Comparative studies of organic matter petrography of the late palaeozoic black shales from Southwestern Poland

International Journal of Coal Geology 71 (2007) 568 – 585 www.elsevier.com/locate/ijcoalgeo

Comparative studies of organic matter petrography of the late palaeozoic black shales from Southwestern Poland Grzegorz J. Nowak Polish Geological Institute, Lower Silesian Branch, al. Jaworowa 19, 53-122 Wrocław, Poland Received 27 December 2005; received in revised form 22 January 2007; accepted 23 January 2007 Available online 1 February 2007

Abstract There are at least two sapropelic units associated with Late Palaeozoic black shales in Central Europe. The older unit, of Late Carboniferous age, is the lower part of the Anthracosia Shales in the Intrasudetic Basin, and the younger one is the well-known Zechstein Kupferschiefer in both the Foresudetic Monocline and the Northsudetic Basin. The first unit is of lacustrine origin, while the second one represents deposition in a shallow marine depositional environment. Both units contain high amounts of organic matter, thus being typical black shales. The organic matter dispersed in these shales was studied petrographically. In general, the vitrinite reflectance of the shales studied indicates variable, but moderate organic matter maturity (0.68–1.25%), equivalent to the oil window. Detailed microscopic studies of the organic material dispersed in the lower unit of the Anthracosia Shales showed that liptinite, especially alginite is the most abundant component. Secondary altered organic matter, i.e. solid hydrocarbons, rarely occurs. Organic components together with mineral matter constitute a lacustrine sapropelic association, a humic (terrestrial) association and an intermediary association. The character and predominance of alginite and lacustrine sapropelic association are indicative of an open-lacustrine depositional environment. In general, this organic composition is typical of type I kerogen. Microscopic analysis of the Kupferschiefer revealed a mixture of liptinite, vitrinite and inertinite macerals, and other organic components such as amorphous sapropelic mass (ASM) and solid bitumens. The most common organic components are liptinite macerals. Bituminite and alginite predominate, and are diagnostic macerals of this unit. The amount of bituminite locally exceeds 85 vol.%. Other liptinite macerals such as sporinite and liptodetrinite, are present in significantly lower amounts, one exception being ASM, which may be present in higher amounts. Humic constituents (vitrinite and inertinite) are rare, present in small amounts in the Kupferschiefer beds. The organic matter composition points to type II kerogen for this unit. © 2007 Elsevier B.V. All rights reserved. Keywords: Sudety Mts.; Foresudetic Monocline; Carboniferous; Permian; Black shales; Organic petrography

1. Introduction Black shales are most often described as argillaceous, argillaceous–pelitic, argillaceous–siliceous and argillaceous–carbonate sediments with higher amounts of E-mail address: [email protected]. 0166-5162/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.coal.2007.01.004

more or less transformed organic matter (OM) responsible for the black or dark grey colour of these sediments. The shales might have originated from different depositional environments. Some metals (i.e., Fe, Au, Cu, Zn, Pt, Pb, Ni, V, U, and others) can be present in significant concentrations forming complex compounds with the organic matter. Aside from the

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Fig. 1. Generalized geological map of the Intrasudetic Basin: Precambrian: 1 — Góry Sowie gneisses; Lower Palaeozoic: 2 — phyllites, amphibolites, gabbros; Lower Carboniferous: 3 — conglomerates and sandstones; Upper Carboniferous: 4 — conglomerates, sandstones, siltstones, shales and coal seams, 5 — rhyolites and trachybasalts; Lower Permian: 6 — sandstones, conglomerates, siltstones, 7 — rhyolites and trachybasalts; Lower Triassic: 8 — sandstones; 9 — Upper Cretaceous; 10 — the places of samples collection (boreholes: 1 — Ścinawka Dolna IG 1, 2 — Bożków IG 1, 3 — Dzikowiec IG 1; 4 — outcrops); 11 — faults.

established significance of the organic matter in the field of fossil fuels, greater recognition has been given to its active role in mineral diagenesis and in the transport and deposition of metals (Saxby, 1976; Giordano and Barnes, 1981; Anderson and Macqueen, 1982; Eugster, 1985; Giordano, 1985; Sverjensky, 1987; Leventhal, 1993; Ewbank et al., 1995; Giordano et al., 2000).

Black shales can be considered source rocks of hydrocarbons and metals such as Au, Cu, Pb, Zn, Pt (Meyers et al., 1992; Leventhal, 1993), frequently of economic interest. An example of such sediments in the Sudety Mountains are argillaceous, argillaceous–pelitic and argillaceous–carbonate shales of Late Palaeozoic (Uppermost Carboniferous), which occur in the Intra-

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sudetic Basin (ISB) within the so-called Anthracosia Shales (AS) deposited in open lake facies (Mastalerz and Nehyba, 1997). The Zechstein Kupferschiefer (KS) of shallow marine origin (Oszczepalski, 1996) is commonly acknowledged as one of the most important metal source rocks worldwide, being well known for its copper and silver mineralizations. The Sudetic Anthracosia Shales, however, are characterized by very poor copper mineralization and their metallogenic potential was critically assessed in the early 1950's by Wyżykowski (1954). The OM abundance in the Anthracosia Shales and its relationship with mineralization has not drawn much attention until now. The problems were only incidentally mentioned in the literature and major stress was put on topics related with isotope and organic geochemistry (Yawanarajah et al., 1993; Speczik et al., 1995). Kupferschiefer typically contains high amounts of organic matter (1–30%, average 6%). The organic matter content in the Kupferschiefer raised the interest of geologists in Germany (Wolf et al., 1989; Koch, 1997). Petrographic studies of organic material from the Polish Kupferschiefer were commenced by Speczik and Püttmann (1987), Speczik (1994) and Sun et al. (1995), who focused their research on the Foresudetic Monocline (the “Rudna” mine) and Northsudetic Basin (the “Konrad” mine). Limited petrographic studies of OM have also been conducted by other researchers (e.g. Sawłowicz, 1991; Yawanarajah et al., 1993). Several papers revealing relationship between mineralization processes within the Kupferschiefer and the role of organic matter have been published in recent years (Nowak et al., 2001; Oszczepalski et al., 2001, 2002; Speczik et al., 2003). Detailed results of organic petrologic research were presented by Nowak (2003) and Nowak et al. (2004). One could put forward a conclusion that the present state of investigation of OM in Late Palaeozoic sediments of SW Poland is still insufficient. As both black shale units, namely the Anthracosia Shales and the Kupferschiefer, represent deposits formed under sapropelic conditions, but in different environments (lacustrine and marine, respectively), the author has undertaken an attempt to compare their organic matter identification and classification, as well as to investigate their origin. The results can be helpful in the determination of the hydrocarbon potential of these rocks. 2. Geological setting The Intrasudetic Basin (southwest Poland) is situated at the NE margin of the Bohemian Massif. Its formation

is a result of late stages of the Variscan orogeny in Europe. The basin is now a small NW–SE trending tectonic unit (Fig. 1) filled with Carboniferous and Permian deposits. Only the upper Carboniferous and lower Permian sediments are of continental origin. Within these sediments lacustrine deposits occur represented by two units (Fig. 2): the Lower and the Upper Anthracosia Shales, of uppermost Carboniferous and Autunian ages, respectively (Górecka, 1981; Jerzykiewicz, 1987; Górecka-Nowak, 1989; Trzepierczyńska, 1994; Górecka-Nowak, 1995). The top of the lacustrine sedimentation is represented by the Walchia Shales, which occur only in the Intrasudetic Basin, similarly as the two above mentioned older units. The Anthracosia layers have yielded internal casts of fresh-water bivalves of the genus Anthracosia, from which their commonly used name stems. These shales have a patchy distribution occurring as flat lensoidal bodies with thickness varying from 20 cm up to 70 m

Fig. 2. The Anthracosia Shales position in the lithostratigraphic column of the late Palaeozoic deposits in the eastern part of the Intrasudetic Basin (after Mastalerz and Wojewoda, 1988, slightly modified): 1 — volcanites and volcanoclastics.

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(several meters on average). The lower Anthracosia Shales represent a more continuous and thick bed than the upper one. Lacustrine sediments of this basin reveal a variety of lithofacies (Mastalerz and Nehyba, 1997). The deposits of the open lake facies are the most interesting from the organic petrography point of view. They are represented by fine-grained sediments, commonly with an admixture of carbonates and generally with high organic matter content. The significant examples of this type of deposits in the Intrasudetic Basin are black or grey sediments of the lower unit of the Anthracosia Shales (Fig. 2). This unit consists, in general, of two intercalated types of sedimentary rocks, i.e. sandstones and shales (Dziedzic, 1959, 1961; Don, 1961; Miecznik, 1989; Bossowski and Ihnatowicz, 1994). The latter are dark grey and black in colour due to the organic matter contained; thin coal laminae form in places. Thin bituminous limestone intercalations were also observed in the shales. The sandstones, however, reveal a clayey or marly matrix (Dziedzic, 1959, 1961). They form layers 10 to 20 cm thick. These rock types often coexist as thin laminae resembling varves. Both these sediment types are not restricted to any particular zone but they are intercalated at both the bottom and the top of the bed. According to the authors mentioned earlier, the occurrences of the Anthracosia

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Shales are known from two sub-regions of the Intrasudetic Basin (Fig. 1): the Wałbrzych area (vicinity of Okrzeszyn) and the Nowa Ruda area (vicinity of Krajanów–Ścinawka Dolna and Ścinawka Górna). The other example of black shales from southwest Poland is the Zechstein Kupferschiefer. It represents a shallow marine transgressive sequence (Oszczepalski, 1996), related to a marine transgression at the beginning of the Late Permian, which flooded parts of Central Europe extending from northern England and the North Sea to the area of Poland. The Kupferschiefer in SW Poland is known in two localities: the Northsudetic Basin and the Foresudetic Monocline (Fig. 3). These two geological units are separated by the uplifted Foresudetic Block and the Żary Pericline, bordered in the south by the Sudetic Marginal Fault, and in the north by the Middle Odra Fault System. These units evolved essentially during the Laramide phase of the Alpine orogeny as foreland structures of the Sudety Mts. The Permian and Mesozoic sequences were probably accumulated on the Foresudetic Block and were eroded during Early Tertiary, when a new fault system was created. The Zechstein polymetalic mineralization of the basin sediments is well known. The Kupferschiefer is commonly acknowledged as one of the most important

Fig. 3. Facies variation map of the Kupferschiefer of the Foresudetic Monocline and the Northsudetic Basin.

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metal source rock worldwide, due to the copper and silver contents. Stratigraphically, the Kupferschiefer belongs to the lower part of the Zechstein sequence. It represents the ore-bearing series consisting of Weissliegendes, Basal Limestone, Kupferschiefer and Zechstein Limestone (Fig. 4). The Kupferschiefer is represented by laminated, marly, organic matter-rich shales, dark grey or black in colour, accumulated in an oxygen-deficient Zechstein basin. It is usually a thin layer (mainly 20 to 80 cm thick). Within the Kupferschiefer two geochemical facies occur, the reduced and the oxidized facies (Oszczepalski and Rydzewski, 1997). The sediments of the first facies represent typical black shales, while the sediments of the second facies were altered by oxidizing (mineralizing) fluids. In the transitional zone, the oxidation and reduction processes overlap. The reduced facies includes the copper-bearing Series containing metalsulphide mineralization; no iron oxides are present. The series occurs not only in Poland, but also over the remaining area of the Zechstein Central European Basin. Another diagnostic feature of this facies, particularly characteristic for the Kupferschiefer, is the black or dark-grey colour of the shales included.

3. Sampling and methods Seventy-two organic-rich rock samples, 36 from the Anthracosia Shales and 36 from the Kupferschiefer, were picked up from outcrops and drill cores in the Intrasudetic Basin (Fig. 1), and from mine profiles and boreholes situated both in the mining area of the Foresudetic Monocline and the Northsudetic Basin (Fig. 3). Most of the Kupferschiefer samples (31) were collected at the Foresudetic Monocline, and only 5 of them were collected at the Northsudetic Basin. The sediments represent a relatively low range of thermal maturity corresponding to vitrinite reflectance values between 0.68 and 1.25% (Nowak, 2003). In order to study the organic matter, polished sections of the samples were examined under oil immersion at magnification 200–500× under reflected white light and fluorescence mode. Polished surfaces of various lithological types (mentioned above) from the lower Anthracosia Shales and the Kupferschiefer. The petrographic research was carried out using a MPM-200 System of Carl Zeiss, which consists of an optical-electronic set including the Axioskop microscope used in normal reflected light observations and equipped with a HBO lamp emitting ultraviolet light, which enables observations of fluorescence of macerals during irradiation, a microphotometer used in vitrinite reflectance measurement (Ro), as well as a computer with original Carl Zeiss Photan computer software. 4. Results 4.1. The Anthracosia Shales

Fig. 4. The Kupferschiefer position in the stratigraphic column of the Zechstein copper-bearing Series (after Oszczepalski and Rydzewski, 1997).

Anthracosia Shales (AS) with high amounts of organic matter contain macerals of all three groups, as well as other organic components (Table 1). In general, liptinite is predominant (Figs 5 and 6), whereas vitrinite and inertinite rarely occur. In the samples studied two types of vitrinite have been distinguished. The first one is a reworked vitrinite of typically light grey colour, whereas the second type is represented by primary (autochthonous) vitrinite with darker grey colour than this of the reworked vitrinite. The autochthonous vitrinite occurs mainly as gelinite forming very thin microlayers or single grains (Fig. 7). Corpogelinite was also observed locally, mainly in elongated or circular forms. The most common maceral in this group is, however, vitrodetrinite, which may represent both the primary and the reworked vitrinite (Fig. 7). The reflectance of the grey vitrinite variety is

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Table 1 Comparison of organic matter dispersed in the black shales studied from SW Poland Anthracosia Shales (AS) Macerals

Kupferschiefer (KS) Other organic components

Vitrinite (seldom): gelinite and Organic–mineral associations corpogelinite and vitrodetrinite. occurring in the AS differ in the intensity and kind of fluorescent Liptinite (dominating): alginite — properties; this is related to the diagnostic maceral of the AS; presence, character and quantity it is represented mainly by of the dispersed organic matter; the lamalginite with rare telalginite; associations can be distinguished in: sporinite — is chiefly lacustrine sapropelic association represented by tenuisporinite; (LSA), humic (terrestrial) cutinite — it has been association (HA) — can be sporadically found mainly as identified based upon relatively tenuicutinite; bituminite high abudance of humic coaly (amorphous organic matter) — matter; intermediate association is widespread; liptodetrinite — (IA) — mixed associations it is fairly common. between sapropelic and humic ones. Inertinite: is the rarest group of components; it is represented Solid bitumens (SB) — secondary mainly by inertodetrinite, products of organic matter fusinite, semifusinite. alteration; their occurrence is rare in the studied horizon (mainly in LSA).

Macerals

Other organic components

Vitrinite is generally common but a minor constituent of the studied horizon; it is represented by two generations of this maceral: autochthonous (mainly structureless gelinite) and allochthonous (vitrodetrinite).

Organic–mineral association— in the Kupferschiefer it is not pure organics but rather organic-mineral matrix, this type of organic-mineral association was determined as amorphous sapropelic mass (ASM)/mineral–sapropelic matrix (MSM).

Liptinite — the commonest organic macerals of the Kupferschiefer horizon; liptinites comprise a class of lipid-rich macerals that include bituminite (commonest), alginite, liptodetrinite and sporinite; alginite A— telalginite and B— lamalginite; it is one of the diagnostic macerals of the shale studied; sporinite is found chiefly as tenuisporinite; other liptinite maceral noticed is liptodetrinite;

Solid bitumens (SB) — often occur in ASM; thucholite is another type of solid bitumen.

Inertinite — is usually rare mainly represented by both micrinite and inertodetrinite.

between this of liptinite and inertinite. When irradiated with ultraviolet light vitrinite does not fluoresce. Inertinite macerals are the rarest components in the AS samples (Fig. 7) with the most common maceral being inertodetrinite. The rest of inertinite mainly comprises fusinite, semifusinite, while secretinite and funginite have been recognized as accessory macerals. Both fusinite and semifusinite display primary cell structure with various degrees of preservation. Rare fragments of both funginite and secretinite have been also observed. In the Anthracosia Shales, liptinite constitutes the most abundant organic constituent. Under the fluorescence mode alginite, bituminite, sporinite, cutinite and liptodetrinite have been distinguished. Alginite appears to be a predominant organic component in the Anthracosia Shales (Fig. 7). Two different types of alginite were distinguished, namely telalginite and lamalginite (Taylor et al., 1998), which earlier were determined as alginite A and B, respectively (Hutton et al., 1980). They differ from each other in the size and morphology, as well as in the fluorescence character. The first one displays slightly brighter fluorescence

compared to the latter (Hutton et al., 1980). In the AS samples, telalginite is largely composed of Botryococcus algal colonies. The most abundant maceral is, however, the second type of alginite mentioned earlier. Basically, lamalginite is indistinguishable in reflected white light, but when irradiated with UV light, it fluoresces yellow to orange. Its fluorescence is relatively intense, much stronger than this of sporinite and cutinite. Lamalginite occurs as single elongate laminae and in microbands composed of laminae of alginite B (Fig. 7). The other structural liptinite macerals occurring in the shales are sporinite and cutinite. Sporinite is represented mainly by tenuisporinite. It mainly occurs as single sporinite visible within a mineral-organic groundmass. The fluorescence colours of this maceral are dark yellow to orange, mostly darker when compared with these of lamalginite. Sporinite is not a significant component. Cutinite is also a rare maceral in the Anthracosia Shales. During the microscopic observation only tenuicutinite has been recognized. It shows dark yellow to orange fluorescence colour when irradiated with UV light.

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Fig. 5. Distribution and organic matter constituents of the Anthracosia Shales from the Ścinawka Dln IG 1 borehole and their relationships with depositional environments.

Bituminite is a typical amorphous organic matter widespread in the Anthracosia Shales. It is a pure organic constituent, without a proper form and shape (Teichmüller, 1974). Bituminite is difficult to distinguish under normal reflected light, but when irradiated with UV light, it shows light brown colour and is characterized by a rather low intensity of fluorescence (Fig. 7). Amorphous organic matter has been observed

in the samples studied in the elongated lenticles and irregular bands or concentrations of undefined shapes. Locally, it may be dispersed throughout the rock. An association of bituminite with alginite is very common in the samples studied, since bituminite originates from the decomposition of alginite, zooplankton and bacteria (Teichmüller and Ottenjann, 1977; Robert, 1979; Hutton et al., 1980; Stach et al., 1982; Taylor et al., 1998).

Fig. 6. Distribution and organic matter constituents of the Anthracosia Shales from the Bożków IG 1 borehole and their relationships with depositional environments.

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Fig. 7. Photomicrographs of dispersed organic matter in the Anthracosia Shales: 1. Band of gelinite and small pieces of vitrodetrinite in siltstone mineral matrix–humic association; normal reflected light (Ro = 0.80%). 2. Fragment of semifusinite of preserved cellular structure–terrestrial association; normal reflected light (Ro = 0.81%). 3. Individual lamalginite occurrences in sapropelic–mineral matrix–lacustrine sapopelic association; fluorescence mode (Ro = 0.78%). 4. Lacustrine sapropelic association composed of lamalginite and bituminite; fluorescence mode (Ro = 0.78%). 5. Type 2 of lacustrine sapropelic association composed of bituminite and lamellas of lamalginite; fluorescence mode (Ro = 0.80%); occurrences of solid bitumens showing yellow fluorescence; UV light (Ro = 0.81%). 7,8. Intermediate association composed of non-fluorescing (black) humic components: vitrinite and inertinite as well as other terrestrial components represented by sporinite showing dark yellow fluorescence colour; UV light (Ro = 0.77%). Explanations: V — vitrinite, Vg —gelinite, Vtd — vitrodetrinite, I — inertinite, Sf —semifusinite; L — liptinite, Lam — lamalginite, Bt — bituminite, Sp — sporinite, LSA — lacustrine sapropelic association, SB — solid bitumen.

Liptodetrinite consists of undistinguishable fragments and detritus of other liptinite macerals. It is characterized by yellow to orange fluorescence colours. Liptodetrinite is fairly common in the unit under study.

Other organic components common in sediments are solid bitumens (Jacob and Hiltmann, 1985). They are relatively sparse in the Anthracosia Shales. Solid bitumens represent secondary residual products connected to

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oil migration. Solid bitumens occur in intergranular spaces or they may form oval, homogeneous “grains” (Fig. 7). They commonly show intense yellow fluorescence and their reflectance is much lower than this of vitrinite. According to Jacob (1989) the solid bitumens present in the Anthracosia Shales can be determined as migrabitumens. The description presented here concerns individual components of organic matter, mainly macerals, and seldom secondary products of their alteration such as solid bitumens. Apart from these organic constituents, also other more complicated organics are present in this unit. They form a natural matrix composed of both organic matter of submicroscopic size and mineral matter. These associations are easy to recognize under the microscope in UV light due to the characteristic fluorescence properties. This category of organics and mineral matter is similar to mineral–bituminous groundmass of Teichmüller and Ottenjann (1977) or matrix-bituminite according to Creaney (1980). A similar category of natural accumulations of organics and mineral matter observed in the Anthracosia Shales was named mineral– sapropelic matrix — MSM (Nowak, 2003). Microscopic observations revealed the presence of several types of these mineral–organic associations in the Anthracosia Shales. They differ in the intensity and kind of fluorescent properties. This is related to the presence, character and quantity of organic matter dispersed within them. The organic–mineral associations recognized in the samples are described below. 4.1.1. Lacustrine sapropelic association (LSA) Much of the organic matter is of sapropelic origin. The main organic components of this association are both alginite and material of algal origin similar to bituminite (Fig. 7). In places solid bitumens may accompany them. Two types in this category have been distinguished under the microscope: • type 1 is characterized by the presence of lamalginite of much more intense fluorescence than the fluorescence intensity of the MSM, which is matrix for alginite; in general, algal material prevailing here points to autochthonous sub-aquatic accumulation (Fig. 7); terrestrial plant material from the land surrounding the Anthracosia Lake is rare or absent; • type 2 shows a more uniform and less intense fluorescence than this of the previous type; bituminite is the dominant organic component, while alginite occurs as single lamellae of lamalginite and as Botryococcus colonies (Fig. 7).

In this association also solid bitumens and liptodetrinite have been encountered. 4.1.2. Humic (terrestrial) association (HA) This is identified on the basis of relatively abundant humic coaly particles visible in the rock as single, thin microbands, lenticles or maceral fragments (Fig. 7). This association contains macerals of terrestrial origin such as vitrinite (mainly vitrodetrinite), inertinite (most frequently inertodetrinite) and liptinite (sporinite and liptodetrinite). The fluorescence observed is weak and related to the liptinite macerals. 4.1.3. Intermediate association (IA) It consists of organic constituents present both in lacustrine sapropelic and humic associations, mainly with sapropelic predominance (Fig. 7). These associations are the most common forms of organic matter in the Anthracosia Shales. Gradual transitions between the particular associations have been commonly observed. 4.2. The Kupferschiefer The samples of the reduced Kupferschiefer facies – a typical representative of black shales – contain significant amounts of organic matter. The petrographic study under the microscope revealed a mixture of all three maceral groups (vitrinite, liptinite and inertinite) and other organic components (Table 1). Most common are liptinite and unstructured organic matter, along with rare vitrinite and inertinite (Fig. 8).

Fig. 8. Ternary diagram of organic matter composition of the Kupferschiefer.

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Vitrinite is a common constituent of the samples examined, though minor in terms of quantity. It is represented mainly by vitrodetrinite with irregular edges or by round particles and local thin bands of gelinite (Fig. 9). Vitrodetrinite has been recognized as both primary and reworked vitrinite. The reflectance of the first type is lower than this of the second one, being similar to the inertinite reflectance. Both inertinite and reworked vitrinite are readily identified in white reflected light, forming the so-called “refractory kerogen” (Taylor et al., 1998). Gelinite, low-reflecting, structureless vitrinite maceral, present mostly in the reduced facies as thin laminae aligned parallel to the shale lamination, represents autochthonous type of this maceral. By contrast to gelinite, high-reflecting vitrodetrinite is an allochthonous vitrinite and may occur not only in typical black shales, but also in reduced and oxidized zones of the unit. This type of vitrinite has the form of oval-shaped bodies and irregular particles showing smooth surface and oxidation rims. Typical inertinite occurs in small amounts mainly as inertodetrinite, while fusinite and semifusinite, oxidized algae and spores, and chitinous insect particles are rare in most samples. These macerals can be distinguished from vitrinite by their reflectance, which is always higher than this of the primary vitrinite present in the same sample. The most abundant component of the inertinite group, however, is micrinite (Fig. 9). The occurrence of this maceral is a diagnostic feature of the reduced Kupferschiefer facies. It is, however, completely absent in the oxidized shales. In the samples studied micrinite always accompanies bituminite. It is visible as small white dots, irregular aggregates and massive lenses. Similar forms of micrinite occurrences in the Kupferschiefer were also described in Germany (Wolf et al., 1989; Koch, 1997) and Poland (Nowak, 2003). Sherwood and Cook (1986) observed these forms in Early Cretaceous oil shales from the Eromanga basin in Australia, and were also recognized by Stasiuk (1993). The latter author, however, did not determine them micrinite, but products of both degradation and microbial alteration of marine organic material. In UV light, neither inertinite nor vitrinite of the Kupferschiefer samples showed fluorescence. Liptinite comprises lipid-rich macerals that include alginite, liptodetrinite, bituminite and sporinite. While the liptinite macerals were readily identifiable by fluorescence microscopy, bituminite was also clearly visible under reflected white light. Alginite occurs as alginite A or telalginite and B or lamalginite (Taylor et al., 1998). Telalginite occurs as

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lensoidal forms, fans or discs often of flattened shapes (Fig. 9) and shows dark yellow fluorescence. Telalginite is a very conspicuous maceral constituent despite its generally low abudance. Lamalginite is, in contrast, the diagnostic maceral of the black Kupferschiefer. In polished sections it appears as thin laminae or irregular streaks oriented along bedding planes that become best visible due to its light to dark yellow fluorescence under ultraviolet irradiation (Fig. 9). In general, the Kupferschiefer alginite is clearly recognizable in UV light, when Ro of vitrinite varies between 0.72 and 0.93%. In samples of higher vitrinite reflectance values (1.00– 1.25%), however, alginite was not encountered (Nowak, 2003). Bituminite is defined as a maceral by ICCP (1993), but in the past it was determined rather as a reference to the kind of maceral group, than to the individual liptinite maceral. In such a meaning it has been used earlier by Koch (1997). Bituminite is the most common organic constituent in the Kupferschiefer ranging from 41 up to 85 vol.% (Nowak, 2003). Bituminite comprises grainy unstructured liptinite mass, which is present in the form of thin bands and lenses concordant to the shale lamination (Fig. 9). The following types of bituminite were distinguished under the microscope: 1. brown fluorescing, unstructured organic matter that appears dark (nearly black) grey–brown in the white light (Fig. 9); often the inclusions of liptodetrinite and/or alginite within bituminite are visible, but the bituminite fluorescence intensity is much lower than this of both alginite and liptodetrinite; 2. dark grey (in white light), unstructured organic matter, for which, type 1 described before forms the background (Fig. 9); type 2 differs from the previous type: its shade is lighter and the form of occurrence is different — it forms thin, typically elongated and strongly divided bands or lenses or unshaped fragments; in white light it resembles vitrinite, from which this type of bituminite differs by darker shade of grey colour and lower reflectance, and still its fluorescence properties are preserved; it shows greyish brown to grey fluorescence colour and low intensity (much lower than these of alginite and liptodetrinite inclusions); microstratification of this bituminite type is emphasised by inclusions of alginite and liptodetrinite (Fig. 9). These types of bituminite are characteristic for shales of the reduced facies. The modification of type 2 is described by the author of this paper as vitrinite-like matter/maceral (see Appendix); Koch (1997), however,

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has defined this kind of material noticed in the transitional zone of the Kupferschiefer, directly as vitrinite-like bituminite comparing it to bituminite I of the Teichmüller and Ottenjann (1977) classification. In white light it is lighter in colour than bituminite of the reduced facies from the same Kupferschiefer sequence. When irradiated with blue light it does not fluoresce. In this feature it resembles normal vitrinite rather than type-2 bituminite. Taking into account the state of art of bituminite, both distinguished types may be compared to bituminite I of the relevant classification proposed by Teichmüller and Ottenjann (1977) or to vitrinite-like bituminite of Koch (1997). However, the vitrinite-like matter/maceral of the Kupferschiefer is not included in the internationally accepted classification of bituminite. Sporinite is found mainly as tenuisporinite of thinwalled miospores with elongated shapes. Liptodetrinite is also encountered. In some samples other types of organic matter were also distinguished. One of them is solid bitumens that can occur in variable amounts. In most cases they show yellow and orange fluorescence (Fig. 9). Under white reflected light solid bitumens display dark grey colour and a lack of the inner structure, and in polarized light they do not display anisotropy. Their reflectance is much lower than the reflectance of both vitrinite and vitrinitelike macerals (see Appendix) in the same sample (Nowak, 2003). The optical properties of the solid bitumens described here, allow the determination of this type of organic material generally as migrabitumen according to the Jacob (1989) nomenclature. Solid bitumens, which are present only in the black shales of the reduced Kupferschiefer facies is thucholite (Fig. 9). According to Kucha and Przybyłowicz (1999) it is composed of two optically different components: isotropic A of Ro from 0.75–2.5%, and anisotropic B similar to graphite. In the Kupferschiefer samples, type

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A of thucholite was observed. Its reflectance varies from 1.18 to 1.37%. In the Kupferschiefer where bituminite/unstructured organic matter and alginite predominate over other macerals, other types of organic matter also occur. They are not pure organics but rather organic–mineral matrix, which can be identified on the basis of characteristic fluorescence properties. This type of organic–mineral association was described as amorphous sapropelic mass (ASM) or mineral–sapropelic matrix (MSM) by Nowak (2003). Sapropelic components occurring in ASM are represented by a mixture of primary lipoidal components of submicroscopic size, consisting of bituminite with both alginite and liptodetrinite, in places with higher solid bitumen contents. ASM can also be found as fine lenses, irregular bands, and irregular agglomerates without distinct outline (Fig. 9). In the reduced facies the predominant role of liptinite was noticed, with a strong prevalence of bituminite and alginite, which are diagnostic macerals for this part of the copper-bearing shale. The quantity of bituminite reaches in places up to 85 vol.%. The other liptinite macerals, as well as other mineral–organic associations such as the amorphous sapropelic mass (ASM), occur in significantly lower amounts. The petrographic characteristics are all indicative of the marine origin of the organic matter with very small terrestrial input. Organic petrography studies of the Kupferschiefer from both transitional and oxidized facies have, however, revealed a difference in the organic composition compared to this of the black Kupferschiefer of the reduced zone (Nowak, 2003; Speczik et al., 2003; Nowak et al., 2004). 5. Discussion Petrographic characteristics of dispersed organic matter in the Anthracosia Shales and Kupferschiefer allow the recognition of the two main sources of

Fig. 9. Photomicrographs of dispersed organic matter in the Kupferschiefer: 1. Thin bands of gelinite, vitrodetrinite and inertodetrinite in the mineral background of the Kupferschiefer, reflected white light (Ro = 0.81%). 2. Occurrences of micrinite (light grey) and bituminite (dark gray) in mineral matrix, reflected white light (Ro = 0.77%). 3. Lamellas of lamalginite showing light yellow colour of fluorescence; UV light (Ro = 0.76%). 4. Single lamellas of lamalginite and deformed discs of telalginite in the bituminite background, UV light (Ro = 0.93%). 5. Bituminite of type 1 (dark gray nearly black) situated between mineral grains (grey), incident reflected light (Ro = 0.73%). 6. In the center of photo-bituminite of type 2 (dark grey) and ore minerals (white), incident reflected light (Ro = 0.73%). 7. The same view as photo 6 but in fluorescence mode — bituminite of type 2 shows weak fluorescence of brown–yellow colour and both lamalginite and liptodetrinite of light yellow fluorescence colour, as well as non-fluorescing ore minerals, UV light. 8. In the center of the photo ASM/MSM of weak yellow–brown fluorescence colour, UV light (Ro = 0.76%). 9. In the upper part of the photo the mineral grain within incrustation of solid bitumen showing yellow fluorescence colour, UV light (Ro = 0.73%). 10. In the center of the photo- nodule of thucholite of stronger reflectance compared to bituminite of this same photo, normal reflected light (Ro = 0.86%). Explanations: Vg — gelinite, Vtd — vitrodetrinite, Id — inertodetrinite, Mi — micrinite, Bt — bituminite, Bt1 — bituminite type 1, Bt2 — bituminite type 2, Lam — lamalginite, Tel — telalginite, Lpd — liptodetrinite, ASM/MSM — amorphous sapropelic mass/mineral sapropelic matrix, SB — solid bitumen, Tu — thucholite.

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organics as terrestrial and aquatic. In the case of the black shales from the Intrasudetic Basin, the aquatic material is of lacustrine origin, whereas in the Kupferschiefer of both the Foresudetic Monocline and the Northsudetic Basin it is represented by organics of marine origin. Vitrinite and inertinite are distinctly humic (terrestrial) components. They represent plant remnants from the immediate surroundings of the Anthracosia Lake and the land near the Zechstein Sea. In the case of the Anthracosia Shales a probable transport medium could be rivers flowing into the lake. Vitrinite and inertinite mostly occur in fine-grained sandstones and sandy mudstones of the Anthracosia beds. These deposits are not representative of an open lake but rather of its shallow zones (Mastalerz and Nehyba, 1997). Like vitrinite and inertinite, sporinite also represents terrigenous organic material of the Anthracosia Shales. This maceral formed from miospores of plants growing on the banks of the lake. In these sediments small amounts of liptodetrinite (probably of sporinite origin) are also encountered. Alginite is a typical lacustrine maceral of the Anthracosia Shales, reflecting accumulation under openlake conditions. The high alginite content is characteristic for most of the fine-grained shales. Both lamalginite and Botryococcus are typical lacustrine components of the Anthracosia Shales. The latter one is mostly associated with bituminite. This fact may point to a genetic relationship between these constituents. In warm climate conditions, which were in certain degree favourable for intensive bioproductivity of algae, anoxic environment of the Anthracosia Lake (indicated by the presence of pyrite) favoured the preservation of the organic matter. After its deposition and the subsequent decomposition to bituminite, it could transform into solid bitumens, which are sporadically encountered in the samples studied. This type of organic matter is connected with the finest-grained lithology, which can be described as bituminous shales. In this type of sediments liptodetrinite is also present. This can be a destruction product of both alginite and sporinite. In some of these deposits sporinite is present as terrigenous component transported by wind or lake currents. Lamination is an important feature of these sediments. Under the microscope, regular concentrations of lamalginite are visible as algal-rich laminae (thinner), intercalated with clay-rich laminae (thicker). The thinner laminae are characterized by more intense fluorescence compared to the thicker laminae. These forms of dispersed organic matter in the Anthracosia Shales represent the lacustrine sapropelic association. In the thicker bands, poorer in alginite, it is also possible to observe a mixture of vitrinite and inertinite. The thicker bands are indicative

of cooler periods resulting in lower bioproductivity of the algal material, when terrigenous organic matter prevailed in their composition. Laminae with more lipoidal constituents represent warmer climate periods of higher bioproductivity. These bands of terrestrial input within the organic matter mainly represent the intermediate association. In summary, the sediments of the open lake facies are characterized by homogeneous organic matter composition. They are laminated, which points to seasonal deposition characteristic of stratified lakes. The Anthracosia Lake represented exactly this type of lake (Mastalerz and Nehyba, 1997). Alginite typically occurs as: (i) abundant microbands largely composed of intensely fluorescing lamalginite; (ii) lamalginite can occur also as individual thin laminae of distinctly strong fluorescence as compared to both bituminite and sapropelic-organic matrix; (iii) algal colonies of Botryococcus, being rarer than concentrations of lamalginite, are associated with both bituminite and sapropelic-organic matrix; (iv) alginite, bituminite and mineral–sapropelic matrix are connected with the most fine-grained sediments of the unit under research and represent sapropelic bituminous shales. The prominent sapropelic character of dispersed organic matter in the Anthracosia Shales is indicative of source rocks of type I. These sediments formed in a fresh water or alkaline lake with an isolated reducing sub-environment and weak currents. These deposits are potentially excellent oil-source rocks, mainly when organic matter maturity is redundant (Nowak, 2003). The origin of the Anthracosia Shales is related to much more humid climatic conditions at the end of the Carboniferous that could be favourable for terrestrial vegetation. This is confirmed by the existence of thin lenses of coal in the Anthracosia unit and the passing of grey colouration of the deposits to fluvial sediments of the higher position in the profile (Fig. 2). However, the formation of the Upper Anthracosia Shales and the still younger Walchia Shales (Fig. 2) or grey sediments among deposits of generally red colouration, is related to the existence of reducing environments in dry and warm climatic conditions similar to the ones observed nowadays in the Lake Rudolph in Africa (Nowak, 2003). The Lower Anthracosia Shales form a continuous layer of grey or black sediments, while the other younger deposits mentioned above form only thin lenses of that colouration. The Anthracosia Shales of the lower layer are also known for the occurrence of low-grade copper mineralization. The petrographic study of the Zechstein Kupferschiefer confirms that aquatic, although marine organic matter is predominant in the samples and that terrestrial

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input was minor (Fig. 8). Besides typical marine organic constituents such as alginite, bituminite, or organics of the MSM, in the reduced Kupferschiefer there occur macerals of primary marine organics represented by fusinitized algae, spores, as well as micrinite and solid bitumens. Alginite (both lamalginite and telalginite) formed from unicellular planktonic or benthonic marine algae or from colonies of algae. Discs may probably represent Leiospheres (Robert, 1980; Taylor et al., 1998). However, thick-walled telalginite of flat-disc shape probably developed from Tasmanites, as it is known from many source rocks of shallow marine environments of the Late Palaeozoic and the Mesozoic ages (Teichmüller and Ottenjann, 1977; Littke et al., 1988; Littke, 1993; Taylor et al., 1998). Bituminite, which is the major organic component in the Kupferschiefer samples studied, originates from bacterial decomposition products of algae and faunal plankton in anaerobic conditions (Teichmüller and Ottenjann, 1977; Robert, 1979; Hutton et al., 1980; Cook et al., 1981; Stach et al., 1982; Murchison, 1987; Taylor et al., 1998). TEM research of bituminite (Taylor et al., 1991) points out that the bituminite of low-rank coals of Carboniferous age is a product of algae biodegradation. The processes mentioned here are indicative for bituminite formation in the Kupferschiefer during early diagenesis and in conditions of oxygen deficiency, as a result of a broadly understood algal material transformation (Nowak, 2003). In the samples studied, the association of alginite and liptodetrinite with bituminite is clearly visible under UV light; both lamalginite and telalginite are common on the surface of bituminite. The presence of pyrite, as well as other sulphides associated with bituminite points to its synsedimentary origin and sapropelic character of the Kupferschiefer basin. Micrinite, which in the formal sense is a maceral of the inertinite group, is commonly known as a maturation product of bituminite in oil shales (Teichmüller and Ottenjann, 1977; Stach et al., 1982; Taylor et al., 1998). In the samples from the unit under investigation, micrinite is associated with bituminite, in a similar way as in other source rocks of shallow marine environments. Taking into account the above presented considerations, it is possible to state that micrinite precursors were of aquatic-marine origin. Solid bitumens, which are present in the shales of the reduced Kupferschiefer facies, are the secondary alteration products of primary lipoidal organic matter (Robert, 1981; Jacob, 1989). Some of the bitumens represent migrating hydrocarbons that could infiltrate the sediment, forming a kind of contact-pore binder or

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filling in pores and fissures in the rock. The petrographic character of solid bitumens present in MSM, however, does not point to their marine origin. Terrestrial components are common, but occur in small amounts in both the transitional and the oxidized facies of the Kupferschiefer (Nowak, 2003). A greater terrestrial input in the organic composition of the Kupferschiefer is observed in the samples of the Northsudetic Basin, when compared to the samples from the Foresudetic Monocline (Fig. 7). The generally higher content of this type of organic matter in the samples of the Kupferschiefer from the Northsudetic Basin indicates that the forests, which acted as sources of progenitors for vitrinite and inertinite and the source of spores grew close to the Zechstein Sea shores. The supply of terrigenous material was more intense compared to the situation in the Foresudetic Monocline. The sediments of the latter region represent parts of the Zechstein Sea at some distance from the shores, resulting in a lower abundance of terrestrial organics in these shales. The above results point to a significant uniformity (of quality and proportion) of the organic matter in the black shales under investigation. This uniformity could be indicative of stable conditions during the formation of the organic-rich sediments. 6. Conclusions Both the Anthracosia Shales and the Kupferschiefer are characterized by high organic matter content typical for black shales. The most abundant organic material found in the rocks studied is organic matter of aquatic origin, lacustrine in the Anthracosia Shales and marine in the Kupferschiefer, with very small terrestrial input. The main organic components are liptinite macerals and unstructured organic matter. The prominence of alginite and the amorphous organic matter is clearly visible in the Anthracosia Shales. Their presence in the finest-grained sediments suggests sapropelic depositional conditions for the rocks containing these organic components. Both organic constituents are main components of the lacustrine sapropelic association. A similar organic matter composition is recognized in the Kupferschiefer. Bituminite is by far the most prominent constituent of the organics dispersed in this unit, while alginite is the second in the volumetric importance. In the Kupferschiefer another category of organics was recognized referred to as mineral– sapropelic matrix. Vitrinite is the next important maceral group, followed by minor inertinite particles.

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The organic matter compositions in the Anthracosia Shales and the Kupferschiefer correspond to both kerogen types I and II, respectively, suggesting that the black shales may be regarded as source rocks for hydrocarbons. Acknowledgements

Table 2 Comparison of the reflectance of vitrinite and vitrinite-like matter in the Kupferschiefer Zone/facies

Rovitrinite (%)

Rovitrinite-like

Reduced facies Transitional zone Oxidized facies

0.72–1.25 0.82–1.33 0.82–1.10

0.41–1.17 0.74–1.04 0.72–0.95 a

a

The studies of the Anthracosia Shales were supported by funds of both the Polish Geological Institute (internal grant no. 6.17.0001.00.0) and the National Committee for Scientific Research (grant no. 2P04D 078 28), while the investigations of the Kupferschiefer were funded by the National Committee for Scientific Research (grant no. 1724/T12 2001 20). The author also acknowledges A.C. Cook and an unknown reviewer for their constructive comments and suggestions to improve the paper. Many thanks are due to K. Christanis, the editor of this issue, whose corrections have substantially improved this paper. Appendix A. Origin of the vitrinite-like matter/ maceral dispersed in the Kupferschiefer Vitrinite-like matter does not occur in the Kupferschiefer of the reduced facies described above, but it is a characteristic organic component of the transitional zone of the Kupferschiefer. Similar types of organics are commonly found in other marine source rocks as reported in literature since 1980. Vitrinite-like matter is distinguished on the basis of optical criteria and its origin has not yet been explained. This type of organic matter does not occur in the maceral classification, but was accepted rather as a secondary product of thermal alteration of organic matter and considered as solid bitumen according to Bertrand and Heroux (1987). The progenitors of bituminite are known, but in the case of vitrinite-like maceral this problem is still open. Buchardt and Lewan (1990) indicated a rather humic than bituminous character of vitrinite-like matter pre-

matter

(%)

Relics of vitrinite-like matter.

cursors, while Koch (1997) analyzing similar kinds of material from Scandinavian Alun Shales classified it as bituminite. Hutton (1987) and Hutton et al. (1994) also classified vitrinite-like matter as a variety of bituminite. In the case of the Kupferschiefer, in papers of Koch (1997) and earlier papers of Polish and international authors (Nowak et al., 2001; Oszczepalski et al., 2002; Speczik et al., 2003), the vitrinite-like maceral was described as vitrinite-like bituminite. The recent petrographic studies by the author of this paper precised and modified the views on the origin and classification of the vitrinite-like maceral. For a proper and more precise recognition of the origin of the vitrinite-like matter it is necessary to analyze its petrographic properties: 1. a vitrinite-like maceral mostly occurs in the form of elongated bands and lenses parallel to the microstratification, angular or rounded; the length varies from 15 to 200 μm; 2. under white reflected light the vitrinite-like matter displays grey and light grey colour and shows no anisotropy; its reflectance is slightly lower than Ro of the proper vitrinite in the same sample; 3. under UV irradiation typical vitrinite-like matter does not show fluorescence (Ro N 0.70%); 4. the occurrence of the typical vitrinite-like matter was observed only in the transitional and oxidized zones of the Kupferschiefer, while in the latter facies, only relics of that material were identified. The vitrinite-like matter description presented here, focused on two aspects of its origin: (i) the source of

Fig. 10. Schematic origin pathway of the vitrinite-like matter in the Zechstein Kupferschiefer.

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organic material and (ii) the final process of its formation. Previous papers indicated that vitrinite-like macerals are derived from polysaccharides (i.e. chitin) of graptolites and chitinozoan. Therefore, vitrinite macerals in the Scandinavian Alun Shales may be products of polysaccharide gelification (Buchardt and Lewan, 1990). Although the source of the polysaccharides remains uncertain, several possibilities include multicellular algal seaweeds, fungal hyphae, and arthropod cuticle. Petrographic properties of the vitrinite-like matter of the Zechstein Kupferschiefer indicate a direct genetic relationship to bituminite types (distinguished above in this paper) that can be listed as follows: • bituminite of type 1 occurring in the shales of the reduced facies, makes a background for bituminite of type 2, which displays some optical similarities to vitrinite, while it still has fluorescence properties; • lack of fluorescing bituminite in the shale of both the oxidized and the transitional zones; • the presence of vitrinite-like matter instead of bituminite in both the transitional and the oxidizing zones; • in the transitional zone, the organic matter was still exposed to thermal influence of hydrothermal fluids, which caused its degradation in the oxidized facies; in the transitional zone these changes were weaker; in this way we can state that the altered bituminite has formed vitrinite-like matter, which is a thermally altered modification of bituminite of type 2; it is still similar to type 2, while the bands of vitrinite-like matter represent bands much thinner than bands of bituminite of type 2; this phenomena can be a result of thermal alteration; • a precursor for the vitrinite-like maceral of the Kupferschiefer was probably the same material as for bituminite. The remarks made above have allowed to construct the scheme of the origin and development of vitrinitelike maceral (Fig. 10). This scheme indicates that vitrinite-like matter can be recognized as a bituminite alteration product. During maturation vitrinite-like matter behaves in a way very similar to vitrinite. The reflectance of vitrinitelike maceral is slightly lower than that of the typical vitrinite (Table 2) (Nowak, 2003; Nowak et al., 2004). In samples of the shales of the reduced facies, the reflectance differences between vitrinite and vitrinitelike matter varies from 0.37 to 0.06% (on average 0.21%), while in the transitional and the oxidized zones from 0.25 to 0.05% (on average 0.18%), and

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from 0.16 to 0.10% (on average 0.13%), respectively. Koch in his paper (1997) informed, however, that starting with the value of 1.25% differences between Ro of both vitrinite and vitrinite-like bituminite are so small, that Ro of the latter may be used as a maturity parameter. References Anderson, G.M., Macqueen, R.W., 1982. Ore deposit models — 6. Mississippi Valley-type lead–zinc deposits. Geosci. Can. 9, 107–117. Bertrand, B., Heroux, Y., 1987. Chitinozoan, graptlite, and scolecodont reflectance as an alternative to vitrinite and pyrobitumen reflectance in Ordovician and Silurian strata, Anticosti Island, Qubec, Canada. Am. Assoc. Pet. Geol. Bull. 71, 951–957. Bossowski, A., Ihnatowicz, A., 1994. Palaeogeography of the uppermost Carboniferous and lowermost Permian deposits in the NE part of the Intra-Sudetic Depression. Geol. Q. 38, 709–726. Buchardt, B., Lewan, M.D., 1990. Reflectance of vitrinite-like macerals as a thermal maturity index for Cambrian–Ordovician Alun Shale, Southern Scandinavia. Am. Assoc. Pet. Geol. Bull. 74, 394–406. Cook, A.C., Hutton, A.C., Sherwood, N.R., 1981. Classification of oil shales. Soc. Natl. Elf-Aquitaine 354–381. Creaney, S., 1980. The organic petrology of the Upper Creataceous Boundary Creek formation, Beaufort–Mackenzie basin. Bull. Can. Pet. Geol. 28, 112–119. Don, J., 1961. The Permo-Carboniferous of the Nowa Ruda region. Zesz Nauk. Uniw. Wr., Nauka o Ziemi, vol. 3, pp. 3–49. Dziedzic, K., 1959. Comparison of Rotliegendes sediments in the region of Nowa Ruda (Middle Sudetes) and Œwierzawa (Western Sudetes). Kwart. Geol. 3, 831–846. Dziedzic, K., 1961. Lower Permian in the intrasudetic basin. Stud. Geol. Pol. 6. Eugster, H., 1985. Oil shales evaporites and ore deposits. Geochim. Cosmochim. Acta 49, 619–635. Ewbank, G., Manning, D.A.C., Abbott, G.D., 1995. The relationship between bitumens and mineralization in the South Pennine Orefield, central England. J. Geol. Soc. (Lond.) 152, 751–765. Giordano, T.H., 1985. A preliminary evaluation of organic ligands and metal-organic complexing in Mississippi Valley-type ore solutions. Econ. Geol. 80, 96–106. Giordano, T.H., Barnes, H.L., 1981. Lead transport in Mississippi Valley-type ore solutions. Econ. Geol. 76, 2200–2211. Giordano, T.H., Kettler, R.M., Wood, S.A., 2000. Ore genesis and exploration: the roles of organic matter. Rev. Econ. Geol. 9 (332 pp.). Górecka, T., 1981. Results of palynological studies of the Youngest Carboniferous of the Lower Silesia area (in Polish) Pr. Nauk. Inst. Gor. Politech. Wroc., Monogr. 19 (58 pp.). Górecka-Nowak, A., 1989. Late Carboniferous spore-pollen assemblages of the Unisław Œl. IG-1 borehole (in Polish, English abstract) Pr. Nauk. Inst. Geotech. Politech. Wroc., Stud. Mater. 19, 51–57 (52). Górecka-Nowak, A., 1995. Palynostratigraphy of the Westphalian deposits of the north-western part of the Intrasudetic Basin (in Polish, English abstract) Acta Univ. Wratisl., Pr. Geol. Mineral. 40. Hutton, A.C., 1987. Petrographic classification of oil shales. Int. J. Coal Geol. 8, 203–231.

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