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Petrographic Characteristicsof Neogene Lignites from thePtolemais and Servia Basins,Northern GreeceAndreas Georgakopoulos, Sevdalina Valcevaa Aristotle University of Thessalonikib Sofia University "St. Kliment Ohridski"Published online: 29 Oct 2010.

To cite this article: Andreas Georgakopoulos, Sevdalina Valceva (2000)Petrographic Characteristics of Neogene Lignites from the Ptolemaisand Servia Basins, Northern Greece, Energy Sources, 22:7, 587-602, DOI:10.1080/00908310050045546

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E nergy Sources, 22 :587 ] 602 , 2000

Copyr ight Q 2000 T aylor & Fran cis

0090-8312 r 00 $12.00 q .00

Petrographic Characteristics of NeogeneLignites from the Ptolemais and Servia

Basins, Northern Greece

ANDREAS GEORGAKOPO ULOS

Department of Mine ralogy-Pe trology-Economic Geology

School of Geology

Aristotle University of Thessaloniki

Thessaloniki, Greece

SEVDALINA VALCEVA

Faculty of Geology and Geography

Sofia University `̀ St. Kliment O hridski’ ’

Sofia, Bulgaria

In this study the petrographic analysis results of Ptolemais and Servia Neogenelignites, Northern Greece, are presented. The geological position, lithotype, andmaceral content of these lignites, as well as some chemical parameters and changesin the reflection of different macerals, are described. The interdependence betweenmaceral content and environmental conditions in the process of peat formation istraced. Petrographic analysis shows that coals are represented by different kinds oflignites from dark brown to black, sem ibright lignites, consisting mainly of the coallithotype humoclarain, rare strips and bands of bright humovitrain, and dullhumodurain. The sample from the Lava deposit in the Serv ia Basin is composed ofgrayish to black, dark humoclarain. The predom inance of humodetrinite macerals( )densinite and attrinite and the low contents of inertinite show that the lignites inthe Ptolemais and Serv ia Basins are formed in limno-telmatic conditions and indifferent m ire types, being sim ilar to herbaceous swamp, fen, or marsh.

Keywords coal petrology, Greece, lignites, macerals, Ptolemais, reflectance ,

Se rvia

Lignite is the most common type of coal in Greece , occurring in more than 60

sedimentary basins. Proven lignite rese rves reach a total of 6,750 Mt; howe ve r, only

3,900 Mt are economically recove rable. During 1998 the lignite production re ached

63 Mt. Lignite supplie s 21 powe r units which have a total capacity of 4,833 MW.

The contribution of lignite to the total e lectric powe r output of the country is

78.4% . The most important era of coal formation in Greece was from the Neoge ne

to the Q uate rnary. During this pe riod a large number of major and minor faults

Received 2 December 1998; accepted 3 June 1999.

Many valuable improvements to the manuscript were suggested by Profs. K. Michailidisand A. Tsirambides, School of Geology, Aristotle University of Thessaloniki, Greece .

Address correspondence to Dr. Andre as Georgakopoulos, Department of Mineralogy-Petrology-Economic Geology, School of Geology, Aristotle University of Thessaloniki, 540

06 Thessaloniki, Greece . E-mail: ageorgak@ geo.auth.gr

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A. Georgakopoulos and S. Valceva588

deve loped and sections of crustal rocks we re depressed , causing the deve lopment

of isolated basins. In the shallow waters of the se basins the plant debris accumu-

lated and formed the most important lignite deposits in Greece : Ptolemais ,

( )Megalopolis , Florina, Drama Koukouzas & Koukouzas , 1995 . Some of the pe tro-

logical characte ristics concerning the lignites from the Ptolemais Basin have been

(examined previously Cameron e t al. , 1984; Kaouras , 1989; V alceva & Geor-

)gakopoulos , 1993; Sakorafa , 1994; V alceva e t al. , 1995 . In this article the pe trologi-

cal characte ristics of lignite s from the Ptolemais and Servia B asins , Northe rn

Greece , are presented.

Geological Setting

The Florina-V egoritis-Ptolemais-Servia graben is located in Northwe ste rn Greece

and is filled with Neogene-Quate rnary sediments. It is subdivided into three

lignite-bearing basins: Florina Basin in the North , Ptolemais B asin in the middle ,

( )and Servia B asin in the South Figure 1 . The Neoge ne-Q uaternary sediments of

the basin are divided into three lithostratigraphic form ations. The lower form ation

( )Upper Miocene to Lower Pliocene consists mainly of conglomerate s , marls ,

( )sands , and clays. The middle form ation Pliocene contains the lignite beds. The

upper Q uate rnary formation consists of terre strial and fluviote rrestrial conglomer-

ate s , late ral fans, and alluvial deposits. The middle formation contains two lignite

( )se ams upper and lower which have been exploited by open-cast mining since

1953. The lignite beds alte rnate with marls , clays , and sands. In the Lava lignite

( )deposit Servia Basin , the Miocene lacustrine deposits contain three xylite r lignite

Figure 1. Simplified geological map of the Ptolemais and Servia Basins area.

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Petrographic Characteristics of Neogene L ignites from Northern Greece 589

( )horizons Antoniadis , 1992; Antoniadis e t al., 1994; Antoniadis & Rieber , 1997 .

( )The deepest horizon 118 ] 130 m depth consists of xylite , xylitic lignite , and lignite

( )inte rcalations. The middle horizon 110 ] 113 m depth , which is the best deve loped

(and the most important for exploitation , consists of a unified lignite bed sample

) ( )under study . The upper horizon 95 ] 100 m depth consists only of xylite .

Materials and Methods

The inve stigations we re carried out with three samples from borehole KNP-20

from the South fie ld and one sample , A-X , from an open mine in the same fie ld.

( ) ( )Samples A-6 69.00 ] 69.20 m depth and A-7 74.00 ] 74.20 m depth are from the

( )upper lignite se am , while samples A-10 113.40 ] 113.50 m depth and A-X belong

to the lower lignite seam. Moreove r , four samples were se le cted from the stock

( ) ( )piles of the different mine fie lds , as follows: Komanos KF , North fie ld B , South

( ) ( ) ( )fie ld SF , and Sector 6 K-6 Figure 1 . Sample A-XI was colle cted from the

( )second lignite horizon in the Lava deposit Se rvia Basin and was used as re fe r-

ence . The coals were characte rized using the following pe trographic analyse s:

lithotype determination , m ace ral analysis , refle ctance me asurements , and chemical

analyse s. The macroscopic me asurements and the lithotype analysis we re carried

out according to the Bulgarian standard lithotype classification for lignites and

( )brown coals Siskov & V alceva , 1983 . The sample s we re crushed to m aximum

particle size of 1 ,000 m m , mounted in epoxy resin , and then ground and polished

( )according to the standard method Stach et al., 1982 . The quantitative m ace ral

analysis was carried out in re flected light and oil immersion using a microscope

equipped with a point automatic integrator. About 500 points we re counted on

e ach block. The re flectance was determined in immersion oil at a monochromatic

( )light l s 546 nm . Proximate and elemental analyse s were performed on the same

sample s.

Results and Discussion

Lithotype Composition

The coals under study represent dark-brown , semibright lignites , consisting m ainly

of the coal lithotype humoclarain. The latte r contains xylain fragments and

humovitrain bands of various sizes. The separate sample s have the ir own specific

lithotype characte ristics. Thus , sample A-6 comprises grayish-brown lignite with

associated sections of light-brown xylain with distinct ce ll structure . Xylain occurs

not only as fragments but also in the form of bands and strias with thickness up to

1 ] 2 mm and rarely up to 1 cm. Humovitrain represents a black , bright m aterial.

Fusain and semifusain exist as small inclusions that dirty the hands and have a

sooty and silky appe arance . The basic humoclarain mass is dark brown , with

compact or striated texture in humovitrain. In humoclarain , inclusions of 2 ] 5 mm

are identified as spots of lacustrine calcareous mud. The latter is a white-pink ,

dusty m aterial that dirties the hands and is probably formed by shell decay. Sample

A-7 appe ars as black , compact , striated coal , with a vitreous conchoidal fracture

which is characteristic of humoclarain. Rare striations and bands of bright humovi-

train and darke r humodurain have been identified. Sample A-10 consists of black ,

semibright humoclarain coal with humovitrain bands. Sample A-X is composed of

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A. Georgakopoulos and S. Valceva590

grayish-black , dark humoclarain coal with corned cracks. They contain inclusions of

crushed white shell mate rial and rare humovitrinite fragments. Lignite from the KF

and K-6 samples is dull , dark-brown to black , with compact to striated texture . The

basic lithotype in both samples is humoclarain. In sample K-6 , small xylain

fragments are found. Samples B and SF are represented by brown-black grounds ,

rarely m assive lignite s with traces of lamination. They consist mainly of hu-

moclarain. Sample A-XI from the Lava deposit consists of black dark lignite with

leaflike appearance , husky cracks , and decay. This sample is rich in fine ly dispe rsed

plant debris and mineral components.

Maceral Composition

The petrographic composition of the lignite s under study was dete rmined by

quantitative mace ral analysis. Table 1 displays the great variation in the quantita-

tive presence of m ace ral groups huminite , liptinite , inertinite , and mine ral m atte r.

( )The Ptolemais coals are rich in huminite components 84 ] 89 vol% , with the

( ) ( ) (exception of sample A-X 42 vol% . Both liptinite 1 ] 13 vol% and inertinite 2 ] 13

)vol% have low to moderate participation. Great variation in the quantitative

( )pre sence of mineral m atte r 1 ] 48 vol% is noted. Two varie tie s , A and B , of both

textinite and eu-ulminite mace rals and of the maceral variety texto-ulminite have

been distinguished in the huminite group. O the r huminite mace rals identified are

attrinite , densinite , ge linite , and corpohuminite . The maceral subgroups humote lin-

ite , humodetrinite , and humocollinite are distinguished. The humotelinite sub-

group varies from 12 to 49 vol% . The humode trinite subgroup is the best repre-

( )sented 30 ] 56 vol% , consisting of a basic mass or mixture of microscopic cell

fragments and more or less amorphous humic colloidal particles. The smalle st

( )contents 1 ] 9 vol% of the humocollinite subgroup are represented by ge linite and

corpohuminite . Ge linite is repre sented by totally ge lified plant tissue fragments , in

only some of the samples studied. Textinite repre sents rem ains of well-pre se rved

unge lified wood and grass tissue s and is characterized by clearly de fined cell

structure and open ce ll lumina that are partially filled by resinite or phlobaphinite

( )corpohuminite . Textinite is identified as various wide bands which , in re flected

light depending on color and refle ctance , are distinguished as textinite A-dark and

textinite B-light. The textinite content is not high , i.e . , 10 vol% of textinite A-dark

in sample A-6 and traces in the othe r samples and 1 vol% of textinite B-light in

some sample s from the Ptolem ais Basin. Textinite has not been found in the lignite

sample from the Se rvia B asin. Texto-ulminite is a partially ge lified plant tissue , and

some of the ce ll lumina are closed and filled with humic substance . In the lignite s

inve stigated , the amount of texto-ulminite A-dark range s from 2 vol% in sample

A-6 to 31 vol% in sample SF. O n the contrary, texto-ulminite B-light comprise s

23 ] 28 vol% of sample A-6 , 2 ] 7 vol% of sample s A-7 and A-10 , and 5 vol% of

sample A-X. Howeve r , it has not been found in the Lava lignite deposit. The

ge lified macerals are rare ly identified , and eu-ulminite A varies from 2 vol%

( ) ( )samples B , SF, and A-6 to 8 vol% samples A-10 and KF . For the light

eu-ulminite B this content is 2 ] 10 vol% for sample A-10 , while ge linite varie s from

( ) ( )1 vol% sample s KF and SF to 7 vol% sample K-6 . Attrinite and densinite are

the most abundant mace rals of the huminite group in all sample s. They repre sent a

mixture of fine to coarse-grained humic particle s. The latte r are associated with

separate ine rtode trinite particles or with semifusinite and fusinite fragments , as

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Tab

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591

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A. Georgakopoulos and S. Valceva592

we ll as with some representatives of the liptinite group as sporinite , cutinite ,

re sinite , and suberinite . In some cases , transitions between attrinite and densinite ,

which is a more compact mass , are obse rved. Corpohuminite is identified as

rounded , oval , or e longated bodie s with equal or highe r refle ctance than that of the

surrounding huminite . The bodie s in the ce ll lumens of the living plant tissue are

( )identified as phlobaphinite and can be cle arly seen both in the dark A and in the

( )light B varie tie s of textinite and texto-ulminite . The liptinite group includes the

coalified debris of the durable parts of the plant tissue with characte ristic morpho-

logical propertie s. Resinite is the most abundant m ace ral from the liptinite group

and in most case s is obse rved as rounded or oval bodie s filling the cell lumina of

( )textinite and texto-ulminite . Sporinite is found in minor amounts 1 ] 3 vol% in

ne arly all samples. Cutinite is de rived from cuticles and is identified most often by

bands associated with separate fragments of both varietie s of A and B textinite ,

texto-ulminite , and ulminite . Suberinite is rare . In the attrinite and densinite basic

mass , remains of the fragmentary maceral liptodetrinite are obse rved , enclosing

particle s formed by the mechanical disaggregation of spore s , cuticle s , resin bodie s ,

e tc. The inertinite group is the second most abundant mace ral group found , since it

constitute s 2 ] 13 vol% . Semifusinite , fusinite , ine rtodetrinite , and sclerotinite have

been identified. Semifusinite and fusinite are characterized by separate small

fragments with cle arly de fined cell structure . O ccasionally, ringlike appearance is

pre sent. Their ove rall amount in the separate sample s varie s from 1 to 4 vol% in

the Ptolemais lignites to 6 vol% in the Lava lignite deposit. Ine rtode trinite occurs

often in angular particle s of various size and re flectance. Its amount ranges from 1

to 9 vol% . Sclerotinite , though its frequent distribution , constitute s 1 ] 2 vol% of

the separate sample s , but shows a gre at variety in morphology. Both single- and

double-celled scle rocii from fungal remains and debris from multice lled scle rocii of

the Plectenchyminite type have been identified. In spite of the gre at m ace ral

varie ty, the total amount of ine rtinite group in the samples investigated is lower

( )than that found in previous studie s , i.e . , 17 vol% Cameron et al., 1984 . The

( )mineral m atte r consists of clay minerals and pyrite in low amounts 4 ] 5 vol% in

all sample s. Samples A-X and A-XI from the Lava deposit consist of 42 ] 46 vol%

mineral matte r. Pyrite commonly occurs in the form of individual framboids ,

spherules , and colonie s or fine to medium-grained aggregate s. Pyrite is usually

associated with the huminite group macerals , filling the cell lumina in textinite and

texto-ulminite or forming cluste rs in ulminite . It is also identified in the densinite

and attrinite m ass. The ove rall mace ral composition of the Ptolem ais lignite , in

terms of mace ral group and mine ral matter distribution , is shown in the te rnary

diagrams of Figure 2.

Chemical Characteristics

The chemical parameters of the Ptolemais lignite s are given in Table 2. The

( a ) ( ) ( )moisture W % varies from 9.9 A-X to 16.4 wt% A-7 . The sample s are

( )characte rized by low to medium ash 7.2 ] 19.4 wt% , with the exception of A-X

( ) ( )43.3 wt% which is in accordance with its high content of clay mine rals 42 vol% .

(Generally, the lignite s under study are of high volatile matte r , 53.8 ] 60.8 wt% on a

) ( )dry ash-fre e basis , with the exception of sample SF 43.1 wt% . In the KNP-20

drill-hole core sample s , the volatile matte r content decre ase s with increase of

( ) ( )depth from 60.8 wt% A-6 to 55.6 wt% A-10 . In B , KF, and K-6 samples , the

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Petrographic Characteristics of Neogene L ignites from Northern Greece 593

( ) ( )Figure 2. Ternary diagrams showing: a maceral group L q I and H and mineral matte r

( ) ( )composition; b maceral group composition L-I-H , on a mineral matter-free basis .

Ptolemais Basin samples: A-6 , A-7 , A-10, A-X , B , KF, K-6 , SF; Servia Basin sample : A-XI.

L s liptinite ; I s inertinite ; H s huminite ; Mm s mineral matte r.

(volatile matte r contents are of similar value . Data of ultim ate analysis on a dry

)ash-free basis show that the carbon content ranges from 62.2 to 71.0 wt% . The

carbon content shows an opposite tendency in volatile matter. With increase of

( )depth an increase of carbon content is observed , from 64.7 wt% A-6 to 71.0 wt%

( )A-10 . The highe r hydroge n content in most lignites is in agreement with the ir low

degree of coalification. The higher content of hydrogen in sample SF is possibly

connected with the highe r percentage of liptinite macerals pre sent. Low hydrogen

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Table 2a

Chemical characteristics of lignites from the Ptolemais Basin

Proximate Ultimate analysis ,

( ) ( )analysis wt% daf wt% RatiosDeptha d daf( )Sample } place m W A V C H N S O H r C O r C

Borehole KNP-20

A-6 69.0 ] 69.2 12.3 16.5 60.8 64.7 4.7 1.4 0.9 28.3 0.87 0.33

A-7 74.0 ] 74.2 16.4 10.1 58.9 65.6 4.0 1.5 0.4 28.5 0.73 0.33

A-10 113.4 ] 113.5 12.9 11.2 55.6 71.0 5.5 1.5 0.2 21.8 0.93 0.23

B } North Fie ld } 13.2 19.4 56.5 64.1 6.1 1.9 1.3 26.5 1.20 0.31

KF } Komanos Fie ld } 13.4 15.0 55.8 62.2 5.7 1.5 0.3 30.3 1.10 0.36

K-6 } Kardia Fie ld } 12.8 10.0 53.8 62.4 5.7 1.1 0.2 30.6 1.10 0.36

SF } South Fie ld } 12.0 7.2 43.1 62.5 6.4 1.3 0.5 29.3 1.23 0.35

A-X } 9.9 43.3 67.0 67.0 3.4 1.3 0.5 27.8 0.60 0.31

adaf s dry, ash-free ; d s dry; a s as received basis

( )3.4 wt% for sample A-X is probably connected to the absence of liptinite

mace rals and the high mineral content of the sample. Nitrogen and organic sulfur

content in all sample s is low and ve ry similar. O xygen is dete rmined by difference

and varies from 21.8 to 30.6 wt% . B ased on volatile matter , carbon , hydrogen ,

( )oxygen content, and H r C , O r C ratios Table 2 , Ptolemais coals can be characte r-

ized as low-rank lignite s , except for sample A-10 , which can be classified between

lignite and subbituminous coal.

Reflectance of Macerals and Coal Rank

Figure 3 shows the distribution of the re flectivity values of the individual mace rals

and mace ral groups. The mace rals cutinite and sclerotinite appear as exceptions ,

since there are two me asurements which are not quite representative. Howeve r ,

they are within the range of the re fle ctance value s of the corre sponding m ace ral

group. While the macerals of the liptinite group show the lowe st me an re flectance ,

R s 0.07 ] 0.13% , those of the huminite group are plotted in an inte rmediaterandom

position. The ir re flectance range s from 0.10 to 0.39% , depending on the degree of

ge lification of the lignin-ce llulose tissue s. Consistent with the degree of oxidation

of the original wood , the ine rtinite group macerals have the highe st re flectance ,

( )R s 0.39 ] 1.01% Table 3 . The ge neral characte r of the variation of re-random

fle ctance of the huminite group macerals in the separate sample s shows some

differences in the me an values for dark-A and light-B varie ties of textinite ,

texto-ulminite , and eu-ulminite . Markedly close are the mean value s for the dark-A

bands of textinite , R s 0.10 ] 0.15% , of texto-ulminite , R s 0.11 ] 0.23% ,random random

and of eu-ulminite , R s 0.15 ] 0.21% . The refle ctance for the light varietie sran dom

change s from 0.20% for textinite B-light, to R s 0.18 ] 0.32% for texto-random

ulminite B and to R s 0.23 ] 0.39% for eu-ulminite B-light. The incre ase inrandom

re flectance from textinite to eu-ulminite both for A-dark and for B-light varie tie s

demonstrate s the dependence of the refle ctivity value s to the degree of homogene-

ity and compaction due to the ge lification process. It can be assumed that the

formation of A-dark and B-light strias of textinite , texto-ulminite , and eu-ulminite

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Petrographic Characteristics of Neogene L ignites from Northern Greece 595

Figure 3. Variation in the reflectivity values of the macerals and maceral groups in the

( )lignite s from the Ptolemais and Servia Basins mean values of re flectivity are also depicted .

Symbols: = s A-6; v s A-7; ` s A-10; q s A-X; B s A-XI.

macerals is prede te rmined by the botanical nature and the diffe rent decomposition

grades of the original plant. The me an re flectance of attrinite and densinite lie s

( )within the range R s 0.16 ] 0.27% and that of corpohuminite phlobaphiniterandom

is 0.24 ] 0.38% . The me an refle ctance of the liptinite group is dete rmined from

sporinite and resinite and range s from 0.04% to 0.13% , re spective ly. Although

conclusions about liptinite re flectance are supported only by the re sults of two

sample s , it is be lieved that these conclusions can be extended to all samples. The

mace rals of the ine rtinite group show the highe st re fle ctances compared to that of

othe r mace rals. Figure 4 shows the variation range of the ir minimum and maxi-

mum refle ctance value s. Howe ver , the mean re fle ctance value for semifusinite lie s

within the range R s 0.37 ] 0.76% , for inertodetrinite R s 0.60 ] 0.73% ,random random

and for fusinite R s 1.01% . These value s sugge st the occurrence only ofrandom

degrado-varie tie s. Because of the ve ry thin ce ll walls , it was practically impossible

to measure the scle rotinite refle ctance . The results obtained in the present study

( ) ( )unambiguously confirm the concepts of Ercegovac 1970 , Jacob 1970 , Siskov

( ) ( )1971 , and V alceva 1979 . They have stated that the variations of the re flectance

of the individual macerals and mace ral groups depend essentially on the type of the

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Tab

le3

Refl

ecti

vit

ym

easu

rem

en

tso

nth

eh

um

init

e,li

pti

nit

e,an

din

ert

init

eg

rou

pm

acera

lso

fth

eP

tole

mais

an

dS

erv

iali

gn

ites

Sam

ple

sM

acera

lM

acera

lan

dgro

up

mace

ral

vari

ety

A-6

A-7

A-1

0B

KF

K-6

SF

A-X

A-X

I

Hu

min

ite

Texti

nit

eA

0.1

0"

0.0

2}

0.1

5"

0.0

2}

}}

}}

}T

exti

nit

eB

0.2

0"

0.0

3}

}}

}}

}}

}T

exto

-ulm

init

eA

0.1

1"

0.0

10.1

8"

0.0

30.2

3"

0.0

30.1

6"

0.0

30.1

5"

0.0

40.1

4"

0.0

20.1

4"

0.0

30.1

6"

0.0

2}

Texto

-ulm

init

eB

0.1

9"

0.0

20.3

2"

0.0

40.2

9"

0.0

20.2

2"

0.0

10.2

3"

0.0

20.2

1"

0.0

20.2

0"

0.0

3}

}E

u-u

lmin

ite

A0.1

5"

0.0

20.2

1"

0.0

30.1

9"

0.0

40.2

1"

0.0

10.1

8"

0.0

30.1

8"

0.0

30.1

9"

0.0

30.1

8"

0.0

20.1

8"

0.0

3

Eu

-ulm

init

eB

0.2

3"

0.0

30.3

9"

0.0

30.3

4"

0.0

40.2

7"

0.0

20.2

8"

0.0

40.2

7"

0.0

20.2

7"

0.0

50.2

9"

0.0

3}

Att

rin

ite

0.1

6"

0.0

40.2

7"

0.0

30.2

6"

0.0

40.0

8"

0.0

2}

0.2

4"

0.0

70.1

1"

0.0

3

Den

sin

ite

}}

}0.0

16

"0.0

10.1

9"

0.0

2}

}G

eli

nit

e}

}}

0.2

7"

0.0

2

Co

rpo

hu

min

ite

0.2

4"

0.0

30.3

8"

0.0

50.3

3"

0.0

5}

}L

ipti

nit

eR

esi

nit

e0.1

3"

0.0

2}

}S

po

rin

ite

0.0

4"

0.0

20.0

7"

0.0

3}

}In

ert

init

eS

em

ifu

sin

ite

0.3

7"

0.0

50.5

0"

0.0

7}

0.7

6"

0.1

50.4

4"

0.0

4

Fu

sin

ite

}}

}}

1.0

1"

0.2

0In

ert

od

etr

init

e0.6

0"

0.1

2}

}0.7

3"

0.0

90.6

4"

0.0

6

596

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Petrographic Characteristics of Neogene L ignites from Northern Greece 597

Figure 4. Facie s diagram and suggested depositional environments for the Ptolemais and

( )Servia lignites according to Diessel , 1986 .

original flora and the degree of its decomposition and ge lification. Me asured

re flectance for the eu-ulminite indicate s a ve ry low coalification stage for sample s

( )A-6 and A-XI 0.15 ] 0.18% , where as for othe r sample s the values range from 0.26

to 0.34% . Corre lations between eu-ulminite re fle ctance , carbon , and volatile m at-

ter content indicate that the coals from the Ptolemais and Servia Basins are of low

rank.

Relationship between Maceral Composition and Depositional Environment

From the coal petrology viewpoint, macerals are the most informative microscopi-

cal ingredients of coal sample s , and there is a close re lationship between m ace ral

composition and coal gene sis. The formation of the Ptolemais and Servia lignite

basins is preconditioned by the late Alpine and Neotectonic deve lopment of the

region. The Florina-V egoritis-Ptolem ais graben was formed by tectonic activity.

This large down-faulted basin is filled by Neogene-Quate rnary continental sedi-

ments containing lignite beds. They are deposited in three lignite basins , the largest

be ing the Ptolemais B asin. Peat formation in the se basins occurred in limno-

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A. Georgakopoulos and S. Valceva598

telmatic conditions and in different mire types , similar to he rbaceous swamps , fen ,

( )or marsh. According to Moore 1995 , the swamps we re rheotrophic mire type with

re latively high leve ls of water and limited drainage parameters. They we re cove red

with high-productive he rbaceous vege tation , but some tree and shrub species we re

( )also found. Palynological investigation by Kaouras 1989 supports the deve lopment

of that kind of ve ge tation in the Ptolemais Basin. Together with monocotylodonous

plant communities , in which there are some sedge s such as Carex and Cladium and

some trace s of repre sentative family groups such as Typhaceae, Gram ineae, Pota-

( )mogetonaceae, Alismataceae, and Sparganiacea, Kaouras 1989 found some spore s

and pollen of fore st tre e s and shrubs of various family groups such as Cupressaceae,

Ephedraceae, Pinacea , and Taxodiaceae from gymnospe rmous and above all from

angiospermous woods , such as Corylus, Acer , Ilex , Betula , Quercus , Fagus, Cas-tanea , Myrica , Nym phaea , Magnolia, Salix, Ulm us, Z elkova , Symploros, etc. O f

minor importance in pe at formation are algae and Pteridophyta species. Pe trologi-

cal investigations confirm that Ptolemais lignites are of autochthonous origin , the

main plant material was deposited in situ , and only part of the liptinite mace rals

( )sporinite and cutinite and inertodetrinite particle s we re transported by the wind

and the spring waters in the pe at swamp. During the formation of the lignite s

under study, ge lification processes played an important role . The fact that 89% of

the m ace ral content be longs to the huminite group and especially to the humode-

( )trinite subgroup 56% shows that during the processes of biochemical form ation

of pe at , the most important role was played by the microbiological processes

coupled with mechanical destruction. Probably, the limited concentration of texti-

nite with well-pre se rved tissue structure , confirms the subordinate role of conifer-

ous woods. The significant quantity of densinite and attrinite shows that the

Ptolemais lignite s are rich in humic groundmass , which contains tiny remains of

tissue s. These macerals are derived m ainly from easily decomposed herbaceous and

shrub plants such as Cyperaceae reed and angiospermous woods in rheotrophic

conditions , permanent high water table , and probably anaerobic conditions. Ac-

( )cording to Moore 1989 , the rates of decomposition of the he rbaceous communi-

tie s are also rapid. On the othe r hand , high productivity of this ve ge tation type

compensated the speed of decomposition of base biomass and allowed the pro-

(cesse s of peat form ation. Some authors Diesse l , 1986 , 1992; Die sse l & Gammidge ,

1998; Kalkreuth & Leckie , 1989; Kalkreuth e t al., 1991; Calder e t al., 1991;

)Marchioni & Kalkreuth , 1991; Marchioni et al., 1994 use various methods for

paleoenvironmental interpre tation based on mace ral analysis and they propose

( )some coal-facie s indexes. Die ssel 1986 proposes the terms `̀ tissue preservation

( ) ( ) ( )index’ ’ TPI and `̀ ge lification index’ ’ GI , and Calde r e t al. 1991 introduced

( ) ( )`̀ groundwate r influence index’ ’ G.W.I. and `̀ ve ge tation index’ ’ V I . These facie s

indice s are proposed primarily for the study of bituminous coals. For the inte rpre -

tation of lignite formation conditions in the Ptolem ais and Servia Basins , it is

proposed that the tissue prese rvation index and the ge lification index be expressed

as follows:

humote linite q semifusinite q fusiniteTPI s

humode trinite q humocollinite q inertodetrinite

huminiteGI s

inertinite

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Petrographic Characteristics of Neogene L ignites from Northern Greece 599

The TPI , through the re lationship between structural m ace rals from huminite

and inertinite groups in the numerator and unstructural macerals from humodetri-

nite and humocollinite subgroups , as we ll as the content of ine rtodetrinite in the

denominator , allows us to account for the degree of humification of m ace ral

( )precursors. At the same time , the ge lification index, according to Diesse l 1992 ,

indicate s the re lative degree of `̀ dryne ss or wetness of autochthonous pe at-forming

( )conditions.’ ’ Using Diesse l’ s diagram 1986 , the studied lignite s from the Ptolemais

B asin fall within facial limits characte rizing pe at swamp of fen type , with relative ly

low values of TPI and average value s for GI with the exception of samples K-6 and

( )SF Figure 4 . It is thus concluded that the m ajor part of the Ptolemais lignites are

of limno-te lmatic type , formed in wet conditions in the lower delta plain. Due to

the predominant participation of tre es and shrub vegetation , it is possible that , in

the southern part of the basin corre sponding to the contemporary South and

Sector 6 mine fie lds , lignite s we re formed in conditions more similar to fore st-land

(pe at. The low values of TPI and GI for the sample from the Lava deposit Servia

)B asin sugge st typically limnic conditions in which dull coal with inertodetrinite is

formed. O n the basis of some criteria used in the classification of modern

( ) ( )pe atlands , Calde r et al. 1991 introduced the groundwater influence index G.W.I.

( ) ( )and the ve ge tation index V I to characterize paleomires. Thus , Calde r et al. 1991

de line ated G.W.I. as the ratio of strongly ge lified tissue s and mine ral matter to

we akly ge lified tissue s. The above authors used in the denominator the quantity of

de smocollinite , which is low , being a product of he rbaceous plants , since they

studied carbonife rous coals. In the present study we consider it more appropriate

to place the mace rals from the humode trinite subgroup in the numerator , together

with othe r more or less ge lified mace rals. In addition , it is thought to be more

precise to use only clay mine rals instead of the total mineral matter. In the case of

the lignite s studied , terms connected with low-rank coals should be used. Thus , the

G.W.I. should be modified as follows:

humode trinite q humocollinite q clay mine ralsG .W .I. s

humotelinite

( )According to Calde r e t al. 1991 , mire s can be broadly subdivided on the basis

of vegetation type , which can be determined by mace rals of forest affinity or

he rbaceous and m arginal aquatic affinity. There fore , vegetation index represents

the ratio between lignin-rich plants of a forest habitat and herbaceous cellulose-rich

ve ge tation , which is partly represented by m arginal aquatic macerals.

humotelinite q fusinite q semifusinite q suberinite q re siniteV I s

humode trinite q humocollinite q liptodetrinite q sporinite q cutinite

In the paleoenvironmental diagram the distribution of the samples of the Ptole-

( )mais B asin and the Lava deposit is plotted in the limnic areas Figure 5 . The

values of G.W.I. for the greate st number of the Ptolem ais samples vary approxi-

mately from 0.7 up to 3 , and it le ads to the conclusion that vegetation ecosystems

have been deve loped in mire , in conditions above or below the water table . The

predominance of herbaceous and shrub plants in the process of pe at formation is

( )proved by the low value s of V I around one .

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A. Georgakopoulos and S. Valceva600

Figure 5. Mire palaeoenvironmental diagram for the lignite s from Ptolemais and Servia

( )Basins according to Calder et al., 1991 .

Conclusions

The coals studied represent dark-brown, semibright lignites , consisting mainly of

the coal lithotype humoclarain with rare striations and bands of bright humovitrain

from the Ptolemais Basin and dark dull lignites from the Servia Basin. The lignite s

from the Ptolemais and Servia B asins are characterized by complex petrographic

composition and consist of almost all mace rals of the three m ace ral groups:

huminite , liptinite , and inertinite . The macerals of the huminite group , e specially

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Petrographic Characteristics of Neogene L ignites from Northern Greece 601

( ) ( )densinite and attrinite as basic constituents , followed by the A dark and B light

varie ties of texto-ulminite and eu-ulminite , are among the most abundant composi-

tional entities identified in the samples studied. The latte r are characte rized by

inte rmediate amounts of macerals of the liptinite and inertinite group. The

re flectance of the individual macerals and maceral groups is varied and is prede te r-

mined both by the botanical nature of the initial plant mate rial and by the degree

of ge lification and fusinization of the lignin-ce llulose tissue during pe at form ation.

B ased on the volatile matte r , carbon , hydrogen , and oxygen content , H r C , O r C

ratios , and me an random re flectance of eu-ulminite , the Ptolemais and Servia coals

are of low rank. On the basis of the pe trological parameters it is concluded that the

major part of the Ptolemais lignites is of limno-telmatic type , formed in the lower

de lta plain in wet conditions, while the Servia lignite s are of typical limnic

formation conditions.

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