Abstract The Yacoraite Formation (NW Argentina) displays important microbialitic deposits of varied features throughout its six sub-basins. With the discovery of important microbialitic hydrocarbon reservoirs and the interest in lacustrine systems due to recent hydrocarbon finds in the pre-salt Cretaceous series of the South Atlantic, the importance of these organo-sedimentary structures has increased considerably. Because of this, in the past decade, numerous works in Yacoraite Formation have focused on its microbialites. In this study, we provide an updated summary of the existing background and state of knowledge of the microbialites in the Yacoraite Formation, which occupy different stratigraphic positions in diverse sub-basins separated by several kilometers. Due to this, these structures have developed under diverse conditions, giving rise to a great variety of structures and morphologies, useful as reliable and high-resolution proxies for paleoenvironmental studies and to discuss important ecological paradigms. In addition, microbialites of Yacoraite Formation show promising petrophysical conditions to be evaluated as reservoir rocks. Based on the large number of deposits mentioned throughout this work, and the morphological and structural variety of their microbialites, we can highlight Yacoraite Formation as one of the most important microbialite-bearing units in Argentina and South America. NW subbasins. subbasins sub basins. basins presalt pre salt Atlantic organosedimentary organo sedimentary considerably decade study kilometers morphologies highresolution high resolution paradigms addition rocks work microbialitebearing microbialite bearing America

For the first progress reporting on the Sustainable Development Goal sub-indicator 6.6.1a in 2020, the South African and global statistics related to wetlands were compared. Firstly, in terms of the total wetland extent, the South African National Wetland Map version 5 (NWM5) represented 87% more inland, surface aquatic ecosystems than the Global Surface Water (GSW) product. More than half of the lacustrine systems and none of the palustrine and arid systems in NWM5 are represented in the GSW layer. Secondly, in terms of changes in the extent of wetlands, both the global and South African statistics showed a decreasing trend in the spatial extent of surface aquatic ecosystems in South Africa. These trends should be further investigated against systematic assessments of decadal drought periods. The hydroperiod information (permanent, seasonal and ephemeral inundation periods) of the GSW products show that South African lacustrine wetlands do not have a single dominant class (>70% of the extent of a polygon) of inundation, but consist of a mosaic of these classes.SIGNIFICANCE: • The South African National Wetlands Map version 5 represents 87% more of the extent of lacustrine, palustrine and arid wetlands than the Global Surface Water products that are used for progress reporting on the Sustainable Development Goal sub-indicator 6.6.1a. • South African and global statistics suggest a decline in the extent of lacustrine wetlands, although a systematic comparison with decadal drought periods is required to confirm these trends. • South African lacustrine wetlands consist of a mosaic of hydroperiod classes (permanent, seasonal and ephemeral inundation periods) with no individual class dominating (>70% of the extent of) wetlands polygons.

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.

RESUMO: A margem continental uruguaia é resultado da fragmentação do supercontinente Gondwana e posterior abertura do Oceano Atlântico, iniciados no Jurássico. Três bacias sedimentares estão presentes na margem continental do Uruguai: a Bacia de Punta del Este, a porção mais austral da Bacia de Pelotas e a Bacia Oriental del Plata. As bacias da margem continental do Uruguai compartilham os clássicos estágios tectono-sedimentares evolutivos das demais bacias marginais atlânticas, incluindo as fases pré-rifte (Paleozoico), rifte (Jurássico-Cretáceo Inferior), transição (Barremiano-Aptiano) e pós-rifte (Aptiano-Presente). Quatro sistemas petrolíferos especulativos foram definidos para a Bacia Punta del Este, baseados na análise de seções sísmicas e dados de poços e no estabelecimento de analogias com as bacias marginais atlânticas productoras de hidrocarbonetos: 1) sistema petrolífero marinho da fase pré-rifte: Devoniano/Permiano-Devoniano/Permiano(?), 2) sistema petrolífero lacustre da fase rifte: Neocomiano/Neocomiano(?), 3) sistema petrolífero marinho da fase pós-rifte cretácea: Aptiano-Cretáceo Superior(?), 4) sistema petrolífero marinho da fase pós-rifte cenozoica: Paleoceno-Paleogeno/Neogeno(?).

ABSTRACT: The Uruguayan continental margin was generated as the result of the breakup of Gondwana and, later, the opening of the South Atlantic Ocean, which began in the Jurassic. Three major areas of Meso-Cenozoic sedimentation are located in the Uruguayan offshore: the Punta del Este Basin, the southernmost sector of the Pelotas Basin and the Oriental del Plata Basin. These basins share the classical stages of tectono-sedimentary evolution of the other Atlantic basins, including the prerift (Paleozoic), rift (Jurassic-Early Cretaceous), transition (Barremian-Aptian) and postrift (Aptian-present) phases. Based on the analysis of basin evolution through seismic sections and well data as well as on the establishment of analogies with productive Atlantic basins, four speculative petroleum systems are proposed for the Punta del Este Basin: 1) Marine petroleum system of the prerift stage: Devonian/Permian-Devonian/Permian(?), 2) Lacustrine petroleum system of the synrift stage: Neocomian-Neocomian(?), 3) Marine petroleum system of the Cretaceous postrift: Aptian-Late Cretaceous(?), 4) Marine petroleum system of the Cenozoic postrift: Paleocene-Paleogene/Neogene(?).

The Cañadón Asfalto Basin, situated in central Patagonia between the North Patagonian Massif and the Golfo San Jorge Basin (Fig. 1), comprises a thick column of Jurassic and Cretaceous sediments accumulated in several depocenters separated by transference zones of basement blocks, namely the Gastre, Gan Gan, Fossatti, Valle de General Racedo, Gorro Frigio and Paso de Indios depocenters (Figs. 2-4). They were included in a major rift zone that later evolved in a complex way with several deformation phases. Sediments were grouped into three megasequences (J1, J2, and K) separated by regional unconformities (Fig.5), overlying a Paleozoic basement, composed of schists and granitoids. The J1 Megasequence (Hettangian-Sinemurian?/Pliensbachian to late Bajocian) is composed of the Las Leoneras Formation, the Lonco Trapial Formation and the Cañadón Asfalto Formation (Figs. 6, 7). The two latter were classicaly considered of Middle to Late Jurassic age but new interpretations indicate these thick sedimentary-volcanic succesions are older (Early to Middle Jurassic), and were accumulated in a relatively short period of time. The passage between units is regarded as transitional in spite of the fact that they are locally separated by erosive or angular unconformities. These discontinuities are typical of high-relief volcanic environments and therefore they lack regional significance. The rift evolved from incipient to juvenile during the sedimentation of the J1 Megasequence. Sedimentation took place in continental environments (fluvial, lacustrine and volcanic) with high volcaniclastic input. The wet, temperate/warm climate favoured a high biodiversity. The black shales of the Cañadón Asfalto Formation represent the Toarcian anoxic global event. The J2 Megasequence (Figs. 8-12) comprises the thick succesion of alluvial and lacustrine sediments of the Cañadón Calcáreo Formation (Oxfordian-Kimmeridgian), which is separated by an angular unconformity from the Cañadón Asfalto Formation. These Late Jurassic sediments were accommodated in small half-grabens limited by uplifted mountain blocks, in a basin-and-rangelike landscape, separated by transference areas, synchronically with a tectonic reactivation of the rift. The J2 Megasequence is partially equivalent to the Anticlinal Aguada Bandera Formation in the Golfo de San Jorge Basin. The warm/temperate climate with dry periods allowed the development of a diverse biota with a rich palynological association in fish-bearing black shales. These shales are overlain by a progradational fluvio-deltaic succession, swiftly accumulated in a short period of time (about 1 Ma), which was partially or totally eroded previously to the Chubut Group sedimentation. From the Tithonian until the Hauterivian an important stratigraphic gap exists. Initillay a regional tectonism took place, related to a dextral shear system that uplifted large areas into the basin. Partial block rotation in a transpressive-transtensive regime controlled by old tectonic lineaments occurred, although the mechanisms of uplifting are not definitely established. The northwest-oriented master faults of the original rift were inverted and sedimentation in the basin almost ceased. This is the most significant tectonic event in the basin and it is recorded by an angular unconformity that separates the Grupo Chubut from the older units. Facies and thickness changes in the basal units of the K Megasequence suggest accomodation space formation at the end of this stage was controlled by active faulting. The K Megasequence (Figs. 13, 14) includes the terrestrial beds of the Chubut Group deposited in Barremian-Campanian times, as well as the shallow-marine deposits of the Paso del Sapo and Lefipán Formations (Campanian-Danian), which represent the first Atlantic transgression into the basin. Both units are separated by a slightly angular unconformity that points to some local tectonism in the Late Cretaceous. The mountain systems collapsed and the basin expanded with a typical sag style because of the slow dissipation of the termal anomaly of the rift, giving place to the accumulation of thick continental sediments of the Chubut Group unconformably overlying all the older units and also the basement. The NW-SE-oriented faults were not anymore the main control in the basin configuration and they were totally or partially replaced by E-W faults, already present in the original grain of the basement. North-south extension, ortogonal to the Pacific subduction margin, took place during this period. Contractional deformation occurred in the western area of the basin during the Paleocene- Eocene and subsidence ceased in the remaining of the basin. This indicates an “old” back-arc compressive deformation represented in the Cañadón Asfalto Basin by the Complejo Volcánico y Piroclástico del Río Chubut Medio, accumulated in caldera settings. Tectonic inversion (Fig. 15) and generalized uplift took place in Oligocene?-Miocene to Recent times, represented by local folding of high variable style and intensity, and generalized faulting of the rocks, represented by several fault systems. Some of the Mesozoic depocenters were totally exposed, whereas others remained partially buried and new Miocene depocenters were formed. The Sierra de Traquetrén was uplifted during this period, along an extensive, NW-SE-oriented fault, that was the former limit of an extensional depocenter. Uplifting was contemporaneous to the formation of the Sierra de San Bernardo in the Golfo de San Jorge basin, located to the southeast of the basin reported in this contribution.

La Cuenca de Cañadón Asfalto, ubicada entre el Macizo Nordpatagónico y la Cuenca del Golfo San Jorge, presenta una importante columna de sedimentos jurásicos y cretácicos acumulados en hemigrábenes pertenecientes a un sistema de rift formado durante la fragmentación de Gondwana. La Cuenca de Cañadón Asfalto incluye varios depocentros sedimentarios denominados Gastre, Gan Gan, Fossatti, Valle de General Racedo, Gorro Frigio y Paso de Indios, limitados por bloques basamentales en zonas de transferencia. La columna sedimentaria jurásica y cretácica puede dividirse en tres megasecuencias principales (J1, J2 y K) separadas entre sí por discordancias de significado regional que se apoyan sobre un basamento de metamorfitas y granitoides del Paleozoico. La Megasecuencia J1 está constituida por la Formación Las Leoneras, la Formación Lonco Trapial y la Formación Cañadón Asfalto, y su edad se extiende entre el Hettangiano- Sinemuriano?/Pliensbachiano y el Bajociano tardío. Se acumuló en ambientes fluvial, lacustre y volcánico durante los estadíos incipiente a juvenil del rift. La Megasecuencia J2 incluye sedimentos aluviales y lacustres continentales correspondientes a la Formación Cañadón Calcáreo, de edad oxfordiana-kimmeridgiana, que se depositaron en depocentros parcialmente coincidentes con los anteriores durante una reactivación tectónica multiepisódica del rift. Durante el Tithoniano tardío - Hauteriviano existe un importante hiato estratigráfico. Durante este lapso se generaron esfuerzos transpresivos-transtensivos con rotación de bloques a escala regional, que originaron levantamientos de grandes áreas de la cuenca y la subsecuente erosión de zonas extensas, aunque el entorno tectónico y su correspondiente campo de esfuerzos se encuentran aún en discusión. El posterior colapso de estas áreas elevadas, con un control tafrogénico inicial y una posterior subsidencia termal, permitió el desarrollo del espacio disponible para la acumulación de la Megasecuencia K, formada por los niveles continentales del Grupo Chubut del Barremiano-Campaniano, al cual le siguieron los depósitos marinos y litorales de las formaciones Paso del Sapo y Lefipán del Campaniano- Daniano, representativos de la primera transgresión atlántica en la cuenca. Como consecuencia de los procesos detallados más arriba, una marcada discordancia angular separa a la base de la Megasecuencia Kde todos los depósitos más antiguos de la cuenca. Posteriormente, durante el Paleoceno tardío-Eoceno, se produjo un episodio tectónico compresivo en el margen occidental de la cuenca, seguido por la acumulación del Complejo Volcánico y Piroclástico del Río Chubut Medio en ambientes de calderas asociadas a un vulcanismo de retro-arco. En el Oligoceno?- Mioceno a Reciente se produjo el levantamiento y la inversión tectónica de la mayor parte de la Cuenca de Cañadón Asfalto, representado por fallamiento generalizado y por plegamiento localizado de intensidad y estilo variables. En este momento se desarrollaron pequeñas cuencas intermontanas limitadas por fallas.

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.

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.

The Gastre Basin is one of the largest intermontane basins of the Patagonian Broken Foreland. It is oblique to the Andean chain and located more than 550 km east of the Andean trench. It was originated by reverse faulting and inversion of pre-existing normal faults during the Middle-Miocene, allowing the preservation of a continuous sedimentary record up to the present. Stratigraphic, sedimentologic and structural observations indicate a pre-tectonic, syn-tectonic and post-tectonic evolution stage. The pre-tectonic stage (late Lower Miocene) was related to a combination of a flexural subsidence event in the foreland in response to the tectonic activity in the fold and thrust belts, and the influence of explosive volcanism over low-gradient sedimentary environments. The syn-tectonic stage (Middle Miocene,) is marked by the contractional deformation event in which the Gastre Basin was structurally configured. During this stage, basin compartmentalization associated with shallow lacustrine systems occurred. The post-tectonic stage (Middle Miocene - Pliocene) involves the post-deformational deposits characterized by deep lacustrine systems under explosive volcanism influence as well as the alluvial and braided fluvial system. During this stage an abrupt decreasing of the volcaniclastic supply, which characterized the Miocene Northpatagonian successions, occurred. This was combined with a major climatic change developed in the Middle Miocene that corresponds with the change from the optimal climate to the aridity period in response to the Andean uplift.

La Cuenca de Gastre ubicada a centenares de kilómetros del margen de subducción, constituye una de las mayores cuencas intermontanas desarrolladas dentro del antepaís fragmentado patagónico. Su origen en el Mioceno medio se encuentra estrechamente vinculado a estructuras contraccionales las cuales exhumaron bloques de basamento pre-mioceno y configuraron el espacio necesario para la acumulación y preservación de un registro sedimentario continuo desde el Mioceno a la actualidad. El presente estudio analiza el relleno neógeno de la Cuenca de Gastre evaluando la relación entre los principales factores que intervinieron en la evolución dinámica de la cuenca y el registro estratigráfico/sedimentario. Sobre la base de un análisis estratigráfico, sedimentológico y estructural se pudo dividir el relleno en etapas pretectónica, sintectónica y postectónica, acotadas temporalmente con edades preexistentes. La etapa pretectónica (Mioceno inferior tardío) se corresponde con un evento de subsidencia regional asociado a la flexión del antepaís, con influencia de volcanismo explosivo en ambientes sedimentarios de bajo gradiente. La etapa sintectónica (Mioceno medio) coincide con la estructuración de la Cuenca de Gastre donde se conformaron depocentros aislados en los cuales se desarrollaron sistemas lacustres efímeros. La etapa postectónica (Mioceno medio -Plioceno) abarca el periodo depositacional caracterizado por grandes lagos bajo influencia de volcanismo explosivo hasta el desarrollo de ambientes aluviales y sistemas fluviales entrelazados. Esta última etapa marcó la merma abrupta del aporte volcaniclástico que caracterizó a las sucesiones miocenas del ámbito nordpatagónico y el pasaje del óptimo climático mioceno al periodo de aridización, producto del levantamiento de los andes.

La aplicabilidad de las aleaciones de aluminio serie 3003 (AA 3003) es diversa en los sistemas industriales (tanques de almacenamiento, equipos químicos, entre otros). Esto se debe a su alta resistencia a la corrosión, como resultado de la formación de películas pasivas en medios oxidantes. Sin embargo, se carece de evidencias que indiquen su comportamiento en aplicaciones lacustres, en las cuales existe una importante formación de biomasa, por lo cual este trabajo describe el comportamiento del AA 3003 en medios exentos de oxígeno (reducidos). Para ello, se colocó el material en inmersión con cultivos bacterianos anaeróbicos, específicamente en medios con bacterias reductoras de sulfato (BRS) y bacterias heterótrofas totales facultativas (BHTF). Ambos tipos de microorganismos proceden de poblaciones sésiles desarrolladas en cupones extraídos del Lago de Maracaibo. Para la evaluación del comportamiento corrosivo se emplearon técnicas electroquímicas y microscópicas. Los resultados indicaron que la AA 3003, ante la presencia de las BHTF y SRB, incrementó la resistencia a la corrosión con el tiempo.

The use of the 3003 series aluminum alloys (AA 3003) is diverse in the industrial systems (storage tanks, chemical equipments, among others). This is due to its high resistance to corrosion as a result of passive films developed in presence of oxidizing media. However, there is a lack of evidence to show their behaviour in lacustrine applications in which there is a significant biomass formation. For this reason, the objective of this paper is to describe the behavior of AA 3003 in oxygen-free (reduced) media. To this aim, the material was settled in immersion with anaerobic bacteria cultures, specifically in media containing sulphate-reducing bacteria (SRB) and total heterotrophic facultative bacteria (THFB). Both types of microorganisms came from sessile populations developed on coupons previously immersed in Maracaibo Lake. Electrochemical and microscopic techniques were used for the evaluation of the corrosive behavior. The results indicated that the AA-3003 resistance to corrosion increased over time, in presence of the BHTF and SRB.

Terrestrial ecosystems have been largely regarded as plant-dominated land surfaces, with the earliest records appearing in the early Phanerozoic (< 550 Ma). However, the presence of biological components much older than plants in habitats as different as soils, peats, ponds, lakes, streams, and dune fields, suggests that much earlier types of terrestrial ecosystems appeared in Earth at least 2700 Ma ago. Microbes were abundant ~3500 Ma ago, and they surely adapted to live in subaerial conditions in peritidal and inarid and semiarid environments, as presently done by terrestrial microbes, which have great and rapid capacity of adapting themselves to changing conditions as suggested by fossil records. Yet, this evidence is rare and indirect in comparison with fossils from shallow or deeper marine environments, and its record has been largely overlooked. Consequently, the notion that microbial communities may have formed the earliest land ecosystems has not been widely accepted nor integrated into our general knowledge. Nowadays, an ample record of shallow-marine and lacustrine biota in ~3500 Ma-old deposits is known, together with evidence of microbial colonization of coastal environments ~3450 Ma ago, and indirect evidence that suggest biological activity in > 3400 Ma-old paleosols. The type of ambiances from where this evidence derives, endorses the idea that life on land perhaps occurred in parallel with aquatic life back in the Archean. The rapid adaptations seen in modern microbes, their outstanding tolerance to extreme and fluctuating conditions, their early and rapid diversification, and their old fossil record, collectively suggest that they constituted the earliest terrestrial ecosystems. It is likely that microbes contributed in forming the biomass-rich cover where plants later evolved. Understanding how life diversified and adapted to terrestrial conditionsis critical to comprehend its impact on the Earth's systems over millions of years.

Los ecosistemas terrestres han sido considerados tradicionalmente como superficies dominadas por plantas, cuyos primeros registros datan del Fanerozoico temprano (< 550 Ma/millones de años). Sin embargo, la presencia de componentes biológicos mucho más antiguos que las plantas en hábitats tan distintos como suelos, turberas, estanques, lagos, arroyos y dunas, sugiere que los ecosistemas terrestres comenzaron a existir en la Tierra hace al menos 2700 Ma. Los microbios fueron abundantes hace ~3500 Ma y sin duda se adaptaron a vivir en condiciones subaéreas, en entornos intermareales y en zonas áridas y semiáridas, como lo hacen actualmente los microbios terrestres, y que tienen una enorme y rápida capacidad de adaptación a condiciones cambiantes. Todo ello está respaldado por el registro fósil. No obstante, esta evidencia es inusual e indirecta en comparación con fósiles de ambientes marinos, superficiales o profundos, y su registro ha sido poco atendido. En consecuencia, la noción de que fueron comunidades microbianas las que formaron los primeros ecosistemas terrestres no ha sido ampliamente difundido ni incorporado conceptualmente en la sociedad. Hoy conocemos un amplio registro fósil de biota marina somera y lacustre a partir de los ~3500 Ma, así como microbios colonizando ambientes costeros desde hace ~3450 Ma y evidencia indirecta de actividad biológica en paleosuelos de > 3400 Ma de edad. El tipo de ambientes, de donde proviene esta evidencia, sugiere que la vida terrestre se produjo casi en paralelo con la vida acuática en el Arqueano. Las rápidas adaptaciones observadas en microbios actuales, su excepcional tolerancia a condiciones extremas y fluctuantes, su rápida y temprana diversificación y su antiguo registro fósil, indican que los primeros ecosistemas terrestres fueron exclusivamente microbianos. Es factible que los microbios contribuyeran en la formación de los primeros suelos donde las plantas se desarrollaron más tarde. Comprender cómo la vida se diversificó y adaptó a las condiciones terrestres es fundamental para entender su impacto en los sistemas terrestres durante millones de años.