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EN
The paper briefly describes a possible application of X-ray computed microtomography studies followed by digital image analysis, enabling petrological assessment of carbonate rocks. The contribution presents an example of a complex, qualitative and quantitative approach aiming at deriving shape, geometry and spatial orientation of rock components as applied for a carbonate reservoir rock sample from the Zechstein Limestone (Ca1) strata. Apart from the basic properties of the analyzed objects, such as volume, surface area and number, detailed shape descriptors were obtained (compactness, sphericity, elongation, flatness, spareness). The presented approach allows for obtaining detailed 3D results at the microscopic scale, enabling extensive characterization of the studied material geometry. The methods proposed could be applied for other rock types as well.
EN
This paper was made using geological and well logging data from the Cuban oilfield area and the Polish Carpathian Foredeep gas deposit to compare the interpretation process and underline similarities and differences between data analysis from two reservoir rocks of different lithology. Data from conventional hydrocarbon deposits, i.e. the Mesozoic Cuban carbonate formation and Miocene shaly-sandy sediments were processed and interpreted using Techlog (Schlumberger Co.) software. Selected approaches were used to determine the step by step volume of shale, total and effective porosity, water/hydrocarbon saturation (Quanti) and for the comprehensive interpretation of well logs (Quanti Elan). Brief characteristics of the carbonate and siliciclastic formations were presented to indicate that the interpretation methodology oriented to the determination of petrophysical properties depends strongly on the type of reservoir. Cross-plots were presented for primary mineral composition recognition, determination of m exponent and resistivity of formation water in the Archie equation. Effective intervals for the carbonate reservoir were calculated according to the Cumulative Hydrocarbon Column methodology. Finally, the results of the interpretation of well logs were presented as continuous curves of mineral composition, including shaliness, porosity and hydrocarbon saturation. The conclusions included recommendations for the effective comprehensive interpretation of well logs in the carbonate and siliciclastic reservoirs.
EN
Although the sedimentation and diagenesis of the Polish Zechstein Limestone strata (Ca1, Permian) already have been investigated, relatively little has been done to resolve their petrophysical potential. Therefore, the gap between sedimentological and petrophysical studies was bridged through an integrated analysis of geological and geophysical data. The results of core description, polarized-light microscopy, well log interpretations and laboratory measurements on core samples were combined with previously published nuclear magnetic resonance (NMR) and X-ray microtomography (μCT) data, especially helpful in the recognition of pore geometry. The Ca1 strata of the Brońsko-1 and Brońsko-2 wells, located on the Zechstein Brońsko Reef (West Poland), were studied to determine the influence of fossils on porosity and permeability. It was concluded that greater diversification of the original biota led to an increase in porosity and variation in pore geometry. While encrusting organisms such as foraminifers promoted the development of channel and fracture porosity, the dissolution of the primarily aragonitic bivalve and gastropod shells and the shells of terebratulid brachiopods often gave rise to the formation of cavernous and mouldic porosity. The channels appear to be most common in the bryozoan-foraminifer biofacies, representing a shallowing of the depositional environment. Caverns, in turn, corresponded to the organisms of the brachiopod-bryozoan and the lightly karstified bivalve-gastropod biofacies, both of which probably experienced the influence of sabkha conditions, leading to a general decrease in porosity. The bryozoan zoecia tended to enhance both primary intraparticle voids, and after their dissolution, secondary intraparticle pores, which showed limited connectivity in the high-energy Acanthocladia biofacies, where considerable fragmentation of fossils took place, hence decreasing the permeability. Anhydrite cementation was found to be the most pronounced factor controlling porosity destruction, while dolomitization enhanced it significantly, especially for the stromatolitic biofacies, where small, unconnected vugs were formed owing to this process. The permeability is typically below 100 mD, and this is caused by the rich diagenetic history of the reef, that recorded marine, sabkha-related and burial cementation, now represented by the different fabrics of anhydrite, calcite, and dolomite.
EN
The main goal was the analysis of parameters describing the structure of the pore space of carbonate rocks, based on tomographic images. The results of CT images interpretation, made for 17 samples of Paleozoic carbonate rocks were shown. The qualitative and quantitative analysis of a pore system was performed. Objects were clustered according to the pore size. Within the clusters, the geometry parameters were analysed. The following dependences were obtained for carbonate rocks, also for individual clusters (due to the volume): (1) a linear relationship (on a bilogarithmic scale) between the specific surface and the Feret diameter and (2) a strong linear relationship between specific surface area and Feret diameter and average diameter of the objects calculated for the sphere. The results were then combined with available results from standard laboratory tests, including NMR and MICP.
PL
W pracy analizowano wyniki pomiarów laboratoryjnych wykonanych na próbkach o zróżnicowanej litologii. Głównym celem było sprawdzenie, jak zmieniają się wartości prędkości fal sprężystych i dynamicznych modułów sprężystych w trójosiowym stanie naprężenia. Pomiary wykonano z wykorzystaniem nowatorskiego zestawu będącego na wyposażeniu Katedry Geofizyki, WGGiOŚ, AGH. Zestaw pomiarowy składa się z komory ciśnieniowej, prasy hydraulicznej i dźwigu oraz generatora fal sprężystych i specjalistycznego oprogramowania. Umożliwia pomiary prędkości fal podłużnych P i poprzecznych S wraz z pełną charakterystyką naprężeniowo-odkształceniową w trójosiowym stanie naprężenia. W pracy przedstawiono wyniki pomiarów uzyskane dla ciśnień okólnych odpowiednio dobranych dla głębokości występowania oraz wieku poszczególnych próbek. Pomiary wykonywano do momentu zniszczenia próbki. Wykonano analizę zmian prędkości przy stopniowym osiowym obciążaniu próbki. W efekcie uzyskano prędkości fal sprężystych oraz charakterystyki naprężeniowo-odkształceniowe. Uzyskano wyższe wartości prędkości fal sprężystych przy symulowanych ciśnieniach złożowych niż podczas pomiarów w warunkach atmosferycznych. Wyniki zestawiono z pozostałymi, dostępnymi rezultatami badań laboratoryjnych, np. porowatościami wyznaczonymi z eksperymentów NMR i porozymetrii rtęciowej. Równoczesne pomiary prędkości fal sprężystych P i S oraz charakterystyka naprężeniowo-odkształceniowa przy symulowanym ciśnieniu górotworu są efektywnym narzędziem do odtworzenia w laboratorium warunków złożowych i uzyskania wiarygodnych wartości dynamicznych i statycznych parametrów sprężystych i geomechanicznych.
EN
The results of laboratory measurements performed on samples with varied lithology were analyzed. The main objective was to see how the values of elastic wave velocity at triaxial stress conditions change. Measurements were made using the innovative equipment located at the Department of Geophysics, Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology. The measuring set consists of a pressure chamber, a hydraulic press, a crane and specialized software. It enables the measurements of the velocity of longitudinal (P) and transverse (S) waves along with full stress-strain characteristics in triaxial stress conditions. The results of the measurements were obtained at reservoir pressure, suitably selected for the depth and age of the individual samples. Measurements were made until the sample was fractured. As a result, the velocity of the elastic waves and the stress-strain characteristics were obtained. A velocity analysis with simulated reservoir pressure conditions was performed, referring to the deformation characteristics of the samples. Higher velocity values were obtained at simulated reservoir pressures than during atmospheric measurements. The results were compiled with the other available laboratory results, such as porosities determined by NMR and mercury porosimetry experiments. The simultaneous measurements of P and S wave velocity and stress-strain characteristics at simulated reservoir pressure are an effective tool for reproducing reservoir conditions in laboratory conditions and obtaining reliable dynamic and static elastic and geomechanical parameters.
PL
Zbadano możliwość ograniczenia ryzyka rozkładu mieszanki wełny mineralnej z azotanem(V) amonu poprzez zastosowanie dodatku wypełniaczy węglanowych wykorzystywanych powszechnie w celu stabilizacji nawozów azotowych na bazie azotanu(V) amonu. Przedstawiono wyniki oznaczeń głównych składników wybranych minerałów węglanowych: wapnia, magnezu, żelaza oraz części nieroztwarzalnych w kwasie solnym. Na tej podstawie wyselekcjonowano wypełniacze, których następnie użyto w badaniach skuteczności stabilizacji mieszanek wełny mineralnej i azotanu(V) amonu z wykorzystaniem węglanów. Pomiary przeprowadzono z zastosowaniem różnicowej analizy termicznej sprzężonej z termograwimetrią i spektrometrią mas (DTA-TG-MS). Użyta w badaniach wełna mineralna stanowiła odpad po jednorocznym cyklu uprawy pomidora. Przed sporządzeniem mieszanek wełna została wysuszona na powietrzu i rozdrobniona do frakcji o średnicy poniżej 0,40 mm.
EN
In this study it was investigated the ability to reduce the risk of the thermal decomposition of mixture of mineral wool and ammonium nitrate by applying carbonate fillers commonly used to stabilize the nitrogen fertilizers based on ammonium nitrate. Paper presents the analysis of the main components of selected carbonate minerals: calcium, magnesium, iron and compounds insoluble in hydrochloric acid. Based on it, the fillers for further tests were selected. They were used in studies on carbonates efficiency in stabilization of the mixtures of mineral wool and ammonium nitrate. Measurements were carried out using differential thermal analysis coupled with thermogravimetry and mass spectrometry (DTA-TG-MS). Used mineral wool was a waste after the annual cycle of tomato crops. Before tests, the rockwool was dried in the air and crushed to a fraction of a diameter below 0.40 m
EN
Sediments of the Dudziniec Formation (Lower Jurassic – Aalenian) outcropping in the Kościeliska Valley (autochthonous unit of the High-Tatric series) are represented by a range of mixed carbonate-clastic deposits. Seven lithofacies have been distinguished based on lithology, sedimentary structures, colour and composition of intra- and extraclasts, with sandstones and crinoidal limestones as end members of a continuous spectrum of facies. The study area represents a shallower part of the sedimentary basin located in the vicinity of source areas, as compared to the Chochołowska Valley region located in the west. Facies characteristics and distribution were controlled mainly by synsedimentary tectonic activity, with sandy varieties representing periods of faulting with enhanced influx of extraclasts, and with crinoidal limestones corresponding to intervals of relative tectonic stability. Such influence of synsedimentary tectonics on the deposition in the Early Jurassic strongly resembles the Middle Jurassic development in the High-Tatric area. Neptunian dykes cutting the Dudziniec Formation, and most probably filled by Lower Jurassic sediments, are yet another indication of tectonic instability of the area in the Early Jurassic.
EN
Mass balance of selected heavy metals (Cu, Cr, Pb, Hg, Zn, Cd) released from waste into leachate during 8 years of landfill exploitation has been calculated. The average release of all analyzed heavy metals did not exceed 1.7%. Heavy metals released in the largest quantities were Cr (0.025 –1.685%), Hg (0.033–1.540%) and Cd (0.082–0.701%). Release of Pb, Cu, Zn was 0.008–0.152%; 0.012–0.085% and 0.007–0.152%, respectively. Cr and Hg do not form an insoluble sulfide precipitate and that is why they are released in a larger amount. Cd and Pb concentrations are positively correlated with the amount of the atmospheric precipitation and the amount of leachates, which means that infiltrating rainfall can leach out these metals from waste. Favorable conditions for leaching of these metals are probably a result of their precipitation as carbonates. A strong correlation between Cu, Zn, and Cr indicates they do not precipitate as carbonates and further they can be subject to desorption processes. In the case of Cu, Zn, Cr and Hg, a positive correlation with the amount of deposited waste was also observed.
PL
Dewońską serię węglanową badano w otworze wiertniczym Trojanowice 2, usytuowanym na północny zachód od Krakowa. Jest ona reprezentowana przez dolomity, z nielicznymi poziomami brekcji śródwarstwowych i warstwę wapienia mikrytowego. Dolomity zawierają ślady pierwotnych struktur, ziarn (bioklasty, peloidy, intraklasty, ooidy) oraz relikty substancji mikrytowej. Powstały one w wyniku wczesnej dolomityzacji wapieni mikrytowych, które osadzały się w płytkim, spokojnym, prawdopodobnie izolowanym środowisku morskim. Serię dolomitową z otworu Trojanowice 2 zaliczono do eiflu–żywetu dolnego na podstawie podobieństwa do dolomitów występujących w innych otworach w masywach górnośląskim i małopolskim.
EN
The Devonian carbonate succession was examined in the Trojanowice 2 borehole located northwest of Kraków. It is represented by dolomites with infrequent intrastratal breccias and a micrite limestone layer. The dolomites contain traces of primary structures, grains (bioclasts, peloids, intraclasts and ooids) and relics of micritic matter. They formed as a result of early dolomitization of micrite limestones deposited in a shallow, quiescent and probably isolated marine environment. The dolomite succession from the Trojanowice 2 borehole has been assigned to the Eifelian–Lower Givetian based on the similarity to the dolomites known from other boreholes in the Upper Silesian and Małopolska blocks.
EN
Deep-marine carbonate buildups constitute one of the most spectacular and enigmatic features found on modern seafloors. Despite some characteristics shared by all the deep-marine carbonate buildups, they represent, in fact, several distinct types, which differ in terms of their geneses, as well as sedimentary, biotic and geochemical features. These structures can be roughly divided into hydrocarbon seep limestones, carbonate-built hydrothermal vents and deep-water coral reefs. The former group include carbonate concretions, lenses, mud mounds and mud volcanoes forming as a result of decrease in alkalinity, caused by an activity of methane-oxidizing microbes. The rare examples of hydrothermal-derived limestone columns, in turn, grow in response to mixing of ambient, cold seawater and warm, Ca2+
EN
Two types of large, branched structures from the Lower Pleistocene (Calabrian) high-energy calcarenites of Favignana Island are described: Faviradixus robustus gen. et sp. nov. and Egadiradixus rectibrachiatus gen. et sp. nov. They may be interpreted as root structures of large plants, trees and trees or shrubs, respectively. The former taxon co-occurs with the marine animal trace fossils Ophiomorpha nodosa, Ophiomorpha isp., Thalassinoides isp. and Beaconites isp. The interpretation as root structures although tentative is probable and can be related to short emergence episodes for the formation of E. rectibrachiatus or to longer emergence, responsible for the discontinuity at the base of the overlying Tyrrhenian deposits, for F. robustus. Calcified root mats of smaller plants associated with the Tyrrhenian or younger emergence surfaces are common.
PL
W obszarze zawartym między miejscowościami: Dębnik, Racławice, Szklary i Dubie w rejonie Krzeszowic i Jerzmanowic już w połowie XV wieku rozpoczęto eksploatację wapieni dewońskich i karbońskich. Początkowo były one wykorzystywane jako kamień budowlany, a po oszlifowaniu jako kamień ozdobny. Wartość ozdobną wapieni wykorzystali budowniczowie wielu obiektów sakralnych głównie w Krakowie, ale także w okolicach Krakowa i Częstochowie. W latach 70. ubiegłego wieku przeprowadzono inwentaryzację 32 kamieniołomów. Zebrany materiał skalny został opracowany pod względem mikrofaunistycznym w płytkach cienkich. Występujące w wapieniach struktury biogeniczne decydują o ozdobnych walorach tych skał węglanowych. Zespół mikroorganizmów wskazuje na późnodewoński i wczesnokarboński wiek tych osadów. Aktualnie skały te są eksploatowane w kilku miejscach, a urobek wykorzystywany jako kamienie łamane i bloczne, m.in. do produkcji betonów, mas bitumicznych, budowli drogowych, kolejowych, a najdrobniejsze frakcje mogą być stosowane jako wapniowo- magnezowe nawozy mineralne.
EN
In the area comprised between the localities: Dębnik, Racławice, Szklary, and Dubie in the region of Krzeszowice and Jerzmanowice already in the half of the 15th century exploitation of Devonian and Carboniferous limestones was started. Initially they were used as building stones, and after polishing as decorative stones. Of the decorative value of limestones took advantage the builders of many sacral objects, mainly in Cracow, but also in the neighbourhood of Cracow and Częstochowa. In the seventies of the past century inventorying of 32 quarries was carried out. The collected rock material was elaborated in the microfaunistic respect in thin plates. The biogenic structures occurring in the limestones decide about the decorative advantages of these carbonate rocks. The complex of microorganisms indicates the Late Devonian and Early Carboniferous period age of these deposits. Currently these rocks are exploited in several places and the mined rock is used as broken and block stones, among others for the production of concretes and bituminous masses, for road and railway structures, and the finest fractions can be used as calcium-magnesium mineral fertilizers.
EN
Five sedimentary facies - neritic carbonate platform, lagoon, tidal flat, swamp and barrier island facies - are recorded in the Lower Permian Taiyuan Formation along with abundant ichnofossils. Common ichnofossils in this formation include Zoophycos villae, Zoophycos brianteus, Nereites cf. missouriensis, Chondrites isp., Gordia marina, Taenidium isp., Thalassinoides isp., Palaeophycus isp., Planolites isp. and a kind of bifurcation trail. From observations of the morphology of Zoophycos spreiten in approximately vertical sections, at least three kinds of spreite laminae are distinguished: ligular, crescentic and rectangular forms. Four types of storm deposits (coded as A, B, C, D) are recognised in the carbonates of the Taiyuan Formation and can be explained forming in shallow marine environments, which are distributed in order from near storm wave base to near fair weather wave base respectively.
PL
Węglanowe skały dewońskie w rejonie śląsko-krakowskim są brane pod uwagę jako perspektywiczne dla pozyskania wód pitnych m.in. dla ludności aglomeracji krakowskiej. Badania hydrogeologiczne tych utworów w rejonie Krakowa wykonano w tym celu w wywierconym otworze Trojanowice-2, zlokalizowanym w pobliżu północnej granicy zapadliska przedkarpackiego. Mimo warunków artezyjskich z ciśnieniem około 15 m nad powierzchnię terenu i miąższości wodonośnych utworów dewonu rzędu 150-250 m ich przewodność hydrauliczna, określona na podstawie wyników próbnych pompowań okazała się stosunkowo mała, od 2,3 x 10/-4 do 2,2 x 10/-3 m2/s. Takie rezultaty badań hydrogeologicznych świadczą, że zasoby eksploatacyjne wodonośnych utworów dewonu w otworze Trojanowice-2 są niewielkie i mogą zaspokoić jedynie potrzeby niewielkiej, lokalnej społeczności.
EN
Devonian carbonates in the Kraków-Silesian region are known as a relatively productive aquifer containing good quality water for drinking purposes. The lack of water resources in the Kraków metropolitan agglomeration is the reason for the beginning of reconnaisance study of the Devonian aquifer groundwater resources. The paper presents some details related to the hydrogeological research of the Devonian carbonate aquifer in the Trojanowice-2 borehole. Despite the occurrence of artesian conditions with 1.5 atm. overpressure above datum level and about 150-250 m of the aquifer thickness, the transmissivities of the Devonian carbonates are relatively low and range from 2.30 x 10/-4 to 2.20 x 10/-3 m2/s. As a consequence, the possible resources of the Devonian aquifer are also relatively low and potentially sufficient only for small, local communities.
EN
Palaeomagnetic studies of the uppermost Jurassic to lower Cretaceous pelagic carbonates in the Krizna nappe in the Strazovske vrchy Mts (Central West Carpathians, Slovakia) revealed the presence of secondary magnetite-related magnetization of exclusively normal polarity (component B), which was most probably acquired during the thrusting episode in the late Cretaceous. Three formations exposed in the Strazovce section were the subject of investigation: Jasenina Kimmeridgian.Tithonian), Osnica (Lower.Middle Berriasian) and Mraznica (Upper Berriasian.Hauterivian). Component B is ubiquitous throughout the section but is strongest in the Mraznica Formation. This formation contains a lot of superparamagnetic particles and shows rock magnetic characteristics typical of chemically remagnetized carbonates. The remaining two formations, although also remagnetized, bear traces of an older, probably primary magnetization (component C). The fold test for component B is apparently positive; however the inclination in pre-folding coordinates is too steep for any expected palaeoinclination of Jurassic to recent age. Additional tectonic correction must be applied to match the palaeoinclinations with expected values. Although there is some uncertainty in this additional correction, all plausible options suggest that the rocks must have been magnetized when they dipped in the opposite direction to the thrusting direction. This interpretation is concordant with the internal tectonics of the Krizna nappe, consisting of imbricated units of duplex-type structure.
EN
The Hith Formation forms the youngest lithostratigraphic unit of the Jurassic Shaqra Group. It represents the culmination of a succession of hypersaline and euryhaline cycles that characterise the Late Jurassic of Saudi Arabia. The Formation is poorly exposed in central Saudi Arabia, but it has been studied in detail in subsurface eastern Saudi Arabia where the upper carbonate member hosts an important hydrocarbon reservoir called the Manifa Reservoir. Chronostratigraphic control is absent from the formation itself, and the Tithonian age is suggested for the Hith Formation based on its stratigraphic position between the underlying Arab Formation of Late Kimmeridgian age, and the overlying Sulaiy Formation, of Late Tithonian to Berriasian age. The Hith Formation needs redefining in the light of new lithological evidence, and a tripartite member scheme is suggested. This includes the lower anhydrite-dominated member here termed the “anhydrite” member, and considered to represent hypersaline subaqueous deposition within a restricted deep lagoon during the lowstand systems tract of the Manifa sequence. A “transitional“ member consists of interbedded anhydrites and carbonates and approximates with the transgressive zone. The overlying “carbonate” member represents the results of a prograding shallow, normal salinity marine succession related to the highstand systems tract. Interbedded carbonates within the evaporites are interpreted to represent superimposition of a higher frequency, possibly 4th order eustatic cyclicity. The “carbonate“ member hosts the Manifa Reservoir, and here proposed as the Manifa Member, consist of five parasequences, each of which represents a shoaling-upwards cycle with a succession of up to five repeated lithofacies and biofacies that commences with a stromatolitic, microfaunally-barren unit followed by fine-grained grainstones with a monospecific but abundant ostracod biofacies. A succession of coarse pelloidal grainstones with rare foraminifera, including Redmondoides lugeoni, Trocholina alpina with a variety of unidifferentiated valvulinids and miliolids then follows, that passes vertically into coarse ooid grainstones, with rare Redmondoides lugeoni, forming the uppermost part of each parasequence.
EN
The Givetian to Frasnian boundary interval in the N part of the Kielce region (Holy Cross Mts.) consists of dark-coloured shales, marls and micritic limestones defined as Szydłówek Beds. The upper parts of the Szydłówek Beds are well exposed in the Kostomłoty-Mogiłki and Górno-Józefka quarries. These sections are situated in Kostomłoty transitional facies zone between the shallow-water carbonate platform and the deeper Łysogóry basin. The uppermost parts of the Szydłówek Beds comprise many fine-grained intercalations: laminated calcisiltites, calcarenites, calcirudites and coquinas beds. The shales, marls and micritic limestones are hemipelagic deposits of deep, quiet and oxygen-depleted basin, whereas grained limestones correspond with shallower water and higher energy environment. Laminated calcisiltites and finer calcarenites originated in the environment below storm wave base and are interpreted as surge-like turbidity flows deposits. Thicker calcarenites, calcirudites, and coquinas beds were deposited about storm wave base and are interpreted as tempestites.
18
Content available remote Vlianie kislotnoj obrabotki na proniacaemost’ karbonatnyh porod
EN
Models of near wellbore region acidizing at pressures below the parting pressure of formation are constructed: one-dimensional model of a wormhole and stochastic model of dissolution structure. In one-dimensional case in wormhole model it is supposed, that the growth direction of dissolution structure is known, and the axis of model is the axis of a wormhole. Results of wormhole modeling were compared to experimental data of one of Russian oil Fields. In two-dimensional case it is impossible to predict growth direction as the dissolution process has stochastic nature. Therefore, the dissolution structure is considered as fractal. Stochastic model is based on model of dielectric-breakdown. On models various characteristics of dissolution structures depending on Damkohler number defined as ratio of convection time to reaction time and Peclet number defined as ratio of diffusion time to convection time were investigated, also acidizing optimum technological parameters were investigated.
EN
Exploitation of the fields of low-permeable deep-laying carbonate collectors DDC is complicated by lithologic factors and physical/chemical characteristics of the production. We offer methods for hydrocarbones production intensification which save the basis of the rock from destruction, and methods of cracks' making, thermodynamic gap, thermal influence.
EN
Variscan syntectonic hy dro ther mal veins of the Prague Synform are important traces of small-scale fluid migration in Lower Palaeozoic sedimentary rocks — a process induced by late Variscan tectogenesis. Two main structural types of Variscan syntectonic calcite veins were recognised during fieldwork. Veins of Type I have an irregular or sigmoidal shape and are often arranged in en echelon arrays. A shearing regime during the formation of this type is deduced. Veins of a second structural type (Type II) have a more regular and straight shape relative to those of Type I and in some places form a dense network. The structural position of the Type II veins is related to structural elements of Variscan folds. Veins were formed due to interlayer-slip combined with fold- related fracturing that gave rise to the infilling of dilational structures. A tensional regime also permits growth of the fibrous veins. Two princpal directions were distinguished within the Type II veins. The first one is NNW–SSE and the second one shows a perpendicular ENE–WSW orientation. These directions seem to be parallel and/or perpendicular to the nappearchitec ture of the Prague Synform. Variscan syntectonic veins crystallised in a relatively closed, rock-buf fered system. Extraction of chemical components from surrounding rocks is indicated by a combined microprobe/cathodoluminescent study and by isotope geochemistry. The carbon isotope values of hydrothermal calcites reflect the carbon isotope composition of the host rocks. The delta exp.13C values of vein calcites and their host Silurian rocks are between –0.29 and –1.98‰ PDB. The same relationships were found between the veins and the host Devonian limestones (from 1.72 to 2.52‰ PDB). Samples close to the Silurian/Devonian boundary show transition values between 0.25 and + 1.16‰ PDB. The Sr-isotopic signature supports a genetic link between the calcite veins and the host rocks. The 87Sr/86Sr ra tio in calcites ranges between 0.708619 and 0.708738 and in wall rocks be tween 0.708755 and 0.709355. Aqueous and hydrocarbon-rich fluid systems have been found in fluid inclusions. Liquid hydrocarbons show mostly a light blue fluorescence suggesting the presence of higher hydrocarbons. They are more abundant in dark Silurian rocks, which are rich in organic matter. Lower salinities (0.5–8.9 eq. wt.% NaCl) and homogenization temperatures with a maximum around 140gradeC are typ i cal for the aqueous (H2O–NaCl) system. The oxygen isotopic composition of fluids ranges between –2.80 and +3.33‰ SMOW. This indicates that transformed formation waters in teracted with the host rocks and/or deeply circulating isotopically depleted meteoric waters. Intersections with the isochore specify border trapping temperatures between 127 and 160grade C and pressures from 300 to 1070 bars.
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