International Journal of Coal Geology 29 ( 1996) 259-272

Petrologic studies of terrestrial organic matter in Carpathian flysch sediments, southern Poland

Marian Wagner Drptrrmrent of Cotrl Deposits Geology, University oj’Mining and Metallurgy, al. Mickiewiczu 30.

30-059 Krakow. Poland

Received 14 December 1993; accepted 21 March 1995

Abstract

In the Carpathian Flysch, coal is present either as exotics of Carboniferous coal deposits or as autochthonous, thin layers of lustrous coal. This paper present the results of the studies of coal-bearing rocks that are coeval with the enclosing flysch sediments. These coals form lenses up to 0.15 m thick. Their morphology precludes an exotic origin. The main petrographic component is collinite with admixtures of poorly fluorescing telinite. Minor components are: exudatinite, sporinite, fusinite, micrinite and sclerotinite. Mineral matter consists of framboidal pyrite clay minerals and quartz.

The random reflectance of telocollinite varies from 0.38% to 0.72%, which corresponds to subbi- tuminous and bituminous ranks. Correlation between chemical analysis, coking properties and reflec- tance measurements, leads to the conclusion that boundary between subbituminous and bituminous coals should be defined by the following values: C = 80wt%; volatiles = 43wt%; calorific value = 32.3 MJ/kg; and R”=0.56-0.57%.

Atypical properties, such as: upper C value (75-80wt%); high volatile matter contents (over 43wt%) and low random reflectance (R” about 0.38-0.57%) in subbituminous coals; low C value (about 80-82wt%); low reflectance (0.560.72%); and good coking properties, of the bituminous coals are attributed to quick coalification during increasing temperature as a result of tectonic stress,

1. Introduction

The presence of coals in the Carpathian flysch sediments has been known for over a century. Their origin is still a matter of discussion. Apart from coalified plant detritus, two other types of organic matter have been identified: I. so called ‘allochthonous’ - detrital angular fragments ranging in size from silt to several

metres across, showing variable petrographic composition and bituminous rank (Turnau, 1970; Mat], 1991);

0 166-S 162/96/S IS.00 0 I996 Elsevier Science B.V. All rights reserved SSDlO166-Sl62(9S)OOOO7-0

260 M. Wugner/ International Journal oj’Coa1 Geology 29 (1996) 259-272

Table I Review of the localization of areas with frequent occurrence of coal exotics and autochthonous coal layers in the Polish Carpathians

Zone Lithostratigraphic unit

Age Coal Autochthonous exotics coal

Skole Nappe

Magura Nappe

Inocerame Beds Maestrichtian + + Babice Shale Paleocene + _

Menilite Beds Oligocene + -

Lacko Marl (Osielec Sandstone) Eocene + Magura Beds Eocene-Oligocene _ +

Silesian Nappe Cieszyn Shale Grodzisk Beds Lgota Beds lstebna Beds Krosno Beds

Tithonian-Hauterivian + + Hauterivian-Barremian + - Albian + _

Paleocene + _

Eocene + +

Podhale Flysch Chocholow Beds Zakopane Beds

Eocene Eocene

_ + _ +

Pieniny Klippen Belt Aalen Flysch Aalenian + +

2. layered and lensoidal accumulations, presumably contemporaneous with the flysch sed- iments and representing subbituminous or bituminous rank (see Wagner, 1980; Mat], 1991).

Layered accumulations of vitrain are common constituents of the carbonaceous shales, which also contain variable amounts of coalified plant detritus (Kotlarczyk, 1979; Wagner, 1980). Other, relatively rare, forms of terrestrial organic matter in the flysch sediments are coalified and, sometimes, petrified stump or branch fragments (Zuber, 1918; Dzulynski and Slaczka, 1958; Kotlarczyk, 1979; Wagner, 1980). The outer parts of these fragments commonly consist of vitrain whereas the interiors are sandstone casts. The enclosing sand- stones and shales occasionally contain preserved prints of aerial roots or leaves (Frankiew- icz, 1974).

Exotic and layered coal is found in numerous localities in the Carpathians (Table 1). Allochthonous coals are most common in stratigraphic units of the marginal parts of the Carpathian nappes between Cieszyn and Przemysl (Figs. 1 and 2). The occurrence of carbonaceous shales is irregular but, roughly, follows the margins of the nappes (Kotlarczyk, 1979). Autochthonous detrital coal beds are known mostly from Eocene and Oligocene sediments, including the Magura, Krosno and Lacko Beds (Dzulynski and Slaczka, 1958; Wagner, 1980; Lipiarski and Peszat, 1984)) as well as from the older units the Inocerame, Menilite and lstebna Beds (Kotlarczyk, 1979). In the Ukrainian parts of the Carpathians, similar accumulations have been described from Miocene and Cretaceous units (Ladyzenski and Sawkiewicz, 1968; Gabiniet and Ripun, 1977).

Autochthonous coals are also known from the Inner Carpathians (i.e., the Pieniny Klippen Belt - Horwitz and Doktorowicz-Hrebnicki, 1932; Makowski, 1947; Birkenmajer and

M. W~lKner/lnternational Journal of Coal Geology 29 (1996) 259-272 261

Fig. I. Tectonic sketch map of the Polish Carpathian flysch and sample localities (after Ksiazkiewicz, 1972). I = Magma Nappe; 2 = Dukla unit; 3 = units of Fore-Magma zone; 4 = Silesian Nappe; 5 = Subsilesian Nappe; 6 = Skole Nappe; 7 = Stebnik unit; 8 = Miocene of Carpathian Foredeep, 9 = Pieniny Klippen Belt: IO= Podhale Flysch; I1 =Tatra area; 12=sampling sites (see Table 2).

Turnau, 1962)) from the Podhale Flysch and its basement (Kuzniar, 1910; Bakowski, 1967; Frankiewicz, 1974) ; and in the Slovakian part of the ‘White Carpathians-upon-Hron’ (Hav- lena, 1964).

Available publications on the Carpathian coals lack, in most cases, detailed petrographic descriptions and credible determinations of coal ranks. In older papers (i.e., Makowski, 1947; Bakowski, 1967), low rank as well as subbituminous/bituminous ranks were men- tioned but diagnostic features were not presented. Most of the authors support the hypothesis that autochthonous coal accumulations originated from plant material supplied to the basin by rivers and were transported by gravitational slides to the flysch depositional environment and matured during subsequent diagenesis and catagenesis (see, e.g., Wisniowski, 1908; Kotlarczyk, 1979). An alternative explanation is that layered coal is a result of the deposition

N S

KRAK6W Samples Samples 6 and 7 1+5 Sample 16 ZAKOPANE

0 12.5 25 km

Fig. 2. Schematic geological sketch of the Polish Carpathians and more important sample localities (after Ksi- azkiewicz. 1972, modified, scale approximate). A = Subsilesian Nappe; B = Silesian Nappe; C= Magura Nappe; D = Pieniny Klippen Belt; E = Podhale Flysch; F= Tatra Mts; G = Miocene of Carpathian Foredeep; H= Silesian coal basin.

262 M. Wagner/International Journal of Coal Geology 29 (1996) 259-272

of organic detritus, derived from the abrasion of Carboniferous coal in a littoral zone of Parathethys (Birkenmajer and Turnau, 1962; Birkenmajer, 1977). The age of coals contem- poraneous with the flysch sediments is still controversial because of the almost complete absence of fossils in the surrounding sediments.

This paper aims to determine coal rank and to discuss the origin of coals hosted within flysch sediments.

2. Methods

Thirty-three coals samples were collected from sixteen localities of Jurassic, Eocene and Oligocene flysch rocks (Fig. 1, Table 2) and subjected to petrographic and chemical analyses. Samples were examined under both reflected and transmitted light as well as under the fluorescence microscope. The reflectance (random R’) measurements were taken under oil immersion (n = 1.5 18) on polished sample blocks, using an Opton MPM-200 photom- eter (546 nm) mounted on an Axioplan-Opton microscope. A magnification of X 600 was commonly used, the area measured being 5 pm in diameter. Chemical analyses followed procedures recommended by the Polish Norm, in agreement with IS0 norms.

The IR spectra were recorded in KBr pellets. The pellet preparation techniques described by Zerda et al. ( 1981) were followed. Pellets were dehydrated in a desiccator for 5 days before recording the spectra on a Specord-75 IR spectrophotometer.

Table 2 Coal samples from the Carpathian Flysch and their petrographic character

Sample Lithostratigraphic Petrographic analysis coal

(see Fig. I ) unit V E I MM R” rank

I. Rokiciny Magura Beds 2. Jordanow Magura Beds 3. Naprawa Magura Beds 4. Lubien Magura Beds 5. Osielec Magura Beds 6. Skawce Krosno Beds 7. Mucharz Krosno Beds 8. Sopotnia Krosno Beds 9. Globikowa Krosno Beds IO. Sekowiec Krosno Beds I I Niechobrz Krosno Beds 12. Labowa Osielec Beds 13. Chocholow Podhale Flysch 14. Koniowka Podhale Flysch IS. Koscielisko Valley Podhale Flysch 16. Biala Woda Aalen Flysch

100 0 0 0 92-98 l-2 14 O-4 97 0 2 I 95 I 2 2 95-96 2-3 l-2 O-l 97-98 0 1 1-2 98-99 o-1 0 O-l 97 1 0 2 99 0 I 0 100 0 0 0 94 I 2 3 92 0 1 7 97 I 1 I 98 0 0 2 97-98 o-1 I l-2 77-99 0.1 O-l O-20

_ 0.38-0.40 0.41 0.38 0.40 0.56-0.61 0.58-0.60 0.72

0.5 1 0.50

0.57 0.51 0.55-0.57 0.45-0.57

subbituminous subbituminous subbituminous subbituminous subbituminous bituminous bituminous bituminous subbituminous subbituninous subbituminous subbituminous subbituminous subbituminous subbituminous subbituminous

V = vitrinite; E = exinite; I= inertinite; MM = mineral matter; R” = random reflectance.

M. Wugner/International Journal of Coal Geology 29 (1996) 259-272 263

3. Coal petrography

Three types of coal accumulations can be distinguished. Type I (Fig. 3A) includes horizontal or slightly inclined lenses of vitrain in thick-bedded ( 1.5-5.0 m) sandstones. The lenses are 0.1 O-O. 15 m thick and continuous over a distance of about 3 m. The hosting sandstones are generally fine-grained and poorly bedded and they are underlain by streaks of coarser-grained sandstone. Locally, graded bedding can be observed. The coal accumu- lations are stumps and branches with their original shapes preserved (Fig. 3A). The outer parts of these forms consist of vitrain ‘veins’ with common ‘apophyses’ penetrating the fractures in the enclosing rock. The internal parts of the stumps are sandstone casts or

0 0,lO 0.20 0.30 0.50 Iml

0.00 or m I 0,lo 0;20 0,30 0,4O 0.50 Iml

lml 0.30

920

C type m

0.00 0 0.10 0.20 0.30 0.40 OS0 Iml

Fig. 3. Lithological pattern of flysch coal-bearing sediments. (A) Geological section of Magura Beds in Jordanow (type I ) ( B ) Geological section of Krosno Beds in Globikowa (type II). (C) Magura Beds in Osielec (type 111). 1 = sandstone and conglomerate; 2 = sandstone; 3 = argillaceous sandstone; 4 = claystone; 5 = coal; 6 = rocks with fossil plant detritus.

264 M. Wagner/international Journal of Coal Geology 29 (1996) 259-272

silicitied internal casts. Beneath such accumulations, numerous, small vitrinite lenticles, arranged oblique to the large lenses, are surrounded by abundant coal detritus. Vitrain ‘apophyses’ connected with the outer zones of stumps resemble roots. However, Kotlarczyk ( 1979) explains their formation by the different compaction rates of plant material and sand. Occasionally, casts of aerial roots as well as prints of leaves and bark have been observed in the close neighbourhood.

Type II (Fig. 3B) coal accumulations include coalified humic detritus (approximately 40 ~01% of the whole rocks). The host rocks are thin-bedded sandstones rich in carbonaceous matter and easily distinguishable by their grey colour. Coal detritus is accompanied by minute vitrain lenticles (from < 1 to 3 mm) which originated from larger wood fragments. Coal lenses and detritus mark the fine lamination of the host sandstones. This type of coal- bearing lithology is most common in the Carpathians and forms the upper parts of fine- grained sandstone beds.

Type III (Fig. 3C) comprises sandy coaly shales. The rocks show thin, horizontal bedding, caused by alternating coal and shale layers. The thickness of coal layers vary from 1 to 3 mm (3 cm maximum). Coal layers more than 3 mm thick are included in the shales as inseparable elements.

All the three types of coal accumulations consist of black vitrain with a highly vitreous lustre. The streak colour is usually brownish-black, sometimes black. Numerous shrinkage cracks cause cubic or platy cleavage.

The main petrographic components of the Carpathian coals are macerals of the vitrinite group (77-100 ~01%). Exinites (O-3 ~01%) and inertinites (o-4 ~01%) are of minor importance. The mineral matter content varies from 0 to 20 ~01% (Table 2). It was found that the petrographic composition of coaly stumps and thicker layers (over 5 mm) is, in general, uniform and perhaps more diversified in comparison with the thin layers. The former consist of collinite (about 75 ~01%) and telinite (ca. < 25 vol%), whereas the latter contain only collinite.

Collinite is represented mostly by telocollinite. This maceral, together with minor gelo- collinite, forms the outer parts of coal accumulations. Inward, it grades into telinite. Collinite contains abundant streaks of micrinite, occasionally clay minerals and streaks of framboidal pyrite. The origin of the latter is related to the bacteria colonies active in the reducing environment. The random reflectance of telocollinite (R”) varies from 0.38 to 0.72% (Table 2). Reflectograms are unimodal, with standard deviation varying from 0.02-0.04% (with 30 samples - the mean of a minimum of 100 measurements of each sample).

Telinite is a less common constituent (up to 25% of vitrinite in thicker layers). Its reflectance is close to that of telocollinite, although it may contain laminae of apparently lower reflectance.

Cells of telinite are usually impregnated with gelocollinite, resinite or clays. In some samples resinite impregnations show brownish-yellow, rarely orange, fluorescence. In less coalified layers (R” < 0.55%)) telinite and telocollinite show spotty or streaky, dark-brown fluorescence of positive alteration. Some shrinkage cracks in collinite are filled with exu- datinite of orange fluorescence. Macerals of the inertinite group (apart from micrinite, which occurs in vitrinite) are represented by small amounts of fusinite and semifusinite as well as by single bodies of sclerotinite. These macerals are usually accompanied by fram- boids or small lenticles of pyrite.

M. Wagner/International Journal of Coal Geology 29 (1996) 259-272 265

Mineral matter includes pyrite, clay minerals, quartz grains and calcite veinlets, the latter filling cracks.

The petrographic composition indicates that the coals studied originated from vascular plants and do not contain algae. Therefore, a suggestion that algal mats participated in their formation (Kotlarczyk, 1979) has not been confirmed. Moreover, the coaly layers do not support the concept of the deposition of exotic coal silt derived from the erosion of Car- boniferous coal formations (Birkenmajer and Turnau, 1962). Instead, the coals show weak bituminization, which is evidenced by minor fluorescence of the humic matter and the presence of micrinite and framboidal pyrite.

4. Chemical properties

Coals from outcrops show variable, occasionally advanced, weathering. This process modifies physical and chemical properties and such samples were not used in the coal rank studies. The data presented below originate from analyses of fresh coals.

The moisture content (W”) is low and varies from 0.3wt% to 8.0wt% (Table 3). Two groups of coals can be distinguished: low moisture, which contains up to 3 wt% and high moisture, which has 5-8 wt% moisture.

Ash content is variable but generally low (3.9-14.lwt%, as received). Higher ash con- tents are related to the presence of silicates, calcite and/or pyrite.

Gross calorific values of the coals studied (dry, ash free, Qd”‘) vary from 26.8 to 34.5 MJ/ kg, depending on the elemental carbon content (Fig. 4). For a wide range of elemental carbon contents this parameter corresponds to the standards given by Van Krevelen ( 1961). Strong linear correlation was found between calorific values and elemental carbon contents (correlation coefficient r = 0.876, standard deviation (T = 0.97 at LY = 0.10). The regression equation is:

Qdn’ = 05492C’” - 11.0683 [MJ/kg]

Volatile matter contents (VMdaf) vary from 38.6wt% to 47.3wt% (Table 3). These values differ from the standard for vitrain for such a C content (Ammosow, 1961; also British Coal Research Association reports) and the discrepancy increases with decreasing reflectance (Fig. 4).

Volatile matter contents are correlated with random rellectance (R”) according to the equation:

VMd”’ = 52.0966 - 18.714OR” [ wt%]

at r-0.88 and a=O.lO. The elemental carbon contents vary from 67.9wt% to 83.7wt%; that is, they correspond

to subbituminous and bituminous coals. Strong correlation has been found with the random reflectance for collinite, according to the formulae (Wagner, 1993) :

C““‘=R”l(a+bR”) [wt%]

where: a=0.001035; b=0.010540; r=0.97, a=0.03 and (~=0.10.

266

Table 3

M. Wagner/International Journal of Coal Geology 29 (I 996) 259-272

Quantitative values of some chemical properties of coal from the Carpathian Flysch

Sample W” A” Q? VM““’ RIa SI” b” CY Hda’ Sd

I Rokiciny 2. Jordanow

3. Naprawa 4. Lubien 5. Osielec

6. Skawce

7. Mucharz

8. Sopotnia 9. Globikowa

IO. Sekowiec

I I. Niechobrz 12. Labowa 13. Chocholow 14. Koniowka 15. Koscielisko Valley

16. Biala Woda

7.0 21.8 28.3 3.3 9.8 31.3 6.7 12.2 30.5 7. I 4.3 29.7 8.0 8.2 31.2 4.0 9.0 31.3 3.8 7.2 31.2 5.2 51.2 34.3 6.2 7.1 34.0 1.3 9.5 34.3 1.8 9.5 33.7 1.5 12.3 33.6 I.1 10.8 34.0 1.3 10.7 34.0 1.6 9.8 34.1 I.1 28.3 34.0 5.8 8.1 31.7 5.2 31.3 33.9 5.2 28.7 32.0 5.6 25.2 31.6 4.2 28.9 32. I 5.7 9.7 31.6 1.4 41.3 26.8 3.8 8.9 32.9 4.8 10.2 31.7 _ 6.9 33.9 1.6 8.9 31.5 3.8 4.0 32.2 4.5 9.3 31.4 7.3 3.9 32.6 4.4 33.1 31.7

_ 44.0 43.7 47.3

45.0 45.0 _

44.8 41.8 41.0 43.0 40.5 40.0 40.6 38.6 _

41.1 43.0 _

42.7 42.8 45.2 44.5 43.8 42.6 39.3 38.3 44.6 40.9 32.7

_ _

5 88 65 _

68 70 _

20 _ _

0 _

0 0 11 25 0 0 33 0

_

_

7 7 7 2 0 0 0 _

0 0

0 0

contr. contr. contr.

contr

100

_

contr.

75.0 5.06 0.90 76.8 5.95 2.09 16.7 5.59 I .oo 74.5 5.30 - 76.9 5.00 2.30 76.8 5.80 I .oo 76.6 5.50 2.61 77.0 6.20 1.30 77.1 6.18 1.10 82.5 5.66 2.30 80.8 5.43 2.00 82.6 6.19 - 81.6 6.80 3.50 82.1 7.30 1.80 80.8 5.70 - 83.0 5.94 1.30 78.0 - 0.80 78.0 5.80 1.35 79.0 6.01 0.80 79.2 5.43 1.80 79.6 - 2.15 79.4 - - 67.9 4.70 9.60 79.5 5.95 4.30 77.1 6.05 1.35

1 l/2 40 80.5 5.90 3.60 2 55 82.5 5.10 2.18 0 - 78.5 - _

0 contr. 77.1 5.95 4.30 2 - 73.8 5.62 0.85 0 _ 73.8 4.66 -

W = moisture; A = ash; Q = gross calorific value; VM = volatile matter; RI = Roga Index; SI = free swelling index; b = dilatation by Arnu-Audibert’s test; C = carbon; H = hydrogen; S = sulphur (total); a = analytical basis; d = dry basis: daf = dry, ash-free basis.

Elemental hydrogen contents (Hdaf) fall in the range 4.7-7.4wt% (Table 3). Higher contents were found in coals rich in resinite and exudatinite (up to 6Swt%). Total sulphur contents (S’) are usually high and vary from 0.85wt% to 9.6wt% Higher sulphur concen- trations are caused by the presence of pyrite.

Some of the coals studied which have elemental carbon contents above 78wt% reveal interesting coking properties. If the Cdar is below 80wt% the agglutination on heating is low (Roga index between 1 and 25, free swelling index+rucible swelling number-between 0.5 and 3.0) and so is the volume contraction (Gray-King coke type B-E, weakly caking). Coals of higher C show good coking properties, with the Roga index varying from 25 to 88, a free swelling index up to 8 and positive dilatation (up to 140%, according to Arnu-

M. Wugner/lnternational Journal of Coal Geology 29 (1996) 259-272 261

dot Qs tMJ/kgl _

33 -

29 -

27 -

25 e 60 68 76

Cdaf

l%l - 64 -

80 -

76 -

72 -

QO 0.2 0.4 0.6 ae R;I%l

Fig. 4. Relationships between: (I) gross calorific value (Qd”‘) and carbon content ( Cdar); (II) volatile matter (VM”“‘) and random reflectance (I?“) ; and (III) carbon content and random reflectance for coal of the Carpathian Flysch. I =after Van Krevelen (1961); 2=after Ammosow (1961); 3=after Agnostin (1971); 4=after Kotter (1960).

Audibert’s test, Gray-King coke type to G8). The best coking properties were found for samples from the Koscielisko Valley, Skawce and Mucharz (Table 3).

The coking properties of the Carpathian coals correspond to the medium or low-volatile ranks (types 34, 35 and 36 according to the Polish Classification System) or to the hypo- medium rank (FSI between 1 and 3) according to Alpem’s Coal Classification (Alpem et al., 1989). Chemical properties corresponding to coking coals are in disagreement with high volatile matter contents, low elemental carbon contents and low reflectances. This could be the result of high pressure conditions contributing a high temperature effect during the coalification process.

268 M. Wagner /International Journal of Coal Geology 29 (1996) 259-272

Fig. S. Representative IR patterns of some samples of coal in Jordanow (J-4) and Koscielisko Valley (K-25).

5. Estimation of coalification rank

The content of elemental carbon, which is commonly accepted as one of the best indicators of coalification level, classifies the samples studied as subbituminous or low-rank bitumi- nous coals. The upper C value for subbituminous coals is 76-77% (chemical criteria of rank, Stach et al., 1975) but for the Carpathian samples it should be raised to about 80%. Up to this value the coals studied still show brownish streaks and give coloured reactions with aqueous solutions of potassium hydroxide and nitric acid (sensitive for humic acids and lignines) . Moreover, these also reveal high volatile matter contents (over 45wt%) and low reflectances (I?” about 0.38-0.57%). This level of elemental carbon content (80wt%) corresponds to a reflectance, R”, of about 0.52%, VM of about 42wt% and a calorific value of 32.3 MJ/kg. Coking properties resemble those of bituminous coals.

Analytical results of the Carpathian coals reveal suppressed reflectances of telocollinite in relation to the elemental carbon contents. Correlation between these two parameters,

Table 4 Approximate percentage of hydrogen in some functional groups (IR analyses)

Sample

Jordanow

Koscielisko Valley

Jet (Boleslawiec) Bituminous coal (Borynia mine)

76.9 5.00 ( 100.0)

82.5 5.10 ( 100.0)

73.0 4.39 ( 100.0)

84.0 4.60 (100.0)

0.66 (13.2)

0.87 (17.1)

0.37 (8.4)

1.06 (23.0)

1.51 (30.2)

1.89 (37.0)

1.60 (36.4)

1.87 (40.6)

2.83 0.70 (56.6)

2.24 0.76 (43.9)

2.42 0.64 (55.2)

1.67 0.82 (36.4)

C”“‘. H”” = carbon and hydrogen content (dry, ash-free basis) ; I-&. bH, = hydrogen share in ahphatic com- pounds; l-t,., r,,, = hydrogen share in aromatic compounds;f,= aromaticity coefficient.

M. Wugner/lnternational Journal of Coal Geology 29 (1996) 259-272 269

although strong, differs from the data from Kotter ( 1960) and Agnostin ( 1971), despite the similar pattern (Fig. 4). Studies of Alpine coals from Loeben (Austria), as well as from Germany and France (Sachsenhofer, 1989), gave similar results of suppressed reflectance. Sachsenhofer quoted the opinion of German specialists who explained suppressed reflec- tance in terms of the presence of submicroscopic resinite intergrowths which impregnate vitrinite and cause a decrease in reflectance. However, in general, this explanation is not convincing. Although increased volatile matter contents and calorific values may influence the C-R” correlation, the lower reflectance should, rather, be related to the less advanced bituminization of organic matter. This process did not result in the formation of bitumens as a separate phase but caused chemical transformation of the wood; for example, its enrichment in aliphatic hydrocarbons in a mildly reducing marine environment. Increased hydrogen content, vitrinite fluorescence and the presence of framboidal pyrite may support such an explanation. It is also consistent with the observations of Karweil ( 1966); Brooks ( 1970) and Stach et al. (1975), who reported bituminization of humic matter during diagenesis of marine arenaceous sediments.

The results of IR spectroscopy support the concept presented above. IR spectra of several samples appear to be similar, especially in the ranges of hydrogen-related bands. Strongly marked are absorption bands of the -CHa group (approximately 2945,2870,1375 and 1135 cm-‘) and methylene group -CH, about 2925,285O and 1465 cm-’ (Alpert et al., 1974; Wagner, 198 1) Bands of the -CH group (between 3 100 and 3000 cm-‘) have not been observed and the absence of the 720 cm-’ band may evidence the occurrence of short, aliphatic chains (Fig. 5).

In the coal structure the aromatic cores are arranged in the form typical of the low-rank coals; that is, they follow the anthracene pattern (1630-1620, 1550, 1390 cm-’ bands, Alpert et al., 1974), substituted at ortho- and meta- positions. This is confirmed by the appearance of 860-900 and 740-780 cm- ’ bands. Moreover, the coal structure also includes -CO groups of, presumably, ketone character (Friedel, 1970).

Hydrogen percentages in the individual functional groups calculated with the method of Oerlet (Oerlet, 1965; Oerlet, 1967) indicate that hydrogen is mostly bonded in methyl (44- 57%) and methylene (30-37%, Table 4) groups. These values show close similarities to those for ‘jet’ (Wagner, 1993) and differ from patterns for coking coals from Borynia mine (Table 4). Hence, it is concluded that the Carpathian coals reveal apparent bituminization features.

6. Remarks on coal genesis

The coal-bearing rocks coeval with the enclosing flysch sediments originated from the transformation of vascular plants. This is evidenced by their petrographic composition (i.e., the presence of telinite, collinite, fusinite and resinite), as well as by the leaf prints and root casts.

The textural and structural features of coal and associated elastics suggest that the dep- osition of plant remains took place during flysch sedimentation. When density flows were moving down the continental slope, gravitational segregation of partly gelified plant remains occurred, which resulted in the occurrence of morphologically diversified coals (detritus,

270 M. Wagner /International Journal of Coal Geology 29 (1996) 259-272

lenses or layers originating from small logs and branches, and coalified stumps) in various flysch sequences.

This plant material was possibly transported by rivers from the adjacent onshore area during floods, which allowed the release of log jams formed in river estuaries. Additional sources of organic matter could also have been fragments of peat and/or subbituminous coals derived from the basin shores.

The present rank of the coals studied does not allow a definite recognition of the depo- sitional history of the coal. However, published data (Lipiarski and Peszat, 1984; M. Mastalerz and K. Mastalerz, 1986) makes the above hypothesis plausible. The primary form of the organic matter seems to have had only a limited influence on the formation of the Carpathian coals. The coals studied do not contain clarain, which has been noticed by Lipiarski and Peszat ( 1984) in a mine ‘Sekowiec’ (West Carpathians) although clarain appears to be the main component of coal exotics. The form of accumulations (extended lenses and layers) does not resemble morphologically the pebbles formed in a littoral zone.

The humic organic matter deposited, together with the flysch sediments, was subjected to typical diagenetic and catagenetic coalification. Additionally, it was slightly bituminized during diagenesis - a process caused by the mildly reducing environment at the sea floor.

The decisive role of dynamic pressure and the resulting temperature increase in the coalification of the Carpathian coals during catagenesis is confirmed by the fact that coals hosted in both the younger Podhale Flysch units and the Magura Nappe belong to the subbituminous type, whereas coals from the Pieniny Klippen Belt, from the older Podhale Flysch units and from the Subsilesian Nappe (underlying the Magura one) show apparent features of bituminous type (Fig. 2).

In terms of the hydrocarbon generation potential of the Carpathian coals (Wassojewitsch et al., 1970; Robert, 1988; Russell and Pearson, 1990, and others), it appears that they represent a maturation level corresponding to the initial oil generation stage. Such a sug- gestion is supported by the average reflectance of telocollinite (R“), ranging from 0.38% to 0.72% and by the presence vitrinite with increased hydrogen content, which is an effect of the bituminization of humic organic matter.

Acknowledgements

Sincere thanks are due to Ing. Jan Bednarz from Rabka for information about localities of coals and for help in gathering material. I also wish to thank very much Prof. Barbara Kwiecinska, Dr. Paul Robert and Dr. Maria Mastalerz for their constructive, critical reviews of this paper.

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