Neuquen Group Research Articles

Unexpected new lizard from the Late Cretaceous of southern South America sheds light on Gondwanan squamate diversity

The record of Cretaceous terrestrial lizards (Squamata) in South America is patchy, with seven species described from north-eastern and south-eastern Brazil, and few isolated records of iguanians and scincomorphans from the Argentinian Patagonia. Herein we describe a new genus and species of Cretaceous lizard, Paleochelco occultato gen. et sp. nov., based on a partial skull (MACN-Pv-N 120) discovered about three decades ago that was unnoticed in the Coleccion Paleovertebrados of the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”. It comes from rocks of the Upper Cretaceous Bajo de la Carpa Formation (Neuquen Group) exposed at the Campus of the Universidad Nacional del Comahue, north of Neuquen City (Neuquen Province). The new taxon was included into a broad phylogenetic dataset of squamates and it was recovered around the base of Polyglyphanodontia in a constrained analysis using a total-evidence backbone. By contrast, the same, but topologically unconstrained analysis found Paleochelco occultato also around the base of Polyglyphanodontia but alternatively as the sister taxon to Polyglyphanodontia + Scleroglossa or as one of the sister taxa to the Mosasauria + Scleroglossa clade. The new finding, as well as other records from Argentina and Brazil, highlights a complex, still unrecovered, evolutionary history for lizards in the Mesozoic of South America.

A New Peirosaurid (Crocodyliformes, Mesoeucrocodylia) from the Upper Cretaceous of Patagonia, Argentina

Abstract. Peirosaurids are a group of Cretaceous continental crocodyliforms from Gondwana. Two species are known from the Neuquen Group in Argentina: Lomasuchus palpebrosus (Portezuelo Formation, late Turonian—early Coniacian) and Gasparinisuchus peirosauroides (Bajo de la Carpa and Anacleto formations, Santonian and early Campanian, respectively). Here, we describe the first peirosaurid from the Cerro Lisandro Formation, Bayomesasuchus hernandezi gen. et sp. nov. The material corresponds to a fragmentary skull and mandible. Although fragmentary, this is the most complete crocodyliform specimen recorded for the Cerro Lisandro Formation. In a phylogenetic analysis Bayomesasuchus is depicted in a polytomy together with South American peirosaurids and the African form Hamadasuchus rebouli.

Estratigrafia y sedimentologia del abanico terminal de la Formacion Candeleros (Grupo Neuquen), Cretácico Inferior, Cuenca Neuquina, provincias de Neuquen y Mendoza, Argentina.

The Candeleros Formation is represented by a succession of deposits that represent terminal fans starting to fill a foreland basin (back-arc) during the Albian. The different sub-environments of the terminal fan suggest low gradients during the onset of deposition of the Rio Limay Subgroup (Neuquen Group). The terminal fan system is represented by distributary zone (TF-DZ), distributary zone-base zone (TF-DZBZ) and base zone deposits (TF-BZ). Its most notable feature is the presence of bitumen in “pockets” and scattered in the sandstone channel fill and crevasse splays deposit. In this system the feeder zone of the terminal fan system has not been identified, however, the distribution of architectural elements and paleocurrent data allow us to infer that the catchment area of the backbone would have been located to the NNW/NW. Distributary zone deposits are characterized by thick deposits of low sinuosity channel, with a high degree of connectivity and strong vertical aggradation of channel belts. Deposits of distributary zone-base zone are characterized by a higher density of channel deposits/distributary plain, but with belt channel less thick, longer laterally, greater width/thickness ratio and connectivity in the braided deposits. The distal parts of the terminal fan are well represented and vary only in the channelized deposits and mantle/floodplain ratio, which is abruptly reduced towards the flood basin connection. The importance of Candeleros Formation deposits is that they are remnants of accommodation that preserved the original architecture and represent exhumed reservoirs.

Mineral reactions associated with hydrocarbon paleomigration in the Huincul High, Neuquén Basin, Argentina

Bleaching of red beds by the migration of reducing pore fluids is a widespread phenomenon, with most previous work on the topic focused on detailed studies in the southwestern United States, and to a lesser extent Germany. Herein, we report on widespread bleaching of Cretaceous red beds in the Neuquen Basin and the relationship of this bleaching to hydrocarbon migration. In the Cerro Granito area of the Huincul High, Neuquen Basin, the basal deposits of the Neuquen Group (Candeleros and Huincul Formations) are bleached. This alteration was apparently controlled by fluid and host-rock composition as well as by the intensity and span of the fluid-rock interaction. Red, fine-grained sandstones and mudstones of the Candeleros Formation were deposited in fluvial and swamp environments and contain authigenic hematite, Na-rich corrensite, micro- and mesoquartz, calcite, and analcite. Coarse-grained sandstones and mudstones of the Huincul Formation, which overlie the Candeleros Formation, were deposited in a braided fluvial system, under more humid and acidic conditions than the Candeleros Formation. Sandstones are similar in composition and texture to the Candeleros sandstones, except they contain less basic volcanic detritus and lack corrensite. Bleached facies in both formations contain bitumen and clusters of calcite + bitumen concretions, and partially dissolved detrital clasts and most cements, including early Fe-oxides, which resulted in an increase in secondary porosity and bleaching of the red beds. Alteration of the Candeleros Formation is confined to medium- to coarse-grained sandstone in which corrensite is partially dissolved and its interlayer charge is satisfied by Ca instead of Na, as in corrensite from the red sandstones. Extensive dissolution occurred in the Huincul Formation, which favored the precipitation of new authigenic minerals such as smectite, mixed-layer chlorite-smectite, and pyrite. Bleaching and associated alteration most likely resulted from interaction of hydrocarbons with the red beds. Hydrocarbon paleomigration in the Cerro Granito area occurred in higher-permeability portions of the Candeleros and Huincul Formations. The seal provided by the Lisandro Formation was breached during uplift driven by Tertiary tectonism, resulting in the exhumation of the Huincul and Candeleros Formations. This study highlights the importance of a variety of alterations, including complex clay mineral paragenesis, contemporaneous with bleaching of the red beds. Such alterations can potentially be used to provide evidence for the passage of chemically reducing fluids associated with hydrocarbons in other regions, including cases where the original red color has been completely removed.

Mineralogical signature of hydrocarbon circulation in Cretaceous red beds of the Barda Gonzalez area, Neuquen Basin, Argentina

The Portezuelo Formation is part of a red bed sequence in the Neuquen Basin assigned to the Neuquen Group (lower Cenomanian–middle Campanian). In outcrops of the Portezuelo Formation in the Barda Gonzalez region, iron oxide and hydroxide cements are only preserved in the less permeable claystone layers. Paleomigration of hydrocarbons and formation waters along the most permeable layers bleached the rocks due to partial to total dissolution of cements and grains and formation of several authigenic minerals: (1) montmorillonite and pyrite in the medium- to fine-grained sandstones and mudstones, and (2) multistage calcite and pyrite in the coarse-grained sandstones and conglomerates. The (Canyon Diablo troilite) of −24.4 to −60‰ values in pyrite point to microbial reduction of a sulfate precursor. The oxidation of hydrocarbons and fluctuations in pH and carbon dioxide pressure caused by organic acids resulted in multiple stages of dissolution and precipitation of calcite. Calcite crystals host hydrocarbon-bearing fluid inclusions (± pyrite) with variable fluorescence color, indicating that hydrocarbon composition changed with time. The intermediate (Peedee belemnite) (−8.11‰ to −8.52‰) and (−9.76 to −9.83‰) isotope composition of calcites may have resulted from mixtures of -rich after the dissolution of local calcrete with -poor from oxidizing hydrocarbons. This contribution provides for the first time key information to predict the distribution of authigenic minerals in reservoir rocks in the basin and improves understanding of the diagenetic history of the Portezuelo Formation.

Large-Scale Bleaching of Red Beds Related To Upward Migration of Hydrocarbons: Los Chihuidos High, Neuquen Basin, Argentina

Abstract The striking arrangement of colorful facies in the sandstones outcrops of the Los Chihuidos high, Argentina, has been attributed to the surface expression of hydrocarbon-induced alteration. The Huincul Formation (late Cenomanian–early Turonian) is part of the thick continental red-bed-dominated Neuquen Group, which consists of meandering fluvial deposits developed in a foreland basin. Visual distinctions reveal four diagenetic facies: red, white, gray, and minor brown sandstones. Differences in the diagenetic mineralogy among sandstones facies are interpreted to depend on the degree of interaction with hydrocarbon-bearing solutions and the relative position of the redox roll front developed during this process. The red facies represents the original oxidized sandstone, with hematite, kaolinite, quartz and albite overgrowths, and calcite cement precipitated under oxidizing conditions during the regional burial diagenesis. The white facies formed during the interaction of red beds with reduced fluids (in presence of hydrocarbons or organic acids), where clasts and cement were partially dissolved, and iron was reduced to Fe2+ due to redox reactions and removed, resulting in the sandstone decoloration and in a marked development of the secondary porosity. Minor montmorillonite replaced kaolinite and detrital feldspars, and a poikilotopic calcite precipitated, filling the pores. The gray and the brown sandstone bound the redox front, which is characterized by the presence of abundant clay minerals and oxide minerals enriched in vanadium and copper. Montmorillonite and secondary hematite are dominant in the more oxidized gray sandstones whereas interstratified chlorite–montmorillonite is more abundant in the more reduced brown sandstones. The coexistence of these minerals indicates metastable reducing–oxidizing conditions at the redox front. Based on diagenetic characteristics, tectonic framework, maturation timing of source rocks, and petroleum-emplacement history, hydrocarbons could have migrated into the Huincul Formation during the Tertiary uplift, but later erosion could have released the hydrocarbons and exhumed the reservoir. This multi-scale investigation of diagenetic features related to burial history and to structure-controlled upflow of hydrocarbons in a succession of siliciclastic rocks enhances modeling of a regional-scale redox system worldwide. Our study offers new insight into the application of authigenic minerals to trace hydrocarbon pathways along red beds and to evaluate the reservoir quality, in the understanding the importance of fluid compositions, mixing, and fluid–rock interaction along a major redox system.

Paleotropical pollen grains from the Neuquén Group, Patagonia, Argentina

This paper discusses the presence of elater-bearing pollen grains and other characteristic paleotropical palynomorphs in the mid to Late Cretaceous Neuquen Group at the El Zampal locality, south of Mendoza Province, Argentina. The elaterates characterize the equatorial paleofloristic province in the Albian-Cenomanian. The species Elateroplicites africaensis is present in the pollen assemblage recovered from the lower section of the Huincul Formation, a basal unit of the studied Neuquen Group. It represents the first record of elater-bearing pollen grains in Argentina and marks their southernmost extension. Other conspicuous paleotropical elements recorded in different lithostratigraphic units of the Neuquen Group include gymnospermous polyplicate pollen grains and angiosperm pollen, including two species of the periporate pollen genus Cretacaeiporites and the triporate pollen species Confossia vulgaris. The paleobiogeographic and biostratigraphic significance of the paleotropical sporomorph record in the Cretaceous palynofloras of the Neuquen Group at El Zampal is herein discussed.

Registro de un dinosaurio Aeolosaurini (Sauropoda, Titanosauria) en el Cretácico Superior (Formación Plottier) del norte de la Provincia de Neuquén, Argentina, y comentarios sobre los Aeolosaurini sudamericanos

RECORD OF AN AEOLOSAURINI DINOSAUR (SAUROPODA, TITANOSAURIA) IN THE UPPER CRETACEOUS (PLOTTIER FORMATION) OF NORTHERN NEUQUEN PROVINCE, ARGENTINA, AND COMMENTS ON THE SOUTH AMERICAN AEOLOSAURINI. The clade Aeolosaurini is represented by several specimens found, so far, only in Argentina and Brazil. The material reported here corresponds to a sauropod titanosaur consisting of four incomplete anterior caudal vertebrae, from the Narambuena Paleontological Site, Rincon de los Sauces, Neuquen Province, Argentina. The specimen comes from the Plottier Formation (late Coniacian-lower Santonian, Upper Cretaceous), Neuquen Group. The specimen has a combination of features that includes it into the clade Aeolosaurini: anterior caudal centra with anterodorsal margin bent forward; prezygapophyses elongated in anterior caudal, in correlation with the extreme displacement of the neural arch forward; and anteroposteriorly elongated articular facets of prezygapophyses, at least in the anterior caudals. However, it differs from other Aeolosaurini by having postzygapophysis with anteroposteriorly short articular facets, not as elongated in the prezygapophyses. This specimen corresponds not only to the fi rst discovery of an Aeolosaurini in the north of the Neuquen Basin (because Rinconsaurus caudamirus Calvo & Gonzalez Riga has been included in another clade, Rinconsauria), but also the oldest record of the group.

Late Cretaceous Uplift in the Malargüe fold-and-thrust belt (35ºS), southern Central Andes of Argentina and Chile

The Cordillera de los Andes is the typical example of a subduction-related orogen. Its present topography is the result of post-Miocene uplift, however, Andean compressional deformation and uplift started in the Late Cretaceous, as increasingly recognized in different sectors of the mountain belt. We present evidences of a Late Cretaceous event of compressional deformation in the southern Central Andes (35oS), reflected in syn-orogenic foreland basin deposits assigned to the Neuquen Group in Argentina and the Brownish-Red Clastic Unit in Chile. Comparison of the facies of these units allows us to recognize a sector proximal to the Late Cretaceous orogenic front, a distal sector with sediment provenance from the forebulge and a western sector where the sediments where deposited within the Late Cretaceous mountain belt. On this basis, we assign the orogenic front to an inverted Jurassic normal fault, the Rio del Cobre fault, and reconstruct the structure of the easternmost Late Cretaceous Andes at this latitude. The change in the location of the orogenic front north and south of 35oS allows us to recognize a long-lived change in behavior in Andean evolution in this sector, which correlates with a change in the shape and the deposits of Mesozoic Neuquen basin.

ORGANIZAÇÃO TERRITORIAL: ELABORAÇÃO DE MAPAS DE RISCO DE EROSÃO HÍDRICA E APLICAÇÃO DE PARÂMETROS MORFOLÓGICOS

A área de estudo abrange 105.803 ha, dentro dos limites da Reserva Natural Protegida de AucaMahuida, no leste-nordeste de Neuquén, Argentina. O clima extremadamente árido e solos de perfil poucoevoluído tornam frágil a paisagem da zona, condição que se intensifica pelas atividades de extração que nelase apresentam. Em particular, o desenvolvimento de linhas sísmicas de exploração petroleira gera a eliminaçãoda cobertura superficial, representando setores potenciais desencadeadores de processos de erosão.Estabeleceu-se um espaço delimitado pelo risco de erosão hídrica tendo em conta declive e característicasdo solo, os quais foram agregados por contexto fisiológico, cobertura vegetal e porcentagem do solodespido. Estes fatores foram definidos a partir da análise de figuras aerofotográficas e multiespectrais,cartográficas, observação direta da paisagem e dados de campo. Para as unidades de inclinação do terreno,a análise da densidade da drenagem, cujo valor guarda uma relação direta com a graduação do terreno,resultou um complemento importante da cartografia. As categorias finais, estabelecidas como ótima, aceitávele mínima, representam setores do terreno sujeitos, de forma decrescente, aos processos erosivos. Ademarcação realizada abrange 21.372 hectares (20,2%) incluídos na categoria ótima, 18.832 hectares (17,8%)na categoria aceitável e 65.598 hectares (62,0%) na categoria mínima. A distribuição das terras assimdefinidas proporcionou uma informação básica no momento de aplicar políticas de organização territorialdentro do setor.

Formation Damage Control: Selecting Optimum Salinity in a Waterflooding Pilot

Abstract Waterflooding in viscous oilfields poses several problems to both the reservoir engineer and the production engineer. Despite unfavourable mobility ratios, it has been noted that injection performance often exceeds theoretically expected values. In the particular case of the waterflooding pilot project across the Cerro Fortunoso field (Malargue, Argentina), the occurrence of several water supplies of widely varying salinity coupled with the usual problems. This paper describes a pilot study designed to determine the optimal salinity of water to be injected, in order to avoid formation damage resulting from clay deflocculation through what is known in the literature as saline shock. As is clearly shown by the results of the study, abrupt changes in the salinity of injected water result in significant decreases in permeability. According to the study, the problem is minimized over certain ranges. Introduction The Cerro Fortunoso field is located in southern Mendoza, Argentina, in an environmental reservation area known as La Payunia, 135 km away from the capital city of Malargue Department (Figure 1). The field is characterized by its complex structure, which consists of a NNE-SSW striking narrow, elongated, and faulted anticline. Four major east dipping, NNE striking thrust faults are predominant. The oil bearing region belongs to the Neuquen Group, and develops along the anticline flanks. A gas cap, consisting mainly of CO2 (85 to 95% molar content), occurs in the upper part of the structure. Geologically, the field involves fluvial deposits exhibiting considerably marked tectonics with high dips (40 ° to 70 °) and intense NE-SW faulting, giving rise to compartmentalized lenticular reservoirs of poor areal continuity. These lenses are sand/shale intercalations with an average porosity in the order of 18% and mean permeability in the 50 mD range. Background There was concern about the feasibility of a secondary recovery project in the Cerro Fortunoso field, which contains a predominantly asphaltene-based, very viscous heavy oil (14 ° API). Complete information regarding the field's main features and its fluids can be found elsewhere(1). Numerical simulation of the reservoir characterization study performed in Canada with Teknica Overseas Ltd. made comple completion of the project feasible(2). The study warned about the potential negative effects of fresh water injection, due to the occurrence of smectite, illite and kaolinite. At an early stage, the most suitable area for implementation of a pilot project was studied and steps were taken to identify for potential water sources. Thus, we faced one of the main difficulties to overcome. As was described above, the field is located in an extremely desertlike environmental protection area where the nearest river (Rio Grande) is 70 km away. No lacustrine deposits or natural springs occur in the area. Water Sources The use of battery-gathered production water was initially ruled out due to low production rates, high emulsion content, and the significant treatment cost that it would require. The use of two additional water sources was also discussed, i.e., production water separated in the Los Cavaos field and production water from a nearby field which is operated by third parties.

A new iguanodontian ornithopod from Neuquen Basin, Patagonia, Argentina

ABSTRACT The discovery of a new iguanodontian ornithopod in the lower units of the Neuquen Group (Rio Limay Formation, early Upper Cretaceous) increases the South American record of this kind of dinosaurs started few years ago with the report of Gasparinisaura cincosaltensis. Anabisetia saldiviai, gen. et sp. nov. is distinguished from all other ornithopods by several features, as a flattened fifth metacarpal, a scapula with a very strong acromial process, and an ilium with preacetabular process longer than 50% of the total ilium length. Anabisetia is more derived than Tenontosaurus and shares with Euiguanodontia (Gasparinisaura + Dryomorpha) the presence of one primary lateral ridge on each maxillary tooth, a broad brevis-shelf and a reduced first metatarsal. Derived features such as the transversely flattened prepubic process and an anteroventrally oriented ischiadic foot link Anabisetia with Dryomorpha (i.e., Dryosaurus, Camptosaurus and Iguanodon). Anabisetia strengths the hypothesis that basal iguanodontian ornithopods were present in South America before its with North America in the Late Cretaceous.