Hydrocarbon alteration in the bituminous salt of the Kłodawa Salt Dome (Central Poland)

Marine and Petroleum Geology 75 (2016) 325e340

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Research paper

Hydrocarbon alteration in the bituminous salt of the Kłodawa Salt Dome (Central Poland)
ska a, *, Tomasz Toboła b Aleksandra Wesełucha-Birczyn a b


w, Poland Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krako
w, Poland Faculty of Geology, Geophysics and Environmental Protection AGH, University of Science and Technology, Mickiewicza 30, 30-059 Krako

a r t i c l e i n f o

a b s t r a c t

Article history: Received 9 May 2015 Received in revised form 8 December 2015 Accepted 25 April 2016 Available online 1 May 2016

The so called bituminous salts occurring in the Kłodawa dome, located in Central Poland, differ from the surrounding salts by their colour change from light to dark brown. This colour is associated with an extremely large amount of hydrocarbon, mainly located in the inclusions. The presence of numerous fluid inclusions has been documented in previous petrologic studies, distinguishing seven main types of fluid inclusion assemblages (FIA) in terms of size, shape as well as the ratio of filling material. However, four types of inclusions were selected in the current investigations according to their unusual optical behaviour. Raman micro-spectroscopy a modern, non-destructive method was used for investigating a single inclusion being a part of FIA. Presented in this paper Raman spectra revealed a unique pattern of bands characterizing the content of the inclusions. The hydrocarbons show a very complex character reflected in the appearance of a strong fluorescence background. A well-marked heterogeneity characterized the inclusions, by diversity in the intensity of the background and in the pattern of the bands characterizing the presence of certain components. One can distinguish the presence of carbonaceous matter showing the different degrees of order. The depth profile and the analysis of the various points of the inclusions indicate that the carbonaceous matter is not evenly distributed in the inclusions but forms a thin, disorganized film on their walls. This film was also found in sites where the inclusions are filled with brine. The certain characteristics associated with the presence of the incipient phase transformation of the organic matter, or slightly transformed organic matter and the lack of light hydrocarbons as well as a number of petrologic features of inclusions indicate that these salt rocks have been subdivided into thermal transformations, accompanied by the recrystallization of the halite and the escape of the more volatile compounds such as methane, ethane, etc. © 2016 Elsevier Ltd. All rights reserved.

Key words: Hydrocarbons Bituminous matter Raman micro-spectroscopy Fluid inclusions Halite Zechstein

1. Introduction Investigations of hydrocarbon fluid inclusions, common in various rock types, are of remarkable importance both from a scientific and economic point of view. The development of analytical methods for their determination allows us to more precisely assess the data necessary for the reconstruction of the migration of petroleum and gases, as well as the environment of entrapment of inclusions. Hydrocarbon identification can be achieved by two types of techniques: conventional, which are accurate but usually destructive, or non-destructive (Munz, 2001; Bourdet et al., 2008).

* Corresponding author.
ska), tob@ E-mail addresses: [email protected] (A. Wesełucha-Birczyn geolog.geol.agh.edu.pl (T. Toboła). http://dx.doi.org/10.1016/j.marpetgeo.2016.04.026 0264-8172/© 2016 Elsevier Ltd. All rights reserved.

The destructive methods that include gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and gas chromatography-initial ratio mass spectrometry (GC-IRMS) allow us to precisely determine hydrocarbon composition, but these data do present a mixture of the average of all, different inclusion content occurring in the studied sample. On the contrary, modern nondestructive methods, such as petrography, micro-thermometry, fluorescence, infrared and Raman micro-spectroscopies provide information about a single fluid inclusion forming part of the fluid inclusion assemblage (FIA). The petrography and microthermometry of FIA are useful tools for the determination of the aspects of time, temperature and pressure of the petroleum migration (Munz, 2001; Bodnar, 1990; Goldstein and Reynolds, 1994; Goldstein, 2001). A great deal of research has been devoted to assess the composition or types of hydrocarbon in the inclusions, which are characterized by such physical parameters as bulk

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density (r), molar volume (Vm), vapour volume fraction (4vap) and homogenization temperature (Th) (Aplin et al., 1999, 2000; Bourdet et al., 2008; Grimmer et al., 2003; Liu et al., 2003; Parnell et al.,
ry et al., 2000, 2002; Tseng and 1996; Teinturier et al., 2002; Thie Pottorf, 2003). The determination of hydrocarbon composition in naturally occurring inclusions is a difficult task because of their chemical complexity and high fluorescence background (Burke, 2001; Zhang et al., 2007). The application of Raman and Fourier-transform infrared spectroscopy allows for the identification of the characteristic vibrations of functional groups such as: CH2, CH3, CO, H2S, CO2, N2 (e.g. Grishina et al., 1992, 1998; Pironon and Barres, 1990, 1992; Pironon et al., 1995a, 1995b, 2000). Some of the works have been devoted to the analysis of model, synthetic inclusions filled with known hydrocarbon content and the comparison of this pattern to naturally occurring inclusions (Zhang et al., 2007). Raman analysis has been particularly promising in the analysis of gaseous non-aqueous volatile components in fluid and supercritical fluid inclusions (Burke, 2001). Hydrocarbon deposits or their agglomerations are very often associated with salt formations. It is due to the special properties of rock salts, which are impermeable and create isolated horizons. The most often hydrocarbon deposits occur in the vicinity of salt domes or ridges which are the main salt bodies induced by tectonic movements. The occurrence of organic matter and hydrocarbons within the evaporate formation is a key topic discussed in the geological literature (e.g. Warren, 1999; Sonnenfeld, 1984). In general, three sources of organic matter are proposed. The first two are connected with the sedimentary environment followed by diagenetic changes. Firstly, the origin of organic matter is associated with salt-loving organisms (algae or bacteria) growing in the upper part of the water body of salt basins. The second source consists of plant debris transported from terrigenous influx. The third one may be connected with tectonic activities, where within the formed shear zones hydrocarbons can migrate into salt rock. Such faults sealed by the recrystallization of halite can cause substantial quantities of hydrocarbons trapped at their borders and within the halite crystals in the form of inclusions and cracks. A visual examination of fluid inclusions appearing in the Kłodawa Salt Dome, discussed in light of the distinction due to the their colour, texture and structural features, and also position in the deposit, has been the subject of previous petrological studies (Toboła, 2010). This study concentrates on the most interesting types of FIA with different geometrical features decrypting their composition, the variable ratio of brine, hydrocarbon and gase phases. Most of them show typical secondary features (eg. Roedder, 1984a,b; Goldstein and Reynolds, 1994) and the absence of primary FIA what suggests the epigenetic origin of a portion of the bituminous salt. However, the internal structure of the Kłodawa Salt Dome is complicated due to its many distortions. An example would be the organic matter already found in another type of epigenetic salt: the
ska et al., 2008). blue jet halite mineral (Wesełucha-Birczyn The largest blue jet halite zones, located at the 575 (the ventilation gallery between chambers KS39 and KS38) and 600 level (chamber KS39), were the source of the samples with the remarkable inclusions that they contained. The characteristic feature in Raman spectra was the blue jet band at the ca. 199 cm
1 marker of the KCl presence in the thin, surrounding area of the studied inclusions. Raman spectroscopy combined with petrology analysis revealed that the dominant fluid component is a mixture of 2
various hydrocarbons, including CH4, CO2 and also ions SO2
4 , CO3 . The next mineralogical rarities are navy-blue, blue and purple forms found in the ventilating gallery at level 562 (Wesełucha
ska et al., 2012a; Zelek et al., 2015). In contrast to the Birczyn

halites with blue jets these coloured halite samples present an unusual concentration of colour centre aggregates. F, R1 and R2 bands together with the plasmon and M-band were identified, and their populations and the dynamics of their transformation were estimated. The other types of rocks which contain hydrocarbons, located in the Kłodawa dome, are the Stinking Shale (T2) and Main Dolomite (Ca2). However, a geochemical analyses of these rocks (Czechowski et al., 2011; Wagner and Burliga, 2014) indicate only short distance migration of hydrocarbons and only within these rock complexes. The aim of our study is to determine if Raman microspectroscopy can help differentiate the chemical composition of petroleum and gases in various kinds of FIA in the unique kind of rock found in the Kłodawa Salt Dome, so called “bituminous salt”. For these trials we selected samples placed at the 600 and 587 m level (Fig. 1, inset), in the vicinity of the blue salts. We believe that a comparison of these two different types of salts i.e. blue and bituminous salts, in the context of hydrocarbon migration, may provide some useful geological information about the environment of such epigenetic rock salts. Raman micro-spectroscopy is a modern, non-destructive method for investigating a single, unique inclusion being a part of FIA. This is a big difference compared to conventional methods, where the analysis of the fluid inclusions requires sample destruction. Destruction of the sample by crushing and subsequent dissolution leads to the escape of volatile compounds such as methane, ethane, and also aromatic hydrocarbons. Therefore, the results obtained in this manner are incorrect and represent the average all the inclusion residues left in the studied sample. In this context previous Natkaniec-Nowak et al., 2001, results can not be compared with the current work, as we distinguish between content within a single inclusion. 2. Materials and methods 2.1. Geological setting The Kłodawa Salt Dome is the largest diapir in Poland. It is located in central Poland and belongs to the Izbica Kujawska e Łe˛ czyca salt ridge (Fig. 1). The development of this salt dome, as well as other salt structures (pillows, ridges, domes etc.) in Poland are strictly connected with the development of the Mid-Polish Trough (MPT). This deep geological structure belongs to the system of epicontinental basins of western and central Europe (Ziegler, 1990). It evolved during the Permian to the Cretaceous Period along the Teisseyre-Tornquist Zone and it is filled with several kilometres of sediment (e.g. Marek and Pajchlowa, 1997; Dadlez et al., 1995; Dadlez, 2001, 2003). During the Late Cretaceous e Paleocene the MPT was uplifted and significantly eroded in the axial part (e.g. Dadlez et al., 1995; Dadlez, 2001, 2003; Krzywiec, 2004, 2006a,b). The inner and outer structure of the dome has been presented in numerous papers (e.g. Burliga, 1994, Burliga et al., 1995; Charysz, 1973; Garlicki, 1991, 1993; Garlicki and Szybist, 1986, 1991; Poborski, 1970, 1974; Poborski and Marek, 1970; Tarka, 1992; Wachowiak, 2010; Wagner, 1994; Werner et al., 1960). They are concerned with such geological issues as the mineralogical and petrological characteristics of salts, the lithological succession of evaporates, and tectonics. The Kłodawa salt deposit is build of rocks, which belong to fully developed PZ2-PZ4 cyclothems (Zechstein). They consist of thin layers of claystone, carbonates, anhydrites and a much thicker coat of various kinds of salt rocks, clayey salts and potash intercalations. All these sediments are strongly deformed and create a very complicated inner structure of deposits. The most often tectonic events show piercing of older salt layers by younger ones and the youngest one, tailing out of the layers. The occurrence


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Fig. 1. Distribution of salt structures in the central part of the Mid-Polish Trough (from Garlicki and Szybist, 1986; Dadlez, 2001; modified by the authors); inset e Geological crosssections through the Kłodawa salt dome.

of narrow folds with high amplitude are the effect of deformations resulting from various rheological properties of rocks. In a general outline, two anticlines elongated in a NW-SE direction predominate in the SW and NE parts of the diapir. Anticlines are separated by the deep central syncline composed of the youngest salt layers. Representative samples of bituminous salt were obtained from a deposit of precise latitude and longitude equal to 52140 26.66400 N and 18 550 21.5400 E, respectively, while the depth below the surface was 600 m and 587 m, marked in Fig. 1 (inset).

Toboła (2010) FIA types nomenclature, due to their remarkable optical behaviour. The first kind of inclusions are those emerging on the surface of the single anhydrite crystals. The second variety are two kinds of inclusions of the type I (the first: gaseous, not fluorescing in the UV light and the second: filled with liquid hydrocarbons, fluorescing in the UV light). Then, the third studied class represents two examples of type III fluid inclusions. The fourth sort are two illustrations of a VII type eye-shaped fluid inclusion showing a very strong fluorescence that varies depending on the locations within inclusion.

2.2. Description of material 2.3. Analytical methods In some parts of the Kłodawa deposit, mainly in the older salts (Na2), one can meet a rock salt that displays colour changes from light to dark brown, that emits the smell of bitumen (NatkaniecNowak et al., 2001; Toboła, 2010). That kind of so-called “bituminous salt” contains a considerable amount of hydrocarbon giving it a specific colour and smell. In the deposit they form a very diverse agglomeration with respect to size, intensity of colour and shape. Most often they form streaks, lenses or layers with a parallel course to the bedding of the surrounded sediments (Fig. 2A). They are very often shaped as nests with irregular contours, sharply separated from the surrounding rocks (Fig. 2B), sometimes forming bands with fuzzy boundaries (Toboła, 2010). Bituminous salts are coarseegrained or crystal salts with the size of the crystals reaching even several centimetres (Fig. 2C). Under macroscopic observations, in spite of the colour of the whole rock, the halite crystals are clean and transparent. Sometimes on their boundaries occur small to several millimetre clusters of dark brown or black matter. We have selected four types of inclusions, according to the

2.3.1. Optical microscopy Six samples taken from the largest and most representative outcrops of bituminous salts were chosen for the preliminary studies. Thick sections for the petrologic and fluid inclusion study were prepared from each of these samples. They were made by cracking the previously separated single halite mono-crystals or by the cutting of more fine-grained rock salt by a low-speed saw. In the next stage, thick sections were ground with sandpaper and polished. A petrological observation of thick plates were performed on the Nicon Eclipse E600 microscope using 5, 20, and 50 magnification objectives. As an additional UV source an outside diode lamp (365 nm) was used. 2.3.2. Raman micro-spectroscopy A hydrocarbon fluid inclusion of selected representative, single, inclusions from a fluid inclusion assemblages (FIA) in the halite samples were chosen and excited with a 785 nm line of HP NIR (high power near IR) diode laser. The laser focus diameter was ca.

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Fig. 2. A) Streaks of bituminous salt in the area of outburst caverns in the main gallery on the level 600; B) Irregular conglomeration of bituminous salt in the area of the outburst caverns in the main gallery on the level 600; C) Coarse-crystalline and crystal bituminous salts from the conglomerations shown on part B; D) Microphotograph in transmitted light (1N) of thick plate with conglomerates of anhydrite crystals and with brown bituminous matter located near the boundary of the halite crystals. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

1e2 mm. Raman spectra were collected with a Renishaw InVia Raman spectrometer (grating 1200 g/mm), equipped with a Peltier cooled CCD detector, working in a confocal mode in a backscattered geometry. A Leica microscope with 100 and 50 magnification objective was used to focus a laser on the samples (NA ¼ 0.90 and 0.70, respectively). Laser power was kept low enough to avoid sample degradation (0.5e1.5 mW). During the point mapping experiments, the sample was shifted on a motorized stage (Prior Scientific) at selected points. The confocal microscope mode allows also for performing depth-resolved measurements with discrete steps, on the micrometer scale. For the mapping experiments, factory supplied software was used (Renishaw, WiRE v. 2.0 and 3.2). Raman images are based on integrated Raman intensities. The Raman spectroscopy method has significant advantages over established conventional techniques regarding specificity, sensitivity, and sample preparation requirements. However, one has to admit that the research material analysis of a single fluid inclusion may be difficult due to its small size (from a few mm to above 1 mm), so a small amount of fluid provides a Raman signal. An additional issue is the fact that CCD-detectors, which are commonly used detectors today, are Johnson- and shot-noise limited, what is mentioned hereafter The Johnson-noise phenomena, is due to thermal fluctuations, so the noise level represents the intrinsic detector noise in the absence of a signal. The shot-noise is associated with the particle nature of light (Perepelitsa, 2006). When the sample spectrum is measured with very low laser power, the noise level is multiplied. A small object's detection is impaired significantly from those effects, and noise can be a big problem. Minor components in fluid inclusions lead to weak bands, so the exact composition of the mixture may be difficult to assess, taking into account that noise can interfere with the observation of the spectrum (Bowie et al., 2000a). Another disorder is that introduced by the fluorescence phenomena,

however, it is more commonly encountered in Raman spectra due to the shorter laser wavelength excitation. This situation may be worse if the sample fluorescent is significant so that there is no possibility to observe any Raman bands above the fluorescent background. Black or dark samples absorb enough radiation from a laser source to increase the temperature (Bowie et al., 2000b). A hot sample emits blackbody radiation. On increasing the laser power supply, the intensity of the Raman bands may grow, but the baseline started to increase for higher wavenumbers because of the effect of the sample heating. The heat as a result of the increased laser power or measurement time, slowly changed the structure of the sample. Sample heating generally causes bands to broaden. Another complication may be in the case of opaque, diffusely scattered material. All of these difficult cases occur in organic fluid inclusion studies. Adjusted measurement conditions must take into account all of the above circumstances, as it is difficult research material. One has to take into consideration that Raman micro-spectroscopy is the only non-destructive method that provides information about the content of inclusions. 3. Results 3.1. Petrographic properties of bituminous inclusions Inclusions on the surface of the anhydrite crystals and very diversified bituminous and liquid inclusions were observed in the halite crystals. Small anhydrite crystals up to 50 mm are most often in the form of agglomerates, which are deployed on the borders of halite crystals (Fig. 2D). They are accompanied by dark brown bituminous matter. Within the halite crystals anhydrite often forms narrow streaks or single crystals up to 0.5 mm in size and


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hypidiomorphic or idiomorphic in shape. On their surface very often numerous fluid inclusions occur. They are filled by hydrocarbons, in a liquid or gas phase. Due to their different position they are considered separately. Previous petrological investigations catalogued seven main types of FIA with intermediate types occurring among them (Toboła, 2010). Such types have been distinguished in respect to their position and orientation to the crystallographic axis, size and shapes of the inclusions, the ratio of the gas to liquid phase, the ratio of solutions to hydrocarbons and optical properties of hydrocarbons. The distribution of all these types within halite crystals is irregular. Some parts of the crystals are free of FIA or have single assemblages. In the other parts of the crystals FIA are frequent and their various types coexist with each other. The size of the inclusions with regard to FIA changes from a few mm to above 1 mm. Their shapes in some FIA are regular (cubic) or highly elongated in one direction (Fig. 3A). Such inclusions are filled with solutions, which are accompanied by gas bubbles or droplets of hydrocarbons. Other types consist of greatly irregular inclusions with rounded boundaries or sometimes flattened shapes (Fig. 3B). Very often such inclusions are linked together to form networks. They are largely filled with hydrocarbons which are transparent or light yellow in colour in transmitted light. Four different types of inclusions: occurring on the surface of the single anhydrite crystals, which must be dealt with separately as well as those described previously as type I, III, VII (Toboła, 2010), due to their notable optical behaviour, were selected for Raman analysis and were re-inspected in transmitted light under a polarized microscope. 3.1.1. Inclusions on the surface of the anhydrite crystals Inclusions on the surface of the anhydrite crystals, occurring as ingrown in halite crystals, are in an overwhelming majority of sizes up to several micrometers (Fig. 4A). These inclusions are mostly opaque in the presence of transmitted light and sometimes show a very weak, blue fluorescence colour under UV light. Only in a few cases was the fluorescence stronger, but it was found in the larger inclusions. Much less common are inclusions of a larger size of up to 40 mm (Fig. 4B). Such inclusions show a transparent area in their central part. In comparison to the inclusions filled with liquid or gas phase they show some other unusual optical features. Generally, an inclusion with gas bubbles shows a clear, sharp rim due to the low index of the refraction of the gases in relation to the liquid phase or especially to the host minerals. However, in the case of large inclusions, developed on the anhydrite surface, the inner part of the phase boundary rim is not sharp but gradually passes to a

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transparent area in the centre. It can be inferred that the composition of the inclusion is not simple. 3.1.2. Type I inclusions The I type of the FIA consists of small inclusions from few to several micrometers and with regular shapes or sometimes slightly rounded boundaries. The course of such FIA is short, does not cover the entire halite crystal, sometimes wavy or bifurcating (Toboła, 2010). Under microscopic observations in the transmitted light three types of filling material have been identified. They are filled most often with transparent or light yellow hydrocarbons in visible light and fluorescing blue under the UV (Fig. 4C and D). Somewhat less commonly the filling material consists of a brine or gas phase. Very often one can observe that the composition of inclusions gradually changes along the FIA zone. In one part of their track they are filled with hydrocarbons, which on the other side passes into the gas phase or solutions (Fig. 4C). Most often such changes are observed in the end fragment of the FIA where hydrocarbons or solutions pass into the gas phase. This is related to the change in the size of the inclusions which in the final parts of the FIA become smaller until they disappear. 3.1.3. Type III inclusions Type III of the FIA is built of much larger inclusions whose length may exceed 500 mm, and they adopt regular, rectangular shapes (Fig. 4E and F). Their courses are longer and often cover whole halite crystals. Inclusions of this type are mostly elongated in the direction of the whole FIA and they are filled with light yellow hydrocarbons accompanied by a slight amount of solutions, sometimes even with a bubble of gases inside liquid hydrocarbons. In the course of the FIA the inclusion shapes are often subject to change and become shorter and thicker. In this case, they are filled with brine within which hydrocarbons are present in the form of small bubbles. Some of the inclusions filled both liquid and gaseous phases with a very different ratio for the two components. 3.1.4. Inclusions the VII type The FIA marked with the number VII consists of the largest inclusions (from 0.1 to over 1 mm) filled with a dark brown phase composed of hydrocarbons with gases in a constant ratio of about 30% (Fig. 5A). In the crossed nicols (NX) hydrocarbons show colours similar to birefringent minerals, so the observed phenomena seems to be related with the rotation of the plane of polarization of the light (Fig. 5B). These optical properties of hydrocarbons gradually disappear during heating at a temperature of about 70  C. Colours appear again at the same temperature during cooling. The gaseous

Fig. 3. A) Cubic inclusions filled with gas phase and highly elongated inclusions, filled mostly with solution (microphotograph in transmitted light e 1N); B) Irregular, flatten inclusions connected together (microphotograph in transmitted light e 1N).

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Fig. 4. A) A group of opaque inclusions on the surface of the anhydrite crystal (microphotograph in transmitted light e 1N); B) Single, larger inclusion on the anhydrite surface with a transparent area in the central part of the inclusion (microphoto in transmitted light e 1N); C) FIA of the small, regular inclusions (type I) filled with light yellow hydrocarbons and gas phase (microphotograph in transmitted light e 1N); D) The same area as in C in UV (365 nm) light; E) Elongated inclusions of type III mainly filled with hydrocarbons and more regular inclusions filled with the solution and gas phase (microphotograph in transmitted light e 1N); F) The same area as in E in UV light. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3.2. Micro-Raman spectra

NaCl second-order Raman spectra, as well as a much weaker, broad band around 500 cm
1 due to third-order Raman scattering (Pasternak et al., 1974). Raman lines corresponding to the OeH stretching mode are observed at 3480 cm
1 and 3590 cm
1, what is
ska et al., in agreement with our previous data Wesełucha-Birczyn 2008.

The diatomic ionic crystals, eg. alkali halides as NaCl, have one formula unit in the cubic unit cell, therefore there is no one-phonon Raman spectrum (Krishnan, 1971). However, an impurity atom in a solid can induce the Raman activity of the atoms in its neighbourhood (Leigh and Szigeti, 1969). Before measuring the Raman spectrum of the inclusions, the halite Raman was recorded (Fig. 6). The colourless mineral gives the dominant band in the spectrum at ca. 340 cm
1 which belongs to

3.2.1. Inclusions on the anhydrite solid inclusion An example of fluid inclusions at the boundary of the anhydrite crystal, which is ingrown in halite crystals, is presented in Fig. 7A (marked with a white oval on the microphotograph; 5 magnification). Anhydrite (CaSO4) is known to accompany the halite rocks as crystals or nodules. Raman spectra measured at points marked with numbers 1e3, show significantly enhanced bands according to sulphate ion (SO4)2
symmetry at 416 cm
1 (n2, (SO4)2
sym.

phase shows similar optical properties on the inner boundary of the transparent area as was observed on the anhydrite surface. Inclusions of the VII type show a blue fluorescence colour under UV light (Fig. 5C).


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331

Fig. 6. Halite mineral, FIA-free area; Microphotograph in reflected light (50 magnification). Micro-Raman spectra in the 3800e200 cm
1 range.

Fig. 5. A) Large inclusion of type VII filled with brown hydrocarbons (microphotograph in transmitted light e 1N). In the left part of the inclusion the hydrocarbons have a uniform colour and contain a gas bubble. In the right part of the inclusion hydrocarbons have a heterogeneous structure and are not so transparent; B) The same inclusion under cross polarized light. Note the right part of the inclusion shows „interference colours“; C) The same inclusion is in UV light. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

bend.), 675 cm
1 (n4, (SO4)2
antisym. bend.), 1017 cm
1 (n1, (SO4)2
sym. stretch) and 1169 cm
1 (n3, (SO4)2
antisym. stretch) (Fig. 7B) (Liu et al., 2009; Frezzotti et al., 2012). A high background in the spectrum in point 3 on the inclusion boundary was observed. An oval Fig. 7B inset shows an enlarged region between 1200 cm
1 and 1600 cm
1 for the 1st measured spot within the inclusion (vide Fig. 7A). The spectrum shows a characteristic band pattern with peaks at: 1446 cm
1 (CH2, CH3), 1420 cm
1 (CH2 bending), 1390 cm
1 (CH3), 1357 cm
1 (CH3), 1326 cm
1 (CC, CH),

1300 cm
1 (CH2 twist) (Larkin, 2011), 1245 cm
1 and 1230 cm
1 (CH3 rocking vibrations and asymmetric CCN stretching and/or NH2) (Snyder et al., 1978). The rectangular inset shows for comparison spectra collected in both the investigated spots within inclusion: no 1 and 2 (Fig. 7B). The second spot clearly shows a different pattern typical for the formation of the carbonaceous matter (CM) with bands at 1603 cm
1, 1412 cm
1 and 1392 cm
1 (Beyssac et al., 2003; Jehli cka et al., 2003; Wopenka and Pasteris,
ska and Natkaniec-Nowak, 2011). It can 1993; Wesełucha-Birczyn be inferred, in agreement with petrographical observations, that the discussed inclusion is not homogeneous, a fluid phase (gas or liquid) dominates in the centre, while the branched hydrocarbon moieties on the edges. Bands observed at point 2 may mark the condensation of the aromatic process by the appearance of a 1603 cm
1 band. Maturation may be announced by transformation into carbonaceous matter occurring on the outer layer, as it is not fluorescing in UV light. However, the discussed bands in spectrum number 3 are partly hidden by a fluorescent background originating possibly from the dispersed organic matter (Burke, 2001; Zhang et al., 2007). 3.2.2. Type I inclusions Raman analysis was performed on two kinds of inclusions of the type I FIA: first, gaseous, not fluorescing in the UV light (vide Fig. 4C and D, the right side of the microphotographs, and Fig. 8) and second, filled with liquid hydrocarbons, fluorescing in the UV light

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Fig. 7. Fluid inclusions accompanying anhydrite crystal, vide Fig. 4B, (A) Microphotograph in reflected light taken with: 5, 20 and 50 magnification (inclusion marked with a white oval); (B) Raman spectra (50 magnification) in the region 3500e120 cm
1. Oval inset presents an enlarged, curve fitted area for point 1, while the rectangular inset presents Raman spectra in point 1 and 2 in the 1700e1200 cm
1 range.

(vide Fig. 4C and D, the left side of the microphotographs, and Fig. 9). The first example of type I FIA gaseous inclusions, built of small inclusions with regular shapes, is illustrated in Fig. 8A with varying magnification: 20, 50 and 100. Even though inclusions are not fluorescing in UV light, they may be regarded as gaseous, Raman depth profile measurements demonstrate a heightened background. It is worth noting the variability of the composition within a single inclusion, as may be seen in the changeability of Raman spectra while sample depth penetrates from 1 to 3 mm (a three spectra step is equal to 1 mm) (Fig. 8B). Inset in Fig. 8C, shows an enlarged Raman spectrum of the selected single inclusion, magnified 100, in the 1700e1200 cm
1 region. Characteristic bands appear at 1595 cm
1 (C]C), 1547 cm
1, 1472 cm
1 (dCH3/dCH2), 1419 cm
1 (CH2), 1358 cm
1 (CH3 bending), 1320 cm
1 (CC) and 1241 cm
1 in the region typical for hydrocarbon bending vibrations
ska et al., 2008; Larkin, (Zhang et al., 2007; Wesełucha-Birczyn 2011). Bands at wavenumbers 1595 cm
1, 1547 cm
1 and 1320 cm
1 mark the process of forming disordered carbonaceous matter (Zhang et al., 2007; Beyssac et al., 2003; Wopenka and Pasteris, 1993). This band pattern is similar to that observed for the 2nd spot of fluid inclusions accompanying the anhydrite crystal

(Fig. 7B), i.e. on the wall of the most intensive band at 1420 cm
1 (CH2) and 1357 cm
1(CH3). In the low energy region there appears a band at 350 cm
1 characteristic for the halite samples (LO), so this signal may come from the surrounding inclusion mineral matrix
ska et al., 2008; Burke, 2001; Krishnan, 1971). (Wesełucha-Birczyn The second example of liquid inclusion of type I located quite deep in the crystal is shown in Fig. 9. This inclusion was studied applying the depth-penetration method (seven spectra into the inclusion depth, with the distance between the spectra equal to 1 mm). Background intensity variability is the most characteristic feature of this type of inclusion shown in Fig. 9B and C. This inclusion seems to be an example of sulphur bearing inclusion: acquisition 2 shows: 865 cm
1 (COS) and 2630 cm
1 (H2S); acquisition 3: 2930 cm
1 (CH4), 2230 cm
1 (CN); acquisition 5: 2550 cm
1 (HS), 1550 cm
1 and 1069 cm
1 (HSO
4 ); acquisition 6: 2930 cm
1 (CH4), 2150 cm
1 (CN); 1550 cm
1 (O2) and 1130 cm
1 (SO2). Aq1 and aq7 show traces of organic/carbonaceous matter, the 1353 cm
1 band means the formation of carbonaceous matter which is located at the border of the tested inclusion. The individual acquisitions presented in Fig. 9D are rather noisy, because the studied inclusion was located deep in the sample (Fig. 9A) and the fluorescent background hindered the observation of the particular


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Fig. 8. Inclusions of type I, vide Fig. 4C, D, (A) Microphotograph in the reflected light taken with: 20, 50 and 100 magnification; (B) Depth-profile Raman spectra taken with 100 magnification in the 1620e1050 cm
1 region, (spectrum 1 e depth 0 mm, spectrum 2 e depth 1 mm, spectrum 3 e depth 2 mm). (C) Raman spectrum for point 1 in the 3200e100 cm
1 range; inset presents an enlarged, curve fitted area in the 1650e1100 cm
1 range.

bands, even if the spectra were background corrected. The signal to noise ratio is satisfactory for the first and second spectrum of the inclusion. Deeper lying layers are composed of diffusely scattered materials as indicated by a blurred bandwidth and a high background. It should be pointed out that all of the bands that are characteristic of the carbonaceous matter are broadened, they are even being smeared into the background, what is characteristic for the disordered phase (Yurtseven and Sherman, 1988; Zhang et al., 2007). 3.2.3. Type III inclusions An exemplary type III fluid inclusion, in visible and UV light, is presented in Fig. 10A. The liquid part of the inclusion is only weakly fluorescing in the Raman scattering (Fig. 10A and B, spectrum no 1). The Raman spectrum shows characteristic bands in the CH2, CH3 group bending region. The curve fitted 1200e1600 cm
1 region (Fig. 10B inset) reveals a similar hydrocarbon content as was observed in the inclusion shown in Fig. 7B. Some weak bands appearing at 464 cm
1 and 526 cm
1 may signify the presence of sulphur compounds in the brine. However, the discussed inclusion shows an unusual fluorescing background, which is not typical for a brine solution. This may indicate the presence of a thin layer which is enclosing this inclusion causing the Raman signal to

blur. The fluid hydrocarbons inside the bubble are fluorescing so strongly (the signal recorded in point 2 is ~40 times more intense than in point 1) that Raman bands are hidden under this background, such that they are not visible (Fig. 10A and B, spectrum no 2). The second example of the type III inclusion, which is not fluorescing in UV light, is shown in Fig. 11. The Raman spectrum reveals a 865 cm
1 band of COS (Grishina et al., 1992), a CO2 1263 cm
1 band, a C3H8 2875 cm
1 band (Burke, 2001; Zhang et al., 2007), water vapour at 3585 cm
1, a broad water band centred at 3540 cm
1, along with halite bands in the 350e400 cm
1 region
ska et al., 2008). (Krishnan, 1971; Wesełucha-Birczyn 3.2.4. TypeVII inclusions VII type inclusion with a characteristic eye-shape is shown in Fig. 12. This fluid inclusion presents a very strong fluorescence in the outer component (microphotograph Fig. 12B and intensity map at point 300 cm
1 in Fig. 12C and D). Therefore, a very low power laser was used, as low as 0.5 mW on the sample. The spectra collected in the depth profile mode (Fig. 12E) show the presence of
1 traces of sulphur: e.g. acquisition 2: 998 cm
1 (SO2
4 ), 1056 cm
1
1 (HSO
) and 1170 cm (SO ); acquisition 3: 1170 cm (SO ) and 4 2 2 2875 cm
1 (H3C8); acquisition 8: 1170 cm
1 (SO2) and 2520 cm
1

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Fig. 9. Inclusions of type I, vide Fig. 4C, D, (A) Microphotograph in reflected light taken with 100 magnification; (B) Depth-profile Raman spectra (9 spectra situated in the mutual 5 mm distance) in the region 3500e120 cm
1, 3D representation; (C) 2D plot; (D) Selected micro-Raman spectra (acquisitions: 1, 2, 3, 5, 6, and 7), vide (A) showing fluid species in inclusion, fluorescence background was corrected; region 3200e500 cm
1.

(HS
); acquisition 9: 865 cm
1 (COS) and 1370 cm
1 (CO2). This inclusion's content and character of Raman spectra seems to point towards a transformation leading to the creation of amorphous CM (Jehlicka et al., 1997). A second example of VII type inclusions is presented in Fig. 13. This one is fluorescing quite significantly in the inner core layer (point 2), the interior shows a lower fluorescence (point 1; 0.8 times lower), while the outer layer shows a very small intensity (point 3 & 4) (Fig. 13B). The spectrum in point 3 seems to come from the hydrocarbon vibrations and the possibly amorphous CM (Fig. 13C) (Jehli cka et al., 1997). The outer layer is also marked as a sulphur bearing inclusion, from the intensive background the 865 cm
1 (COS) and the 2630 cm
1 band of H2S can be resolved (Fig. 13D, point 4).

hydrocarbons and complicated processes of recrystalization of halite crystals (Toboła, 2010). Their position in the halite crystals indicates a secondary origin and in this context they show petrologic similarity to those observed in cracking planes (type 2) by Pironon et al. (1995a,b). The only exception is the inclusions gathered on the anhydrite crystals, which, because of their position can be considered as primary or pseudosecondary in origin (Goldstein and Reynolds, 1994; Roedder, 1984a, b), indicating that hydrocarbon migration occurred during the cracking and recrystalization of the halite. Raman analysis has allowed for the observation of the presence of light and aromatic hydrocarbons in single inclusions what was not possible with conventional spectroscopic methods (NatkaniecNowak et al., 2001).

4. Discussion

4.1. Inclusions with transient phases

Previous petrologic investigations of natural bituminous salt (halite) from the Kłodawa Salt Dome showed various kinds of types of FIA, which may indicate different stages of migration of

4.1.1. Inclusions on an anhydrite solid inclusion Raman analyses of all bituminous inclusions point to their complex character. In most cases they show very strong


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Fig. 10. Inclusions of type III; (A) Microphotograph, with marked two points of measurement, in reflected light taken with 20 and 50 magnification; (B) Raman spectra (50 magnification) in the region 3500e120 cm
1; (C) Inset presents an enlarged, curve fitted area for point 1 in the 1500e1100 cm
1 range; (D) inset presents the 600e400 cm
1 range (point 1).

fluorescence, what makes it difficult to identify them. Similar observations were noted by Pironon et al. (1995a,b). In some cases, one can detect the characteristic features of the distribution and composition of organic matter in inclusions, which display transition phase features in the process of organic matter creation. The first example is found in the fluid inclusions placed on the surface of the anhydrite ingrown in the halite crystals. In the central part of these inclusions, Raman spectroscopy confirms the presence of long-chain aliphatic hydrocarbons, with a well developed d(CH2) band at 1420 cm
1; methylene/methyl (A1420/A1357) area ratio is equal to 1.11 (Fig.7B, point 1). These kinds of hydrocarbons in normal conditions form a liquid phase. However, branched hydrocarbons on the edges of these inclusions show an A1420/A1357 area ratio equal to 0.90 (Fig. 7B, point 2). Additionally, the presence of the 1603 cm
1 band (Fig. 7B point 2, rectangular inset), characteristic for condensed ring aromatics (Colthup et al., 1964), may indicate the occurrence in addition to a significant amount of the liquid phase also a solid phase forming the inclusion's envelope or a

mixture of both phases. The most outer part of the inclusion shows very high fluorescence (Fig. 7B, point 3) in comparison to its inner part (Fig. 7B, points 1 and 2). Such fluorescence is typical for unsaturated organic structure aggregation which is a transient phase guide to CM formation and is associated with the disordered structures (Stasiuk and Snowdon, 1997; Wopenka and Pasteris, 1993). Therefore, it may indicate the presence of solidified bitumens on the envelope of the inclusions (Jehli cka et al., 1997). As was found by Jehlicka et al. (1997) solid bitumens may form grains of sizes in the range from several to hundreds of nanometres in length. In the case of inclusions on an anhydrite surface such grains may constitute denser packed structures on the inclusion walls what leads to higher fluorescence. Towards the centre of the inclusions the density of the particles gradually decreases as proposed in Fig. 14. This diffuse structure, not visible directly under optical microscopic observations, may be responsible for the characteristic reflection, refraction and interference of the transmitted light.

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solid, long chain hydrocarbons at the end parts of the course of the FIA located near the boundary of the halite grains suggests that in these end part inclusions have been unsealed and re-equilibrated during recrystalization. Such a transformation caused the escape of the lighter hydrocarbons as more volatile compounds and remain the heavier ones. 4.1.3. Type III inclusions Raman spectra, very similar to that observed on the anhydrite solid inclusion, were obtained for type III of the FIA in the piece of the inclusion filled by the solution (Fig. 10A). Raman bands confirm the presence of long chain aliphatic hydrocarbons with a well developed d(CH2) band at 1420 cm
1, and by a methylene/methyl (A1420/A1357) area ratio equal to 1.53 (Fig. 10, point 1). However, the discussed inclusion shows an unusual fluorescing background that is not typical for a brine solution, therefore it may indicate the presence of a thin layer which surrounds the inclusion. Such a layer probably consists of conjugated double-bonded hydrocarbon structures with an admixture of diffuse, carbonaceous matter. In the part of the inclusion filled with liquid hydrocarbons (Fig. 10, point 2) their identification was impossible due to high fluorescence. On the contrary to the above described inclusion, another example of type III inclusions filled with brine and gas phase did not show traces of the presence of CM. The gas phase consists of COS, CO2, H2O (vapour) and light hydrocarbons (C3H8) (Fig. 11). 4.2. Geothermometer in bituminous salts

Fig. 11. Inclusions of type III, vide Fig. 4. E, (A) Microphotograph in reflected light taken with 20 magnification; (B) Raman spectrum in the 3500e120 cm
1 region.

4.1.2. Type I inclusions A similar distribution of organic matter was also observed for the type I inclusions filled with hydrocarbons, which show rather weak fluorescence under UV light (Fig. 9). The depth profile of the Raman measurement demonstrates the presence of a thin film of fluorescing matter located on the border of the inclusion signalled by the presence of the CM D-band at c.a. 1353 cm
1. The inner part is not as fluorescing and consists of lighter hydrocarbons with a considerable amount of sulphur compounds. In the end parts of the course of this type of the FIA usually appear inclusions which previously were considered as being filled with a gas phase due to their optical properties (Toboła, 2010). The thick black rim or lack of transparency was initially considered to be an optical effect associated with the very small size of the inclusions. However, the obtained Raman spectra show the process of a solid CM phase formation commencing on the walls of the inclusion. This process may be inferred from the analysis of the methylene/methyl (A1420/A1357) area ratio which is equal to 0.60 (Fig. 8, spectrum 1). The predominance of branched hydrocarbons (CH3) over long-chain hydrocarbons marked by CH2 vibrations may be an indication of a solid phase formation. In relation to the course of the process like a thick dark rim is formed around the inclusion with opacity observed in the transmitted light. The position of the FIA in the halite crystals and especially the characteristic distribution of the filling materials may indicate the processes that took place after their formation. The presence of the liquid, slightly fluorescing in UV light hydrocarbons with dissolved gaseous ingredients such as CH4, C2H6, C3H8, COS, H2S occurring in the central part of the course of the FIA and the occurrence of the

4.2.1. Type VII inclusions One of the processes that gives rise to the formation of organized CM in rocks is the saturation of a fluid with respect to the solid C phase (Wopenka and Pasteris, 1993). We believe that such a process affecting the aromatic groups is observed in type VII inclusions. The observed strong fluorescence which may result from the presence of the condensed ring aromatics (Burke, 2001; Stasiuk and Snowdon, 1997), points towards the incidence of an aromatic ring of compounds forming a layer surrounding the interior of the inclusion. The process of solidification of fluid inclusions is observed, being still far from the formation of even the poorly structured solid phases (Jehli cka et al., 1997). In all the above-mentioned inclusions filled with hydrocarbons the presence of organic substance, which exhibits various degrees of order according to the Raman analysis was also assured. It occurred mainly on the walls of the inclusions forming a thin film, the inclusions content is not homogenous but rather, diverse in character. Such types of organic matter were found in different geological environments often associated with thermal alternation (Jehli cka et al., 1997, 2003, 2007, 2009; Wopenka and Pasteris, 1993). In general, these works indicate the type and degree of metamorphism, which affects the arrangement of the carbonaceous matter and is manifested by specific Raman bands. In comparison to the above literature examples, the presence of slightly transformed organic phases may be inferred from data obtained for bituminous salts in the Kłodawa salt dome. This suggests that after or during a period of hydrocarbon migration through the cracks and crevices when they were trapped in the inclusions, they were probably subjected to a weak (relatively low temperature) metamorphism, which led to its partial degradation and transformations. The precise temperature of the transformation is impossible to assess, as the studied matter is subject to the continuous process of conversion. Some laboratory experiments (Teinturier et al., 2003) show that changes of oil composition begins at 250  C, but at higher temperatures it is more visible. The other laboratory experiments under


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Fig. 12. Inclusions of type VII, vide Fig. 5, (A) Microphotograph obtained by blending reflected and UV light taken with 20 and (B) 50 magnification, respectively; (C) Depthprofile intensity map at point 300 cm
1, selected acquisitions are marked; (D) 2D representation of the micro-Raman depth profile (9 spectra separated by a distance of 5 mm) collected in the centre of the microphotograph magnified 50; 3500e120 cm
1 region; (E) Selected micro-Raman spectra (acquisitions: 2, 3, 8 and 9), vide (A) showing fluid species in inclusion, fluorescence background was corrected; region 3200e700 cm
1.

higher temperatures show long-chain hydrocarbons splitting into shorter-length chain compounds resulting finally in an increase in the molar volume and pressure within the inclusions (Heager and Ostertag-Henning, 2012). Guillaume et al., 2003, suggested a temperature as low as 145  C for coexisting petroleum and aqueous inclusions. Summing up the investigated inclusions show characteristic features, which can be understandable as a pre-development carbonaceous phase formation (inclusion I and VII). 4.2.2. Comparison with the blue jet halites Adjacent deposits of blue halites in the Kłodawa salt dome present examples of the carbonaceous phase, one case is shown in
ska et al. (2008). Wesełucha-Birczyn All carbonaceous forms are related to the graphite lattice. In perfect crystalline CM the prominent mode which appeared at ca. 1600 cm
1 is called the G band and is assigned to the vibration of carbons within the polyaromatic structure (the E2g vibration mode of graphite). There also emerged D1 band at ca. 1350 cm
1, called

the defect band, commonly used to evaluate the amount of disorder in CM, attributed to a breathing mode. The poorly organized CM shows also other bands of which D2 at ca. 1620 cm
1, due to inplane defects and heteroatoms, it is important. Different parameters are used to estimate the CM degree of organization like the D1/ G intensity ratio (R1 ratio), and D1/(G þ D1 þ D2) area ratio (R2
ska et al., 2012b). ratio) (Beyssac et al., 2003; Wesełucha-Birczyn The R2 area ratio parameter evolution along the blue jet section was estimated to be around 0.48e0.71. When applying a new thermometer relationship (Beyssac et al., 2002), these values point towards the 430e321  C range and seem to be much higher in temperature than what is supposed to be in the investigated bituminous salt region (authors data, in preparation). Although local heating of unknown origin cannot be excluded the bituminous salt indicates a significantly lower temperature impact. In the Kłodawa salt dome such a high range of temperatures has been stated in PZ3 cyclothem (the top part of the Younger Lower Halite (Na3d) unit, the bottom part of the Younger Potash (K3) unit) and also in two units of the PZ4 cyclothem (the Underlying Halite

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Fig. 13. Inclusions of type VII, vide Fig. 5, (A) Microphotograph in the reflected light taken with 20 magnification; (B) Microphotograph in the reflected light taken with 50 magnification with an intensity map at point 300 cm
1 in the four measurement locations; (C) Raman spectrum in the region 1500e1100 cm
1 taken in the measurement point no 3; (D) Raman spectrum in the region 3200e700 cm
1 taken in the measurement point no 4, fluorescence background was corrected.

Fig. 14. Representation of the process of the formation of the encapsulation layer in the inclusions in the bituminous salts, which may be responsible for the characteristic reflection, refraction and interference of the transmitted light.

(Na4a0) and the lower part of the Youngest Halite (Na4) unit) (Wachowiak and Toboła, 2014). Under natural conditions, metamorphic changes may have taken place at a lower temperature but over a much longer period of time (the time factor) resulting in a similar effect of transformation in the rock with regard to temperature. The cracking reactions and the catalytic effects on the mineral surface which provide new more volatile components e.g. methane and other short-chain hydrocarbons (Heager and Ostertag-Henning, 2012) may be responsible for an increase in pressure in the inclusions and their leakage. This facilitated the escape of the lighter hydrocarbons. The remnants of the cracking processes (not so volatile components) remain in inclusions. Such processes are probably responsible for the lack of light hydrocarbons in inclusions observed in bituminous salt. Such an environment considerably

facilitated the recrystallization of halite crystals which explains the observed behaviour of the FIA as e.g. a decrease in the size of the inclusions at the end parts of the course of the FIA leading finally to their disappearance, which is accompanied by a change in their chemical composition. In comparison with geochemical data obtained for Stinking Shale (T2) and Main Dolomite (Ca2) (Czechowski et al., 2011; Wagner and Burliga, 2014) bituminous salt represents the secondary concentrations of hydrocarbons. After their entrapment they were subjected to thermal transformation which leads to aggregation and finally the generation of the transition phases towards carbonaceous matter. The bituminous salts inclusion similarity with blue jet halite salts may be seen in one of the characteristics. The solution in the latter inclusions is saturated with potassium halide which crystallizes on the walls of the inclusions, so in the surrounding of the
ska et al., inclusions the KCl marker is noticed (Wesełucha-Birczyn 2008).

5. Conclusions The Raman analyses performed on bituminous salts revealed some characteristic features of hydrocarbon inclusions. These studies complemented very well earlier petrological observations (Toboła, 2010). These studies have shown in particular that: * the content of different hydrocarbons in inclusions is not uniform * hydrocarbons are accompanied by carbonaceous matter which exhibits a small and different degree of order of the internal structure, * CM is distributed in a specific manner to form a thin coating on the borders of an inclusion or on the gas and the liquid phase


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limits (type VII). This seems to be a phase in the organic matter condensation process, * this film occurs even in inclusions filled with brine, * there is a shortage of light hydrocarbons and particularly methane, even in gaseous inclusions, however, in the latter, a carbonaceous substance and heavier hydrocarbons were found, which should normally occur in a liquid state. The carried out observations suggest that after the hydrocarbons were entrapped in the inclusions they passed a slight thermal transformation, leading to a carbonaceous matter generation. This transformation was accompanied by the recrystallization of halite, unsealing inclusions and the escape of the most volatile components. Acknowledgement T.T. work was supported by the Polish Ministry of Science and Higher Education, financed under Project AGH No. 11.11.140.320. References Aplin, A.C., Macleod, G., Lartera, S.R., Pedersenb, K.S., Sorensenb, H., Boothc, T., 1999. Combined use of confocal laser scanning microscopy and PVT simulation for estimating the composition and physical properties of petroleum in fluid inclusions. Mar. Pet. Geol. 16, 97e110. Aplin, A.C., Larter, S.R., Bigge, M.A., Macleod, G., Swarbrick, R.E., Grunberger, D., 2000. PVTX history of the North Sea's Judy oilfield. J. Geochem. Explor. 69e70, 641e644. Beyssac, O., Goffe, B., Chopin, C., Rouzaud, J.N., 2002. Raman spectra of carbonaceous material in metasediments: a new geothermometer. J. Metamorph. Geol. 20, 859e871.
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