Neuquen Basin Research Articles

Algunos aspectos limnológicos abióticos de las cuencas de los ríos Limay y Neuquén con especial referencia al embalse Ramos Mexía

The Negro river tributaries are the Limay and Neuquen rivers, which constitute the Andean eastern drainage system betweem 36" and 41" S. Huge reservoirs have been constructed, as a part of a hydroelectric power program and also for flood control purposes.
 Morphometric and lithological differences accounts for thermal and chemical distinctive fractures between these reservoirs.
 The Ramos Mexía impoundment and Pellegrini off-channel reservoir are wind mixed all over the year, while in the deeper Los Barreales and Mari Menuco stratification develops during the summer.
 The annual heat budget of the Ramos Mexía has been raughly estimated in 36131, 30760 and 31047 cal cm-2 for the years 1978, 1979-1980 and 1980-1981 respectively. These estimates are higher than those for others lakes situated on the Andes mountains in a region of more oceanic climate.
 The waters of the system are well oxygenated, neutral and soft. The Limay basin waters are the more diluted, with an average conductivity of 30 μScm-1 near the glacial lake Nahuel Huapi, and 67 μScm-1 in the Ramos Mexía artificial lake. Conductivity seasonal changes are related with discharge flow rate patterns and with level changes in the reservoirs. The Neuquen basin waters present conductivities ranging from 75 μScm-1 near the Andes, to 250 μScm-1 in Mari Menuco reservoir, while the Pellegrini attains to 3600 μScm-1.
 Both rivers (and R. Mexía artificial lake) have calcium-bicarbonate type waters, beeoming richer in sulphate and sodium as they move seaward through a semiarid region. In Los Barreales and M. Menuco reservoirs bicarbonate and sulphate may change their relative positions during the annual hydrologic cycle. The Pellegrini dosed basin belong to the sulphate-chloride sodium type.
 Reactive silica concentration is rather high throughout the year, without showing depletion to any important extent due to biogenic activity, except in the Pellegrini artificial lake.

Source rocks in foreland basins: A preferential context for the development of natural hydraulic fractures

Bedding-parallel veins of fibrous calcite (also called “beef”) occur in many sedimentary basins, especially those containing low-permeability strata with organic source material for petroleum. The formation of such veins is commonly linked with fluid overpressure in these source rocks. In this review, we demonstrate that beef veins are most commonly present in foreland basins worldwide or in basins that recorded a compressive tectonic period. The formation of beef veins is related to two main phases: (1) the initiation of bedding-parallel fracture and (2) the infilling of the fracture. Previous structural studies have shown that formation of beef veins occurred during a period of compressive stress activity. This is especially the case for the Wessex Basin (United Kingdom) and the Neuquen Basin (Argentina). In this paper, we provide more observations for other basins: the Cordillera Oriental (Colombia), the Paris Basin (France), the northern Pyrenees (France), the Uinta Basin (United States), the Tian Shan Mountains (central Asia), and the Appalachian Mountains (United States). In the Paris Basin, beef vein formation is dated at 155 Ma (U/Pb calcite method) and is coeval with the compressional deformation in the eastern part of the basin. Because of the timing of generation for such veins and even if the theory and the experiments of fracturing demonstrate that bedding-parallel fractures can be generated only with a distributed fluid overpressure, the formation of beef veins seems to be a consequence of both fluid overpressures and a compressional tectonic stress.

Chemostratigraphy of the Pliensbachian, Puesto Araya Formation (Neuquén Basin, Argentina)

In a preliminary attempt to establish an isotope stratigraphy, strontium, carbon and oxygen isotope ratios were determined from marine biogenic carbonates of Pliensbachian age, in the context of scheme of local ammonite Zones correlatable to the European Standard Zonation. Two sections, rio Atuel and arroyo Serrucho, of the mainly siliciclastic Puesto Araya Formation, Neuquen Basin, south-western Mendoza, Argentina, were studied. Specimens of the bivalve genera Weyla Bhom and Gryphaea Lamarck were selected for the isotopic determinations because of their low-Mg calcite original mineralogy and widespread presence. Scanning electron microscopy, X-ray diffraction and X-ray fluorescence spectrometry techniques were used to control the good degree of preservation of most of the biogenic material, as evidenced by pristine fabrics, 100% calcite composition and Sr, Mn and Fe concentrations. Although strontium isotope ratios are slightly scattered, it is possible to compare them with those of the Early Jurassic seawater reference curve. Carbon isotope signals show two relative maxima, correlatable with those recorded for the upper part of the Ibex Zone and the middle part of the Margaritatus Zone in various European sections, indicating the possible global significance of these events. d18O values were found to be unreliable for isotope stratigraphy, as they are largely depleted in comparison to those of coeval unaltered marine carbonates.

The Neuquén Super Basin

With more than 6000 m of sedimentary thickness and several superimposed petroleum systems, the Neuquen Basin of Argentina has all the elements to be considered a super basin. The basin developed during the Triassic–Early Jurassic in a rift environment that generated a localized petroleum system. Continued subsidence during the Early Jurassic resulted in the first marine ingression (Los Molles Formation, total organic carbon [TOC] 1%–7%). This unit matured 120 to 55 m.y.a., before the formation of major structures, with the exception of the Huincul high. A fast marine flooding in a retroarc setting occurred during the latest Jurassic–Early Cretaceous. At its base lies the Vaca Muerta Formation, a 50- to 1000-m-thick world-class source rock, composed by calcareous shales and marls (TOC 2%–9%). This unit reached maturity at 95 Ma, when the only traps available were structures along the Huincul high or stratigraphic. A new marine ingression occurred during the Early Cretaceous, depositing bituminous shales and marls (Agrio Formation, TOC 2%–5%) that matured during the Paleogene. These superimposed petroleum systems, combined with different structural settings, gave rise to numerous plays and trapping configurations that resulted in the discovery of 14 billion BOE. In addition, the unconventional potential of the Vaca Muerta is now being developed, with estimated resources of 91.5 TCF and 14.3 billion bbl of oil. The Neuquen Basin has gone through three main phases of development: conventional, tight, and unconventional. After a century of production, the basin still shows a wide variety of opportunities for both conventional and world-class unconventional plays.

Evaluación de un proceso de bioestimulación aplicado a suelos áridos contaminados con hidrocarburos del petróleo

La biorremediación ha demostrado ser una técnica eficaz para la recuperación de suelos contaminados con hidrocarburos, especialmente porque no genera otros residuos que requieran ser tratados, además de ser un proceso económicamente viable y amigable con el medio ambiente. Es sabido que el mejoramiento de lascondiciones ambientales y nutricionales de la microflora autóctona de los suelos puede incrementar significativamente los procesos de biodegradación lo cual puede lograrse modificando la humedad y la disponibilidad de nutrientes (N, P y O2 fundamentalmente) en suelos pobres, es decir, aplicando una técnica de bioestimulación. El objetivo de este trabajo fue evaluar la capacidad biodegradadora de los microorganismos autóctonos presentes en un suelo de tipo árido contaminado con hidrocarburos del petróleo (HTP) de la zona de Catriel Oeste (cuenca neuquina), mediante una técnica de bioestimulación en microcosmos. Se utilizaron sistemas microcosmos conteniendo 200 g de suelo, los cuales fueron bioestimulados (BIO) ajustando la proporción de nutrientes (C:N:P 100:10:1). Por otra parte, se realizaron controles comunidad (CC) en microcosmos sin bioestimular. Ambos sistemas se incubaron a 25ºC manteniendo la humedad al 15% y se mezclaron periódicamente, cada 3 días, con el objeto de airear el suelo. Se tomaron muestras al inicio, a los 28 y a los 42 días, y se determinaron la concentración de HTP, actividad microbiana total (AMT), recuento de bacterias heterótrofas aerobias totales (BHAT) y bacterias degradadoras totales (BDT).Ambos sistemas evaluados (CC y BIO) mostraron una reducción significativa del contenido de HTP (88%), la cual estaría relacionada con los incrementos observados en la AMT (4,3 y 3,7 veces para los sistemas CC y BIO, respectivamente), y con el aumento del número de BHAT y BDT (2 órdenes de magnitud en ambos sistemas).Se puede concluir que la aireación del suelo parece ser un mecanismos simple y adecuado para la remoción de hidrocarburos en este suelo y que la aplicación de una técnica de bioestimulación no mejora la remoción del sistema donde solo se contempló la incorporación de aire a través del mezclado. Esto sugiere que es conveniente el desarrollo de un proceso que mejore las condiciones de aireación con el objeto de favorecer en mayor medida la biodegradación de los hidrocarburos del petróleo.

Tectonic control on hydrocarbon generation in the northwestern Neuquén Basin, Argentina

The petroleum systems of the Malargue fold–thrust belt in the northwestern Neuquen Basin, Argentina, comprise multiple reservoir and seal rocks and three major source rocks of the Lower Jurassic (Los Molles Formation [Fm.]), the lower Tithonian to lower Valanginian (Vaca Muerta Fm.), and the lower Hauterivian to lower Barremian (Agrio Fm.). The thermal history of the Mesozoic source rocks has been reconstructed using one-dimensional and two-dimensional modeling. The most important factors that affected the source-rock maturation are the timing of maximum Late Cretaceous to Paleogene burial and the heat flow during back-arc extension. We postulate that synclines have been buried over longer periods and source-rock maturation ceased earlier in anticlines, accordingly. Hydrocarbon generation from the Vaca Muerta Fm. and Agrio Fm. has started during the Campanian. Despite late-stage magmatic activity causing local thermal perturbations, the models suggest that the thermal field has been dominated by conductive heat transport and that heat flow has been a response to the evolution from back-arc extension to orogenic shortening. High heat flows of 85 mW/m2 during back-arc extension between the latest Cretaceous and Paleogene have been modeled. Two main source pods supply hydrocarbons until the present. They are related to structurally deep footwall positions of thrust faults, active since the Late Cretaceous, and to deep frontal synclines, having formed through late-stage thick-skinned tectonics since the Neogene. Modeling of hydrocarbon fluid type is consistent with existing oil fields exhibiting light and medium oils with API between 22° API and 39° API, charged from early- to peak-mature source rocks.

Igneous petroleum systems in the Malargüe fold and thrust belt, Río Grande Valley area, Neuquén Basin, Argentina

Abstract The Rio Grande Valley (Neuquen Basin, Argentina) is a large oil field where voluminous igneous sill complexes are emplaced in different levels of the sedimentary sequence in a fold and thrust belt setting. These sills are predominantly emplaced in organic-rich units such as Vaca Muerta and Agrio Formations and are critical elements of the defined petroleum system, as they affect the thermal maturity of the surrounding source rocks, and also act as naturally fractured reservoirs. In this contribution, we integrated structural sections, borehole data, core descriptions, petrophysical laboratory tests and organic geochemistry measurements to characterize the impact of the magmatism in the petroleum system of the Rio Grande Valley oil field. Especially, we focused in evaluating the impact of the sill-complexes in hydrocarbon generation, migration and accumulation. Our data shows that: (1) intrusions are preferably emplaced in organic rich units; (2) a large number of intrusions is observed in areas intensely deformed by imbricated thrusts; (3) an increase in the number of intrusions drives stronger and more extensive maturation processes in the Vaca Muerta formation, enhancing notably the cracking of kerogen to hydrocarbon within this unit; (4) where the number of intrusions increases, the concentration of total gas and methane also increases, given that all sills are suitable reservoirs; (5) igneous rocks provide a low resistance path for fluids flow and act as the main reservoirs in the study area; (6) the reservoir quality of igneous intrusions is dominated by the combination of matrix and fracture framework properties; (7) zeolites are the most common type of cement in these reservoirs; (8) deep sills located in the Vaca Muerta formation produce larger volumes of hydrocarbons relative to shallower intrusive reservoirs. The Rio Grande Valley oil field offers a world-class example of the implications of igneous complexes in hydrocarbon generation, migration and accumulation in a compressive tectonic setting of fold and thrust belt.

New paleofloristic elements and stratigraphic considerations for the Nestares Formation (Lower Jurassic, Argentina)

In this contribution we describe new elements of the paleoflora of Nestares Formation in its type section, exposed along both banks of the Limay River, close to the Alicurá dam (southern margin of Neuquen Basin). Samples were collected from fossiliferous level AL 18 corresponding to black shales and mudstones, interpreted as overflow events from main fluvial channels, as well as avulsion events that cut the flood plain. Neocalamites suberosus Bomfleur, Escapa, Serbet, Taylor and Taylor, Equisetites patagonica Herbst, Todites cacereii Escapa and Cúneo, Osmundopsis rafaelli Escapa and Cúneo, Cladophlebis antarctica Halle, Goeppertella macroloba Herbst, Goeppertella neuqueniana Herbst, Goeppertella stipanicicii Herbst, Dictyophyllum sp., Dicroidium odontopteroides Gothan, Scleropteris grandis Artabe, Morel and Zamuner, and Cycadolepis lanceolata Menéndez are described for the first time for this unit. The presence of elements characteristic of Triassic floras, such as Dicroidium odontopteroides and Goeppertella stipanicicii illustrate the early Mesozoic affinity of the Nestares paleoflora. Stratigraphic relationships of Nestares Formation are analysed considering sedimentological and environmental features as well as paleobotanical content, and support a Sinemurian age for this unit.

ICHNOFABRICS FROM A CRETACEOUS EOLIAN SYSTEM OF WESTERN ARGENTINA: EXPANDING THE APPLICATION OF CORE ICHNOLOGY TO DESERT ENVIRONMENTS

The Lower Cretaceous (Valanginian) Mulichinco Formation of the Neuquen Basin in western Argentina is host to important hydrocarbon reservoirs, encompassing a wide variety of sedimentary facies, including thick eolian deposits in its lower interval in proximal positions. Ten ichnofabrics are characterized based on the analysis of cores from the El Mangrullo oil field. These ichnofabrics have been grouped in four associations, representing eolian dunes, eolian sand sheets, interdunes, and fluvial sheet floods. In terms of the ichnofacies model, both the Scoyenia and Octopodichnus-Entradichnus ichnofacies are identified. Ichnologic information has been integrated with sedimentologic and sequence-stratigraphic information. The studied succession comprises a 3rd-order depositional sequence that is subdivided into three 4th-order sequences stacked in a backstepping pattern as a result of a rise in the water table. The base of the 3rd-order sequence is represented by the intra-Valanginian unconformity that in this area separates marine deposits below from continental deposits above. Overall the 3rd-order sequence reflects the vertical transition from a dominance of eolian dune deposits to eolian sand sheet and fluvial sheet flood deposits, the latter intercalating with marginal-marine intervals. Application of available conceptual frameworks to understand trace-fossil distribution in desert environments suggests that the eolian Mulichinco ichnofauna indicates a temporal evolution from hyper-arid to arid and semi-arid conditions. The results of the present analysis argue against the common assumption of deserts as barren of life and provide further support to the notion of an archetypal eolian ichnofacies. This study expands the realm of application of ichnology in subsurface to eolian environments by providing a characterization of an ichnofauna from a desert setting based on core analysis.

Paleothermometry and distribution of calcite beef in the Vaca Muerta Formation, Neuquén Basin, Argentina

The term “beef” describes bedding-parallel calcite veins found commonly in the organic-rich matrix of unconventional resource plays. Although some authors have interpreted beef to be an early diagenetic feature, these calcite veins are commonly attributed to precipitation at high temperatures and localized overpressure during hydrocarbon generation. The temperature at which the beef formed is thus crucial to ascertain the process of beef genesis. We use the novel methodology of clumped isotope analysis to constrain both the temperature at which beef forms and the isotopic composition of fluids present during formation. For this study, we use beef from basinal sections of the Vaca Muerta Formation in the Neuquen Basin, where veins are commonly up to approximately 10 cm (∼4 in.) thick and are laterally continuous over 1 km (0.6 mi). The calcite veins occur in isolation or in association with concretions and ash layers. Sequence stratigraphic boundaries have little influence on distribution, and only a low correlation between beef and total organic content or beef and ash layers exists. The internal crystal structure of beef varies largely, suggesting both syntaxial and antitaxial growth forms. The δ18O values of beef range from approximately −12‰ to −9‰, and the δ13C values vary between approximately −1‰ and 1‰. The surrounding mudstone and concretion fracture fills (calcite) show little difference isotopically when compared to the beef itself. The δ18O values of nearby concretions range from approximately −3.5‰ to 1‰, and the δ13C values vary between approximately 6‰ and 11‰. Clumped isotope analysis of beef in the Vaca Muerta Formation indicates temperatures between approximately 140°C and 195°C, whereas the surrounding mudstones vary from approximately 120°C to 150°C. The corresponding formation fluid δ18Ow values range from 8.5 to 14.5‰. These temperature data are higher than the maximum temperatures suggested by published studies modeling the basin’s thermal and burial histories. If these models are correct, the clumped isotope data indicate that the growth of beef in the Vaca Muerta Formation required the input of hydrothermal fluids from greater depths. Alternatively, the geothermal gradient or burial depth was underestimated in these models.

Late Cretaceous paleobiogeography of Braarudosphaera bigelowii

Abstract The Late Cretaceous paleobiogeography of the coccolithophore Braarudosphaera bigelowii is reconstructed based on 331 stratigraphic occurrences and complemented by 307 neighboring absences. During the Cenomanian B. bigelowii was found throughout the European seaways, at the base of the North America Interior Seaway, at the paleo-Atlantic margin of South America, in the Neuquen Basin, on the southern tip of the Indian plate, and on the Kerguelen Plateau. During the Late Cretaceous, its range gradually expanded: northwards along the North Sea, into the North American Interior Seaway, eastwards through the interior European seaways, across central Russia, southeastwards into China, and along the Asian coast up to Japan. The Falkland Plateau appears to have played a pivotal role in the colonization of the eastern coast of South America, the Atlantic and Indian Ocean margins of Africa, Madagascar, India, western Antarctica, and Australia. By the end of the Maastrichtian, migration extended northwards towards the Arctic, but did not reach the northernmost regions of the North Atlantic. Because biogeographic information is scarce for the northern coast of South America, for several areas along the African margin, and for the overall Pacific coasts, it is difficult to resolve the biogeographic history in these areas. The presence of B. bigelowii could not be confirmed on the northern coast of South America or on the North Atlantic African margin. It is also not possible to ascertain whether the African margin facing the Indian Ocean was completely colonized by the end of the Cretaceous. Sparse observations suggest that the Pacific coast of North America was colonized by B. bigelowii during the Santonian. However, even though data suggests a subsequent northward colonization direction, it is not possible to accurately reconstruct the North Pacific migration paths of B. bigelowii between the Santonian and the Maastrichtian.

Non-depositional and erosional “offshore” bioeroded hardgrounds from the Lower Cretaceous of the Neuquén Basin, Argentina: Insights into their sequence-stratigraphic implications and controls

Abstract Hardgrounds are important surfaces for basin analysis and oil exploration, representing in some cases significant markers of the sedimentary basin fill. In the Neuquen Basin, bioerosion structures are common on the shell surfaces of benthic organisms, but bioeroded hardgrounds are comparatively uncommon. In the Pilmatue Member of the Lower Cretaceous Agrio Formation (Valanginian-Hauterivian) two examples of bioeroded hardgrounds are described in detail, allowing to recognize contrasting palaeoenvironmental and sequence-stratigraphic contexts, and in turn, discussing the potential major controlling factors in each example. In both cases Trypanites isp. and Gastrochaenolites isp. are described, interpreted as belonging to a Trypanites ichnofacies. The two cases are developed in different environmental conditions: one in non-depositional offshore conditions at the top of a parasequence (i.e., transgressive surface); and the other in offshore erosional settings with the omission surface located in an intra-parasequence position, with no obvious sequence-stratigraphic connotation. These marked differences in the palaeonvironmental conditions (non-depositional vs erosive) and sequence-stratigraphic context (inter vs intra-parasequence occurrence) interpreted for these example allowed us to propose different controlling factors related to the generation of the hardgrounds. Despite these differences, namely long periods of non deposition and low-energy conditions vs shorter time and high-energy (erosive) conditions, in both cases a Trypanites ichnofacies is developed, representing an important aspect to be considered in the characterization of the basin evolution based on omission surfaces.

First Pterosaur Post-Cranial Remains from the Lower Cretaceous Lohan Cura Formation (Albian) of Patagonia, Argentina

In this contribution, we present the first pterosaur post-cranial bone from the Lohan Cura Formation (Albian) of the Cerro de los Leones locality (Picun Leufu, Neuquen Province). The material is an incomplete left ulna, preserved in three dimensions, and composed of the proximal epiphysis and part of the diaphysis. The element shares several affinities with derived pterodactyloid pterosaurs, such as a diaphysis with a sub-oval cross-section, thin bone walls, pneumatic foramina in the dorsal surface of the proximal epiphysis and between the cotyles, and wingspan reconstruction indicating a medium-size specimen. An analysis of the microstructure allowed us to evaluate the ontogenetic stage of the specimen. The thin-section from the mid-shaft shows a wide and sub-circular medullary cavity, encircled by a thin cortical bone ring. In the innermost cortex, secondary lamellar bone forms a distinct and avascular endosteal layer, while the cortical layer is dominated by a well vascularized primary bone with coarse parallel fibers, as in other pterodactyloids. The presence of an avascular endosteal lamellar layer, an unremodeled cortical layer dominated by parallel-fibered bone, and a well ossified proximal epiphysis suggest that the specimen was an advanced juvenile or sub-adult with active-growth at the time of death. Considering the limited pterosaurian fossil record of Argentina, the new pterosaur specimen not only contributes to the reconstruction of the paleoecosystem of the Lohan Cura Formation in the central Neuquen Basin, but also improves our knowledge on the pterosaur taxonomic diversity during the Early Cretaceous of Patagonia.

The coprolite Lumbricaria Münster in the Early Tithonian of the Neuquén Basin, Argentina: new evidence for a holothurian producer

Lumbricaria Munster is described for the first time outside the Tethys domain from distal facies of the Tithonian Vaca Muerta Formation, Neuquen Basin, Argentina. The studied material consists of elongate, convolute, cylindrical coprolites, showing an overlapping pattern, and commonly exhibiting constrictions. Internally, coprolites show a densely packed fabric, where the particles show the distinctive morphology of saccocomid ossicles. These specimens are assigned to Lumbricaria intestinum Munster and three morphotypes are defined: (a) morphotype 1 shows a disordered convolute structure; (b) morphotype 2 is shorter and has a non-convolute arrangement; and (c) morphotype 3 has a spiral arrangement. Coprolites are preserved within microbial laminites, as well as concretions in calcareous mudstones. In this paper we discuss the possible producers of these coprolites, where evidence from the studied material would support a holothurian producer.

Reconstruction of palaeoenvironmental conditions of the Vaca Muerta formation in the southern part of the Neuquén Basin (Tithonian-Valanginian): Evidences of initial short-lived development of anoxia

Abstract The Vaca Muerta Formation is a famous source rock being largely present in Argentina. The formation was examined in the southern part of the Neuquen Basin through clay-mineral assemblage composition, as well as organic and inorganic geochemical characteristics. In total, 259 samples were analyzed on both sides of the Huincul Arch (major E-W structure that divided the southern part of the basin into two depocentres). South to this structure (Picun Leufu area), the total organic carbon content (TOC) can reach 20% but is generally ranging from 0.1 to 6%. To the north (Covunco area), average TOC does not exceed 0.5%. Clay-mineral assemblages indicate an evolution of the sources of clastic supply through time in response to evolving weathering/erosion at the regional scale. Redox-sensitive trace-element distribution shows that the particulate iron shuttle process operated, with an initially-euxinic depositional environment that evolved rapidly to oxygenated seawater and suboxic sediments. Our results suggest an episodically restricted circulation pattern that occurred at the beginning of the deposition of the Vaca Muerta Formation (highest TOC content).

AMMONITES OF THE SUBFAMILY ZAPALIINAE FROM THE LOWER TITHONIAN OF ESTANCIA MARÍA JUANA, VACA MUERTA FORMATION (PORTADA COVUNCO MEMBER), NEUQUÉN BASIN, ARGENTINA

A new collection of ammonites from the Picunleufuense Zone (standard base of the Andean Tithonian) of the locality Estancia Maria Juana (southern Neuquen Basin, Argentina) has provided abundant and well preserved material of new transients of Indansites picunleufuense and Choicensisphinctes platyconus. These transients are described and a detailed review of the early evolution of the Indansites lineage is presented. The meaning of changes in rib density, variations within the microconchs (males) and the length of the bodychamber in Indansites picunleufuense are discussed. It is concluded that the changes in rib density which characterize the successive macroconchs of the transients indicate changes in the rate of shell-growth. The more densely ribbed phragmocone of later transients would have had lower growth rates, which would also explain their smaller adult size. The microconchs show high variation in adult size suggesting high plasticity in the size-age maturation, most likely caused by influence of seasonal environmental conditions. A large small-macroconch-like lapetted microconch, coming from the close locality Picun Leufu, is interpreted as a new case of sex-change.

Pumice clasts in cross stratified basalt-dominated sandstones and conglomerates. Characteristics and depositional significance: Huarenchenque Fm (Neuquén, Argentina)

The Huarenchenque Fm is a Pleistocene clastic sedimentary unit that crops out in the SW of the Neuquen Basin, Argentina. This unit is made up of cross stratified basalt-dominated sandstones and conglomerates with pumice clasts in a fluvial context. The roundness of these pumice clasts, the numerous fragments of shards and their association with polymodal basalt-rich clasts in cross-bedded conglomerates strongly suggest that these clasts were transported together during hydraulic flow. Pumice clasts are usually buoyant in cold water whenever their density is lower than 1 g/cm3. However, since their density exceeds that of water during sediment transport, they form part of the sedimentary record. A flume was employed to yield fresh insight into the behavior of these clasts mixed with sands during transport and accumulation. The hydraulic equivalence of both materials was calculated by evaluating the density of the pumice clasts and that of the quartz sands. The pumice clasts sank as a result of the interaction of pumice-rich pyroclastic flows with a moving mass of shallow water. However, they retained their buoyancy after recovery from the sedimentary record. The sinking process is therefore rapid and reversible.

Stable isotope and fluid inclusion study of sediment-hosted stratiform copper deposits from the Neuquén Basin, Argentina

The Los Chihuidos and El Porvenir deposits of the Neuquen Basin are examples of sediment-hosted stratiform Cu deposits generated by interaction of hydrocarbons and formation water with host red beds and metal-charged basinal brines. During early diagenesis of red beds precipitated hematite, kaolinite at 60 °C from meteoric water followed by calcite 1 (δ13C − 8 to − 3.3‰) and barite (δ34S + 4.1‰) with increasing temperature (75–85 °C) from an evolved surface fluid (δ18Ofluids + 0.9 to + 2.7‰). During the Tertiary Andean orogeny, hydrocarbons and formation water migrated and reacted with the red beds resulting in bleaching of the sandstone. Smectite (fluid δ18O − 2.2‰ and δD − 73.7‰), chlorite-smectite mixed-layer minerals (fluid δ18O − 6.9‰ and δD − 84‰), pyrite (δ34S + 10.2‰), and calcite 2 (δ13C − 12.9 to − 6.8‰) formed as by-product of the redox reactions. Calcite 2 formed from low-salinity fluids (0.4 to 5.9 wt% NaCl equiv.) at slightly higher temperatures (125–145 °C) at El Porvenir and at Los Chihuidos deposit (80–105 °C). During subsequent uplift, metal-charged basinal brines flowed into the bleached sandstone and precipitated chalcopyrite-bornite (δ34S + 12.3‰) followed by chalcocite-spionkopite (δ34S − 64 to + 4.1‰). Calcites 3a (δ13C − 19 to − 10.1‰) and 3b (δ13C − 31.4 to − 9.5‰) that accompanied Fe-Cu and Cu sulfides, respectively, formed from saline fluids (up to 21.3 wt% NaCl equiv.) at temperatures of 159–70 °C. The δ18O values (+ 5.6 to + 11.4‰) of fluids in equilibrium with calcite 3a are similar to oilfield and basinal brines. Fluids in equilibrium with calcite 3 in Los Chihuidos and calcite 3b in El Porvenir show much lighter δ18O values (− 7.3 to − 4.6‰ and − 0.6 to + 2.3‰, respectively), which suggests the involvement of methane as the main reductant and possibly meteoric water interaction.

TAPHONOMY AND PALEOECOLOGY OF LOWER CRETACEOUS OYSTER MASS OCCURRENCES FROM WEST-CENTRAL ARGENTINA AND EVOLUTIONARY PALEOECOLOGY OF GREGARIOUSNESS IN OYSTERS

Lower Cretaceous (lower Hauterivian) oyster mass occurrences (OMOs) dominated by the gryphaeid small oyster Ceratostreon from the Neuquen Basin (west-central Argentina) are analyzed in terms of taphonomy and paleoecology in order to characterize their origin, reconstruct the oyster-dominated paleocommunity, and assess their paleoenvironmental implications. A laterally extensive oyster-bearing sedimentary interval with high oyster abundance was analyzed at three localities situated along a 75 km N-S transect. Three different types of OMOs were differentiated: biogenic bioherms with dominance of encrusting life habits, biogenic autobiostromes with dominance of soft bottom recliners, and mixed sedimentologic-biogenic parabiostromes with signs of reworking. The development of these different types of OMOs indicates a high nutrient input that favored high oyster proliferation, whereas the different life habits adopted by the oysters indicate a difference in sedimentation rate throughout the studied level: reclining oysters indicate a higher sedimentation rate than cementing ones. This Lower Cretaceous study case is framed in a general context of global shift of OMOs from a Tethyan distribution during the Jurassic to a mainly eastern Pacific distribution in the Cretaceous, occupying both coastal and deep continental shelf. Also, there is a taxonomic shift from primarily gryphaeid OMOs during the Jurassic and Lower Cretaceous to primarily ostreid OMOs during the Upper Cretaceous. Cenozoic OMOs are found in marginal marine environments and are exclusively built by ostreids. An increase in predation pressure from the mid-Mesozoic onwards could have pushed OMOs to marginal marine environments where predators cannot thrive and force a taxonomic shift towards brachyhaline taxa.

Gestión del conocimiento y desafíos en PyMEs proveedoras de la cadena de hidrocarburos en la Cuenca Neuquina. Avance de investigación y reflexión para el diseño de políticas

The document refers to a set of aspects that stand out in the development of the small and medium enterprises of hydrocarbons in the Neuquen Basin, in the Argentine Norpatagonia. The investigation is motivated, on the one hand, by recent changes in the energy sector in general, and hydrocarbons in particular, the fall in oil prices and a trend towards cleaner energies. And on the other hand, at a structural level, due to the dynamics of innovation that has opened up with the development of unconventional reservoirs for companies in the SME segment, which make up the global value chains for gas and oil. The new development phase of hydrocarbons requires new technical systems in the drilling and completion of wells and new extraction procedures, as well as changes in inputs, components and equipment. They mobilize a new organization of work, the increasing introduction of ICTs, the taking of ad hoc information, specific training, and a rigorous coordination that generated a new division of work upstream. In this framework, from an evolutionary approach to the economy, a set of problems faced by groups of regional SMEs that provide goods and services from the electronic and metal-mechanical sector are analyzed. It inquired about the routines of firms in the construction of technological capabilities, the development of new processes and products, external links and internal management improvements, changes in productivity, and commercial competition in the new scenario of volatility of oil prices.