Neuquen Basin Research Articles

Ontogeny and autecology of an Early Cretaceous trigoniide bivalve from Neuquén Basin, Argentina

Understanding ontogenetic variation is fundamental for adequate species definition and is the key for recognizing evolutionary relevant processes like heterochrony or developmental constraints. The larval and post-larval shell ontogeny and the ecology of the trigoniide bivalve Myophorella garatei are described in this paper. The species occurs in offshore transition facies of the late Valanginian Pilmatue Member of the Agrio Formation in the Neuquen Basin, Argentina. The larval shell has a rather small prodissoconch I; and if prodissoconch II is present, it is rather weakly developed. From these data, a larval stage of low dispersal capability is inferred for Myophorella garatei, either short-lived planktotrophic or nonplanktotrophic. The study of post-larval development included general shell shape and ornamentation. To assess general shell shape a geometric morphometric analysis was performed on the lateral view, together with a study of allometry for the shell width. As a result, two main allometric st...

Porosity evolution and crystallization-driven fragmentation during weathering of andesite

[1] A 10 m thick andesitic sill intrusion from the Neuquen Basin, Argentina, shows spectacular examples of spheroidal weathering and Liesegang banding. The Liesegang patterns demonstrate how andesite blocks, initially cut out by a preweathering joint set, are subdivided by fractures formed during the spheroidal weathering process. The stresses that cause fracturing originate from the growth of ferrihydrite and calcite in the pore space of the andesite, partly at the expense of original ilmenite, amphibole, and plagioclase. The porosity evolution and fracture formation during progressive weathering was characterized by scanning electron microscopy studies, X-ray computed tomography, and He- and Hg-porosimetry. Fresh andesite has a porosity of approximately 8%, and a major fraction (>80%) of the pore volume is composed of pores less than 10 μm in diameter. The extent of pore filling during weathering increases with pore size. Pores more than 100 μm are almost completely filled by an intimate intergrowth of calcite and ferrihydrite, whereas pores less than 10 μm are filled less than 50%. The fracturing associated with spheroidal weathering is caused by mineral growth in the largest pores, which account for 10%–20% of the total porosity. The periodic precipitation of the weathering product to form Liesegang bands indicates a significant supersaturation threshold before nucleation commences. The increase in the weathering product growth rate with increasing size is therefore most likely due to higher nucleation probabilities in larger pores.

Ostrácodos (Crustacea) de la Formación Allen (Cretácico Tardío), Cuenca Neuquina, Argentina

A new microfossil association was found in the Allen Formation at Loma Puntuda (Neuquen Basin, Rio Negro Province, Argentina). It is represented by scarce charophyta and numerous carapaces and valves of ostracods from the families Ilyocyprididae (such as Ilyocypris riograndensis and several species of Neuquenocypris) and Limnocytheridae (with the species Wolburgiopsis neocretacea and Vecticypris sp.). Molluscs, fragments of dinosaur eggshells and a plesiosaur remains had been registered previously in the same profile. This kind of association of non marine with a few marine fauna seems to indicate that the Allen Formation at Loma Puntuda was deposited in a shallow, fresh to oligohaline water body, near the coast. © 2011 by the Sociedade Brasileira de Paleontologia.

Technology Focus: Formation Evaluation (August 2011)

Technology Focus Reportedly, companies are struggling to find petrophysicists for their subsurface teams, especially companies exploiting unconventional resources that require a major petrophysical effort to unlock their reserves potential. How has this state of affairs come about? Undoubtedly, there are fewer routes into the discipline because few universities offer degrees in the subject. Most petrophysicists either have a logging-company background or are professionals from other disciplines who developed a taste for it. Yet, there are more-deep-seated issues at play, concerning the nature of the job itself and how petrophysicists are perceived in the industry. Practitioners must spend considerable time performing the less-glamorous tasks of gathering, checking, loading, merging, shifting, and correcting raw data before any analysis can be performed. This may discourage professionals from joining the discipline before they can appreciate its richness. Some petrophysicists feel undervalued. Their main workload comes early in a project and ends when they pass their well/rock-property data to the geomodelers. By servicing several teams, particularly in operational environments, they end up belonging to none and feeling isolated. Some suspect that other disciplines offer greater career mobility, with increased chances of fast tracking into management. In reality, the role has a unique multitasking and technically challenging nature, with a blend of fundamental science and applied practices in which reservoir studies are interjected with designing laboratory core-analysis programs and monitoring wellsite operations. Thus, it seems that a make-over is required to enhance the petrophysicist’s image, standing, and popularity. To address the reported shortage, the role must be broadened to attract and retain high-caliber people. Newcomers must be taught integrated working practices instead of how to push buttons of sophisticated software that provides analysis products of which they have little understanding. Quality-focused training from academia and the industry is essential to achieve this aim. For their own part, petrophysicists must contribute more than porosity, saturation, net-reservoir, and permeability data. They must step into the limelight and be acknowledged by peers for their help and advice in all areas of established subsurface workflows, while providing input throughout a project’s life. Petrophysicists perform a complex and onerous role, synthesizing multifarious data into a single coherent interpretation. Their work impinges on every discipline, providing deliverables for drillers, geologists, geophysicists, reservoir simulators, and production engineers. We need more of these valuable people. Formation Evaluation additional reading available at OnePetro: www.onepetro.org SPE 137766 • “Barnett Shale (Mississippian), Fort Worth Basin, Texas: Regional Variations in Gas and Oil Production and Reservoir Properties” by Y. Tian, SPE, Texas A&M University, et al. SPE 134515 • “Novel Approach To Quantifying Deepwater Laminated Sequences Using Integrated Evaluation of LWD, Real-Time Shear, Porosity, Azimuthal Density, and High-Resolution-Propagation Resistivity” by Katerina Yared, SPE, Baker Hughes, et al. SPE 121313 • “Petrophysical-Analysis Method To Identify ‘Sweet Spots’ in Tight Reservoirs: Case Study From Punta Rosada Formation in Neuquen Basin, Argentina” by C. Naides, Petrobras.

An exceptional storm accumulation of nautilids in the Lower Cretaceous of the Neuquén Basin, Argentina

Cichowolski, M., Pazos, P.J., Tunik, M.A. & Aguirre-Urreta, M.B. 2011: An exceptional storm accumulation of nautilids in the Lower Cretaceous of the Neuquen Basin, Argentina. Lethaia, Vol. 45, pp. 121–138. An exceptional accumulation of nautilid shells of the species Cymatoceras perstriatum (Steuer) is reported and described in the Lower Cretaceous Agrio Formation of the Neuquen Basin (west-central Argentina). The bed represents a storm deposit in a shallow-water environment within the mid-ramp. The evidences of a storm-related origin of the bed come from the petrographic analysis and taphonomic features of the shells, specially the sedimentary infill pattern. The shells are dispersed in patches within the stratum, without any orientation relative to the bedding plane. It is proposed that the shells were floating after the death of the animals, although most of them have an almost complete living chamber. The presence of some heavily encrusted shells suggests that there is a mixing of specimens with different drift times. A variety of factors related to the origin of such high number of nautilid shells are discussed, including a transgressive stand system tract, the possible existence of a gregarious behaviour, changes in salinity and wind directions. □Lower Cretaceous, Nautilids, Neuquen Basin, shell accumulation, storm deposit.

Un nuevo Mesoeucrocodylia cretácico del norte de la Cuenca Neuquina, Argentina

A NEW CRETACEOUS MESOEUCROCODYLIA FROM THE NORTH OF THE NEUQUEN BASIN, ARGENTINA. In this contribution, a new specimen of Mesoeucrocodylia from levels attributed to the Plottier Formation (Cretaceous, Upper Coniacian) is described in the locality Yacimiento Narambuena, Rincon de los Sauces, in the north section of the Neuquen Province. The material includes an incomplete subadult specimen with mostly articulated postcranium of an approximate length of 60 cm. The study and comparisons to allow distinguish the specimen from other Mesoeucrocodylia previously known from this same basin and suggest the presence of a new taxon, increasing the diversity of this clade in this period in the Neuquen Basin. The specimen from Rincon de los Sauces presents postcraneal characters previously attributed to Notosuchia and Neosuchia, both clades mainly defined by cranial characters. This set of primitive and derived characters prevents the location of its precise phylogenetic position among the Mesoeucrocodylia.

U/Pb ages on detrital zircons in the southern central Andes Neogene foreland (36°–37°S): Constraints on Andean exhumation

Abstract U/Pb dating on detrital zircons was performed in the Pampa de Carrizalito depocenter of the Late Miocene foreland basin associated with the Southern Central Andes orogenic front. This reveals Andean and pre-Andean components in magmatic derived zircons inhomogeneously distributed through the sequence. Andean, Grenville, Pampean, Famatinian and Gondwanic components reveal a complex source distribution from either the Main Andes, Coastal Cordillera and basement foreland areas. These are discussed showing different patterns in the context of the Andean orogenic cycle. Cretaceous and Jurassic components that are partly related to Mesozoic batholiths, developed at the western slope of the Andes at these latitudes, have a very contrasting behavior through the sequence: While Jurassic grains are represented from base to top, Cretaceous ones dilute upwardly. This is explained through the progressive uplift of the Southern Central Andes that could have created a barrier to Cretaceous and Jurassic detritus, while the older ones could have had either an alternative source area represented by the inverted rift system of the Huincul Ridge in the foreland area and the Cordillera del Viento in the hinterland area or the reworking of Jurassic sedimentary sequences of the Neuquen basin. Finally, a progressive enrichment in pre-Andean components to the top of the sequence is interpreted as related to the development of a broken foreland and the consequent rapid expansion of the orogenic front at the time of development of a slab shallowing setting in the region as shown by previous works.

Toarcian–Aalenian (Early–Middle Jurassic) radiolarian fauna from the Los Molles Formation, Neuquén Basin, Argentina: Taxonomy and paleobiogeographic affinities

Abstract This paper reports the occurrence of a Toarcian–Aalenian (Early–Middle Jurassic) radiolarian fauna in the Los Molles Formation, Neuquen Basin, Argentina, as well as comments on its paleobiogeographic affinities. The micropaleontologic analysis was carried out in fine-grained rocks from a turbiditic section of the Los Molles Formation. These samples were first chemically processed using only hydrogen peroxide (H 2 O 2 ), and afterward treated with acetic (CH 3 COOH) and hydrofluoric (HF) acids. The first chemical procedure permitted the recovery of only few spongy spumellarians, while the second one enabled to recover more diversified radiolarian assemblages. In general, the studied fauna presents low diversity and abundance, with a strong dominance of spumellarians over nassellarians. The fauna is composed by the genera Paronaella , Homoeoparonaella , Praeconocaryomma , Archaeocenosphaera , Orbiculiformella , Praeparvicingula , and some unidentified spumellarians and nassellarians. According to paleobiogeographic models, the studied Toarcian–Aalenian fauna presents a mid to high latitude affinity. It is possible to infer from those data a bipolar distribution of some taxa, such as Praeparvicingula and probably Praeconocaryomma , between the Northern and Southern hemispheres since the Early Jurassic (Toarcian).

Fault framework and kinematic evolution of inversion structures: Natural examples from the Neuquén Basin, Argentina

Mesozoic tectonic inversion in the Neuquen Basin of west-central Argentina was investigated by analyzing a three-dimensional seismic and borehole data set over prominent inversion structures related to transpressional tectonics along the Huincul arch. This conspicuous strike-slip deformation has been active since the Early Jurassic to Early Cretaceous and caused the reactivation of normal faults and the inversion of Triassic half grabens, some of which are imaged by the seismic data. Detailed structural and stratigraphic mapping allowed the identification of two main fault systems associated with inversion structures: (1) deep faults that affected basement and synrift strata where preexisting faults were selectively reactivated during inversion based on their length and (2) shallow faults that affected postrift and syninversion strata. Normal faults formed at high angle to the reactivated half-graben bounding fault as a result of hanging-wall expansion and internal deformation as it accommodated the shape of the curved footwall during oblique inversion. Structural restorations suggest that contraction during inversion was initially accommodated by folding and internal deformation of synrift sedimentary wedges, followed by displacement along half-graben bounding faults. We suspect that during late inversion, the weight of the overburden inhibited additional fault displacement and folding became the main shortening-accommodating mechanism. Natural examples described in this study exhibit significant along-strike variation in structural style and high structural complexity associated with relatively small amounts of inversion, which suggest the need for incorporating more complex deformation scenarios into analog models. Fault framework development and its linkage to a specific mechanism (e.g., hanging-wall deformation because of oblique inversion) enables the predictive analysis of subseismic faulting and fracture distribution, which can impact our understanding of the petroleum systems in the Neuquen Basin's northern embayment, especially regarding the significant fault development within the Cuyo Group, which may impact the Los Molles petroleum system.

New crustacean microcoprolites from the Lower Cretaceous (middle Berriasian–lower Valanginian) of the Neuquén Basin, Southern Mendoza, Argentina

Three new ichnotaxa of crustacean microcoprolites from the Neuquen 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 Neuquen 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.

Frequency content versus area coverage of 3D seismic, a key consideration for exploration and development of a shallow stratigraphic heavy oil trend in Neuquen Basin, Argentina

Exploring for shallow targets onshore normally involves low drilling cost but higher seismic cost to illuminate objectives with desired resolution. However, in underexplored acreage, the area covered by 3D seismic becomes an issue and should be balanced against the resolution needed to identify drillable prospects. If the play concepts are not well understood, exploration expenditures should be focused on wide 3D seismic acquisition and on cheap exploration drilling. If an economic discovery occurs, more sophisticated seismic acquisition could focus on the discovered reservoir. A “focused on target” acquisition might increase cost and limit the area extent.

Kinematic analysis of a transtensional fault system: The Atuel depocenter of the Neuquén basin, southern Central Andes, Argentina

Abstract The Atuel depocenter of the Neuquen basin originated as an Upper Triassic to Lower Jurassic rift system, later inverted during the Andean contractional deformation. In order to study the extensional architecture and the kinematic evolution of this depocenter, we collected a large amount of field and sub-surface data, consisting of slip data from outcrop-scale normal faults, thickness and facies distribution within the synrift deposits, and structural data from angular and progressive unconformities. The Atuel depocenter has a NNW trend, showing a bimodal distribution of NNW and WNW major faults (first and second order faults). On the other hand, from kinematic indicators measured on outcrop-scale faults (third and fourth order faults), we found a mean NE internal extension direction, which is oblique to the general trend of the sub-basin. Taking these particular characteristics into account, we interpreted the Atuel depocenter as an oblique rift system. We evaluated two mechanisms in order to explain the development of this transtensional system: 1) reactivation of upper-crustal NNW-oriented Paleozoic shear zones, and 2) oblique stretching of a previous NNW-oriented lithospheric weakness zone.

Modeling an atypical petroleum system: A case study of hydrocarbon generation, migration and accumulation related to igneous intrusions in the Neuquen Basin, Argentina

In the Altiplanicie del Payún area (Neuquen Basin, Argentina), immature source rock sections intruded by up to 600 m thick Tertiary laccoliths show full spectrum maturity aureoles over hundreds of meters from the contacts. Commercial oil accumulations (20–33°API) and oil shows are located along the entire column, both in sandstone/carbonate and fractured igneous reservoirs. A challenging numerical model that included the emplacement of the intrusive bodies, with extreme temperature ranges and unusually short calculation time steps, has been done with the aim to better understand hydrocarbon generation and migration processes related to these thermal anomalies. A 2D petroleum system model achieved satisfactory results when accounting for thermal maturation, oil and gas generation, composition, migration, and known accumulations. This atypical petroleum system is characterized by thermal anomalies lasting thousands of years that are the result of the progressive cooling of the igneous intrusions. Host source rocks were exposed to a wide range of temperatures that varied in time and space generating different maturity products. High generation pressures, source rock fracturation, and convective water flows facilitated migration and mixing of hydrocarbons and the charge of the igneous bodies as they were fractured during thermal contraction. Oil and source rock analyses were done in order to calibrate and support modeling results. Geochemical correlations suggest an in situ generation related to the igneous intrusions. In particular, diamondoids' measurements show mixing processes of high-mature (cracked) with low-mature hydrocarbons. Oils generated and cracked close to the laccoliths and oils generated from more distant source rock sections, less affected by the thermal anomalies, were probably mixed as they migrated towards the igneous bodies and shallower reservoirs. The integration of a wide set of geochemical analyses and recent modeling techniques based upon time and temperature calculation performance enhancements, led to novel insights on this atypical petroleum system.

Short Note: Second Jurassic marine reptile from the Antarctic Peninsula

Except for the rich record from the Neuquen Basin (e.g. Gasparini & Fernández 2006), Jurassic southern Gondwanan marine reptiles are relatively rare. A tooth discovered in the Bean Peaks, Ellsworth Land, Antarctic Peninsula (Fig. 1) represents the southernmost, and only the second record of Jurassic marine reptiles from the Antarctic Peninsula. Comprising a single, incomplete tooth, the specimen is unable to be assigned to a species, but the paucity of Gondwanan Jurassic marine reptile material means this find adds significant palaeobiogeographical information.

Depositional environments and hydrocarbon potential of the Middle Jurassic Los Molles Formation, Neuquén Basin, Argentina: palynofacies and organic geochemical data

A multidisciplinary analysis of palynofacies in a sequence-stratigraphical framework, TOC (total organic carbon) and TAI (thermal alteration index) analyses, has been applied to outcrop samples of the uppermost Los Molles Formation (Middle Jurassic), Neuquen Basin, Argentina, in order to characterise the palaeoenvironmental and palaeo-climatic conditions during the deposition of this unit. Five types of palynofacies (P-l to P-5) have been identified and are interpreted to indicate a restricted marine to inner neritic environment. In P-1 and P-4, a marine environment close to the terrestrial source area with moderate oxidizing conditions and energy, is suggested. In P-2, the assemblage of freshwater algae, acritarchs and prasinophytes suggest a marginal marine environment influenced by fluvial discharge. In P-3, the marine microplankton content reflects conditions ranging from a marginal-marine (sub-normal salinity) to an inner neritic environment. In P-5, a dysoxic marine environment (probably marginal) is suggested. Warm and relatively humid (abundance of Cheirolepidiaceae in association withAraucariaceae) and locally humid (presence of swamps or ponds, on the alluvial plains) conditions are inferred. TOC content (65% of the analyzed samples reach TOC values over 1%), TAI values (2 to 2+, transitional between an immature phase and the window of liquid petroleum generation) and kerogen type (P-1, P-2 and P-5 show transitional characteristics between kerogen type II and III, while P-3 and P-4 show characteristics of kerogen type III and occasionally type IV), suggest that, in the studied area, the Los Molles Formation has some hydrocarbon potential. However, kerogen state suggests that the anoxic-dysoxic conditions of the site of deposition were not optimum for its preservation.

Facies de patch reefs en la Formación Picún Leufú (límite Jurásico/Cretácico) en la región de Zapala, Cuenca Neuquina

Patch reefs facies in the Picun Leufu Formation (Jurassic/Cretaceous boundary) in the Zapala region, Neuquen Basin, Argentina. In the locality of Cerrito Caracoles, situated in the nearby of Zapala city, in the western central region of the Neuquen province, Argentina, the basal part of the Picun Leufu Formation (Jurassic/Cretaceous boundary) crops out. The facies and microfacies association analysis points out to an inner shelf margin environment, with development of well preserved patch reefs. The description of these bodies (coral and algae bafflestone, bryozoan bafflestone and algal boundstone), and of a low relief mound reef (skeletal algal packstone) are presented in this paper. The associated facies are represented by low energy deposits (mudstone), bar complexes (sandy skeletal packstone and skeletal packstone) and channels (skeletal intraclast floatstone and intraclast skeletal ooidal floatstone).

REDESCRIPTION AND PHYLOGENETIC POSITION OF CAYPULLISAURUS (ICHTHYOSAURIA: OPHTHALMOSAURIDAE)

Abstract The ophthalmosaurid Caypullisaurus from the Late Jurassic–Early Cretaceous of the Neuquen Basin, Argentina, is redescribed based on new information from recent discoveries. Cladistic analysis of Caypullisaurus, based on previous ichthyopterygian data sets and using NONA, yielded two most parsimonious trees. Two clades are recognized within the Ophthalmosauridae. Caypullisaurus is found to be nested with Brachypterygius and Platypterygius. Simultaneous, unconstrained analysis, using unambiguous character optimization, is suggested as the best way to analyze data sets with large amounts of missing data.

Faunal evidence for reduced productivity and uncoordinated recovery in Southern Hemisphere Cretaceous-Paleogene boundary sections

The mass extinction at the Cretaceous-Paleogene boundary is generally explained by a severe crisis in primary productivity, following a catastrophic bolide impact. Consistent with this scenario, Danian mollusk-dominated benthic shelf ecosystems of southern middle paleolatitudes (Neuquen Basin, Argentina) are characterized by (1) a stratigraphically limited low in macrofossil abundances; (2) an increase in starvation-resistant, nonplanktotrophic deposit feeders and chemosymbionts; (3) a reduction in the average body size of individuals; and (4) individuals with inactive lifestyles being more common than in the late Maastrichtian. Return to pre-extinction conditions of the various synecological attributes occurred over unequal time spans, indicating that recovery was uncoordinated with respect to ecological traits. Global comparison of ecological patterns suggests that reduced food supply (1) was a controlling factor in both hemispheres; (2) affected macrobenthic marine faunas at various distances from the Chicxulub impact site; and (3) was more effective in siliciclastic environments as compared to oligotrophic carbonate settings.

Estratigrafía de 'sin-rift' (Triásico Superior-Jurásico Inferior) de la Cuenca Neuquina en la sierra de Chacaico, Neuquén, Argentina

La sierra de Chacaico (Neuquen, Argentina) constituye una de las localidades mas importantes para el analisis de la estratigrafia y relaciones espaciales del relleno inicial de la Cuenca Neuquina. Por medio de estudios estructurales y sedimentologicos de campo ha sido posible distinguir la naturaleza volcano-sedimentaria de la secuencia de sin-rift asi como su evolucion estratigrafica durante el periodo extensional Triasico Superior-Jurasico Inferior. La sucesion de sin-rift puede subdividirse en tres etapas evolutivas. La parte inicial esta integrada por volcanitas basicas a intermedias y depositos sedimentarios volcanoclasticos, mayormente gruesos. La seccion media se halla dominada por depositos piroclasticos primarios y reelaborados y finaliza con delgadas secuencias carbonaticas lacustres. En el techo de esa seccion aparecen localmente lavas basalticas. La seccion superior consiste de una asociacion de depositos clasticos gruesos (conglomerados y brechas) y piroclasticos primarios de caida y de flujo. Toda el area estudiada conformo un unico depocentro de sin-rift cuyos margenes estaban orientados en direccion E-W a ENE-WSW. El borde sur funciono como la estructura de fallamiento normal mas importante, hacia la cual los espesores de la secuencia fueron maximos. El depocentro fue invertido tectonicamente de manera compleja, con generacion de anticlinales asociados a fallas normales invertidas. Algunas de esas estructuras anticlinales reflejan la existencia de escalones estructurales internos dentro del depocentro, asociados a antiguas fallas normales oblicuas de orientacion noreste. El patron estratigrafico y estructural de la secuencia de sin-rift es comparable al de la dorsal de Huincul, uno de los rasgos morfoestructurales mas prominentes en la evolucion del sector sur de la Cuenca Neuquina.

Estratigrafia de 'sin-rift' (Triasico Superior-Jurasico Inferior) de la Cuenca Neuquina en la sierra de Chacaico, Neuquen, Argentina.

Syn-rift stratigraphy (Upper Triassic-Lower Jurassic) of the Neuquen Basin at the Sierra de Chacaico, Neuquen, Argentina. The sierra de Chacaico (Neuquen, Argentina) is one of the most important localities to study the Upper Triassic-Lower Jurassic syn-rift sequence of the Neuquen Basin. Structural and sedimentological analyses have been carried out in order to depict the stratigraphic evolution of the infill. The syn-rift sequence evolved in a volcano