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ÑÏÈÑÀÍÈÅ ÍÀ ÁÚËÃÀÐÑÊÎÒÎ ÃÅÎËÎÃÈ×ÅÑÊÎ ÄÐÓÆÅÑÒÂÎ, ãîä. 65, êí. 1-3, 2004, ñ. 157-166

REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 65, part 1-3, 2004, p. 157-166

Maceral composition and depositional environmentof the coals from Beli Breg basin, Bulgaria

Alexander Zdravkov, Jordan Kortenski

University of Mining and Geology “St. Ivan Rilski”, 1700 Sofia, BulgariaE-mail: alex_zdravkov@yahoo.com; jordan_kortenski@hotmail.com

À. Çäðàâêîâ, É. Êîðòåíñêè. 2004. Ìàöåðàëåí ñúñòàâ è óñëîâèÿ íà îòëàãàíå íà âúãëèùàòà îòÁåëîáðåæêèÿ áàñåéí, Áúëãàðèÿ. – Ñïèñ. Áúëã. ãåîë. ä-âî, 65, 1-3, 157-166.

Ðåçþìå. Áåëîáðåæêèÿò âúãëèùåí áàñåéí å ðàçïîëîæåí â Çàïàäíà Áúëãàðèÿ â ðàìêèòå íà Áóðåëñêàòà ðàçëîìíàçîíà. Âúãëåíîñíèòå ñåäèìåíòè ñà ïðåäñòàâåíè îò àëåâðîëèòè, ïåñú÷ëèâè è êàðáîíàòíè ãëèíè è äî ïåò âúãëèùíèïëàñòà, îò êîèòî ñàìî åäèí èìà ãîëÿìà äåáåëèíà (äî 35 m) è å ðàçïðîñòðàíåí â öåëèÿ áàñåéí. Âúãëèùàòà ñà èçãðà-äåíè îò ðàçëè÷íî ãîëåìè ñâåòëî- äî òúìíîêàôÿâè êñèëèòíè îñòàíêè, âêëþ÷åíè â òúìíà ìàòîâà îñíîâíà ìàñà. Ñèçâúðøåíèòå ïåòðîãðàôñêè èçñëåäâàíèÿ áå óñòàíîâåíî, ÷å âúãëèùàòà ñå îòëè÷àâàò ñ ãîëÿìî ìàöåðàëíî ðàçíîîá-ðàçèå, êîåòî, ñ èçêëþ÷åíèå íà äåòðîãåëèíèò è âòîðè÷íèòå ëèïîèäíè ìàöåðàëè áèòóìèíèò è åêññóäàòèíèò, âêëþ÷âàâñè÷êè îñòàíàëè ìàöåðàëè. Ìàöåðàëíèÿò àíàëèç ïîêàçâà, ÷å ìèêðîêîìïîíåíòèòå îò ãðóïà õóìèíèò ïðåäñòàâëÿ-âàò îñíîâíèÿ ãðàäèâåí åëåìåíò íà âúãëèùàòà, êàòî ñúñòàâëÿâàò äî 91 îáåìíè ïðîöåíòà. Ñúäúðæàíèåòî íà ìàöå-ðàëè îò ãðóïà ëèïòèíèò äîñòèãà äî 8%, êàòî ïðåîáëàäàâàò ìèêðîñïîðèíèò, ñóáåðèíèò è ðåçèíèò. Èíåðòèíèòîâèòåìàöåðàëè ñà äèàãíîñòèöèðàíè â ìèíèìàëíè êîëè÷åñòâà. Èç÷èñëåíè ñà èíäåêñèòå íà òîðôåíèÿ ôàöèåñ, êîèòî âñú÷åòàíèå ñ ïåòðîëîæêèòå îñîáåíîñòè íà ìèêðîêîìïîíåíòèòå ïîêàçâàò, ÷å âúãëèùàòà ñà îáðàçóâàíè â ëèìíî-òåëìàòè÷íî ðåîòðîôíî îâîäíåíî áëàòî, õàðàêòåðèçèðàùî ñå ñ èíòåíçèâåí ìèíåðàëåí ïðèòîê. Âúç îñíîâà íà óñòà-íîâåíèòå ïîêàçàòåëè (îòðàæàòåëíà ñïîñîáíîñò, ñúäúðæàíèå íà îðãàíè÷åí âúãëåðîä, òåìïåðàòóðà íà ìàêñèìàëåíäîáèâ íà âúãëåâîäîðîäè) å ïîòâúðäåí íèñêèÿò ðàíã íà âúãëèùàòà, êîèòî òðÿáâà äà ñå ïðèåìàò êàòî ïðåõîä îòòîðô êúì ëèãíèòè.

Êëþ÷îâè äóìè: ëèãíèòè, ìàöåðàëè, ìàöåðàëåí àíàëèç, ðàíã, óñëîâèÿ íà îòëàãàíå, Áúëãàðèÿ.

Abstract. The Belibreg coal basin is situated in West Bulgaria, within the boundaries of the Burell fault zone. The coal-bearing sediments are represented by sandy clays, sandstones, sandy and lime clays and up to 5 coal beds. Among them onlyone has greater thickness (up to 35 m) and spatial distribution across entire basin. The coal is composed of fine- to coarse-grained xylitic fragments with light- to dark-brown colour, mounted by dull groundmass. The microscopic investigationsrevealed the coal is characterized by great maceral diversity, which excludes only detrogelinite and the secondary lipoidmacerals (i.e. bituminite and exsudatinite). The maceral composition is dominated by the macerals from huminite group,which constitute about 91 % of the coal. The average amount of liptinite macerls is 8%. Among them microsporinite,suberinite and resinite predominate. The inertinite group macerals were established only in minor amounts. The petrologicalproperties, as well as the indices of the coal facies indicate deposition in limnic-telmatic rheotrophic mire, characterized byintensive mineral influx. The coal is at low coalification stage and represents a transition from peat to lignite, as indicated bythe low values of the reflectance measurements, total organic carbon and Tmax.

Key words: lignite, macerals, maceral analysis, coal rank, depositional environment, Bulgaria.

Introduction

The Beli Breg coal basin is situated in West Bulgaria,about 45-50 km from the city of Sofia. It belongs to theSofia coal province (Šiškov, 1997). The coal bedsoccur within the Pliocene sediments of the LozenetzFormation (Zagorchev et al., 1995), represented bycoarse and medium-grained gravel and sands, sandyclays, sandstones, lime and sandy clays. Thesesediments are deposited in a 90 km2 graben-sincline,which is a part of the so-called Burrell fault zone(Goèev et al., 1970). The whole up to 150 m thicksequence is deposited with base discordance overdenudated Jurassic and Early Cretaceous limestones

and dolomites, and Late Cretaceous terigenous andcalcareous sediments, as well as the very wide spreadacross the region volcano-clastic sediments andvolcanic lavas. The later are separated in two unofficialunits (Zagorchev et al., 1995), which are representedby tuffs, agglomerates, thin layers of limestones andsandstones, along with thin, but vast volcanic lavaswith andesite, latite, trachybasalt and basalt compo-sition. The Upper unit contains also small subvulcanicbodies of andesites. The Burell fault zone (Goèev et al.,1970) is a wedge-shaped tectonic zone with north-west orientation and maximum width of 15 km. Themain fault structures have general orientation 110-125o

and are thought (Zagorchev et al., 1995) as the main

158

conductive zone for the subvulcanic intrusions. Thezone is divided to different blocks by faults with 60o,45o and 0o orientation.

The Beli Breg coal basin is 15 km2 (Yovchev, 1960)and contains up to 5 coal beds, of which only one hasconstant thickness (up to 35 m with average thicknessof 12.47 m) and occurrence across the basin. Thebasin is subdivided to two districts – Tzatzarovtzi andNedeliste. The former one was closed in 1990 becauseof insufficient coal reserves and in present days miningactivities take place only in Nedeliste district.

The present paper is the first complete study on thepetrography of the Beli Breg coals. Fluorescencemicroscopy and Rock Eval pyrolysis and maturationanalysis were applied for the first time for the Beli Bregcoals. Some information regarding the maceralcomposition was reported by Platschkov, Stoikova(1961) and Konstantinova (1966). The coal macerals,established by them (mostly from the humotelinitesubgroup), were described in transmitted and reflectedlight, but the present ICCP nomenclature for low rankcoals was not applied in the description. Liptiniticmacerals were only mentioned, but no described. Theaims of this study were: i) determination and detaildescription of macerals and their properties; ii)establishing the maceral indices in order to reconstructthe environment and settings of the paleomire; iii)combining different analytical procedures, some ofwhich (Rock Eval pyrolysis) were not used before toconfirm the low rank (Šiškov, 1997) of the coals.

Methods

The present study is based on 76 channel samples,taken from the main coal seam in Nedelishte district.For microscopic investigations the samples werecrushed to a maximum size of 1 mm, mounted withepoxy resin, ground and polished. Maceral analysiswas performed by Single-scan method (Taylor et al.,1998) with Leica MPV microscope, equipped withreflected white and blue irradiation light and 20×/0.40,50×/0.85 and 100×/1.25 objectives for oil immersioninvestigations. At least 300 points were counted, usingautomatic point counter “Prior G”. Huminite reflec-tance was measured on four samples. At least 50 pointswere measured per sample, using Yttrium-Aluminum-Garnet standard with reflectance 0.899%. The organiccarbon contents were determined with Leco CS 300analyser on samples pretreated with concentratedhydrochloric acid. Rock Eval pyrolysis using aRockEval 2+ instrument was performed on 6 samples.As a maturation parameter Tmax (the temperature ofmaximum hydrocarbon generation) was determined.Ash and moisture contents measurements followedstandard procedure (Deutsches Institut für Normung,1978a, 1978b).

Results and discussion

According to the terminology and descriptions,recommended by the International Committee for Coal

and Organic Petrology (ICCP, 1993; 2001) the lignitesfrom Beli Breg basin are typical xylite-rich coals (Tayloret al., 1998), containing weakly altered xyliticfragments mixed with detritic material. According toKonstantinova (1966) the amount of the xylite is lessthan 25 vol. %. The later is pale-brown to dark brownwith different size of the fragments – from whole woodstems to small particles, spread within the dull brownto dark brown groundmass. Wood fragments occurparallel to the bedding, but no distinct xylite layers canbe seen. The main coal seam is interbedded with locallydistributed small layers and lenses of calcareous andclay sediments and often shows transitions to coalshales, suggesting dynamic tectonic conditions duringdeposition of the organic material. The randomhuminite reflectance was measured on eu-ulminite A tobe 0.18%. The value of this parameter is slightly lowerthen the value 0.22%, described by Šiškov (1997).Organic carbon content ranges from 34.6 to 73.5%(daf) with mean value 60.3% (daf), and the moisturecontent – from 8 to 24%. The coals are very rich in ash– on dry basis the ash content ranges from 10.53 to49.73% with mean value 31.41%, which is close to28.5% reported by Yovchev (1960). As a maturityparameter the temperature (Tmax) of maximumhydrocarbon generation was measured to be about364oC, corresponding to immature organic matter(Taylor et al., 1998). According to the German andNorth American classifications of coalification stages(Taylor et al., 1998), we should consider the Beli Bregcoals, possessing the chemical and physical parametersdescribed above, to be a transition from peat to lignites.The low values of Tmax, as well as the immaturity of theorganic matter could be interpreted as an indication ofthe early diagenesis stage of lithogenesis. Furthermore,as it will be shown below, the organic matter is still onthe stage of biochemical gelification (Taylor et al.,1998). This is indicated by the presence of high texto-ulminite content, with highly deformed and swelled cellwalls, as a result of this process. The presence ofdetritic particles, containing preserved cellulose, withinthe humodetrinite groundmass reveals that the coalswere subjected to temperature not exceeding 35-40oC,which is the ideal temperature for bacterial destructionof the cellulose (Stach et al., 1982).

Macerals from the huminite group

The petrographic analysis (Table 1) reveals that the BeliBreg coals are exceedingly rich in huminite. All thesubgroups and macerals from this group have beenrecorded in considerable amounts. Textinite is the mostabundant maceral from the humotelinite subgroup(Table 1). It has very low reflectance and frequentlyshows strong colored internal reflections (Plate I-3),which makes the observations very difficult. The cellcavities are usually empty (Plate I-1, 2) or filled withresinite (Plate I-4) and rarely with corpohuminite (PlateI-1, 3, 4). Cell walls are in most cases deformed (PlateI-1, 5) as a result of the softening and swelling of thetissue, caused by the biochemical gelification. Impreg-nated with resinite (Plate I-4) or tannins cell walls

159

possess regular form, because of their high resistancein the gelification process. Under fluorescent lighttextinite (Plate I-2) has light to dark brown colors, as aresult of the high cellulose content still preserved in thecell walls. Transitions to texto-ulminite can frequentlybe seen (Plate I-5, 6). Both macerals have dark greycolor and occur only as “A” variety. They are the majorcomponents, composing weekly altered woodfragments and roots. Eu-ulminite (Plate I-6; Plate II-1;Plate III-9) is quite rare in these coals. Its amount isless than 5% from the humotelinite subgroup. In mostcases it associates with texto-ulminite and textinite,indicating strong alteration of the wood (Plate I-6). Asa component of some roots it exists as “A” and “B”varieties (Plate III-9), but usually it has dark grey colorand low reflectance and appears mostly as “A” type.Transition to telogelinite (Plate II-1) can rarely be seen.

Humodetrinite subgroup is represented by bothattrinite and densinite macerals. The later is quite rarelyobserved mostly as layers and lenses in attrinite (PlateII-1, 3; Plate III-9). The most abundant maceral fromthis subgroup is attrinite (Plate II-2, 5). It is composedof small detritic particles very fine mixed with humicgels and minerals (Plate II-2). Often attrinite showsweak brownish fluorescence, as a result of thecellulose, still preserved within the detritic particles(Plate IV-2, 5, 7). Typical constituent of thegroundmass is gelinite, in particular porigelinite. Thelater exists as small droplets (Plate I-5) between thedetritus and occasionally it fills small cavities within thehumodetrinite (Plate II-6). Porigelinite has alsoprecipitated within the cells of structured macerals(Plate I-3; Plate II-4). Solid humic substances,identified as eugelinite was established in small amountas a part of attrinite (Plate II-5).

Beli Breg coals were found to be rich incorpohuminite macerals (Table 1), thus indicating theenrichment of the organic material with tannins. Thetwo maceral types from this subgroup were observedin considerable amounts (Table 1). Phlobaphinite is theprevailing maceral from this subgroup. It fills the cellsof bark tissues (Plate II-6; Plate III-6; Plate IV-3, 4)and occasionally textinite cell cavities (Plate I-3, 4). Insome cases the formation of corpohuminite could berelated to precipitation of humic gels within the cellcavities of some easily decomposing tissues (Plate II-4). The other corpohuminite maceral – pseudo-phlobaphinite was also observed as round bodies (PlateI-5; Plate II-2) within the humodetrinite.

Macerals from the liptinite group

The amount of the macerals from this group is shown inTable 1. Their color in fluorescence light is bright yellowto yellow-green in accordance to the low rank of thecoals (Taylor et al., 1998). Sporinite was established asflattened elongated and thread-like bodies (Plate III-1, 4,8; Plate IV-1, 5, 8). Round (Plate III-3) or triangularsporinites can rarely be observed. Because of the goodpreservation in some spores relicts of the internal

cellulose cover (“intina” after Stach et al., 1982) are stillvisible. Spores possess in most cases intact sporo-pollenin layer suggesting short transportation or none atall. The later indicates autochtonous or hypoauto-chtonous origin of the sporinite. Sporangium with nume-rous spores has also been found in these coals (Plate III-2). The maceral is easily identified in fluorescent light,but in reflected light no distinction can be made withmineral inclusions, except when the spores are includedwithin the densinite groundmass (Plate II-3).

Cutinite has been identified as leaf protection (PlateIII-7, 8, 9). It is thick and in fluorescent light itscharacteristic form copying the leaf cell structure canbe observed. The color in fluorescent light is yellow,yellow-brown to yellow-green. In reflected light itshows very dark grey color with strong internalreflections (Plate III-9), but in distinction with the otherliptinite macerals can easily be identified, because of itsspecific shape. The phyllo-vitrinite (an informal namefor describing tissues, derived from leafs (Stach et al.,1982) it covers has different degrees of tissuepreservation (Plate III-9). Single thin cutinite tread-likehardly curved and deformed bodies (Plate IV-1, 2) canalso be found.

Suberinite is an abundant maceral in Beli Breg coals(Table 1). It usually forms the bark of plant roots (PlateIII-6) and rarely can be seen as long linear bodies,representing bark tissue of plant stems (Plate IV-3, 4).The cell walls are thin and curved. The color influorescent light is yellow-brown or yellow-green. Inreflected light it has slightly darker grey color, than theassociated phobaphinite. The cells are always filled withtannin derived humic substances (phlobaphinite) (PlateII-6; Plate III-9; Plate IV-3, 4) and very rarely withporigelinite. It was found in one sample some of theroots to be slightly fusinized (Plate II-6), most probablyas a result of fungal activity. In this case suberinite hasvery dark grey to black color.

Resinite was identified mainly as round bodies (PlateIII-5, 6) filling resin ducts within the plant and roots.Its color in reflected light is dark gray (Plate I-4) withinternal reflections, and in fluorescent light ranges fromyellow-green to yellow-brown. Detritic resinite wasfound only in one sample and it is not typical for thesecoals.

Alginite is in small amount (Table 1). It forms smallelongated bodies (Plate III-1; Plate IV-1, 5) with hardlyidentifiable structure. Decomposed alginite was alsoestablished in few samples (Plate IV-6). Fluorinite wasdetermined for the first time in the coals from thisdeposit. It forms groups of small round bodies withstrong fluorescence in yellow-brown and yellow-green(Plate IV-7, 8). Rarely fluorinite can be found scatteredin detritic groundmass (Plate III-1). Its origin is fromessential oils in plant leafs (Tailor et al., 1998), whichcan easily be seen in its association with cutinite andphillovitrinite. Occasionally the fluorinite amountwithin the leaf is so great that it occupies the whole leafshape (Plate IV-7). All unidentifiable particles of theliptinitic macerals were counted as liptodetrinite (PlateIII-2, 8; Plate IV-2, 5, 6, 7).

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P L AT E I . Macerals from Beli Breg coal basin – humotelinite subgroup: 1, textinite “A” (T) and chorpohuminite (Ch), 500×; 2,same as 1, fluorescent light, 500×; 3, textinite “A”, showing strong internal reflections, 200×; 4, resinite (R) and corpohuminite (Ch),filling cell cavities of textinite “A”, 200×; 5, transition of textinite “A” (T) to textoulminite “A” (TU), along with gelinite (G),corpohuminite (Ch) and framboidal pyrite (Py), 500×; 6, transition of textinite (T) to textoulminite (TU) and eu-ulminite (EU), 200×.All photos (except 2) were made with reflected white light under oil immersion

Ò À Á Ë È Ö À I . Ìàöåðàëè âúâ âúãëèùàòà îò Áåëîáðåæêèÿ áàñåéí – ïîäãðóïà õóìîòåëèíèò: 1 – òåêñòèíèò „A“ (T) èêîðïîõóìèíèò (Ch), 500×; 2 – ñúùàòà êàòî 1, ôëóîðèñöåíòíà ñâåòëèíà, 500×; 3 – òåêñòèíèò „A“, ïîêàçâàù ñèëíèâúòðåøíè ðåôëåêñè, 200×; 4 – ðåçèíèò (R) è êîðïîõóìèíèò (Ch), çàïúëâàùè êëåòú÷íèòå îòâîðè íà òåêñòèíèò „A“, 200×;5 – ïðåõîä îò òåêñòèíèò „A“ (T) êúì òåêñòîóëìèíèò „A“ (TU), ãåëèíèò (G), êîðïîõóìèíèò (Ch) è ôðàìáîèäàëåí ïèðèò(Py), 500×; 6 – ïðåõîä îò òåêñòèíèò (T) êúì òåêñòîóëìèíèò (TU) è åóóëìèíèò (EU), 200×. Âñè÷êè ñíèìêè (ñ èçêëþ÷åíèåíà 2) ñà íàïðàâåíè â ìàñëåíà èìåðñèÿ ïîä îòðàçåíà ñâåòëèíà

P L AT E I I. Macerals from Beli Breg coal basin – humodetrinite and humocollinite subgroups: 1, eu-ulminite (EU) in densinite(D), 500×; 2, attrinite (At) groundmass with corpohuminite (Ch), inertodetrinite (Id), macrinite (M) and fungal spores (F), 500×; 3,densinite groundmass, 500×; 4, humic gels (Ch), formed within the cell structure of former plant tissue, 500×; 5, eu-gelinite (G) inattrinite (A), 200×; 6, porigelinite (G) and suberinite (Sb) with filled with corpohuminite (Ch) cell openings, 500×. All photos weremade with reflected white light under oil immersion

Ò À Á Ë È Ö À I I. Ìàöåðàëè âúâ âúãëèùàòà îò Áåëîáðåæêèÿ áàñåéí – ïîäãðóïè õóìîäåòðèíèò è õóìîêîëèíèò: 1 –åóóëìèíèò (EU) â äåíñèíèò (D), 500×; 2 – àòðèíèòîâà (At) îñíîâíà ìàñà ñ êîðïîõóìèíèò (Ch), èíåðòîäåòðèíèò (Id),ìàêðèíèò (M) è ãúáíè ñïîðè (F), 500×; 3 – äåíñèíèòîâà îñíîâíà ìàñà, 500×; 4 – õóìóñíè ãåëè (êîðïîõóìèíèò – Ch),îòëîæåíè â êëåòú÷íèòå îòâîðè íà ðàñòèòåëíà òúêàí, 500×; 5 – åóãåëèíèò (G) â àòðèíèò (A), 200×; 6 – ïîðèãåëèíèò (G) èñóáåðèíèò (Sb), ÷èèòî êëåòú÷íè îòâîðè ñà çàïúëíåíè ñ êîðïîõóìèíèò (Ch), 500×. Âñè÷êè ñíèìêè ñà íàïðàâåíè â ìàñëåíàèìåðñèÿ ïîä îòðàçåíà ñâåòëèíà

Macerals from the Inertinite group

The coals usually contain inertinite macerals less thanone per cent (Table 1). Only a few samples have highinertinite content. Pyrofusinite (Plate V-1, 2) andpyrosemifusinite (Plate V-3) in them are in considerableamounts, among with inertodetrinite, showing so called“bogen” structure (Diessel, 1992). High temperaturecrown fires are probable for the formation of thesemacerals, when only the strongly lignified tissuessurvive through the incomplete combustion. Althoughautochthonous formation is possible for some of theinertinite, especially for fusinized roots (Plate V-4) it ismore likely the major part of the inertinites to be blowninto the swamp from distant fires. Evidence for suchtransportation is the high inertodetrinite content,derived from fusinite, as well as the fact that only thedeeper parts of the fusinized tissues with thick cellwalls and thus harder than the strongly fusinized oneshave been identified. Typical constituent of the sampleswith low inertinite content is macrinite (Plate V-5, 6)with medium to light grey color. Its probable formationis through the oxidation of humic substances near tothe peat surface, although bacterial activity and locallow temperature fires (Plate V-4) are also possible.However, the latter is not very probable and the presen-ce of fuzinized roots and humic gels could be related tothe fungal activity (Moore et al., 1996). Fungal remains(ICCP, 2001) are common in all samples. They arerepresented by twin- and multi-celled spores (Plate V-6) and roundish sclerotia relicts (Plate V-5, 7, 8).Plectenchyma tissues can be determined too.

Indices of the coal facies

Maceral ratios used for paleoenvironmentinterpretations are based on the assumption that coalmacerals are plant and environment-dependant andthus can be used to assess the characteristics of thepaleomire. There have been various suggestions tocharacterize the coal facies on the basis of the maceralratios (Diessel, 1986; Diessel, 1992; Calder et al.,1991). Diessel (1986) introduces two indices – TPI(Tissue Preservation Index) and GI (Gelification Index)for interpretation of paleoconditions for Permianbituminous coals. This indices were later also appliedfor lignites and soft brown coals (Kalkreuth et al.,1991, Kolcon et al., 1999; Iordanidis et al., 2003 andmany others). The TPI can be used to determine thedegree of humification of plant tissues, because it iscontrasting less humified structured and stronglyhumified unstructured tissue-derived macerals(Diessel, 1992). In addition TPI is also an indirectindicator of the type of the vegetation. In this way highTPI values suggest predominantly wood-derivedtissues or high rate of subsidence, resulting inpreservation of the structure of the macerals. Low TPIvalues indicate either predominantly herbaceousvegetation in the paleomire or very low subsidence rate,accompanied with advanced humification, leading tostrong decomposition of the plant material (Diessel,1992). The GI has been defined as a measure of thedegree of wet conditions (Diessel, 1992), because it istaking into account the presence of inertinite macerals,which are indicators for dry conditions. There has been

16121 Ñïèñàíèå íà Áúëãàðñêîòî ãåîëîãè÷åñêî äðóæåñòâî, êí. 1–3, 2004

Tabl

e 1.

Mac

eral

com

posi

tion

(vol

. %, m

iner

al m

atte

r fre

e), m

iner

al m

atte

r con

tent

(vol

. %) a

nd fa

cies

indi

ces o

f the

Bel

i Bre

g lig

nite

s. Таблица

1. Мацерален

състав

(об.

%, без

минерални

примеси

), съдърж

ание

на минерални примеси

(об.

%) и

индекси

на торфения

фациес във въглищата

Sam

ple

Mac

eral

per

cent

age

H

tel

Hde

t G

el

Ch

?H

um

S C

Su

b R

A

l Fl

Ld

?

Lipt

Fs

SF

s F

M

Id

?In

ert

BB

1

4.0

63.6

4.

0 1.

0 72

.7

4.0

4.0

5.0

2.0

1.0

15

.2

23.2

B

B 2

75

.0

6.0

4.9

5.3

91.2

0.7

1.1

3.5

5.

3 1.

1

0.7

1.

8 3.

5 B

B 3

31

.2

44.6

5.

7 7.

4 88

.9

1.0

0.7

1.0

0.3

0.

3 2.

4 5.

7 0.

3

1.0

0.7

3.4

5.4

BB

4

50.2

19

.0

9.2

13.6

91

.8

3.4

2.7

0.7

6.8

1.0

0.

3 1.

4 B

B 5

9.

4 24

.2

33.7

6.

4 22

.2

37.7

66

.3

BB

6

25.2

39

.6

9.4

15.8

89

.9

1.0

0.

7 0.

7

1.

3 3.

7

2.4

1.3

2.

7 6.

4 B

B 7

20

.2

44.8

13

.8

12.8

91

.6

1.0

1.

3 0.

3 0.

3 0.

3 2.

0 5.

4 0.

3

2.0

0.

7 3.

0 B

B 8

31

.0

44.3

5.

7 7.

7 88

.7

1.0

0.7

1.0

0.3

0.

3 2.

3 5.

7 0.

3

1.3

0.7

3.3

5.7

BB

9

26.1

39

.9

12.7

11

.7

90.4

4.

2 0.

7 1.

1

1.1

7.1

2.5

2.5

BB

10

21.6

46

.8

9.8

16.2

94

.3

1.0

0.3

0.

3 1.

0 2.

7

0.3

2.0

0.

7 3.

0 B

B 1

1 46

.3

28.2

9.

4 11

.1

95.1

2.

1 0.

7 0.

7

0.7

4.2

0.3

0.

3 0.

7 B

B 1

2 19

.0

61.4

5.

3 4.

2 89

.8

1.4

0.4

0.7

0.7

2.8

5.9

1.1

0.

7

2.5

4.2

BB

13

16.7

64

.3

2.7

10.2

93

.9

0.7

1.0

0.3

2.

0 4.

1

0.7

1.4

2.0

BB

14

24.3

56

.3

6.3

7.6

94.4

1.

0

0.3

0.3

1.0

0.3

2.1

5.2

0.3

0.3

BB

15

23.7

29

.5

24.1

15

.3

92.5

1.

4

1.0

0.7

2.0

5.1

0.3

1.

4

0.7

2.4

BB

16

22.6

45

.5

11.5

9.

4 88

.9

0.7

0.7

0.3

0.7

3.8

6.2

0.3

0.

3 2.

1 2.

1 4.

9 B

B 1

7 18

.8

52.7

8.

5 15

.0

95.0

1.

5

0.4

1.9

0.

4 2.

7

3.

1 B

B 1

8 14

.4

51.2

5.

7 17

.7

88.9

0.

7

1.3

2.

0 4.

0 1.

3

1.0

1.0

3.7

7.0

BB

19

29.0

40

.1

3.9

19.4

92

.5

0.7

0.4

1.

1 1.

8 3.

9

2.

2 0.

4 1.

1 3.

6 B

B 2

0 29

.1

42.9

7.

1 12

.8

91.9

1.

4 0.

3 0.

3

0.3

1.4

3.0

6.7

0.7

0.

7 1.

3 B

B 2

1 17

.4

55.8

6.

4 12

.4

92.0

0.

7

0.3

0.3

0.7

2.0

0.7

0.3

0.7

0.7

3.7

6.0

BB

22

39.5

30

.4

9.4

16.1

95

.3

0.3

0.

7 1.

7

1.

0 3.

7

1.

0

1.

0 B

B 2

3 20

.5

63.1

2.

6 9.

3 95

.5

0.4

0.4

1.5

2.2

0.4

1.

9 2.

2

162

Tabl

e 1.

con

tinue

d Таблица

1. продълж

ение

BB

24

20.5

63

.1

2.6

9.3

95.5

0.

4

0.

4 1.

5 2.

2 0.

4

1.9

2.2

10.7

4.

2 0.

3 0.

3 B

B 2

5 31

.0

39.1

11

.6

7.5

89.1

4.

1 1.

0 0.

7

0.7

3.

7 10

.2

0.3

0.

3 0.

7 2.

0 1.

9 0.

7 0.

6 B

B 2

6 25

.6

56.9

7.

2 5.

8 95

.5

0.

4 0.

9

0.4

0.

9 2.

7

0.

4

1.4

1.8

25.7

3.

7 0.

4 0.

4 B

B 2

7 26

.6

41.9

14

.2

11.8

94

.4

0.3

1.

4 0.

7

0.

3 2.

8

2.

8

2.

8 3.

7 2.

7 0.

7 0.

5 B

B 2

8 40

.6

40.2

7.

4 7.

0 95

.1

0.4

0.

4 1.

2

1.

2 3.

3

0.

8

0.8

1.6

18.7

1.

8 1.

0 0.

8 B

B 2

9 33

.9

39.3

7.

1 8.

8 89

.1

0.

3 1.

0 1.

4

1.

7 4.

4 0.

3

1.

7 4.

4 6.

4 1.

7 1.

7 0.

8 0.

7 B

B 3

0 23

.0

55.3

8.

3 6.

5 93

.1

1.4

0.

3

0.3

3.

4 5.

5

0.7

0.3

0.

3 1.

4 3.

0 3.

2 0.

4 0.

4 B

B 3

1 33

.6

47.8

6.

9 6.

6 94

.9

0.4

0.4

1.8

2.5

1.1

1.

5 2.

6 8.

7 2.

1 0.

7 0.

6 B

B 3

2 23

.3

45.5

11

.1

13.9

93

.7

0.7

1.

4 1.

4

0.

7 4.

2

1.

4

0.7

2.1

4.0

3.2

0.6

0.4

BB

33

22.8

49

.0

7.7

12.7

92

.3

0.3

2.

0 0.

7

1.

7 4.

7

2.

0

1.0

3.0

0.7

3.1

0.5

0.4

BB

34

13.0

51

.2

18.4

14

.0

96.6

0.

7

0.

7 0.

3

2.4

2.7

2.3

6.6

0.3

0.2

BB

35

26.5

48

.3

7.7

5.7

88.2

0.

7 1.

0

0.7

2.0

4.4

1.

0 1.

7 1.

7 3.

0 7.

4 0.

7 2.

4 0.

6 0.

5 B

B 3

6 36

.4

37.1

7.

0 14

.7

95.2

1.

5 1.

5

2.9

0.4

1.

5

1.

8 9.

3 1.

9 1.

1 0.

8 B

B 3

7 29

.8

52.0

6.

2 4.

1 92

.1

0.3

1.7

1.0

3.

4 6.

5

1.

4

1.

4 2.

7 2.

2 0.

6 0.

5 B

B 3

8 29

.1

39.9

9.

5 16

.2

94.6

0.

7

1.4

0.7

1.0

3.7

1.7

1.7

1.3

2.3

0.8

0.6

BB

39

36.7

37

.8

7.1

12.2

93

.9

0.7

0.

7 1.

0

0.

7 3.

0 1.

4

1.0

0.

7 3.

1 2.

0 1.

6 1.

0 0.

8 B

B 4

0 33

.2

51.8

2.

2 3.

3 90

.5

0.7

1.5

0.7

3.7

2.9

9.5

8.7

2.0

0.6

0.6

BB

41

29.0

53

.7

2.7

6.6

91.9

0.

8

0.8

0.8

0.4

0.8

3.5

6.9

0.

4 0.

4

0.4

1.2

13.7

2.

6 0.

5 0.

5 B

B 4

2 57

.8

14.5

9.

9 2.

8 85

.1

0.4

1.

1 1.

4 0.

4

0.7

3.9

11.0

11

.0

6.0

0.6

3.8

2.4

BB

43

35.2

44

.3

0.9

3.6

84.0

0.

5

0.5

0.5

2.3

4.6

6.9

15.0

0.

9 0.

9 27

.0

2.2

0.7

0.8

BB

44

60.1

24

.3

2.1

4.5

91.0

1.

0 2.

1

1.0

2.1

6.3

2.1

0.

7 2.

8 4.

0 0.

6 2.

3 2.

2 B

B 4

5 21

.0

58.1

2.

4 10

.7

92.1

0.

3

1.0

1.4

0.7

0.3

1.7

5.5

0.7

1.

7 2.

4 3.

0 3.

5 0.

4 0.

3 B

B 4

6 38

.0

32.0

10

.8

10.1

90

.9

1.7

0.

3 1.

0 0.

3 1.

3 1.

3 6.

0

2.

0

1.0

3.0

1.0

1.4

1.1

0.9

BB

47

22.4

54

.8

2.3

12.4

92

.0

1.0

1.0

1.0

0.3

2.3

5.7

2.3

2.3

0.3

3.1

0.4

0.4

BB

48

7.0

77.6

0.

9 7.

5 93

.0

5.1

5.1

1.9

1.9

28.7

16

.4

0.1

0.1

BB

49

21.8

56

.0

2.4

10.1

90

.3

0.7

3.

7 1.

7 0.

7

3.0

9.7

0.7

3.2

0.5

0.4

BB

50

78.4

5.

4 3.

0 9.

1 96

.0

3.

7

0.

3 4.

0

1.

0 0.

2 14

.4

9.3

BB

51

63.4

16

.8

3.0

12.7

96

.0

0.3

0.3

1.

3

1.

0 3.

0

1.

0

1.

0 0.

7 0.

5 3.

5 3.

2 B

B 5

2 29

.9

56.4

2.

0 4.

4 92

.6

0.3

1.0

0.7

3.

4 5.

4

0.

3

1.7

2.0

0.7

2.1

0.5

0.5

BB

53

63.8

11

.7

0.4

6.7

82.5

0.

8

0.4

1.7

5.8

2.1

5.4

16.2

0.

4

0.8

1.2

2 0.

6 2.

7 4.

9 B

B 5

4 60

.7

19.6

4.9

85.2

0.

7 1.

4 2.

1 3.

5 0.

4 0.

7 4.

9 13

.7

0.4

0.

7 1.

0 5.

0 0.

5 2.

4 3.

0

163

Tabl

e 1. c

ontin

ued

Таблица

1. продължение

BB

59

30.4

50

.9

1.5

4.6

87.4

1.

9 0.

4

1.1

1.9

4.

9 10

.2

2.3

2.3

12.3

2.

3 0.

5 0.

6 >

1000

BB

60

77.5

9.

4

5.2

92.0

0.

9

2.

3 1.

4

1.9

6.6

1.4

1.4

29.0

0.

6 5.

3 7.

2 55

.0

BB 6

1 57

.6

21.4

8.3

87.2

1.

4 0.

7 1.

4 0.

7 1.

4 0.

7 5.

5 11

.7

0.7

0.

3 1.

0 3.

3 0.

6 2.

0 2.

7 16

8.7

BB 6

2 5

32.8

0.

5 5.

7 89

.1

0.5

3.1

2.1

2.

6 8.

3

0.

5

2.1

2.6

36.0

1.

5 1.

3 1.

4 24

.1

BB 6

3 45

.5

39.4

0.

8 6.

1 91

.7

2.7

0.4

0.4

1.

1

1.9

6.4

1.5

0.

4 1.

9 12

.0

1.3

1.0

1.1

121.

2 BB

64

38.1

43

.7

1.9

7.8

91.4

1.

1

0.7

1.9

1.5

2.

6 7.

8

0.

4

0.4

0.7

10.7

1.

7 0.

8 0.

8 10

3.0

BB 6

5 72

.3

15.0

1.

5 2.

6 91

.2

0.4

0.4

0.7

2.2

1.1

4.7

0.4

3.

7 4.

0 8.

7 0.

4 3.

7 3.

6 19

.8

BB 6

6 10

.1

69.4

1.

9 4.

5 85

.8

1.9

0.4

1.1

1.1

2.2

1.9

5.2

13.8

0.

4 0.

4 10

.7

8.6

0.2

0.1

27.3

BB

67

20.1

62

.3

0.7

5.9

88.9

1.

0

4.2

1.0

0.7

3.

8 10

.7

0.3

0.3

3.7

3.6

0.4

0.3

58.6

BB

68

53.0

29

.5

0.8

6.0

89.2

0.

8

1.6

2.0

0.8

3.

2 8.

3

1.

6

0.8

2.4

16.3

1.

0 1.

6 1.

7 67

.2

BB 6

9 8

9.4

0.8

2.7

92.9

5.5

1.2

6.7

0.4

0.4

15.0

0.

4 8.

1 7.

9 >

1000

BB

70

14.6

66

.0

2.4

5.9

88.9

1.

0

4.5

1.0

0.7

3.

8 11

.1

4.0

5.4

0.3

0.2

> 10

00

BB 7

1 78

.0

10.3

1.

8 1.

8 91

.9

0.4

5.9

1.5

7.7

0.4

0.4

9.0

0.3

7.0

6.5

> 10

00

BB 7

2 51

.5

37.5

1.

5 2.

7 93

.2

0.4

0.4

1.

5 0.

8

2.7

5.7

0.4

0.

8 1.

1 12

.0

1.0

1.3

1.3

68.7

BB

73

44.6

33

.2

1.7

6.9

86.5

1.

4 3.

5 1.

0 2.

8 1.

0 1.

0 1.

7 12

.4

0.3

0.

7

1.

0 3.

7 1.

0 1.

2 1.

3 13

0.3

BB 7

4 53

.8

30.7

1.

8 2.

2 88

.4

0.9

0.

4 4.

0 0.

9 1.

3 1.

8 9.

3

2.

2 2.

2 25

.0

1.1

1.6

1.6

24.3

BB

75

13.3

68

.1

1.1

7.5

9 0.

7

4.3

0.7

0.4

1.

8 7.

9

1.

8

0.4

2.1

7.0

6.3

0.3

0.2

37.4

BB

76

68.4

16

.7

4.8

3.4

93.3

0.

4

4.

8

1.

1 6.

3

0.

4

0.

4 10

.3

0.5

4.0

3.2

> 10

00

HTel

= hu

mot

elini

te; H

Det =

hum

odetr

inite

; Gel

= ge

linite

; Ch

= co

rpoh

umin

ite; S

= sp

orin

ite; C

= c

utin

ite; S

ub =

sub

erin

ite; R

= re

sinite

; A =

alg

inite

; Fl =

fluo

rinite

; Ld

= lip

tode

trini

te; F

s = fu

sinite

; SFs

= se

mifu

sinite

; M =

mac

rinite

; F =

fung

inite

; Id

= in

erto

detri

nite;

MM

= m

iner

al m

atter

; GW

I = g

roun

d wa

ter in

dex

(Cald

er e

t al.,

199

1); V

I =

vege

tatio

n in

dex

(Cald

er et

al.,

1991

); TP

I = ti

ssue

pre

serv

ation

inde

x (D

iesse

l, 19

92);

GI =

geli

ficati

on in

dex

(Dies

sel,

1992

). HT

el = хумотелинит;

HDet

= хумодетринит

; Gel

= гелинит;

Ch

= корпохуминит

; S =

споринит

; C =

кутинит

; Sub

= суберинит;

R = резинит;

A = алгинит;

Fl =

флуоринит

; Ld

= липтодетринит

; Fs =

фузинит

; SFs

= семифузинит;

M =

макринит;

F = фунгинит

; Id

= инертодетринит

; MM

= минерали;

GW

I = индекс на грунтовите води

(Cald

er et

al.

, 199

1); V

I = индекс на растителността (

Cald

er et

al.,

1991

); TP

I = индекс на запазване

на тъканите (

Dies

sel,

1992

); GI

= гелификационен

индекс (

Dies

sel,

1992

). 16

1

164

Fig. 1. Cross-plot of TPI versus GI

Ôèã. 1. Äèàãðàìà íà âúãëèùíèÿ ôàöèåñ, ïîêàçâàùà îòíîøåíèåòî íà èíäåêñèòå TPI è GI

a discussion whether fusinite, semifusinite andinertodetrinite are appropriate indicators, because theycould be washed or blown into the mire system, or canbe a result from crown fires, which are not necessary aconsequence of dry conditions (Calder et al., 1991;Scott, 2000, 2002). However, these macerals werecalculated in the formula, because usually their contentsare very low and their presence does not change thetrends in GI values, which suggests continuously wetconditions during deposition of Beli Breg coals. Theformulas, used for calculation of Diessel’s indices ofcoal facies were:

initeinertodetrmacriniteitehumodetrinfusinitetesemifusiniulminitetextiniteTPI

+++++=

initeinertodetrfusinitetesemifusinimacrinitehuminiteGI

+++=

Similar approach to assess the paleoenvironmentalconditions in the mire was made by Calder et al. (1991).They are describing two maceral indices – GWI(Ground Water Index) and VI (Vegetation Index) inrespect to the classification of the mires proposed byMoore (1987). The GWI is a ratio of strongly to weaklygelified macerals. Detritic mineral matter content is

used in the numerator of the formula to determine thetype of the mire. The VI contrasts macerals of forestaffinity with those of herbaceous and marginal aquaticaffinity (Calder et al., 1991) and thus be an indicator ofthe vegetation type. Calder’s indices were calculatedfor Beli Breg coals using the following formulas:

ulminitetextinitematter mineralitecorpohumingeliniteitehumodetrinGWI

++++=

cutinitesporiniteniteliptodetrialginiteiniteinertodetritehumodetrinresinitesuberinitetesemifusinifusiniteulminitetextiniteVI

++++++++++=

For interpreting the paleoenvironment a cross-plotdiagram of TPI versus GI (Fig. 1) and VI versus GWI(Fig. 2) were used. Most of the samples from Beli Bregbasin are characterized by low TPI and VI values,suggesting increased contribution of herbaceousvegetation, which is usually easily decomposingthrough the humification process or strongdecomposition of the plant material, due to severehumification of wood tissues. There are also severalsamples with high TPI values, thus indicating thepresence of high plant vegetation in the paleomire.According to the diagrams and after taking intoaccount the petrographic data we will speculate that thedeposition of the Beli Breg coals was processed in

Terrestrial

165

limno-telmatic to telmatic environment frompredominantly herbaceous vegetation, mixed withhigher plants. Limnic environment is less probable. Thelatter is characterized by high liptinite and particularlyhigh alginite content, which is not the case with thestudied coals. Although the origin of part of the lip-todetrinite in the samples could be related to alginite, thelatter was established only in small amount in the coals,thus indicating restricted development of open-watersurfaces within the mire. Transitional limno-telmaticenvironment is more probable if we have in mind thepresence of locally distributed lenses of clays and sandyclays within the coal bed. According to Diessel (1992)the paleomire should be defined as fen or forestedswamp. It is also possible the low TPI to be a result ofstrong decomposition of wood fragments, as a conse-quence of severe humification of the tissues due toincreased bacterial activity in calcium-rich environment(Kortenski, Zdravkov, 2003), combined with slow rateof subsidence. The high contents of gelinite and corpo-huminite (Table 1), as well as the presence of framboi-dal pyrite (Plate I-5; Plate II-3), which is thought tohave bacterial origin as a result of the activities of sul-fate reducing bacteria, could be interpreted in mainte-nance of this suggestion. In this process only the most

resistant tissues, usually impregnated with resins andtannins ones, survive the decomposition and are de-posited relatively intact within the coals. Forest swampis the most probable site of deposition in this case.

According to Calder et al. (1991) we shouldconsider the type of the paleomire as swamp to forestswamp. The coals were formed under preferentiallyrheotrophic conditions with high ground water input.

The inertinte content in the samples is very small,resulting in high GI values (Fig. 1). The latter suggestcontinuously wet conditions through deposition,although some seasonal dryings are not excluded, asindicated by the presence of macrinite. A typicalconstituent of the inertintie group is funginite, whichcontributors are the fungi, attacking the wood tissue.Because the fungi exist only in the upper oxygenatedpeatigenic layer, the presence of funginite could beconsidered as an indication of oxic conditions duringplant deposition.

Conclusions

A complex of petrographical and analytical investi-gations were performed on the coals from Beli Breg

Fig. 2. Cross-plot of VI versus GWI

Ôèã. 2. Äèàãðàìà íà âúãëèùíèÿ ôàöèåñ, ïîêàçâàùà îòíîøåíèåòî íà èíäåêñèòå VI è GWI

166

(Ïîñòúïèëà íà 28.01.2004 ã., ïðèåòà çà ïå÷àò íà 30.06.2004 ã.)

deposit in order their properties to be established. Theresults from the petrographical investigations revealthat the coals are exceedingly rich in macerals fromHuminite group. Among them the contents of humo-detrinite and structured macerals in most cases havesimilar values. The high gelinite and corpohuminitecontents suggest advanced humification of the planttissues, as a result of enhanced bacterial activity incalcium-rich environment. Liptinite macerals wereestablished using fluorescent light. Microsporinite,suberinite and resinite are the main contributors of thisgroup. The contents of inertinite macerals are very low.Among them funginite is common in small amounts allsamples, suggesting oxic conditions during depositionof the organic matter. A complex of different analyticalprocedures was performed in order the coal rank to bedetermined. According to the results the Beli Breg coalsshould be considered as a transition from peat tolignites. For reconstruction of the paleoenvironment themaceral contents were arranged in four petrographicindices, which along with the special features of the

macerals, established by the petrographic analysis areused to determine the depositional environment. Theseindices reveal that the organic material was depositedunder rheotrophic continuously wet limno-telmaticconditions. The coals are a result of deposition of eitherpredominantly herbaceous vegetation, mixed withtrees, forming fen type paleomire, or deposition ofstrongly humified and decomposed organic matter,formed in forest swamp paleomire with mixedherbaceous and tree vegetation.

Acknowledgments: Financial support from theSocrates/Erasmus, through a short-term researchscholarship awarded to A. Zdravkov, is greatlyacknowledged. The petrographical and analiticalinvestigations were conducted at the Department ofGeosciences – Geology and Economic Geology,Montanuniversitaet Leoben, Austria. The help of theresearchers from this department is greatlyappreciated. Special thanks are expressed to Prof. R.Sachsenhofer.

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