Maracaibo Basin Research Articles

Workflow of the In Situ Combustion EOR Method in Venezuela: Challenges and Opportunities.

In situ combustion (ISC) is one of the oldest thermal enhanced oil recovery methods to have been applied in Venezuela to increase the production of highly viscous crude oils, with a first field application in 1959 in the Tia Juana Field-Lake Maracaibo Basin. This method, which is characterized by high energy efficiency, consists of injecting air into the reservoir where exothermic oxidation reactions initiate to increase the mobility of the oil. Compared to other thermal enhanced oil recovery methods such as steam injection, ISC has a lower environmental impact in terms of water and fuel consumption, and emission of gases as the produced gases can be reinjected or stored. Several ISC projects have been carried out in Venezuela in Tia Juana, Morichal, Miga, and Melones fields. Although the technical results have been satisfactory in terms of viscosity reduction and improved crude oil properties (such as °API), other important aspects of project evaluations have not been convincing due to the following factors: high temperatures in producing wells, acid gases management, generation of complex emulsions, corrosion, and high CAPEX and OPEX costs. Nevertheless, additional research work has been conducted on process optimization, using catalysts and hydrogen donors, to better address these other factors. Due to the great need to increase hydrocarbon production in Venezuela and to the advantages of ISC as an upgrading technique where low-carbon fuels and hydrogen as byproducts are generated, this paper presents a revisit of ISC projects in Venezuela from R&D technical aspects to field applications. It seeks to identify the main insights regarding the success and failure of the evaluated projects and make substantiated recommendations in the case of future applications of this technology.

The La Luna Formation, Venezuela: A prospective unconventional reservoir

Since the early 2000s, the exploitation of unconventional reservoirs has become very important to the oil and gas industry because of their high potential source of energy and economic value. Venezuela possesses a world-class hydrocarbon source rock in one of the most prolific hydrocarbon basins in the world, namely the Cretaceous La Luna Formation in the Maracaibo Basin. Outcrop and core samples collected from the northwestern Maracaibo Basin provide the database for this study. A comprehensive multiscale characterization of the samples is undertaken to unravel the stratigraphic properties of the petroleum system. In addition, a geochemical approach is taken to evaluate the prospectivity of the La Luna Formation as an unconventional resource in the Maracaibo Basin. Rock-Eval pyrolysis and biomarker data indicate that the La Luna Formation is dominated by type II kerogen, indicating an oil-prone marine organic matter origin. Total organic carbon values range between 3.85 wt% and 9.10 wt%. Distributions of isoprenoids, steranes, and terpanes including gammacerane and monoaromatic steroid hydrocarbons indicate a hypersaline, marine carbonate anoxic depositional environment. Thermal maturity parameters indicate that most of the cores are currently in the oil window. This combined stratigraphic geochemical study indicates that the La Luna Formation has excellent potential as an unconventional reservoir for oil and gas in the study area.

Assessment of terrigenous and marine sourced oils mixtures: Los Manueles field, Maracaibo basin Venezuela

Seven crude oil samples from Los Manueles field, Maracaibo Basin, Venezuela, were analyzed to evaluate oil mixtures associated with different oil charges into the reservoirs. Analyses of the bulk physicochemical parameters suggest variations in the API gravity, the concentration of saturated and aromatic hydrocarbons, NSO compounds + asphaltenes, sulfur, vanadium, nickel, and the biomarkers distribution. The oils were divided in two groups: G-I with high saturated hydrocarbons and low NSO compounds + asphaltenes, sulfur, vanadium and nickel, a bimodal distribution of n-alkanes, high Pr/Ph and oleanane index, low steranes index, low abundance of tricyclic terpanes and C35S/C34S < 0.54 and G-II with low saturated hydrocarbons and high NSO compounds+ asphaltenes, sulfur, vanadium and nickel, an unimodal distribution of n-alkanes with low Pr/Ph and oleanane index, high steranes index, abundance of tricyclic terpanes and C35S/C34S > 0.70. G-I has a higher contribution of terrigenous organic matter compared to G-II, characterized by a higher contribution of marine organic matter. Source rock lithology biomarker indicators suggest marine shale as the source rock for oils of terrigenous origin. The results indicate that oils were generated by two independent source rocks, La Luna Formation and a secondary source rock with terrigenous organic matter, probably represented by the Capacho Formation.

Early Eocene (Ypresian) palynology of marine sediments from the colombian Caribbean

The Caribbean area is currently considered a frontier basin for hydrocarbon exploration; however, the knowledge of the Cenozoic geological evolution is controversial and requires to be reviewed as new information becomes available. This study integrates for the first-time calcareous microfossils and palynomorphs and proposes a biostratigraphic framework for the early Eocene (Ypresian), in two marine sequences obtained from the ANH Piedras Blancas 1-X and ANH San Cayetano 1-X wells drilled in the Sinu-San Jacinto basin. This information was compared with palynological publications in the Llanos, Llanos Foothills, Middle Magdalena Valley, Catatumbo, and Maracaibo basins. The new information from the Caribbean suggests that the marine palynomorph events reported in the Llanos are diachronic, but they concur with global records in low-middle latitude. Similarly, we extend the biostratigraphic range of some terrestrial palynomorphs considered traditionally of Oligocene-Miocene until Ypresian. In the studied wells lateral changes of facies (turbiditic fan to outer fan-abyssal plain) seem to control the preservation and abundance of calcareous microfossils (calcareous nannofossils and planktonic foraminifera), however, the terrestrial palynology did not show stronger variation.

THE LA LUNA/RÍO NEGRO(.) PETROLEUM SYSTEM AT THE URDANETA WEST FIELD, LAKE MARACAIBO BASIN, NW VENEZUELA: 1D BASIN MODELLING AND SECONDARY OIL MIGRATION

This paper investigates the timing of hydrocarbon generation in the northern part of the Urdaneta West field in the NW of the Lake Maracaibo Basin, NW Venezuela, based on 1D basin modelling at three wells referred to as wells X, Y and Z. Kitchen areas were identified and secondary migration directions were inferred based on analyses of the thermal and burial history of the Upper Cretaceous La Luna Formation source rock and the geochemistry of 20 oil samples from the Río Negro Formation reservoir. Aliphatic hydrocarbons in the oil samples were analysed by gas chromatography – mass spectrometry (GC-MS) while the vanadium-nickel and sulphur contents were determined by energy dispersive X-ray spectrometry and inductively coupled plasma optical emission spectroscopy, respectively. Bulk and molecular characterizations indicated that the oils originated from a marine carbonate source rock containing oil-prone Type II kerogen, consistent with generation by the La Luna Formation. Burial and thermal history modelling in the study area indicated that the La Luna source rock at wells X, Y and Z reached the oil window during the late Eocene, mid-Eocene and early Paleocene respectively. 1D model results from the three wells showed that hydrocarbon generation began in the early Eocene. The transformation ratio of the La Luna Formation source rock in the modelled wells reached values of 35%, 98% and 100% by the end of the Eocene. In the Urdaneta West field, two different oil charges appear to have mixed in the Río Negro reservoir. Both oil charges were generated by the La Luna Formation source rock but at different times. A first charge of less mature oil occurred in the middle-late Eocene (Phase 1 generation), and a second, more mature oil charge took place in the Miocene – Quaternary (Phase 2 generation). The kitchen area for the first oil charge is inferred to have been located to the north and NE of Urdaneta West; that for the second oil charge to the south of the field. This migration model is supported by observed variations in the geochemical compositions of the oil samples analysed from different wells in the Urdaneta West field.

Three-dimensional magnetotelluric imaging of the Mérida Andes, Venezuela

The 100km wide Mérida Andes extend from the Colombian/Venezuelan border to the Coastal Cordillera. The mountain chain and its associated major strike-slip fault systems in western Venezuela formed due to oblique convergence of the Caribbean with the South American Plates and the north-eastwards expulsion of the North Andean Block. Due to the limited knowledge of lithospheric structures related to the formation of the Mérida Andes research projects have been developed to illuminate this zone with deep geophysical data. In this study, we present three-dimensional inversion of broadband magnetotelluric data, collected along a 240km long profile crossing the Mérida Andes and the Maracaibo and Barinas–Apure foreland basins. The distribution of the stations limits resolution of the model to off-profile features. Combining 3D inversion of synthetic data sets derived from 3D modelling with 3D inversion of measured data, we could derive a 10 to 15km wide corridor with good lateral resolution to develop hypotheses about the origin of deep-reaching anomalies of high electrical conductivity. The Mérida Andes appear generally as electrically resistive structures, separated by anomalies associated with the most important fault systems of the region, the Boconó and Valera faults. Sensitivity tests suggest that the Valera Fault reaches to depths of up to 12km and the Boconó Fault to more than 35km depth. Both structures are connected to a sizeable conductor located east of the profile at 12–15km depth. We propose that the high conductivity associated with this off-profile conductor may be related to the detachment of the Trujillo Block. We also identified a conductive zone that correlates spatially with the location of a gravity low, possibly representing a SE tilt of the Maracaibo Triangular Block under the mountain chain to great depths (>30km). The relevance of these tectonic blocks in our models at crustal depths seems to be consistent with proposed theories that describe the geodynamics of western Venezuela as dominated by floating blocks or orogens. Our results stress the importance of the Trujillo Block for the current tectonic evolution of western Venezuela and confirm the relevance of the Boconó Fault carrying deformation to the lower crust and upper mantle. The Barinas–Apure and the Maracaibo sedimentary basins are imaged as electrically conductive with depths of 4 to 5km and 5 to 10km, respectively. The Barinas–Apure basin is imaged as a simple 1D structure, in contrast to the Maracaibo Basin, where a series of conductive and resistive bodies could be related to active deformation causing the juxtaposition of older geological formations and younger basin sediments.

New approaches to distinguish shale-sourced and coal-sourced gases in petroleum systems

Current approaches relating thermogenic gases to either shale source rocks (predominantly type II kerogen) or coal source rocks (predominantly type III kerogen) are not reliable and not globally applicable. This is because these mostly empirical approaches were developed using small poorly-constrained datasets from limited locations. The evaluation of a large global dataset of molecular and isotopic properties of gases from unconventional shale and coal reservoirs suggests that two genetic diagrams based on stable carbon isotopes of methane and ethane, δ13C-C2H6versus δ13C-CH4 and δ13C-CH4versus Δ(δ13C-C2H6 – δ13C-CH4), provide the best separation of shale-sourced and coal-sourced gases. Newly designated genetic fields and shale/coal separation lines on these diagrams were tested and validated using data from five petroleum systems with, likely, only shale (class B and A organofacies) source rocks (the Maracaibo Basin in Venezuela, the Guajira Basin in Colombia and the Rub Al Khali Basin in Iran) and only coal (class F organofacies) source rocks (the Southern Permian Basin in Germany and the Sichuan Basin in China). The practical usefulness of this new approach to gas-source correlations was demonstrated in two case studies from petroleum systems with debated source rock organofacies (the Mozambique Basin in Mozambique and the Indus Basin in Pakistan). These better constrained and more reliable diagrams with genetic fields and shale/coal separation lines represent a new tool for the evaluation of petroleum systems.

Ethno-ornithological notes and neglected references on the Harpy Eagle Harpia harpyja in western Venezuela

Harpy Eagle Harpia harpyja has been documented only recently (2004) in the Lake Maracaibo basin of western Venezuela, specifically in the central Sierra de Perijá, at 1,100 m. Observations in the southern plains of the basin are reported from heretofore neglected sources published in 1599, 1889 and 1893. Two overlooked photographs of dead birds dating from 1947–51 (Perijá Mountains) and 1959 (Santa Bárbara del Zulia) are reproduced. Several other records are established (in 1974, the 1980s, 1994/95, 2002 and 2006), based on empirical observations and material evidence collected by anthropologists who have visited the still heavily forested area inhabited by the Barí people since the early 1960s. Circumstantial evidence of the use of Harpy Eagle bones and feathers by the indigenous Barí provides additional ethno-ornithological information. Although Harpy Eagle is currently categorised as Vulnerable in Venezuela, the cumulative historical evidence coupled with Species Distribution Modelling analysis predictions of suitable habitat locally available to the species suggests it might still be frequent in the western and southern Lake Maracaibo basin, where considerable expanses of tropical forest are conserved within four major protected areas and an indigenous reserve.

Origin and Biodegradation of Crude Oils from the Northernmost Fields in the Bolivar Coastal Complex (Zulia State, Venezuela)

The organic geochemical features of 30 sampled oils from the northern Bolivar Coastal Complex (Lake Maracaibo Basin, NW Venezuela) were examined by combining carbon isotope, classical biomarker, and extended diamondoid analyses to clarify source facies and to assess the thermal maturity and extent of biodegradation of the oils analyzed. In this work, oils are understood as a mixture of two episodes of petroleum generation from the La Luna Formation: a paleobiodegraded oil pulse during Paleogene times and a late pulse having a higher maturity in the post-Oligocene. For the oil samples analyzed, results revealed a mixing composed of different proportions of almost a terrestrially derived siliciclastic-sourced and a purely marine carbonate-sourced oil pulse. Moreover, two main groups of oils were identified by means of hierarchical cluster analysis. Finally, inter- and intrafield variations in the extent of biodegradation were also assessed using two classification schemes (Peters and Moldowan, and Manco scales).

Palynostratigraphy and lithostratigraphy of Upper Cretaceous and Paleogene outcrop sections, Mérida Andes (Maracaibo Basin), Western Venezuela

Detailed palynologic and lithostratigraphic studies of outcrop sections on the western flank of the Mérida Andes in Western Venezuela were undertaken to establish a framework for interpreting and correlating regional and local unconformities from the outcrop to subsurface data. The Upper Cretaceous to lower Paleogene section of the Maracaibo Basin consists of laterally continuous rock units attributed to the Mito Juan and Barco/Catatumbo formations, which are characterized by marine sediments deposited relatively close to shore. The continuity of plant and dinoflagellate species across the Cretaceous-Paleogene boundary in this area may have potential significance to K/Pg studies elsewhere. The lower to upper Paleogene Los Cuervos, Mirador, and Carbonera formations were predominantly deposited in non-marine environments, though palynologic and stratigraphic data from each unit show the variable influence of marine and lacustrine conditions. A new chronostratigraphic framework for the study area (the “Venezuelan Composite Standard”) was developed based on first and last appearances of spores, pollen, and dinoflagellates, and three pollen acme events and calibrated to the latest time scale. Graphic correlation plots of the most complete outcrop sections at Río Lobaterita, Río Lora, and Río Chama indicate the presence of significant hiatuses in time, due to erosion and non-deposition (or a combination of the two) reflecting the complex structural and depositional history of the southeastern Maracaibo Basin. A regionally significant upper Paleocene to lower Eocene unconformity, as well as several local and regional intra middle Eocene unconformities appear to have been caused by a drop in base level (sea level plus structural uplift) forming incised valleys over much of the study area. Unconformities are also present in the upper middle Eocene to Oligocene and represent ravinement surfaces caused by transgressive marine reworking of pre-existing units. These surfaces are often marked by the presence of dinoflagellates within the upper Eocene Carbonera Formation. Depositional environments during much of the Upper Cretaceous to Paleogene succession vary from fluvial-floodplain to marginal marine, with newly noted periods of widespread lacustrine deposition in all geologic units. Temporal differences between similar Paleogene lithostratigraphic units in northeastern Colombia and southwestern Venezuela are likely due to the influence and timing of structural events on regional and local depositional environments.

Magnetotelluric imaging of the Mérida Andes and surrounding areas in Venezuela

SUMMARYThe Caribbean and South American tectonic plates bound the north-eastwards expulsion of the North Andean Block in western Venezuela. This complex geodynamic setting resulted in the formation of major strike-slip fault systems and sizeable mountain chains. The 100-km-wide Mérida Andes extend from the Colombian/Venezuelan border to the Caribbean coast. To the north and south, the Mérida Andes are bound by hydrocarbon-rich sedimentary basins. Knowledge of lithospheric structures, related to the formation of the Mérida Andes, is limited though, due to a lack of deep geophysical data. In this study, we present results of the first broad-band magnetotelluric profile crossing the Mérida Andes and the Maracaibo and Barinas–Apure foreland basins on a length of 240 km. Geoelectrical strike and dimensionality analysis are consistent with 1-D or 2-D subsurface structures for the sedimentary basins but also indicate a strong 3-D setting for the Mérida Andes. Using a combination of 2-D and 3-D modelling we systematically examined the influence of 3-D structures on 2-D inversions. Synthetic data sets derived from 3-D modelling allow identification and quantification of spurious off-profile features as well as smoothing artefact due to limited areal station coverage of data collected along a profile. The 2-D inversion models show electrically conductive basins with depths of 2–5 km for the Barinas-Apure and 2–7 km for the Maracaibo basins. A number of resistive bodies within the Maracaibo basin could be related to active deformation causing juxtaposition of older geological formations and younger basin sediments. The most important fault systems of the area, the Boconó and Valera Faults, cross-cut the Mérida Andes in NE–SW direction along its strike on a length 400 km and N–S direction at its centre on a length 60 km, respectively. Both faults are associated with subvertical zones of high electrical conductivity and sensitivity tests suggest that they reach depths of up to 12 km. A sizeable conductor at 50 km depth, which appears consistently in the 2-D sections, could be identified as an inversion artefact caused by a conductor east of the profile. We speculate the high conductivity associated with the off-profile conductor may be related to the detachment of the Trujillo Block. Our results partially support the ‘floating orogen hypothesis’ developed to explain the geodynamic evolution of western Venezuela and they highlight the relevance of the Trujillo Block in this process.

Eficiencia reproductiva de las angiospermas de un bosque inundable en la cuenca del lago de Maracaibo (Venezuela)

La relación fruto/flor, relación semilla/óvulo y fecundidad relativa fueron evaluadas en 25 especies de un bosque inundable en la cuenca del lago de Maracaibo (Venezuela) y correlacionadas con el número y costo de las estructuras reproductivas. Estos estimadores, junto con la biomasa asignada a frutos y semillas y la relación pericarpio/semilla, fueron analizados entre formas de vida, sistemas reproductivos y síndromes de dispersión de semillas. En general, la relación fruto/flor y la fecundidad relativa fueron bajas mientras que la relación semilla/óvulo fue alta. La relación fruto/flor estuvo asociada negativamente con el número de flores por inflorescencia, y al igual que la fecundidad relativa, con el peso del fruto y de la semilla. La relación semilla/óvulo estuvo negativamente relacionada con el número de óvulos por flor y con el peso del fruto. La relación fruto/flor y la fecundidad relativa fueron mayores en especies herbáceas, autógamas y/o de dispersión abiótica que en sus contrapartes leñosas, xenógamas y/o zoocoras las cuales presentaron mayor peso semilla, y en el caso de las especies xenógamas, también mayor relación pericarpio/semilla que las autógamas. La relación semilla/óvulo fue mayor en especies de dispersión abiótica que en las zoocoras. Estos resultados sugieren una fuerte influencia del número y costo de las estructuras reproductivas en la eficiencia reproductiva de las especies.

Floral biology and phenological overlap of angiosperms from a flooded forest, lake Maracaibo basin, Venezuela.

Floral biology and phenological overlap of angiosperms from a flooded forest, lake Maracaibo basin, Venezuela.

Re-Os geochronology for the NIST RM 8505 crude oil: The importance of analytical protocol and uncertainty

The National Institute of Science and Technology (NIST) research material (RM) 8505 is a Venezuelan crude oil certified for its vanadium concentration. It has recently been proposed as a matrix-matched standard for interlaboratory comparison of Re-Os isotopic analyses while serving as a benchmark for petroleum-based Re-Os method development. Here, the NIST RM 8505 oil is characterized using a multi-solvent asphaltene precipitation, permitting interlaboratory Re-Os data comparison and evaluation of techniques used to derive Re-Os isochron ages. We present a detailed discussion of analytical blank sources, critical evaluation of analytical uncertainties, method improvements and data corrections. Additionally, we provide a comprehensive discussion on the effect of data population size and analytical uncertainty on isochron statistics and the robustness of isochron ages. In addition to NIST RM 8505 (2.43 ± 0.15 ng/g Re, 30.0 ± 0.7 pg/g Os), we provide the first Re-Os data for NIST SRM 1634c (1.73 ± 0.01 ng/g Re, 32.5 ± 0.8 pg/g Os) and EnviroMAT SCP Science (39 ± 1 pg/g Re, 1.01 ± 0.02 pg/g Os), two other commercially available hydrocarbon trace metal standards.The application of several asphaltene (ASPH) precipitations using different n-alkane solvents (pentane, heptane and decane) for the NIST RM 8505 significantly improved the spread of data in the 187Re/188Os-187Os/188Os space. Multi-solvent asphaltene precipitations yield an asphaltene-only Model 1 isochron (75 ± 24 Ma) and the maltene-crude oil-asphaltene triplets yield a more precise Model 1 isochron age of 78.5 ± 2.3 Ma with a 187Os/188Osinitial of 0.877 ± 0.021. Our age is considerably older compared to a previously reported Model 1 age of 62.7 ± 5.7 Ma based on C7 ASPH-crude oil-MALT triplets (Liu and Selby, 2017) and considerably younger than the Model 1 age of 98.4 ± 9.5 Ma based on ASPH separates (Liu et al., 2019). The analytical reasons leading to these age differences are discussed in this paper.The geological context for the NIST 8505 oil is unknown, therefore we use trace metal data (Ni, V, Fe, Mo, etc.) to derive plausible constraints for the origin of this oil. The NIST 8505 oil shows trace metal data similar to published data for oils from the Urdaneta district, the La Paz, Mara and Lagunillas oil fields and source rocks of the La Luna Formation in the Maracaibo Basin, Venezuela. In this geological context, our ~79 Ma age for the NIST 8505 oil implies a Late Cretaceous early hydrocarbon generation event from older Upper Cretaceous source rocks and overlaps with the youngest age of potential source rocks in the Maracaibo Basin. However, the age of large-scale oil generation in the Maracaibo Basin is significantly younger, lasting from the Oligocene to the Pliocene.

A new species of Cetopsis from the Guiana Shield (Siluriformes: Cetopsidae: Cetopsinae).

A new species of Cetopsis is described from Guiana Shield drainages in Guyana and Suriname. The new species is found in the Konawaruk River and tributaries, Essequibo River basin, Guyana, and in the Mauritie Creek, tributary to the Tempati River, upper Commewijne River basin, Suriname. The new taxon can be distinguished from all congeners by a combination of features: dark spots on sides of the body eye-sized or larger, dark, bilobed patch at the base of the caudal fin, absence of a dark humeral spot, absence of dark pigmentation along the fin-membrane posterior to the first dorsal-fin ray, dark pigmentation at the base of the dorsal fin, dark spots extending ventrally to the bases of anal-fin rays, and 41 total vertebrae with 28 caudal vertebrae. Data on internal anatomy of the new species were incorporated into a previously-published phylogenetic analysis and resolves the position of the new species as the sister group of C. motatanensis, from Lago Maracaibo basin. The new Cetopsis is the first species of the genus known to occur exclusively in the Guiana Shield.

Sandbox models of fault-bend folding: A new investigation with a pre-existing fault ramp

This study presents the results of analogue models of fault-bend folds (FBFs) developed over a pre-existing fault dip ramp with a non-outcropping upper fault flat. To determine the boundary conditions that control the formation of FBFs, experiments were performed with quartz sand and glass microbeads, both with and without intercalations of thin horizons of mica flakes. We varied the initial thickness, the ramp dip angle, and the basal friction coefficient of the lower fault flat. The analogue models revealed that the most important factor for the formation of FBFs was the rheological behaviour of the analogue material. The elasto-plastic frictional behaviour of the glass microbeads is fundamental for the formation of Mode I-FBFs (with interlimb angles higher than 90°), which is independent of the angle of the pre-existing fault ramp and the basal friction along the lower fault flat. In the sand models, the formation of FBFs requires a high initial stratigraphic thickness, resulting in a significant increase in the normal stress and/or in the cohesion strength. In glass microbeads, the models developed structures very similar to the FBFs described in the carbonates of the Maracaibo Basin (Venezuela) as well as those within the Appalachian thrust belt (USA).

ГЕОЛОГИЯ АПТ-АЛЬБСКИХ ПОРОД КАРБОНАТНОЙ ПЛАТФОРМЫ ОСАДОЧНОЙ ГРУППЫ КОГОЛЛО И ПОСЛЕДСТВИЯ АНОКСИДНЫХ ОКЕАНИЧЕСКИХ СОБЫТИЙ БАССЕЙНА МАРАКАЙБО (СЕВЕРО-ЗАПАДНАЯ ЧАСТЬ ЮЖНОЙ АМЕРИКИ)

Актуальность исследования обусловлена необходимостью проведения дополнительных поисково-разведочных работ на нефть и газ в северо-западной части нефтегазоносного бассейна Маракайбо, которые позволят повысить рентабельность разработки действующих месторождений и расширят возможности поиска новых залежей углеводородов в западной части Венесуэлы. Анализируемая осадочная толща Коголло, представленная формациями Апон, Лижур и Марака, включает промышленно продуктивный интервал, который слагают карбонатные отложения и нефтематеринские породы мелового периода. Литологическая характеристика нефтематеринских пород указывает на аноксидные океанические события при формировании формации Апон. Первое событие соотносится с осадконакоплением пачки Мачикес, а второе – с кровлей пачки Пиче. Обе пачки принадлежат к формации Апон. Рассматриваемые события способствовали формированию нефтематеринских пород высокого генерационного потенциала углеводородов, чем объясняется интерес данного исследования. Основной целью исследования является изучение фациальных условий формирования отложений формации Апон в разрезе обнажения континентальной части бассейна Маракайбо и их корреляция с ближайшими глубокими скважинами для определения стратиграфического местоположения коллекторов и их возможной связи с интервалами потенциальной нефтематеринской породы. Объекты: обнажения карьера Цементос Кататумбо С.А. в горной системе Периха, где выделяется карбонатная тоща нижней группы Коголло, а также глубокие поисковые скважины X-1, X-15, X-21, X-14 и X-23. Имеющиеся варианты корреляции отложений в обнажении горной системы Периха недостаточно обоснованы и требуют уточнения. Методы: седиментологический и геохимический анализы карбонатных пород группы Коголло в пределах в карьере Цементос Кататумбо С.А., штат Сулия, Венесуэла, включающие макро- и петрографическое описание пород, биостратиграфический анализ, изучение содержания общего органического углерода в породе, данных гамма-каротажа по разрезу обнажения и в глубоких скважинах. Результаты. Выделено 14 микрофаций, связанных с условиями седиментации в пределах склона карбонатного бассейна. В последовательности переслаивания отложений формации Апон выделяются участки максимальной трансгрессии моря и скрытые стратиграфические несогласия. Аппроксимированная и оценочная корреляция, учитывающая стратиграфию, литофации и данные гамма-каротажа, была проведена в обнажении карьера Цементос Кататумбо С.А. и сопоставлена с разрезами нефтяных скважин X-1, X-15, X-21, X-14 и X-23.

New bird records from the arid Cúcuta Valley, north-east Colombia

Summary. Avian inventories of the poorly known tropical dry forest in the Cucuta Valley, north-east Colombia, yielded new distributional data for 15 bird species including several range extensions along the east slope of the East Andes, or filled distributional gaps between the Serrania de Perija and Merida Andes of Venezuela, and between the Maracaibo basin in Venezuela and eastern Llanos of Colombia. Some of the new records are of fairly common but easily overlooked species associated with dense habitats, whereas others concern open-country species whose spread has apparently been promoted by landscape transformation. Further work will probably yield additional new records in the region, especially in the transition from dry forest of the Cucuta Valley to more humid habitats in the Catatumbo and adjacent Andes of Colombia and Venezuela.

Taxonomic review of Trans-Andean species of Pimelodus (Siluriformes: Pimelodidae), with the descriptions of two new species

We review the trans-Andean species of Pimelodus from Colombia, Panamá, and Venezuela. Based on meristic and morphometric data of preserved specimens, four of five species reported from this region are considered valid and two new Colombian species are described. Here we review Pimelodus coprophagus Schultz, 1944 from Lake Maracaibo Basin of Venezuela and Colombia; Pimelodus grosskopfii Steindachner, 1879 from Magdalena River Basin; Pimelodus navarroi Schultz, 1944 from Lake Maracaibo Basin of Venezuela and Colombia; and Pimelodus punctatus (Meek & Hildebrand, 1913) from Atrato, Baudó, and Tuyra River Basins of Colombia and Panamá. Pimelodus crypticus new species is described from the upper Cauca river drainage. Pimelodus yuma new species is described from the Cauca, Magdalena, and Sinú river drainages. A key for species identification and geographical ranges is provided. We also reidentify trans-Andean specimens previously reported as Pimelodus blochii Valenciennes, 1840, a widespread cis-Andean species, or species complex, that ranges across the coastal rivers of the Guianas and Brazil and the Orinoco and Amazon Basins.

Embryonic development of the annual killifish Austrofundulus limnaeus: An emerging model for ecological and evolutionary developmental biology research and instruction.

Austrofundulus limnaeus is an annual killifish from the Maracaibo basin of Venezuela. Annual killifishes are unique among vertebrates in their ability to enter into a state of dormancy at up to three distinct developmental stages termed diapause I, II, and III. These embryos are tolerant of a wide variety of environmental stresses and develop relatively slowly compared with nonannual fishes. These traits make them an excellent model for research on interactions between the genome and the environment during development, and an excellent choice for developmental biology laboratories. Furthermore, A. limnaeus is relatively easy to maintain in a laboratory setting and has a high fecundity, making it an excellent candidate as an emerging model for studies of development, and for defining the limits of developmental buffering in vertebrates. This study reports for the first time on the detailed development of A. limnaeus and provides a photographic and illustrated atlas of embryos on the two developmental trajectories possible in this species. Developmental Dynamics 246:779-801, 2017. © 2017 The Authors Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.