Search Results (7)

Coprolites from the Oligocene Menilite Formation of the Outer Carpathians in southeastern Poland were investigated to reveal the diversity of prey fishes consumed by coprolite producers. The material comprises 186 coprolites from seven localities. The coprolites are either sub-spherical, or elongate, and although classified into eight shape categories, display a morphological continuum. The phosphatic matrix is preserved in 28% of the specimens. Fish remains, including bones and scales, are preserved in 94% of the coprolite specimens. In 31% of specimens, these remains belong to the orders Perciformes, Gadiformes, Clupeiformes, and Aulopiformes. Prey sizes were estimated and compared to the sizes of fishes preserved as articulated skeletons from the same formation, that inhabited the Carpathian Basin of the Paratethys. The results demonstrate that coprolite analysis provides a significant paleontological data, which can be applied to infer fish diversity in other regions of the Paratethys, as well as in other sedimentary basins. Full article

The paper presents the geochemical characteristics of 26 selected oil seeps, more than half of which are remnants of old oil wells. The samples were collected from three tectonic units: the Magura, Silesian, and Skole units in the Polish part of the Carpathians. The analyzed seeps are mainly located on outcrops of Inoceramian beds within the Magura nappe, the Krosno Beds and Transition Beds in the Silesian nappe, as well as the Menilite Beds of the Skole unit. The study primarily focused on genetic characteristics, which were used to correlate the seeps with the oils from the deposits of these tectonic units and to assess the degree of secondary alterations. All hydrocarbon seeps were analyzed in terms of their location on surface cross-sections, and attempts were made to assign them features based on the classification proposed in 1952, which takes into account the tectonic characteristics of the regions where the seeps were identified. In the general genetic characterization, these seeps did not show significant differences, suggesting a similar source of supply as the crude oils. Among the analyzed seeps, three genetic groups were distinguished. For correlation purposes, information from published materials on crude oils and their genetic characteristics was used. Of the five classification types described in the literature, only two could be assigned to those occurring in the Carpathians. Considering the tectonic structure and the location of the seeps (based on surface cross-sections), it has been determined that most of the analyzed seeps are the result of migration along faults connecting source rocks or, less frequently, deformed deep accumulations with the surface. Full article

The research presented in the article was undertaken in order to better investigate the generation potential of the Oligocene Menilite Formation due to its importance as source rocks within the Outer Carpathian Basin. The non-isothermal decomposition of the selected Carpathian source rock was studied to determine the kinetic parameters of the pyrolysis process. The kinetic parameters of bulk rock and separated kerogen were determined using the model-free Kissinger, Kissinger–Akahira–Sunose (KAS), and Friedman methods. The pyrolysis process exhibits a complex reaction mechanism. The obtained apparent activation energy (Ea) and pre-exponential factor (A) values depend on the extent of conversion, suggesting that the process involves multiple reaction steps. This dependence is very similar when calculated using both isoconversional methods, Friedman and KAS; however, the calculated values of the kinetic parameters differ depending on the method used. It was found that the activation energy of kerogen is lower than that of bulk rock, and the reaction maximum was shifted to higher temperatures. This shift is attributed to the presence of clay minerals in the rock. The values of average activation energy and the pre-exponential factor found in this study are relatively high, possibly due to the nature of the short-chain organic matter contained in the source rock. Full article

The aim of the research presented in this article was to analyse the processes of source-rock decomposition, including kinetic parameters of pyrolysis, in relation to the type of the organic matter and its maturity. The examined source rocks were Menilite shales from several units within the Flysch Carpathians (Poland). The samples were analysed with use of thermal methods, including Rock-Eval and thermogravimetry coupled with an FTIR detector. Kinetic parameters were determined with use of the model-free integral isoconversion method Kissinger–Akahira–Sunose. The observed gas evolution from the source rocks indicates two stages of organic matter decomposition for some samples. The main stage of pyrolysis takes place in the temperature range from 300 to 500 °C, while the secondary—cracking—takes place in the temperature range from 500 to 650 °C. Using FTIR, we detected vibrations derived from N-H groups, which provide information on the presence of nitrogen in the organic matter, and indicate a low maturity level. C=C stretching vibrations of aromatic hydrocarbons prove a higher maturity of organic matter. The Menilite source rocks have different activation energies, which are related to different organic and mineral compositions. The maturity of organic matter does not have a decisive influence on the kinetic parameters. A high share of carbonates in the rock increases the value of the apparent activation energy. The high share of bituminite within maceral components reduces the value of activation energy. Full article

The study of the source rocks was carried out with the use of various analytical methods in order to assess their generation potential and to predict the decomposition products of organic matter. The selected samples from the Menilite Beds from the Silesian and Dukla units, as well as the Istebna layers from the Silesian unit, which are classified as weak and medium source rocks in the Carpathian oil system, were examined. The generation potential and type of the products obtained from the pyrolysis of the analyzed source rocks, despite the often comparable overall content of organic matter, are significantly different. Menilite shale generated a higher abundance of hydrocarbons (alkanes, alkenes, and isoalkanes) by stage pyrolysis, which suggested that the organic matter of Menilite shale is different from the Istebna source rocks. Moreover, the thermogravimetric analysis showed a two-stage weight loss in the case of Menilite shales, while the Istebna shales were characterized by a one-stage weight loss at higher temperature. For the Istebna layers, n-alkanes from the C₁–C₅ range were detected as the main pyrolysis products, which proves the gas-forming type of the organic matter dispersed in these sediments. Rock-Eval analyses showed that the organic matter reached a degree of maturity corresponding to the early thermocatalytic processes (the initial oil window stage) and therefore was able to generate liquid and gaseous hydrocarbons. The comparison of the decomposition temperatures of the organic matter from the Rock-Eval and TG analyses allowed us to conclude that both measurements correlate well and can be equally used to assess the level of thermal transformations of organic matter. Full article

Hydrocarbon exploration under thrust belts is a challenging frontier globally. In this work, 1-D thermal maturity modeling of the Paleozoic–Mesozoic basement in the northern margin of the Western Outer Carpathians was carried out to better explain the thermal history of source rocks that influenced hydrocarbon generation. The combination of Variscan burial and post-Variscan heating due to elevated heat flow may have caused significant heating in the Paleozoic basement in the pre-Middle Jurassic period. However, the most likely combined effect of Permian-Triassic burial and Late Triassic–Early Jurassic increase of heat flow caused the reaching of maximum paleotemperature. The main phase of hydrocarbon generation in Paleozoic source rocks developed in pre-Middle Jurassic times. Therefore, generated hydrocarbons from Ordovician and Silurian source rocks were lost before reservoirs and traps were formed in the Late Mesozoic. The Miocene thermal overprint due to the Carpathian overthrust probably did not significantly change the thermal maturity of organic matter in the Paleozoic–Mesozoic strata. Thus, it can be concluded that petroleum accumulations in the Late Jurassic and Cenomanian reservoirs of the foreland were charged later, mainly by source rocks occurring within the thrustbelt, i.e., Oligocene Menilite Shales. Finally, this work shows that comprehensive mineralogical and geochemical studies are an indispensable prerequisite of any petroleum system modelling because their results could influence petroleum exploration of new oil and gas fields. Full article

An extensive infrared (IR) spectroscopy study using transmission, specular and diffuse reflectance, and attenuated total reflection (ATR) was undertaken to characterise opal-AG, opal-AN (hyalite), opal-CT and opal-C, focussing on the Si-O fingerprint region (200–1600 cm⁻¹). We show that IR spectroscopy is a viable alternative to X-ray powder diffraction (XRD) as a primary means of classification of opals even when minor levels of impurities are present. Variable angle specular reflectance spectroscopy shows that the three major IR bands of opal are split into transverse optical (TO) and longitudinal optical (LO) components. Previously observed variability in powder ATR is probably linked to the very high refractive index of opals at infrared wavelengths, rather than heterogeneity or particle size effects. An alternative use of ATR using unpowdered samples provides a potential means of non-destructive delineation of play of colour opals into opal-AG or opal-CT gems. We find that there are no special structural features in the infrared spectrum that differentiate opal from silica glasses. Evidence is presented that suggests silanol environments may be responsible for the structural differences between opal-AG, opal-AN and other forms of opaline silica. Complementary studies with Raman spectroscopy, XRD and scanning electron microscopy (SEM) provide evidence of structural trends within the opal-CT type. Full article