. From ca. AD 1870/1880 to 1976/1977 a progressive climate improvement after a sustained increase in effective moisture occurred along the region, reflected by the intermediate lake levels achieved since the second half of the nineteenth century (Period II; Fig. 9). During the last ~ 40 years the highest lake levels of the analyzed period were established, leading to the development of the present-day hydrological conditions (Period I). These results allow improving the models based on past hydroclimatic variability in areas located east-southeast of American Arid Diagonal (Bruniard, 1982; Piovano et al., 2009), and provide critical information to decipher South American Monsoon System activity in its southernmost influence area.

En este trabajo se presenta una revisión de diferentes estudios paleolimnológicos previamente publicados y desarrollados en la región subtropical Argentina, con la finalidad de efectuar comparaciones latitudinales de la respuesta hidrológica de estos sistemas lacustres frente a las variaciones de la circulación atmosférica asociada a la dinámica del Sistema Monzónico Sudamericano desde la Pequeña Edad de Hielo (PEH) hasta la actualidad. Con este objetivo se analizan y comparan los registros paleolimnológicos recientes (~ 250 años) de las lagunas Mar Chiquita (Córdoba), Melincué (Santa Fe) y Encadenadas del Oeste (Buenos Aires). La necesidad de analizar integradamente la variabilidad hidroclimática de alta (1 a 101 años) y baja frecuencia (102 años en adelante) en el centro de Argentina toma relevancia a partir del gran “salto hidroclimático” ocurrido durante la década de los años 70 en el sudeste del continente sudamericano. Este cambio caracterizado por un aumento notable en las precipitaciones ha sido registrado como uno de los mayores saltos hidrológicos ocurridos en ambientes continentales a nivel global. Debido a que algunos patrones de variabilidad climática se caracterizan por períodos largos, es difícil discernir si la variabilidad ambiental observada es natural o bien corresponde a una señal de cambio con múltiples forzantes (antrópicos + naturales). En este sentido las reconstrucciones hidroclimáticas basadas en indicadores múltiples (sedimentología, geoquímica, bioindicadores, isótopos estables) permiten conocer la variabilidad ambiental durante un período superior al percibido por los habitantes de una región afectada, aportando a la sociedad el conocimiento básico para abandonar la idea del clima estacionario, suministrando además herramientas para efectuar eficientemente la Gestión Integrada de los Recursos Hídricos. Las reconstrucciones paleohidrológicas y paleoambientales de las secuencias estudiadas indican que en general durante la finalización de la PEH predominaron condiciones áridas a lo largo de la región Pampeana, reflejadas por los niveles bajos a extremadamente bajos de las lagunas, con episodios de fases lacustres de niveles intermedios de menor duración. La PEH se habría extendido hasta la década de 1870/80 AD, momento que es indicado por el pasaje de sistemas lacustres efímeros a perennes. A partir de ca. 1870/80 AD y hasta 1976/77 AD se produce un mejoramiento climático progresivo a partir de un incremento sostenido de la humedad efectiva, que se refleja en los niveles intermedios alcanzados por las lagunas desde la segunda mitad del siglo XIX. Durante los últimos ~ 40 años se establecieron los niveles lacustres más altos registrados desde la PEH, dando lugar al establecimiento de las condiciones actuales de las lagunas. Los resultados obtenidos permiten perfeccionar los modelos planteados sobre la variabilidad hidroclimática pasada en las regiones ubicadas hacia el E-SE de la Diagonal Árida Sudamericana y aportan información crucial para descifrar la actividad del Sistema Monzónico Sudamericano en su zona de influencia más austral.

The Late Cretaceous sedimentary rocks of the Anacleto and Allen Formations in the area of Paso Córdoba comprise lacustrine and eolian deposits. Lacustrine systems are represented by offshore and shoreface deposits, with associated deltaic systems. Offshore deposits are composed of mudstones with abundant mica content, organic matter, and Corbicula molds. Shoreface facies shows tabular banks of fine-grained sandstones, bioturbated by suspension feeders (Skolithos, Arenicolites) and ornamented burrows (Spongeliomorpha), and subordinately tabular banks with high concentration of fragmented bioclasts produced by storm events. The deltaic systems shows the typical upward-coarsening arrangement, generated by the progradation of medium to fine-grained sandstones of the delta-front, bioturbated by Skolithos and Arenicolites, on the heterolitic deposits of the prodelta. Eolian deposits are represented by dunes and dry and wet interdunes. Dune systems are composed by sets up to 10 m thick, integrated by fine to medium-grained sandstones with large scale planar and tangential cross stratification, which laterally pass to dry interdune deposits with vertebrate traces and root marks. The wet interdune facies form lenticular bodies of small regional extension, composed by heterolitic facies bioturbated by Taenidium, Skolithos, Arenicolites, vertebrate traces and root marks. The analyzed section shows a marked aridity from base to top, where the lacustrine system with the Skolithos and Scoyenia ichnofacies (Anacleto Formation) passes transitionally into a wet interdune system with Skolithos and Scoyenia ichnofacies, and to dunes and dry interdunes with the Entradichnus ichnofacies (Allen Formation).

Las sedimentitas cretácicas tardías de las Formaciones Anacleto y Allen expuestas en el área de Paso Córdoba, representan depósitos lacustres y eólicos. Los sistemas lacustres muestran sucesiones de centro de lago (offshore) y zonas marginales (shoreface), con facies deltaicas asociadas. Los depósitos de offshore conforman cuerpos tabulares de pelitas finamente laminadas con abundante contenido de micas, materia orgánica y moldes de Corbicula. Las facies de shoreface muestran bancos tabulares de areniscas finas bioturbadas por organismos suspensívoros (Skolithos, Arenicolites) y trazas ornamentadas (Spongeliomorpha), y de manera subordinada bancos tabulares con abundantes concentraciones de bioclastos acumulados durante eventos de tormenta. Los sistemas deltaicos muestran el típico arreglo grano creciente, generado por la progradación de areniscas finas a medias correspondientes a un frente deltaico, bioturbadas con Skolithos y Arenicolites, sobre depósitos heterolíticos de prodelta. Los sistemas eólicos muestran depósitos de dunas e interdunas secas y húmedas. Los sistemas de dunas, están compuestos por sets de hasta 10 m de espesor integrados por areniscas medianas a finas con estratificación entrecruzada planar y tangencial de gran escala, que lateralmente pasan a areniscas con estratificación paralela y laminación ondulítica asimétrica, correspondientes a depósitos de interdunas secas, con trazas de vertebrados y rizolitos. Las interdunas húmedas conforman cuerpos lenticulares de escasa extensión y poco espesor, integrados por heterolitas bioturbadas por Taenidium, Skolithos, Arenicolites, trazas de vertebrados y rizolitos. En su conjunto la sección analizada muestra una progresiva aridización desde la base al techo, reflejada por sistemas lacustres con icnofacies de Scoyenia y Skolithos de la Formación Anacleto, que pasan en transición a sistemas de interduna húmeda con icnofacies de Scoyenia y Skolithos, y a dunas e interduna seca con icnofacies de Entradichnus, de la Formación Allen.