Neuquen Basin

The Vaca Muerta Formation in the Cerro Domuyo area shows an interesting intercalation of facies with opposite paleocurrents. The unit is represented by outer ramp to basinal facies with a westward direction of progradation. However, in its middle section, slope deposits correlatable with the Huncal Member, intercalate with slumped strata verging northeast. This interval is composed of carbonate facies and it is probably associated with the development of a slope related to a carbonate platform or a distally steepened carbonate ramp. Based on the ammonoid fauna, the age of the Vaca Muerta Formation ranges from the early Tithonian to the late Berriasian, but it could also reach the early Valanginian. The Huncal Member yields representatives of the Substeueroceras koeneni Biozone (Upper Tithonian), hence its age is older than that proposed in its type locality allowing its correlation with units exposed in the Chilean territory.

Lower Cretaceous trackways assignable to xiphosurids were recently found in tidally influenced marginal-marine deposits of the Agrio Formation (Patagonia, Argentina). The aim of this paper is to describe these trace fossils in detail, discuss their conditions of preservation, make palaeoecological and taphonomic inferences from them, and analyse the importance of their palaeogeographic location. These trace fossils are assigned to Kouphichnium, and five track morphotypes are established. Microbially induced sedimentary structures (MISS) are associated with the trackways. Scanning electron microscope (SEM) studies document the involvement of microbial mats in the preservation of the trackways by the presence of cyanobacteria-like filament sheaths. The microbial mats enabled preservation of the tracks by binding and biostabilisation of the sediment surface. The mostly likely producers of the trackways are from the subfamily Limulinae. The studied surface could represent a high-tide mating ground associated with a very shallow water deposit on a warm Cretaceous tidal flat. These records are the first convincingly documented trackways produced by xiphosurids in the Early Cretaceous worldwide and the second fossil record of this group from the Cretaceous in the Southern Hemisphere

Resumen: Los depósitos continentales de la Formación Challacó constituyen la etapa final de acumulación del Grupo Cuyo (Jurásico inferior a medio) en el sector sur de la Cuenca Neuquina. Para sus afloramientos más occidentales, a partir del análisis de facies y cuerpos sedimentarios, se han definido cuatro asociaciones principales de facies.

Cretaceous bakevelliids in Argentina are restricted to the Lower Cretaceous. They are recorded in shallow marine deposits in two Mesozoic basins located in the Andes foothills in Patagonia. In the Austral Basin (44(-55(S) there is only one genus, Gervillella, represented by a single specimen from the Barremian. In the Neuquén Basin (30(-40(S) two genera, Gervillaria and Gervillella, occur, ranging from the Berriasian to the Lower Barremian. In the Pilmatué Member of the Agrio Formation two species are identified: Gervillaria alatior (Imlay) and Gervillella aviculoides (J. Sowerby). The former is also recorded in Mexico while the latter is more widespread, occurring in Europe, Asia, and Africa. In the Bajada del Agrio section they come from eight tabular shell beds located near and on top of shallowing-upwards cycles. They were abundant only in four of these levels. These shell beds are interpreted as having been deposited in the mid-ramp (middle of cycles), and upper mid-ramp (top of cycles). A functional analysis of shells revealed two life habits: epibyssate and endobyssate.

The Early Cretaceous marine deposits of the Agrio Formation are widely distributed in southern Mendoza and Neuquén provinces, Argentina. The stratigraphic distribution of upper Valanginian to upper Hauterivian organic walled dinoflagellate cysts was evaluated at the Agrio Formation, at Bajada del Agrio locality. The assemblages exhibit a relatively moderate to low diversity and those with greater abundance are dominated by a small number of species such as Circulodinium distinctum, Cribroperidinium spp., Exochosphaeridium spp., Florentinia mantellii, Kiokansium unituberculatum, and Oligosphaeridium complex. Three diagnostic bioevents of lowest (LO) and highest (HO) stratigraphic occurrences of taxa calibrated with the local ammonoid zonation were identified for the Early Cretaceous of the Neuquén Basin: the LO of Callaiosphaeridium sp. (base of Holcoptychites neuquensis Zone, earliest Hauterivian), the LO of Cymososphaeridium validum (uppermost Hoplitocrioceras gentilii Zone, upper early Hauterivian) and the HO of Cymososphaeridium validum (lowermost Crioceratites diamantensis Zone, late Hauterivian). The studied assemblages are compared with Early Cretaceous assemblages from the Northern Hemisphere. In general, the association of dinoflagellate cysts together with the selected diagnostic species exhibit a clear affinity with those of the Mediterranean region.

RESUMEN Se realizaron estudios sedimentológico-estratigráficos en los depósitos fluviales innominados del Jurásico Medio de la Cuenca Neuquina surmendocina, que afloran en el anticlinal de Malargüe y Bardas Blancas. En el primero de ellos se reconocieron fa-cies de sistemas fluviales entrelazados gravo-arenosos que se apilan en tres secuencias depositacionales mostrando un decreci-miento paulatino en el espacio de acomodación, en tanto que en el segundo se reconocieron facies de sistemas fluviales anasto-mosados que se agrupan en dos secuencias depositacionales con un incremento progresivo del espacio de acomodación. En el anticlinal de Malargüe las relaciones estratigráficas y el patrón de apilamiento sugiere la asignación de estos depósitos al Bajo-ciano tardío-Bathoniano y su correlación con la Formación Lajas, por lo que se propone la denominación de Formación Pues-to Pacheco nov. nom., con su estratotipo en la sección del arroyo Loncoche. En el área de Bardas Blancas la presencia de clastos de calizas y fragmentos de ostras en la base de la unidad permitiría establecer que los depósitos fluviales se habrían depositado con posterioridad a la discordancia Intracaloviana. En este sector se le asigna una edad Caloviana media-tardía y se los asig-na a la Formación Lotena. ABSTRACT Facies analysis and stratigraphic assignment of Middle Jurassic unnamed fluvial deposits in the Southern Mendoza Neuquén Basin Stratigraphic-sedimentological studies were performed on Middle Jurassic unnamed fluvial deposits of the Southern Mendo-za Neuquén Basin, cropping out in the Malargüe anticline and Bardas Blancas. In the first area we recognized braided fluvial systems facies stacked in three depositional sequences showing a gradual decrease in the accommodation space, whereas in the second we recognized anastomosing fluvial systems facies grouped into two depositional sequences with a progressive increase in the accommodation space. Stratigraphic relationships and stacking pattern in the Malargüe anticline suggests the assignment of this unit to the late Bajocian-Bathonian and its correlation with the Lajas Formation, so the name of Puesto Pacheco Formation nov. nom. is proposed, with its stratotype in the Loncoche creek section. In the Bardas Blancas area the presence of limestone clasts and oysters fragments at the base of the unit, would establish that unnamed fluvial deposits would have been deposited after the Intracallovian unconformity. In this area it is given a middle-late Callovian age and the assignment to the Lotena Formation.

"Storm deposits (tempestites) have been extensively studied in the sedimentary record, particularly those deposits with hummocky cross-stratification, knowing their bathymetric ranks, facies models and their hydrodynamic conditions (Harms et al., 1975; Dott y Burgeois, 1982; Dumas y Arnott, 2006). However, detailed studies in carbonate sediments are relatively scarce. Recently, other types of interference generated at the picnocline interface (internal waves) were proposed to interpret similar deposits without being controlled by the position of the of storm-wave level (Pomar et al., 2012). The Tithonian - Valanginian deposits in the southern Mendoza - Neuquén Basin are particularly interesting because of their association with a homoclinal carbonate ramp system. During the Late Jurassic - Early Cretaceous a series of marine sequences were developed throughout the basin that are grouped under the Mendoza Group. In the southern Mendoza area it includes the Vaca Muerta Formation (early Tithonian - early Valanginian), the Chachao Formation (early Valanginian) and the Agrio Formation (early Valanginian - early Barremian) (Figs. 1 and 2).
The Vaca Muerta Formation is widely distributed over the entire Neuquén Basin. It consists of dark bituminous shales, marls and limestones deposited in response to a rapid and widespread marine transgression originated from the Pacific Ocean, as consequence of a tectonic phase of compressional relaxation (Legarreta and Uliana, 1991). While initial studies show significant variations in the proportions of different lithologies, sedimentological knowledge is still general, with the exception of contributions from the south of the basin (Spalletti et al., 2000, 2008; Scasso et al., 2002, 2005) and southern Mendoza area (Doyle et al., 2005; Kietzmann et al., 2008, 2011).
Storm deposits are well developed in the Vaca Muerta Formation. Based on tempestites characteristics and their associated beds four distinct deposits have been identified in the Bardas Blancas area (Fig. 3): (1) packstones with lowangle cross-stratification, (2) packstones/grainstones with large scale hummocky cross-stratification, (3) rudstones/grainstones with small scale hummocky cross-stratification, and (4) laminated wackestones/packstones with intralaminar normal gradation (Figs. 5 and 6). Packstones with low-angle cross-stratification can be interpreted as anisotropic hummocks deposits or low relief megaripples generated under combined flows during major storms in the middle ramp. A complete sequence of HCS consists of three divisions (Sa-Sc) associated with the storm event, and an upper unit (Sd) that represents the fairweather period between major storm events. Unit Sa starts with an erosion base and consists in low angle cross-stratified rudstones/grainstones. Unit Sb The unit begins with a second order surface and is composed by packstones and grainstones with hummocky cross-stratification. Unit Sc is represented by peloidal packstones with ripple marks, and finally the unit Sd consists of laminated wackestones/packstones. Laminated wackestones/packstones with intralaminar normal gradation consist of bioclastic wackestones/packstones composed of saccocomids remains or a rhythmic alternation of peloidal packstones and sandy layers with current ripple marks, which probably represents the distal expression of the storms. Variations from this sequence allow us to make some comparison with other ancient carbonate storm deposits (Kreisa, 1981; Monaco 1992, Sami y Descorchers, 1992; Molina et al., 1997; Zhou et al., 2011). Although deposits of the Vaca Muerta Formation are compositionally similar to those described by Molina et al. (1997), the ideal sequence is similar to that recognized by Monaco (1992) (Fig. 10). The division proposed by Monaco (1992) seems to be the most accurate, since it is based on the recognition of structures generated under different hydrodynamic conditions rather than genetic interpretations associated with the phases of the storm.
Comparing the described storm-influenced deposits with ancient and modern storm deposits examples, a relative water depth of 25 to 50 m is estimated for the formation of the HCS limestone facies. Even assuming its origin from internal waves, the position of the pycnocline in warm seas and small basins would be found within the same depth range (Nordberg et al., 2000), so that the deposits described in this paper may be important in future palaeogeographical studies in the Neuquén Basin."

En la literatura el término biofacies ha sido utilizado con diferentes significados de los cuales el ambiental o ecológico es el más importante . Esta connotación del término cobró fuer-za en los estudios de faunas bentónicas actuales los cuales demostraron que distintos sectores de las plataformas están caracterizados por asociaciones o biofacies particulares. Estas biofacies generalmente se van reemplazando con el aumento de la profundidad respondiendo a cambios físicoquímicos e interacciones biológicas y en el registro pueden aportar datos útiles en interpretaciones paleoambientales .

Variations in the sedimentary organic matter were documented throughout the Agua de la Mula Member (late Hauterivian) of the Agrio Formation, at a combined section in the type area of the Agrio Formation; the base at Agrio del Medio and the middle to top at Bajada del Agrio. A main organic-rich interval was identified in the basal Agua de la Mula Member, dominated by marine-derived Amorphous Organic Matter (AOM), coinciding with the highest Total Organic Carbon (TOC) content, between 1.4 and 3.8 wt.%, suggesting dysoxic conditions. The rest of the Member is predominantly characterized by terrestriallyderived organic matter, mainly phytoclasts, with low TOC values, around 1% or lower, indicating predominantly oxic depositional settings. By integrating stacking pattern and shell beds analysis, four depositional sequences SQ1eSQ4 were recognized. The organic-rich, finely laminated bituminous black shales of the Spitidiscus riccardii zone constitute a mayor and rapid inundation defining a Transgressive System tract (TST), related to a third order asymmetrical mesosequence dominated by a thick High System Tract (HST). It represents the most widespread and important flooding episode within the Neuquén Basin during the late Hauterivian. Inside sequences of higher frequency (SQ1, SQ2, SQ3, SQ4) of probably fourth order were recognized and analysed including several ammonids zones (Spitidiscus riccardii, Crioceratites schlagintweiti, C. diamantensis and Paraspiticeras groeberi). With the exception of the oxygen-controlled, basinal and outer ramp settings indicated for the TST1, which is equivalent to the TST of a lower order sequence, and the lower TST2, respectively, the prevalence of well oxygenated, inner to middle ramp depositional environments, is suggested for the rest of the sedimentary succession and emphasized in HST of SQ2, SQ3 and SQ4. Thus, a shallowing-upward trend with improved oxygenation is recorded through the Agua de la Mula Member, reflected by decreasing TOC, AOM content and preservation state of the organic matter. Based on the whole rock fluorescence analysis of the two selected organic-rich intervals from the Spitidiscus riccardii and the lowermost Crioceratites diamantensis zones, the presence of hydrocarbons suggests a very early in situ generation.

Durante el intervalo Tithoniano-Berriasiano el engolfamiento Neuquino se comportó como una cuenca parcialmen-te cerrada, limitada hacia el oeste por un arco de islas volcánicas poco elevado, y conectada por estrechos pasajes marinos con el océano Pacífico ). Bajo estas con-diciones, durante el Tithoniano temprano, luego de un período de mar bajo dominado por condiciones de sedimentación clástica continental, Formación Tordillo de edad kimmeridgiana, se registró RESUMEN La Formación Vaca Muerta (Tithoniano-Berriasiano) consiste en una alternancia rítmica de lutitas negras, lutitas grises, margas y limolitas, con mudstones, wackestones, packstones, floatstones y rudstones bioclásticos. La asociación de facies en la sección del arroyo Loncoche, permitió definir 12 litofacies y 8 microfacies, dominadas por moluscos, equinodermos, foraminíferos, braquiópodos, serpúlidos y radiolarios. Se distinguieron cuatro asociaciones de facies correspondientes a los subambientes de cuenca, rampa externa (distal y proximal) y rampa media. La utilización de la relación Nassellaria/Spumellaria permitió estimar un rango de profundidades menores a 200 metros. El patrón de apilamiento y la distribución vertical de facies permitió la distinción de tres secuencias depositacionales, y el reconocimiento de un sistema tithoniano de rampa homoclinal y un sistema berriasiano de rampa homoclinal de mayor gradiente. La secuencia depositacional 1 consiste en facies de cuenca y rampa externa distal y se caracteriza por un patrón retrogradacional. Presenta un espesor de 124 m, y se extiende desde la Zona de Virgatosphinctes mendozanus hasta la base de la Zona de Corongoceras alternans. Las secuencias depositacionales 2 y 3 consisten en facies de rampa externa y rampa media. Están caracterizadas por un patrón agradacional y progradacional. El espesor de la secuencia 2 es de 66 m y se asigna a la Zona de Corongoceras alternans, mientras que la secuencia 3 alcanza 78 m y corresponde a las zonas de Substeueroceras koeneni y Spiticeras damesi.

"Three new ichnotaxa of crustacean microcoprolites from the Neuquén Basin, Argentina, are described in this paper: Palaxius rahuensis Kietzmann n. isp. (early Valanginian), Palaxius mendozaensis Kietzmann n. isp. and Palaxius malarguensis Kietzmann n. isp. (middle to late Berriasian). In addition, a Favreina ichnospecies from the late Berriasian e early Valanginian is reported for the first time for the Neuquén
Basin. Controls on the microcoprolite distribution could be related to their biostratigraphic position, sedimentary processes, facies distribution, and diagenesis. Changes in microcoprolite diversity may reflect a shallowing facies trend."

This paper provides an updated taxonomic inventory of the bivalve fauna collected in the Pilmatué Member of the Agrio Formation of the Neuquén Basin, west-central Argentina, places the fauna in its palaeobiogeographic setting, and addresses its palaeoecological significance. Thirty-one Late Valanginian to Early Hauterivian bivalve species within 24 genera were identified. A large part (32%) of the identified bivalve species occur over a wide geographical area: from the Pacific coast of South America to Europe, North Africa, Central Asia and East and South Africa; some are also recorded in Japan. A relatively high degree of endemism (26%) is shown, suggesting that some of the bivalve species had barriers to their dispersal; larval strategy and length of larval development were probably important. A significant number (42%) of the bivalve taxa are left in open nomenclature as they are probably new species. Bivalve guilds are described to interpret palaeoecology, in particular the ecospace utilization. Guilds are based on tiering, life habit, and feeding category. Eight guilds are recognized: free-lying epifaunal, cemented epifaunal, epibyssate, boring, endobyssate, shallow burrowing, deep burrowing and deep burrowing with symbiotic bacteria. The fauna is composed only of suspension-feeders indicating that food resources were dominantly in suspension, in agreement with the predominantly shallow-water aspect of the study deposits. The ecospace utilization in the shoreface is broader than in the offshore shelf, suggesting more favourable living conditions and/or a wider range of different habitat types represented.

A lo largo del Cretácico la Cuenca Neuquina registra dos momentos distintivos de rocas marinas, uno que abarca el lapso Berriasiano-Barremiano temprano y otro, más restringido, que abarca el Maastrichtiano. En ambos intervalos se conocen abundantes faunas de invertebrados que han sido estudiadas por más de cien años, lo que ha permitido tener un razonable conocimiento desde el punto de vista sistemático. Sin embargo, no existe información actualizada sobre sus afinidades paleobiogeográficas. Estas afinidades están íntimamente ligadas a la evolución geodinámica de la Cuenca Neuquina. Durante el Cretácico temprano la cuenca estaba conectada con el océano Pacífico a través de un arco de islas, permitiendo la llegada de faunas norandinas y tethyanas a lo largo del margen occidental de Sudamé-AMEGHINIANA (Rev. Asoc. Paleontol. Argent.) -45 (3): 593-613. Buenos Aires, 30-09-2008 Abstract. PALEOBIOGEOGRAPHIC AFFINITIES OF THE CRETACEOUS INVERTEBRATES OF THE NEUQUÉN BASIN. Paleobiogeographic affinities of Cretaceous marine invertebrates of the Neuquén Basin are analyzed based on a recent systematic revision. Two different marine intervals are considered. The first one corresponds to the Berriasian-Early Barremian when the basin was connected to the Pacific Ocean through a volcanic arc. The second is restricted to the Maastrichtian, when the basin was open to the Atlantic Ocean. During the first, the nautilids are monospecific showing Andean affinities. The ammonoids are represented by six families of tethyan affinities. Twenty genera and subgenera are replaced in time through immigration events, alternating between Andean and pandemic forms. The bivalve fauna has tethyan affinities, although a significant number of taxa are endemic. The decapods show similarities with others from England and Germany. The echinoids are represented by seven genera of different paleogeographic distribution, including endemic or Andean forms and others with a nearly cosmopolitan distribution. Maastrichtian mollusk faunas show affinities with the Weddellian Province. Near the K/P boundary and during the Danian the weddellian forms were replaced by warm-waters taxa from northern Brazil, the Caribbean and northern Africa. It is proposed that during the Early Cretaceous, paleotemperatures in the Neuquén Basin were similar to those in the Tethys, but probably not so high, whereas for the Maastrichtian, a global cooling would have caused the northern expansion of Weddellian forms. Finally, around the K/P boundary, a new global warming probably enhances the replacement of these faunas by other typical from low latitudes.

"Resumen
La presencia de crinoideos saccocómidos en la Cuenca Neuquina es uns hallazgo relevante, ya que constiruye el resgistro más temprano del orden Roveacrinida en el Hemisferio Sur y el primer registro de Saccocoma fuera de la región del Tethys. El material fue estudiado a partir de laminas delgadas provenientes de la Formación Vaca Muerta y pueden ser asignadas a los géneros Saccocoma Agassiz y Crassicoma Sieverts-Doreck y Hess. Las placas radiales aparecen en el sector de la rampa externa proximal, mientras que lo elementos de los brazos aparecen tanto en la rampa externa proximal como distal. Los restos fueron encontrados formando dos tipos de depósitos: elementos dispersos en wackestones bioclásticos, típicos del HST, y como concentraciones sedimentarias (microfacies de Saccocoma) asociadas mayormente al TST.

Abstract
Presence of saccocomid crinoids in the Neuquén Basin is an important finding since it is the earliest record of Roveacrinida in the Southern Hemisphere and the first record of Saccocoma outside the Tethys. The material was studied in thin sections from the Vaca Muerta Formation and it can be assigned to the genera Saccocoma Agassiz and Crassicoma Sieverts-Doreck and Hess. Radial plates appear on the proximal ramp, while elements of the arms appear in the proximal and distal outer ramp. Dispersed Saccocoma elements are typical of HST, while Saccocoma sedimentary concentrations are associated with the TST."

Taphonomic and palaeocological studies of fossil assemblages from the transgressive and highstand succession of the Vaca Muerta Formation (lower Tithonian to upper Valanginian) in Loncoche Creek, Rahue Creek and Cuesta del Chihuido, Mendoza province was carried out. A range of paleoenvironments that include mid, outer and basin deposits of carbonate ramp has been determinated based on integrated studies of taphofacies, biofacies, lithofacies and microfacies. In the mid ramp zone were recognized the following taphofacies: autoparabiostromes types 1, and 2 as well as concentrations of bivalves, gastropods and serpulids. Meanwhile, biofacies included autobiostromes rich in grypheids and serpulids. In the outer ramp zone were recognized parabiostromes types 1 and 2, ammonite and aptychus pavements, bioclastic detritus, molluscs and brachiopods pavements, besides bioturbated nodular limestones and truncated ammonites. In the outer ramp zone, biofacies are characterized by a high diversity showing: Lingularia-Discinisca, infaunal bivalves, epistominid foraminifers, filament bivalves, besides of pectinidae, oysters and inoceramid bivalves, hardgrounds and microbial mats. Taphofacies and biofacies data allow to estimate relative sea level changes, sedimentation rates, substrate consistency, oxygenation, nutrient levels and productivity.

El texto aborda distintas aristas del conflicto en torno a la producción de hidrocarburos no convencionales en el yacimiento Vaca Muerta, en Argentina. Una de las disputas centrales tiene como protagonistas a las comunidades mapuche, las empresas y el Estado provincial y nacional. El trabajo analiza la resistencia que desarrolla la comunidad mapuche de Campo Maripe que reclama la propiedad de su territorio ancestral ubicado en el corazón de la explotación de los recursos no convencionales, en la provincia de Neuquén, distinguiendo cómo el Estado y los empresarios han recurrido a instrumentos judiciales y represivos para desalojar a la comunidad de estas tierras. Se partirá aquí del estudio del tramo final del juicio acontecido en la ciudad de Neuquén en 2019, donde fueron acusados de usurpación seis miem- bros de la comunidad Campo Maripe. La escena del juicio permite apreciar valoraciones, percepciones y acciones divergentes que se mo- vilizan entre los actores involucrados en el enfrentamiento con refer- encia al territorio, la naturaleza, y la mirada sobre el otro. Desde una perspectiva de análisis sociológico y cualitativo, se aporta a una re- flexión sobre la modalidad que adoptan los conflictos sociales en tor- no al fracking en Vaca Muerta, los motivos de las resistencias y algu- nas de las estrategias que adopta el capital para proseguir con la ex- plotación de los bienes de la naturaleza para la producción de energía.


Abstract
The text focuses on different aspects of the conflict surrounding the production of unconventional hydrocarbons in Vaca Muerta, Argen- tina. One of the central disputes has as protagonists the Mapuche community, the provincial and national state, and companies. The work analyzes the resistance developed by the Mapuche community of Campo Maripe, which claims ownership of its ancestral territory located in the heart of the exploitation of unconventional resources, in the Province of Neuquen, distinguishing how the State and busi- nessmen have resorted to judicial and repressive instruments to evict the community from these lands. It will start from the study of the final stretch of the usurpation trial that occurred in the provincial city in 2019, where the accused were the six members of community of Campo Maripe. The trial thus acts as a prism that allows us to appre- ciate divergent valuations, perceptions and actions that are mobilized between the actors involved in the confrontation with reference to the territory, nature, and the gaze on the other. From a sociologic and qualitative analysis perspective, it contributes to a reflection on the modality adopted by social conflicts around fracking in Vaca Muerta, the reasons for the resistance, and on some of the strategies that cap- ital adopts to continue exploiting the assets of nature at the current stage of energy production.

"Subtropical carbonates from the Callovian Calabozo Formation, and their diagenesis, Neuquen Basin, MendozaPprovince. Detailed study of Callovian carbonates of the Calabozo Formation (30 m) in western Argentina, reveals the abundance of benthic carbonates particles produced by organisms that are light dependent, and non-skeletal grains such as ooids and peloids. The biota consists of bivalves, dasyclads (Salpingoporella annulata Carozzi, Cylindroporella annulata Carozzi, and Heteroporella sp.), scleractinian corals, echinoderms, cyanobacteria (Cayeuxia (Rivularia) piae Rech-Frollo, and Cayeuxia (Rivularia) kurdistanensis Elliot), oncoids, gastropods, forams, and calcispheres as well as ostracods, and bryozoans in relatively minor quantities. Allochemical particles suggest for the shallow marine limestones of the Calabozo Formation a Photozoan
Association under subtropical seawater conditions. The petrographic features allow to recognize seven microfacies, differentiated by particle types, fossils and depositional texture: 1) criptalgal bindstone; 2) bioclastic-peloidal wackestone; 3) bioclastic-intraclastic wackestone; 4) bioclastic-peloidal-
terrigenous wackestone, 5) coral framestone, 6) peloidal-bioclastic-intraclastic packstone, and 7) oolitic-bioclastic-peloidal packstone-grainstone. The recognition of microfacies groups constitute two palaeoenvironmental associations: inner ramp and middle ramp settings. Diagenetic studies are based on examination of stained thin sections, through conventional petrography and under cathodoluminescence. Early diagenetic processes are micritization and precipitation of peloidal micrite and acicular calcite. These cements predate granular and syntaxial calcite cemets. Cathodoluminescent petrography allows to identify three morphologic types of clear cements: (1) fine acicular crystals, (2) granular cements, and (3) syntaxial cement rims on echinoderm particles. Description of the CL signature has evolved to discrimination as either, non-luminescent, dully luminescent red/orange, or brightly luminescent yellow. The earlier acicular calcite cement is non-luminescent, on the other hand, the predominantly
dully luminescent red/orange, or brightly luminescent yellow of interparticular and intraparticular granular calcite and syntaxial cements indicate a shallow burial meteoric-phreatic diagenetic environment."

La producción de hidrocarburos en la provincia del Neuquén comenzó en el año 1918 y a partir de ese momento se ha producido gas y petróleo de reservorios convencionales correspondientes a las diferentes formaciones que integran la columna de la Cuenca Neuquina.
El aumento en la demanda energética de los últimos años ha provocado un cambio de paradigma que llevo a considerar nuevas técnicas para la exploración y desarrollo de los hidrocarburos y de esta manera comenzaron a adquirir mayor relevancia los reservorios en lutitas y areniscas compactas (shale y tight). Estos reservorios, denominados como No Convencionales, están integrados por rocas que contienen gas y/o petróleo  y para que su extracción sea económicamente rentable es  necesario métodos de estimulación a través de fracturas hidráulicas en etapas.
La puesta en producción de este tipo de reservorio ha impactado de manera positiva en la producción y reservas de gas y petróleo de la provincia de Neuquén, atenuando la declinación de la producción y reservas de los reservorios convencionales.
El presente trabajo tiene como finalidad realizar una caracterización geológica de los principales reservorios tight y de baja permeabilidad que se encuentran en producción y proponer una distribución areal en base a los antecedentes disponibles.

Las facies marinas de la Formación Agrio (Valanginiano-Barremiano temprano, Cuenca Neuquina) poseen un abundante contenido fosilífero el cual ha sido estudiado desde fines del siglo XIX. Grupos tales como amonoideos, bivalvos, gasterópodos, serpúlidos, briozoos y equinoideos, cuentan con revisiones recientes, mientras otros grupos como los corales no han recibido la misma atención. Dada la importancia de las facies coralinas como indicadores paleoambientales y paleoecológicos, y la necesidad de contar con una taxonomía actualizada, se ha  emprendido una revisión taxonómica basada en nuevas colecciones. Para su correcta determinación los ejemplares fueron cortados longitudinal y transversalmente, se realizaron pulidos de las superficies y se obtuvieron cortes delgados y láminas de acetato. Los cortes fueron escaneados para obtener imágenes de alta resolución, de las cuales, usando un software especialmente diseñado para el estudio de este grupo (Paleotax/Measure), se obtuvieron datos morfométricos en cantidad suficiente para realizar estudios estadísticos. Los resultados
preliminares indican que la fauna de corales de la Formación Agrio consistiría en alrededor de 19 especies pertenecientes a las familias Actinastraeidae, Cladocoridae, Columastraeidae, Leptophyliidae,
Madreporidae y Thamnasteriidae. Los géneros ya identificados incluyen a: Actinastraeopsis Sikharulidze, Ahrdorffia Trauth, Eocolumastrea Löser y Zell, Holocoenia Milne Edwards y Haime, Microphyllia d'Orbigny, Ovalastrea d'Orbigny, Periseris Ferry y Stelidioseris Tomes. Estos nuevos
hallazgos cambian radicalmente el conocimiento de las faunas de corales cretácicos de Argentina al registrar una diversidad mucho mayor a la reconocida previamente. Estos resultados impactarán sobre
los esquemas paleobiogeográficos existentes para el Cretácico de Sudamérica.

Aetostreon pilmatuegrossum sp. nov., a large and very convex ostreid from the Pilmatué Member of the Agrio Formation (Neuqué n Basin, Argentina), is described based on specimens recovered from upper Valanginian beds of the Pseudofavrella angulatiformis and Neocomites sp. ammonite subzones. This work also includes a general morphologic discussion of the well-known Lower Cretaceous oysters from Europe, Asia and Africa, most of them considered synonymous of Aetostreon latissimum (Lamarck) in the last decades. The left valves of these oysters share a set of morphological characters that seems to respond to a very distinct but conservative anatomical pattern inherited from their direct ancestor, instead of evidence for their taxonomic uniformity at the species level. Specifically, they show differences in several characters and/or their degree of development and co-occurrence in a particular growth stage, which probably have systematic value, as in the species here described. Aetostreon pilmatuegrossum sp. nov. is probable closely related to an undescribed lower Valanginian species recorded in the Chachao Formation of the Neuqué n Basin, and also has affinities with an association of Barremian oysters from South Africa that seems to be its direct descendant.

Las rocas del Cretácico Inferior de cuenca Neuquina son excepcionales desde el punto de vista estratigráfico y paleontológico. Los excelentes afloramientos y su abundante contenido fosilífero permiten realizar buenas correlaciones entre localidades y el estudio detallado de las faunas registradas. En el presente trabajo se aborda un estudio interdisciplinario de una sección estratigráfica completa de la Formación Agrio en su localidad tipo, con el objetivo de realizar una zonación bioestratigráfica integrada de amonoideos, bivalvos, nanofósiles calcáreos y palinomorfos. Por primera vez para la unidad se describe y figura una zonación completa de bivalvos compuesta por trigonioideos e inocerámidos. El estratotipo analizado se ubica en las cercanías de la localidad Bajada del Agrio en la zona de confluencia de los ríos Salado y Agrio en el centro de la provincia del Neuquén. Allí se realizó un perfil capa a capa de los miembros Pilmatué y Agua de la Mula. Se identificaron, a lo largo del perfil, 39 niveles portadores de amonoideos y se colectaron un total de 74 muestras de diferentes niveles de lutitas, arcilitas y fangolitas negras y grises para analizar su contenido de palinomorfos y nanofósiles calcáreos. Además se identificaron 41 niveles portadores del género Steinmanella y cuatro niveles portadores de Neocomiceramus curacoensis (Weaver) para establecer la zonación de bivalvos. Como resultado se obtuvo la primera biozonación integrada de amonoideos, bivalvos, nanofósiles calcáreos y palinomorfos para la Formación Agrio abarcando el intervalo Valanginiano tardío-Barremiano temprano. En el Miembro Pilmatué se reconocieron cuatro zonas de amonoideos, ocho subzonas de amonoideos y dos zonas de bivalvos que comprenden el lapso Valanginiano tardío-Hauteriviano temprano. En el Miembro Agua de la Mula se reconocieron cuatro zonas de amonoideos y dos zonas de bivalvos que representan el lapso Hauteriviano tardío-Barremiano basal. Una zona de bivalvos ha quedado sin definir en la Zona de Spitidiscus riccardii debido a la falta de datos taxonómicos. Los grupos fósiles analizados presentan claras afinidades paleobiogeográficas con grupos registrados en el Tethys durante el Cretácico Temprano. Los puntos de correlación más fuertes con la zonación estándar están basados en amonoideos y bioeventos de nanofósiles, mientras que los bivalvos se caracterizan por ser endémicos de la región y por lo tanto de utilidad sólo regional. Los palinomorfos continentales poseen afinidades gondwánicas mientras que los marinos tienen, al igual que los invertebrados, claras afinidades mediterráneas.

Accumulation within the unconformity-based Hauterivian Avilé Sandstone of the Neuquén Basin, Argentina, was characterized by a close interaction between fluvial and aeolian processes developed after a major relative sea-level drop that almost completely desiccated the entire basin and juxtaposed these non-marine deposits on shallow-and deep-marine facies. Aeolian deposits within the Avilé Member include dune (A1) and sand sheet (A2) units that characterize the lower part of the unit. Fluvial deposits comprise distal flood units (F1) interbedded with aeolian dune deposits in the middle part of the succession, and low-(F2) and high-sinuosity (F3) channels associated with floodplain deposits (F4) towards the top. The internal characteristics of the aeolian system indicate that its accumulation was strongly controlled by water-table dynamics, with the development of multiple horizontal deflation super surfaces that truncate dune deposits and form the basal boundary of flood deposits and sand sheet units. A long-term wetting-upward trend is recorded throughout the entire unit, with an increase in fluvial activity towards the top and the development of a more permanent fluvial system overlying a major erosion surface interpreted as a sequence boundary. The upward increase in water-table influence might be related to relative sea-level rise, which controlled the position of the water table and allowed the accumulation of tabular aeolian units bounded by horizontal deflation surfaces. This high-frequency, eustatically driven process acted together with a long-term climatic change towards wetter conditions.

Cretaceous megainvertebrates and their biostratigraphic significance.- A synthesis of the Cretaceous megainvertebrates is presented by stage. This is an update of the information presented in the first version of the Geology and Natural Recourses of Neuquén published in 1978. A brief summary of the Jurassic-Cretaceous boundary is also provided due to the present uncertainties about its definition on biostratigraphic grounds. The text deals with the presence and distribution of several invertebrate groups, both in marine and continental settings. Among them mollusks such as ammonoids, nautiloids, bivalves, gastropods, as well as crinoids and echinoids, cnidarians, bryozoans, annelid polychaetes, sponges and decapod crustaceans. In the Early Cretaceous (Berriasian-Hauterivian) the fossil invertebrate fauna is mostly marine, with abundant nektonic and benthonic forms associated with the Pacific transgression. In the Barremian, the abundance and diversity decrease dramatically and only ...

The Los Chihuidos and El Porvenir deposits of the Neuquén 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 (δ 13 C − 8 to − 3.3‰) and barite (δ 34 S + 4.1‰) with increasing temperature (75–85 °C) from an evolved surface fluid (δ 18 O fluids + 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 δ 18 O − 2.2‰ and δD − 73.7‰), chlorite-smectite mixed-layer minerals (fluid δ 18 O − 6.9‰ and δD − 84‰), pyrite (δ 34 S + 10.2‰), and calcite 2 (δ 13 C − 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 (δ 34 S + 12.3‰) followed by chalcocite-spionkopite (δ 34 S − 64 to + 4.1‰). Calcites 3a (δ 13 C − 19 to − 10.1‰) and 3b (δ 13 C − 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 δ 18 O 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 δ 18 O 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.

evaporites at a depth of 700-900 m. The size of such a process is unusually large onshore (630-810 km 3 ) but mimics the gravity gliding observed in deltas and passive margins. Since this process disconnects zones with a shallow stress field from deeper crustal levels, it could allow extension above a compressive deformation front and should not be interpreted merely as a record of the crustal stress regime. large-scale gravity gliding of the cover down the slope of a structural high could also explain some of the extension observed in mountain hinterlands.

The genus Steinmanella Crickmay is recorded in several Lower Cretaceous marine units of the Neuquén Basin. It is particularly abundant at the transition between the Vaca Muerta and Mulichinco formations. This paper presents a taxonomic revision of this fauna, discusses the stratigraphic range of each species, and describes and interprets the associated lithofacies based on detailed field sections, newly collected specimens and revision of previous fossil collections. Four sections were measured in northern Neuquén comprising the upper beds of the Vaca Muerta Formation and the lower ones of the Mulichinco Formation. The Steinmanella fauna was dated accurately on the basis of a precise ammonoid zonation. The species were found in the Neocomites wichmanni and Lissonia riveroi zones of early Valanginian age. Specimens were collected in situ from dark grey shales, alternating siltstones, wackestones and mudstones, and rudstones. Three species were identified: Steinmanella curacoensis (Weaver), S. quintucoensis (Weaver), and S. subquadrata sp. nov. Steinmanella curacoensis has an oval outline, poor demarcation of carinae, flank and corselet ribs partially intercalated at the median part of the valve, and oval escutcheon. Steinmanella quintucoensis has a furrow below the marginal carina, subrectangular outline, robustly tuberculated flank ribs, and lanceolate escutcheon. Steinmanella subquadrata sp. nov. has a subquadrate outline, well-marked carinae, and oval escutcheon ornamented with thin ribs and small elongated tubercles.

La Formación Vaca Muerta contiene una fauna excepcionalmente rica y variada de invertebrados y vertebrados marinos; sin embargo solamente algunos de estos grupos han sido estudiados desde los trabajos iniciales de Behrendsen (1891). Los trabajos más modernos prestaron particular atención a la fauna de amonites debido al especial interés en los estudios estratigráficos (e.g.

The La Manga Formation constitutes most of the sedimentary record of the Callovian-Oxfordian in the Neuquén Basin. This stratigraphic unit represents the middle part of the Lotena Mesosequence, which is dominated by carbonates with interbedded shales, marls, and occasional sandstones. Based on detailed measured stratigraphic section, the depositional environments and the sea-level history of the La Manga Formation have been interpreted. Petrographic and field observations led to identification of nine facies distributed in two informal units. Unit 1 was deposited on a outer ramp setting, while deposition of the unit 2 took place in intertidal-supratidal environments. A condensed level close to the base of unit 1 has yielded Rehmannia sp., Rehmannia cf. paucicostata (Tornq.) and Homoeoplanulites sp., from the Lower Callovian BONDENBERI-PROXIMUM Zones, and Peltoceratoides sp., and Rursiceras sp., from the Upper Callovian and also in the Lower Oxfordian Peltoceratoides-Parawedekindia Z...

Nerineoid shell beds are described for the first time from Lower Cretaceous deposits of southern South America. These come from carbonates near the top of the Agrio Formation in southern Mendoza Province, west-central Argentina. To envisage the origin of the nerineoid shell beds, a taphonomic study was carried out, which indicated that these represent within-habitat time-averaged, primary sedimentological concentrations with a secondary biogenic imprint related to a relatively high local production of nerineoid shells. The associated palaeoenvironments were studied through a facies analysis of the carbonate succession including the shell beds. The carbonates were deposited in a homoclinal ramp system and depict a shallowing upward trend from mid to inner ramp. The individuals lived and accumulated in oolitic shoals within the inner ramp, in a shallow, well-lit, high-energy setting above fair-weather wave base. Substrate was oxygenated and loose. The nerineoids are shown to belong to one species of the genus Eunerinea, and through the functional morphology of the shells they are tentatively interpreted as infaunal or semi-infaunal. It is suggested that the recorded monospecific nerineoid shell beds indicate that the palaeoenvironmental conditions may have been favourable for the development of abundant populations of these gastropods in the northern part of the Neuquén Basin during a short time interval in the Hauterivian-Barremian boundary. This could have been related to a brief warming episode, but other factors may have also been involved.

Osagids-types oncoids from La Manga Formation and their paleoecological significance, La Vaina Creek, Mendoza. Microbial oncoids have been found in the Oxfordian limestones of the La Manga Formation in the La Vaina section at Potimalal River, Mendoza province. The oncoids ocurr either in packstone or floatstone-rudstone or are scattered in the wackestones. They are mostly elliptical, ameboidal and subordinately spherical

Organic-rich sediments were deposited in the deeper sectors of the Neuquén Basin during the latest Jurassic and the Early Cretaceous. This paper presents the results of a detailed examination of these deposits in the northern-most extension of the basin, in the Mendoza Province, and explores their wider significance for palaeo-oxygenation studies.

Penecontemporaneous decimetre-scale soft-sediment deformation structures are reported from the basal part of the Upper Jurassic-Lower Cretaceous Vaca Muerta Formation, in the Malargüe-Las Leñas area of the back-arc Neuquén Basin (Mendoza Province, Central Andes). The deformed interval (Amarillas bed) is only 0.3 to 0.9 m thick but occurs in a wide area, larger than 1500 km 2 . Its age, determined by ammonite biostratigraphy, is Early Tithonian. The soft-sediment deformation structures were generated in finely laminated, partially consolidated, organicrich, carbonate microbialites that were deposited in open-marine, poorly oxygenated settings, apparently devoid of any significant slope. Those structures include boudins of different sizes and complexity, a variety of folds, normal (listric) dm-scale faults, sub-horizontal detachment surfaces and other features, which are part of several larger-scale, complex slump structures. Deformation was dominantly plastic but near to the ductile-brittle field transition. On the basis of the observed soft-deformation structures, their geographic distribution, their lateral homogeneity, and the geodynamic framework of the basin in which it was generated, the Amarillas bed can be tentatively attributed to a large, intermediate-depth earthquake that occurred within the plate that subducted beneath the Andean continental margin and the Neuquén back-arc basin.

The lithofacies and macrofossil guilds of the Agrio Formation (Upper Valanginian -Lower Barremian) have been analysed using evidence from sedimentological, taphonomic and palaeoecological studies. The study area is Agua de la Mula and adjacent regions in central Neuquén. Seven lithofacies have been recognized in the field, which indicate that the Agrio Formation was deposited in an open-marine, ramp depositional system under storm influence. Lithofacies indicate conditions that range from low-energy basin to high-energy inner ramp. Outer and mid-ramp deposits are the most abundant. Macrofossils have been grouped into 16 guilds based on tiering, life habit and feeding category. The guilds indicate normal benthic oxygen level, normal salinity, and soft -firm muddy and sandy bottoms. Suspension-feeders are more common than deposit-feeders suggesting the predominance of suspended food particles over deposited food resources. A low input of siliciclastics and, possibly, other palaeoceanographic conditions allowed the development of oolitic facies in the inner ramp and coral patch reefs in the upper mid-ramp for a limited period of time.