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EN
X-ray computed tomography (CT) is one of the most accurate methods used in the analysis of drill cores, providing a non-invasive method of studying rocks and imaging their internal structure. Discussed technique gives the possibility to reproduce the CT image in various directions, without the necessity of mechanical interference in the rock material, resulting in the core destruction. Carbonate rocks are a specific group of rocks, very difficult to interpret due to a high variability of a number of parameters, such as: lithology, mineral composition, biogenic structures content, porosity, permeability, and others. The method of X-ray computed tomography (CT) can be very helpful in the analysis of various carbonate rocks features. Application of the X-ray computed tomography before dividing the core into archive and so-called ‘working’ parts can be very useful for the core documentation and archiving. The tomographic examination, carried out in appropriate time, allows to preserve a complete image of the core. X-ray computed tomography data can be used for various analyses and interpretations, including geophysical logs and borehole imaging. Continuous profiles of some parameters (such as density or porosity) along the studied core intervals also can be calculated from the tomographic image.
EN
The upper Olenekian-Middle Triassic succession of the Tatricum domain (Central Western Carpathians, southern Poland) includes a few horizons of breccias, which are intercalated with early-diagenetic dolostones. On the basis of macroscopic and microscopic (including cathodoluminescence) observations, the paper presents a new interpretation of the genesis of the breccias and their diagenetic history. The rocks studied range from monomictic, cemented mosaic packbreccias to chaotic, unsorted, monomictic, particulate rubble floatbreccias. The processes that preceded the formation of the breccias encompassed the precipitation of evaporites and the early-diagenetic dolomitization of lime muds. The solution-collapse breccias were formed during episodes of cyclic sediment emersions in the upper Olenekian and Middle Triassic, as the result of gradual sediment collapse after karstic dissolution of the intercalated evaporites. After the brecciation process, during diagenesis the rocks were subjected to cementation by sulphate minerals and next, to multi-stage dolomitization. Later tectonic processes led to fracturing and even re-brecciation of the previously formed solution-collapse breccias.
EN
Dolomitisation was the main diagenetic process in the Upper Permian Zechstein Limestone of the Wolsztyn High-dolomite cementation (“over-dolomitisation”) also occurred. The rocks studied usually have a mixed mineralogy and represent a continuous spectrum from pure limestone to pure dolomite. This is due to varying degrees of dolomitisation, dolomite cementation and dedolomitisation. There are two main types of dolomite: replacement dolomite (mostly planar unimodal dolosparite mosaics that are mainly fabric-destructive) and cement dolomite (planar isopachous rims and pore-filling non-planar saddle-dolomite crystals). The timing of dolomitisation and dolomite cementation is difficult to ascertain, but comparing petrographical and geochemical data indicates that the reef carbonates were dolomitised shortly after deposition in a near-surface sabkha/seepage-reflux and then in burial systems. It seems that many of the dolomites gain their present isotopic composition when buried in relatively high-temperature conditions, as shown by low oxygen isotopic ratios ( δ18O as low as –9‰ PDB) and the presence of saddle dolomite. No isotopic support for a water-mixing mechanism is documented.
EN
A comparative sedimentological analysis of the Upper Jurassic–Lower Cretaceous deposits carried out on drill-cores from the southern part of the Carpathian Foredeep allowed us to distinguish thirteen main microfacies types. The results of microfacies analyses and stratigraphical data made it possible to propose a lithological subdivision of the southern part of the Upper Jurassic and Lower Cretaceous sediments of the Carpathian Foredeep basement between Kraków and Rzeszów. In the analysed wells, three main sedimentary complexes were distinguished, embracing the following intervals: (i) Callovian–Oxfordian, (ii) Kimmeridgian and (iii) Tithonian– Berriasian–Valanginian. The Oxfordian, Kimmeridgian and Tithonian deposits represent the outer – mid homoclinal ramp facies, whereas the Berriasian and Valanginian deposits belong to the inner homoclinal ramp facies. Complexes of microbial-sponge reefs, with a distinct relief, could be recognised in the Upper Oxfordian sediments only. The development of these buildups took place in a basin typified by diversified morphology, determined by the block-type structure of the Palaeozoic basement and synsedimentary tectonics, which brought about substantial variability in thickness of the Oxfordian sediments. At the end of the Oxfordian, large complexes of the reef facies were replaced mainly by microbial-sponge and microbial-coral biostromes developed during the Kimmeridgian and Tithonian. In the principal part of the studied area (except the western part of the described fragment of the Carpathian Foredeep; Kraków area) during the Kimmeridgian, Tithonian, Berriasian and Valanginian, sedimentation occurred in a basin typified by homogeneous morphology, which resulted in a wide extent and comparable thicknesses of the distinguished facies types. In the studied sections, indications of partial or complete dolomitization were observed in a large part of the sediments. Four generations of dolomite document a complex diagenetic history with multiple episodes of dolomite formation: from early diagenetic environment to late burial conditions.
EN
Paleomagnetic and petrological analyses were performed on Devonian carbonate rocks from the Kielce region (Janczyce 1 borehole, Dule, Łagowica escarpment, Budy Quarry) in the Holy Cross Mts. Rock samples were selected from localities with different degree of thermal alteration, diversified lithology and stratigraphy. Investigated carbonates, excluding those from the Budy Quarry, revealed traces of the Early Permian remagnetization related to magnetite. The intensity of the Late Variscan remagnetization is linked to rocks affected by the second stage of dolomitization with increased thermal maturity in the northern part of the Kielce region. The magnetic signal is probably related to rocks’self-cooling, fixed as a result of the latest Carboniferous to Early Permian uplift.
EN
Rare-earth elements (REE) were determined for the Upper Jurassic limestone and dolomites from the following outcrops: Góra OEw. Anny, Kostrze Quarry, Księża Góra, and Skały Twardowskiego. REE patterns are similar for all the investigated samples. Dolomites and limestone are enriched in light REE, they exhibit positive La anomalies, and negative Ce and Eu anomalies. Negative Ce and Eu anomalies are typical for oxidizing environments during dolomitization processes. Distinct enrichment in light REE comparing to heavy REE indi-cates that the sea water was not the only component of dolomitization fluids.
7
Content available remote Dedolomityzacja w górnojurajskich skałach węglanowych z okolic Krakowa
EN
The Upper Jurassic limestones in the vicinity of Cracow underwent extensive dedolomitization process. Petrographic and cathodoluminescent analyses of carbonates in four test areas confirm the dedolomitization as have been developed with various intensity. The alteration of dolomite into calcite occurs as centripetal and centrifugal dedolomitization. Both processes lead finally to a complete disintegration of the dolomite crystals; calcite pseudomorphs after dolorhombs are the end products. These calcite pseudomorphs are abundant in limestones of St. Anna Mt. and in the Kostrze quarry, but are scarce in the Twardowski Cliffs area and in the outcrop of Księża Mt., which indicates a less advanced and slower dedolomitization process in the latter two areas. Most probably the initiation of dedolomitization started from the moment when a carbonate bank emerged from the sea water (Vierek, 2003); temperature of mixing fluids decreased considerably, whereas Ca 2+/Mg+- ratio in the same fluids increased.
EN
The paper presents the results of petrographic investigations (included macro- and microscopic observations, X-ray and differential thermoanalyses) of the Upper Jurassic carbonate rocks from about 20 boreholes from the region on the east from Tarnów. The research shows that dolomitized carbonate rocks arc products of the dolomitization of fragmented earlier and partially redeposited limestone fragments. The effect of more intensive dolomitization of limestones is formation in some of levels porous structures, which allows to acknowledge them as reservoir levels for hydrocarbons.
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