Diagenesis, provenance and reservoir quality of Triassic TAGI sandstones from Ourhoud field, Berkine (Ghadames) Basin, Algeria

The Triassic TAGI (Trias Argilo-Gréseux Inférieur) fluvial sandstones are the main oil reservoirs in the Berkine Basin, Algeria. Nonetheless, their provenance and diagenesis, and their impact on reservoir quality, are virtually unknown. Samples from the Ourhoud field, representing the Lower, Middle and Upper TAGI subunits, were studied using a combination of petrographic, mineralogical and geochemical techniques. The Lower TAGI sandstones have an average framework composition of Q98.3F0.6R1.1 and 95% of the quartz grains are monocrystalline. By contrast, the Middle–Upper TAGI sandstones have an average framework composition of Q88.3F9.8R1.9 and 79.7% of the quartz grains are monocrystalline. The Lower TAGI quartz arenites derived from Paleozoic siliciclastic rocks, whereas the Middle–Upper TAGI subarkoses originated mainly from metamorphic terrains. This change in provenance is a potential criterion for correlation within the TAGI. Also, this change has contributed to the significantly different diagenetic paths followed by the Lower TAGI quartz arenites and the Middle–Upper TAGI subarkoses. Grain-coating illitic clays are abundant in the Lower TAGI, where they exert a critical control on reservoir quality. These clays are interpreted as pedogenic and/or infiltrated in origin and to have had, in part, smectitic precursors. Shallow burial Fe-dolomite cementation was favored in the downthrown block of the field-bounding fault, where it contributed to the poor reservoir quality. Magnesite–siderite cements are multiphase. The earliest generation is composed of Fe-rich magnesite that precipitated during shallow burial from hypersaline fluids with high Mg/Ca ratios, probably refluxed residual brines associated with the Liassic evaporites. Later magnesite–siderite generations precipitated during deeper burial from waters with progressively higher Fe/Mg ratios. Authigenic vermicular kaolin largely consists of dickite that replaced previously formed kaolinite. Dickitization was followed by late-stage illitization related to the dissolution of detrital and authigenic K-feldspar. Quartz, the most abundant cement, was mainly sourced by the pressure- or clay-induced dissolution of detrital quartz and is a critical factor controlling the reservoir quality. Overall, quartz cement is more abundant in the Lower TAGI than in the Middle–Upper TAGI, and this increase correlates with a decrease in average porosity. Within the Lower TAGI, quartz cement abundance is stratigraphically very variable, which is in part related to facies controlled variations in grain-coating clay, resulting in major vertical variations in reservoir quality. Anhydrite and barite cements postdate quartz overgrowth. The sulfate necessary for their formation was likely sourced by deep subsurface dissolution of Late Triassic–Liassic evaporites

Электропривод регулирующей трубопроводной арматуры на базе синхронного двигателя с постоянными магнитами

Цель работы – создание нового поколения регулирующих взрывозащищенных электроприводов с минимальными габаритными размерами, массой и себестоимостью, не уступающих по точности регулирования и функциональным характеристикам регулирующим электроприводам производства других фирм. В процессе работы был произведен расчет и выбор электропривода. Проведено моделирование и анализ работы привода в разных режимах.The purpose of the work is to create a new generation of regulating explosion-proof electric drives with minimum overall dimensions, weight and cost, which are not inferior in regulation accuracy and functional characteristics to regulating electric drives produced by other companies. During operation electric drive was calculated and selected. Simulation and analysis of the drive operation in different modes were carried out

Introducción a la Geología de campo: un itinerario en el área nordeste de Madrid

Esta práctica de campo se dirige a estudiantes de últimos cursos de enseñanza secundaria y a los de primer curso de enseñanzas universitarias (Geología, Biología, etc.) y pretende ser una primera toma de contacto con materiales y procesos geológicos en el campo. El itinerario propuesto permite apreciar en el campo aspectos de geología básica, en concreto conceptos referentes a: Petrología, reconocimiento de los principales tipos de rocas ígneas, metamórficas y sedimentarias. Tectónica/Geología estructural. Cartografía geológica. Geomorfología. Historia geológica de la región

Stable isotope composition of carbonate components of Rhaetian shallow-water limestones of the Wombat Plateau

Stable oxygen- and carbon-isotope ratios of Rhaetian (upper Triassic) limestone samples from the Wombat Plateau, northwest Australia, were measured to explore possible diagenetic pathways that the material underwent after deposition in a shallow-water environment, before plateau submergence in the Early Cretaceous. Host sediment isotopic values cluster near typical marine carbonate values (d18O ranging from -2.57 per mil to +1.78 per mil and d13C, from +2.45 per mil to +4.01 per mil). Isotopic values of equant clear calcite lining or filling rock pores also plot in the field of marine cements (d18O = +1.59 per mil to -2.24 per mil and d13C = +4.25 per mil to +2.57 per mil), while isotopic values for neomorphic calcites replacing skeletal (megalodontid shell) carbonate material show a wider scatter of oxygen and carbon values, d18O ranging from +2.73 per milo to -6.2 per mil and d13C, from +5.04 per mil to +1.22 per mil. Selective dissolution of metastable carbonate phases (aragonite?) and neomorphic replacement of skeletal material probably occurred in a meteoric phreatic environment, although replacement products (inclusion-rich microspar, clear neomorphic spar, etc.) retained the original marine isotopic signature because transformation probably occurred in a closed system dominated by the composition of the dissolving phases (high rock/water ratio). The precipitation of late-stage equant (low-Mg?) calcite cement in the pores occurred in the presence of normal marine waters, probably in a deep-water environment, after plateau drowning. Covariance of d18O and d13C toward negative values indeed suggests influence of meteorically modified fluids. However, none of the samples shows negative carbon values, excluding the persistence of organic-rich soils on subaerial karstic surfaces (Caribbean-style diagenesis). Petrographical and geochemical data are consistent with the sedimentological evidence of plateau drowning in post-Rhaetian times and with a submarine origin of the >70-m.y.-long Jurassic hiatus

(Figure 2) Stratigraphic distribution of Schizosphaerella in DSDP Hole 79-547B

The Jurassic (hemi)pelagic continental margin deposits drilled at Hole 547B, off the Moroccan coast, reveal striking Tethyan affinity. Analogies concern not only types and gross vertical evolution of facies, but also composition and textures of the fine sediment and the pattern of diagenetic alteration. In this context, the occurrence of the nanno-organism Schizosphaerella Deflandre and Dangeard (sometimes as a conspicuous portion of the fine-grained carbonate fraction) is of particular interest. Schizosphaerella, an incertae sedis taxon, has been widely recorded as a sediment contributor from Tethyan Jurassic deeper-water carbonate facies exposed on land. Because of its extremely long range (Hettangian to early Kimmeridgian), the genus Schizosphaerella (two species currently described, S. punctulata Deflandre and Dangeard and S. astrea Moshkovitz) is obviously not of great biostratigraphic interest. However, it is of interest in sedimentology and petrology. Specifically, Schizosphaerella was often the only component of the initial fine-grained fraction of a sediment that was able to resist diagenetic obliteration. However, alteration of the original skeletal structure did occur to various degrees. Crystal habit and mineralogy of the fundamental skeletal elements, as well as their mode of mutual arrangement in the test wall with the implied high initial porosity of the skeleton (60-70%), appear to be responsible for this outstanding resistance. Moreover, the ability to concentrate within and, in the case of the species S. punctulata, around the skeleton, large amounts of diagenetic calcite also contributed to the resistance. In both species of Schizosphaerella, occlusion of the original skeletal void space during diagenesis appears to have proceeded in an analogous manner, with an initial slight uniform syntaxial enlargement of the basic lamellar skeletal crystallites followed, upon mutual impingement, by uneven accretion of overgrowth cement in the remaining skeletal voids. However, distinctive fabrics are evident according to the different primary test wall architecture. In S. punctulata, intraskeletal cementation is usually followed by the growth of a radially structured crust of bladed to fibrous calcite around the valves. These crusts are interpreted as a product of aggrading neomorphism, associated with mineralogic stabilization of the original, presumably polyphase, sediment. Data from Hole 547B, along with inferences, drawn from the fabric relationships, suggest that the crusts formed and (inferentially) mineralogic stabilization occurred at a relatively early time in the diagenetic history in the shallow burial realm. An enhanced rate of lithification at relatively shallow burial depths and thus the chance for neomorphism to significantly influence the textural evolution of the buried sediment may be related to a lower Mg/Ca concentration ratio in the oceanic system and, hence, in marine pore waters in pre-Late Jurassic times

Dinosaur nests at the sea shore

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Do co‐worker conflicts enhance daily worries about job insecurity: A diary study

The long‐term negative consequences of job insecurity on employees’ health and well‐being have been demonstrated by several studies, but there is very little evidence on the daily experience of job insecurity and on the factors that may influence it. Therefore, we investigated whether short‐term changes occur in the experience of job insecurity and whether these are influenced by daily co‐worker conflicts. We carried out a diary study, in which 66 employees answered a questionnaire over the course of five working days. We conducted a multilevel analysis in which we included co‐worker conflicts as a predictor, and type of contract, emotional stability, and aggregated job insecurity perceptions as control variables. Our results revealed that job insecurity varies on a daily level, and that 23 per cent of the variance could be explained at a within‐person level. Co‐worker conflicts were a significant positive predictor for perceived job insecurity in subsequent days after controlling for aggregated job insecurity perceptions at person level. Reversed causation was not found. Practical implications for organisations should focus on the promotion of positive social relations in the work environment in order to mitigate or avoid the negative consequences of social stressors in uncertain times

Why do Illegitimate Tasks Cause Pain? Qualitative Job Insecurity as an Underlying Mechanism

Musculoskeletal complaints are widespread and highly relevant stress-related consequences calling for the detailed exploration of antecedents. We propose that illegitimate tasks (i.e., tasks that do not conform to an employee’s occupational role) constitute one of these work-related antecedents. This study further examines whether illegitimate tasks are associated with concerns about deteriorating working conditions (qualitative job insecurity) as a mechanism leading to musculoskeletal pain. This hypothesis was tested in a German longitudinal sample with 109 employees using a time lag of six weeks. Supporting our assumptions, the results revealed an indirect effect of qualitative job insecurity on the relationship between illegitimate tasks and musculoskeletal pain controlling for the initial level of musculoskeletal pain. The underlying effects remained significant under control of age, sex, and type of contract. To the best of our knowledge, this is the first study to show that illegitimate tasks predict musculoskeletal complaints by raising concerns about future deterioration in working conditions. Especially when it seems unavoidable to assign tasks that do not correspond to an employee’s occupational role, supervisors should make sure that illegitimate tasks are distributed fairly among team members and conveyed in an appreciative manner

Relazione sul Workshop «Paleontologia e biostratigrafia dei sedimenti ammonitiferi toarciano-bajociani in successioni di alto morfostrutturale dell' Appennino umbro-marchigiano: l'area di Monte Nerone. Correlazioni con altre regioni della Tetide occidentale». (Piobbico, 2-14 agosto 1993)

This report is the synthesis of the field work and discussions held during the workshop «PaIaeontology and biostratigraphy of Toarcian-Bajocian Pelagic Carbonate PIatforms ammonitiferous sediments of umbro-marchean Apennines: the Monte Nerone area. Correlations with other western Tethys regions» (Piobbico, CentraI ItaIy, august 2-14, 1993). It presents a preliminary proposition of biohorizons for rock correlation in the investigated area, following the proposais of Italian Commission on Stratigraphy on definition of biostratigraphic units. The sampied «body of rock strata» consists on 113 beds, 25,60 metres thick, where 30 biostratigraphic surfaces (biohorizons) has been recognized