International Journal of Coal Geology 87 (2011) 237–252

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International Journal of Coal Geology

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Evolution of lignite seams within the South Moravian Lignite Coalfield basedon certain qualitative data

Jan Jelínek a,⁎, František Staněk a, Ladislav Vizi b, Josef Honěk c

a Institute of Geological Engineering, Faculty of Mining and Geology, Vysoká škola báňská - Technical University of Ostrava, 17. listopadu 15/2172, Ostrava-Poruba 708 33, Czech Republicb Faculty of Mining, Ecology, Process Control and Geotechnology, Technical University Košice, Park Komenského 19, Košice 042 00, Slovakiac Opavská 150, Ostrava-Pustkovec 708 00, Czech Republic

⁎ Corresponding author. Tel.: +420 597325468; fax:E-mail address: jan.jelinek@vsb.cz (J. Jelínek).

0166-5162/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.coal.2011.06.017

a b s t r a c t

a r t i c l e i n f o

Article history:Received 20 December 2010Received in revised form 1 June 2011Accepted 29 June 2011Available online 12 July 2011

Keywords:Late MioceneCoal seamLigniteQualitative parametersFault zoneVienna BasinCzech Republic

This paper focuses on evolution of lignite seams (the Pannonian) in the South Moravian Lignite Coalfield(SMLC). It is based on data analysis (seam geometry, ash yield, sulfur content, and lithology) from more than3300 boreholes and many channel samples. The results show that the Vienna Basin in the Pannonian periodgradually developed into a freshwater bay. In the Early Pannonian the sedimentary environment wastectonically calm. The salinity of the sedimentary environment was changing as a consequence of recurringtransgressions. The studied area was under the influence of rivers flowing into the region from the west,north, and northeast. In the upper part of zone B (Papp's classification of the Pannonian sediments), especiallyin the northern areas of the SMLC, suitable conditions for coal-bearing sedimentation (the Kyjov seam)occurred. Zones C–F were characterized by simple or incomplete cyclic sedimentation processes. The ViennaBasin opened and the subsidence between the Steinberg fault zone and Lužice–Lanžhot fault zone(interconnected with the Polešovice fault zone) took place in the SMLC. At the beginning of zone F theswamp areas suitable for Dubňany seam formation developed in the SMLC. The coal-forming conditions wererepeatedly restored. The sedimentary cycles with the coal-bearing deposits occurred also in zone G, howeveronly in the central and southern parts of the SMLC. The increasing thickness of the deposits in zone G and theincreasing number of cycles with lignitic layers in the southern part of the SMLC indicate a shift of the suitableconditions for swamps towards the south and into the overlying rocks. A distinct tectonic deformation of thelignite seam in the SMLC started only in the Pliocene, when due to the change of the stress field in the ViennaBasin the rejuvenation of the tectonic zones of the pull-apart system took place towards the NE–SW and NW–

SE to NNW–SSE.

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1. Introduction

For more than 160 years the Vienna Basin (VB) and its northernpart, the so-called South Moravian Lignite Coalfield (SMLC), havebeen subjects of intensive studies, focusing on structural geology,tectonic structure, sedimentology, lithofacial analysis, sequentialstratigraphy and paleography of the area (Decker and Peresson,1996; Fodor, 1995; Harzhauser et al., 2003, 2004; Kováč et al., 1997,1998, 2004; Lankreijer et al., 1995; Linzer et al., 2002; Royden, 1985;Seifert, 1992; Strauss et al., 2006; Wessely, 1986). However, themajority of these studies has not dealt with the development of thenorthern part of the VB (in the SMLC) in the Late Miocene thoroughly.

The SMLC is located in the southeastern part of the Czech Republic(Fig. 1). It has been reported that coal first appeared in the SMLCduring the Badenian era. However, only the lignite seams in thePannonian strata have brought economic benefits and have been

mined for decades. In total more than 70 lignite mines have beenopened. Currently, only twomines remain active (Fig. 1). The first oneis an underground mine called Mír, situated in the area of Mikulčice–Hodonín in the Czech part of the VB. This mine produced 400,000 t oflignite in 2009. The second active mine is the underground mineGbely Baňa Záhorié, situated in the Slovakian part of the basin. Itsmaximal annual production of lignite was 500,000 t in 2005. Atpresent the annual production is about 155,000 t of lignite per year.Today, lignite is no longer seen as an interesting fuel alternative, but,conversely, it is increasingly used as a rawmaterial for agriculture andin the chemical industry.

In this paper we present a study of the SMLC based on tens ofthousands analyses frommore than 3300 boreholes andmany channelsamples. With such a high number of data this study is able to capturethe geological evolution of the area and the qualitative parameters oflignite which is present here. Our first aim is to reconstruct thedevelopment of the coal seam in the Late Miocene (the Pannonian) inthe SMLC on the basis of selected technological parameters. Oursecond aim is to assess the mutual relationship between tectonicfaulting and sedimentary development of the seam coal.

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Fig. 2. Cross-section 1–1′ through the Hovorany–Kyjov Part and Moravian Central Depression. The location of the cross-section is shown in Fig. 4.

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2. Geological background

TheVB is a typical pull-apart basin, situated along the transform faultzone (Peresson and Decker, 1997) separating the Eastern Alps from theWestern Carpathians and the Bohemian Massif (Ratschbacher et al.,1991). It is a 150 km long and 60 km wide irregular rhomboidaldepression, prolonged in the NE–SW direction (Lankreijer et al., 1995;Wessely, 1986). During its evolution the basin was gradually filled byMiocene, Pliocene and Quaternary sediments. Hölzel et al. (2009)estimated the thickness of the Miocene sediments to be approximately5500 m. The depocenter is located in the central part of theVB (Kováč etal., 2004). The lignite-bearing Pannonian sediments were depositedduring the final stages of the evolution of the VB.

From the Eggenburgian to the Early Badenian times the VB wasdeveloping in the piggy-back regime (Peresson and Decker, 1997;Seifert, 1992). Since the Middle Miocene it has been developing in thepull-apart regime (Decker and Peresson, 1996). The VB evolutionduring the pull-apart stage was crucially influenced by the sinistralfaults along the Malé Karpaty Mountains and along the frontier of theMagura nappes (Fodor, 1995). According to Wessely (1986) theechelon pattern of the main faults and of the depocenters togetherwith their curved course gives evidence of the strike–slip tectonics(Fig. 1). However, Jiříček and Seifert (1990) explained this observa-tion by a successive opening of the VB center from the south to thenorth along the Steinberg fault and Lužice–Lanžhot fault zone (Fig. 1)from the Early until the Middle Badenian time.

During the Middle Badenian time marine sedimentation wasgradually replaced by continental sedimentation, which was accom-panied by a decrease of the environmental salinity (Kováč et al.,2004). In the marginal areas of the former VB the break ofsedimentation between the Sarmatian and the Pannonian ages wasdisplayed (Magyar et al., 1999). However, in the central part of the VB,including the Moravian Central Depression (MCD), Čtyřoký (2000)presumed a continuous transition from Sarmatian to Pannoniansediments. The VB was gradually transformed into a saline bay of thePannonian sea. This bay successively spread towards the northeastinto the Hradiště Graben (Honěk et al., 2001). In the Late Panonniantime Jiříček and Seifert (1990) presumed a sedimentation ofterrestrial deposits only. During zones B and F according to Papp'sclassification of the Pannonian sediments (1951), extensive swampswere formed in the flat areas (Fig. 2). These swamps gave rise to thelignite seams (the Kyjov and Dubňany seams and other coal seams inthe roof rocks of the Dubňany seam).

Tectonic activity in the VB continued in post-Pannonian time. Thisis proven by the tectonic deformation of the both Kyjov seam andDubňany seam (Figs. 1 and 2). The most tectonic deformation is in thearea of the Steinberg, Lužice–Lanžhot, and Polešovice fault zones.These fault systems limit theMCD to the northwest and southeast andat the same time they separate it from the remaining SMLC parts. The

Fig. 1. Location of the South Moravian Lignite Coalfield and its individual parts in the ViennaPart) and the Dubňany seam (the Moravian Central Depression and Rohatec–Bzenec–Strážndots show the distribution of the Pannonian delta lobes (modified from Harzhauser et al., 2

important strike–slip faults with vertical throws of more than 100 mbranch into the individual faults which bend and further branch intosmaller faults (Fig. 1). The fault throw on these normal faults reachesvalues of tens of meters (Fig. 2). In consequence of the normalkinematics of the faults, the tectonic blocks form a step-shapedpattern. The smaller normal faults, which are characterized by strike–slip and splaying normal faults, are understood as associated faults ofthe Steinberg fault complex (Jelínek et al., 2009). These faults weredescribed by Hinsch et al. (2005) as a system of arch–bentinterconnected faults decreasing their dip towards the depth.

The Lužice–Lanžhot fault zone and the Polešovice fault zone(Fig. 1) are formed by several prominent echelon faults which arelinked together by the arch–bent faults with a N–S to NE–SWorientation (Fig. 1). To the southwest the faults are branched intopartial fractures with a fault throw of tens of meters. The resultingblocks dip towards the basin (Jelínek et al., 2009). This phenomenonwas explained by Hinsch et al. (2005) as “negative flower structures”.The faults are steeper and do not form complicated structures. Similarstrike–slip faults were described by Strauss et al. (2006).

In this paper we only address the Pannonian (Late Miocene)basin–fill in the SMLC.

3. Late Miocene basin–fill

The Pannonian sediments in the SMLC were deposited in twodifferent facies zones— the basinal and marginal ones. For the basinalfacies the predominance of clays is typical. Such a development tookplace mainly in the central and southern part of the MCD and theRohatec–Bzenec–Strážníce Part (RBSP) (Fig. 1). The marginal faciesoccurred in the areas west and northwest of the Steinberg fault zone,the northern part of the MCD, the Hovorny–Kyjov Part (HKP), and theKelčany–Domanín Part (KDP). This development is characterized by agreater amount of sands, silty sands as well as silts.

The sedimentary description of the LateMiocene in the SMLC usedin this article is based on the classification by Papp (1951). To identifyindividual series we adopted a terminology well-established for theSMLC area (Fig. 3). This terminology of the Pannonian segments ismore suitable for the geological situation in the SMLC than theterminology used by Čtyřoký (2000). Čtyřoký (2000) divided thePannonian sediments into the Bzenec Formation (zones A–F), theDubňany Formation (zone F) and the Gbely Formation (zones G–H).His lithostratigraphic units naming is based on the type profile fromthe northern part of the MCD— the openpit GV-1 (localized in Fig. 4)of Mine Osvobození (Fig. 1). This type of profile is not applicable atthe central and southern parts of the MCD. It covers neither thethickness of the Coal series (the Dubňany Formation) towards thenorth, nor the Transitional series between the Coal and Variegatedseries (the development between the Dubňany and Gbelyformations).

Basin. Map of the base of the Kyjov seam (the Hovorany–Kyjov and Kelčany–Domanínice Part). The tectonic pattern is taken from Jelínek et al. (2009). Dotted lines and small004). Positions of some major mines are also given.

Fig. 3. Lithostratigraphic division of the South Moravian Lignite Coalfield with main tectonic events and sedimentary evolution of the Vienna Basin.

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3.1. Early Pannonian

The sedimentation in the Early Pannonian — zone A (Papp, 1951)started in the SMLC by the Basal sand series (Fig. 3). Basal sedimentsin the marginal parts of the SMLC are represented by light gray fluvialsands (Harzhauser et al., 2004). The thickness of this basal unit

reaches up to several tens of meters. In the Austrian part of the VBthese sediments are called “the transitional beds” and are representedby sands and gravels. The base of the Early Pannonian succession isformed by Sarmatian green-gray and gray silty clays of the highestzone E (Papp, 1951). In the MCD central part these clays graduallychange into the Panonnian zone A without basal sand sediments.

Fig. 4. Map of the thickness of the Kyjov seam (the Hovorany–Kyjov and Kelčany–Domanín Parts) and the Dubňany seam (the Moravian Central Depression and Rohatec–Bzenec–Strážnice Part) estimated from 3300 exploratory boreholes and many channel samples. The figure depicts the position of the openpit GV-1 of Mine Osvobození and cross-sectionlines.

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Zone B in the SMLC is mainly presented by the Gray Series (Fig. 3),which is comprised of gray, mostly sandy calcareous claystones. In themarginal areas of these clays up to 10 m thick yellow or light gray fine-grained sands canbe found. These sands form thebaseof theKyjov seam(Fig. 5, cross-section 2–2′). The Kyjov seam occurs in two separatedparts (Fig. 1; HKP and KDP). The total geological thickness of the seamvaries between 0.5 and 5.4 mwith an average thickness of 2.9 m (Fig. 4).

In the northern part west of Kyjov, many silty or sandyintercalations occur in the seam. Their number and thickness increasetowards the north (Fig. 5, cross-section 2–2′). This shows theinfluence of a stream flowing into the area of lignite-forming swamps

from the north. Close to the southern margin of the HKP the seamsplits into two benches. Their thicknesses decrease southwards from70 to 60 cm and further to the south the seam thins out. Theintercalation is formed by up to 7 m thick fine-grained sands (Fig. 5,cross-section 2–2′).

In the KDP the Kyjov seam has a uniform thickness of about 3.5 m.Towards the east, the number and thickness of shaly and sandypartings increase. Thus, the total seam thickness reaches 5.5 m(Fig. 4). The mean thickness of the seam in the KDP is 2.4 m.

The Yellow-sand series of zone C (Fig. 3) exists in themarginal partof the SMLC. It is a complex of cyclically changing sand beds, silts, clays

Fig. 5. Correlation schemes of the Hovorany–Kyjov Part (cross-section 2–2′) and the Rohatec–Bzenec–Strážnice Part (cross-section 3–3′). The location of the cross-sections is shown in Fig. 4.

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and lignitic layers (Fig. 5, cross-section 2–2′). Towards the south andmiddle of the basin, the sand series successively turn into the clayfacies. The thickness amounts to several tens of meters. The totalthickness of the Early Pannonian sediments (zones A–C) in the SMLCreaches up to 250 m.

In the Austrian part of the VB Janoschek (1951) named sedimentssimilar to the Yellow-sand series as “großen unterpannonen Sand”[=big Early Pannonian sand]. This unit is mainly a sandy successionwith up to 200 m thick scattered gravels. These deposits give evidenceof a fluvial system that entered the VB near Mistelbach (Fig. 1) andshed its delta into the northern part of the VB (Harzhauser et al.,2004). These sediments were identified as the Hollabrunn–MistelbachFormation (Fig. 3). The thickness of the Early Pannonian sediments inthe northern part of the VB is about 500 m. Southwards its thicknessdecreases to 140 m (Harzhauser et al., 2004).

3.2. Middle Pannonian

The Middle Pannonian includes all deposits that have beenassigned to zones D and E by Papp (1951). Zone D in the SMLC wasformed by Gray-pelitic series sediments (Fig. 3). In the marginal areasof the SMLC this formation comprises of gray silts and silty clays.During the SMLC basin development, green and gray silts as well asgray clays occurred near the base. In higher locations of this zone, 10to 15 cm thin lignitic layers appear occasionally. The thickness of thisformation is about 100 to 150 m. A lignitic layer in the Austrian part ofthe VB was used as a marker bed for well-log correlation (Janoschek,1951). However, Janoschek (1943) ranked this layer as D1 (=basezone D).

On the sediments of the Gray-pelitic series lie deposits of the Gray-green series (Fig. 3) of Pannonian zone E. This series has a simplecyclic structure. The sedimentation cycles are composed of green-grayor yellow-gray fine-grained sands with the spots of green and green-

Fig. 6. Correlation schemes of the Dubňany seam of the Moravian Centr

gray clays. Along the margins of the SMLC, environments suitable forthe formation of lignite clays and root soils were locally formed. Thethickness of this series is about 150 to 200 m. The total thickness ofthe Middle Pannonian series in the northern part of the VB isapproximately 300 m. In the Slovak area of the VB Jiříček (1985)described the blue and grayish clay formation. Harzhauser et al.(2004) described in zone E in the Austrian part of the VB blue-greenmarls and clays [informally termed “Inzersdorf Tegel” (Brix, 1989)],which are according to him widely spread throughout the VB.

3.3. Late Pannonian

The Late Pannonian comprises zones F, G and H by Papp (1951), andis characterized by the ubiquitous occurrence of thin lignite seams in itsbasal parts andby a sandy–marly upper part (Harzhauser et al., 2004). Inthe SMLC the sedimentation started with the lignite-bearing Coal series(zone F of Papp, 1951). The lower boundary of the Coal series is situatedat thebase of theDubňany seam(Fig. 3). TheDubňany seam in the SMLCoccurs in two separate areas. The first one, theMCD, has larger area andcontains the largest reserves of lignite in the SMLC (Fig. 1). In thenorthern part, the seam is uniform,withoutmajor partings. Towards thecenter of the MDC the partings, which are mainly formed by clays andsilty clays, occur. However, moving westwards the silty clays containmore and more coarse-grained material.

In the central part (approximately in the area between Mutěniceand Hodonín), there are two significant partings, which divide theseam into three individual coal beds (Fig. 6, cross-section 5–5′).Towards the west and south, the partings become more considerable,the inorganic admixture in the seam increases, the seam thicknessalso increases (Fig. 6, cross-section 4–4′ and cross-section 6–6′), butconversely the quality of the lignite decreases. In these marginal partsof theMCD the individual coal beds are built up by coaly rocks or rockswith coal admixture.

al Depression. The location of the cross-sections is shown in Fig. 4.

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The partings occur also at the northeastern margin of the MCD.Eastwards from the central part the number of the partings andthickness of the individual partings increase. At the eastern margin ofthe MCD these partings split the seam into two coal benches.

The geological thickness of the Dubňany seam is between 4 and5 m (Fig. 4) in the northern part of the MCD. From the central parttowards the south and west, the geological thickness increases up to12 m by splitting the seam into a series of benches (Fig. 6, cross-section 4–4′). In the west the economic thickness of this seamdecreases below 2 m (Honěk et al., 2001). The average thickness of theDubňany seam is 6.4 m.

The Dubňany seam in the RBSP splits into three coal bedsseparated by two partings (Fig. 5, cross-section 3–3′). The lowerparting has an average thickness of 2 m with maximum of 4.2 m. Theintercalations are formed by lignite clays or clays with a coaladmixture. In several places gray clays, marls, and sporadicallysands can be found. Jiříček (1985) presumed that these are the fluvialsands. The average thickness of the seam is 5.5 m with a maximum of11.2 m. The average thickness of the bottom seam bench is 1.4 m; theaverage thickness of the upper seam bench reaches 1.6 m (Fig. 4).

In the MCD the Coal series represents a complex of rocks with acyclic structure. Regressive parts of the cycles form gray, calcitic, fine-grained sand with layers of gray or even green-gray silts. Towards theoverlying rock the silt and clay constituent increases in the sandlayers.

There are seven cycles in the overlying rock of the Dubňany seam.Five of them have developed in the entire area of the MCD. In thesefive cycles, three lignitic layers occur. The Coal series thickness in thenorthern part of the MCD is from 32 to 35 m. Southwards thethickness increases only between Hodonín and Mutěnice, reachingfrom 70 to 80 m. Further southwards, the thickness stays at thisparticular level (Fig. 7, cross-section 4–4′).

Less significant cyclic structure can be found in the Coal series inthe RBSP (Fig. 5, cross-section 3–3′). The number of cycles is the sameas in the MCD, however the amount of silts and especially sands ismuch lower than in the RBSP. The thickness of the Coal series in theRBSP is from 35 to 75 m, which corresponds to the Coal seriesmaximal thickness in the MCD.

In the Slovakian part of the VB, a parallel of the Coal series(Harzhauser et al., 2004), the up to 200 m thick Čary Formation(Bartek, 1989), consisting of lignites, lignitic clays, silts, and sands, canbe found. In the Austrian part of the VB the lignite-bearing part of theLate Pannonian (zone F) was called “the lignitic series” by Janoschek(1943). The lignite-bearing sequence is comprised of two seams. Themain lignite seams attain a thickness of 1.5 m and 6.1 m in theSollenau pits and increase in thickness up to 6 m and 10 m atZillingdorf (Bechtel et al., 2007).

The Variegated series, belonging to zone G and H by the Papp's(1951) classification (Fig. 3), is typical for the SMLC and is situated inthe direct roof of the Coal series (Fig. 7, cross-section 4–4′). This seriesis in the MCD composed of gray clay complex, in which thin layers ofgrayish, yellow-gray, reddish, yellow-brown, and red clays occur. TheVariegated series is preserved in the incomplete thickness. Thethickness of the series in the MCD is variable and dependant upon thedeposit depth of the Dubňany seam. As a consequence of erosion, thisseries is absent in the north, towards the south of Dubňany thethickness increases. In the area between Mutěnice and Hodonín thethickness reaches up to 180 m. Further to the south, the thickness isinfluenced by the deposit depth of the Dubňany seam.

The development of the Variegated series in the RBSP is different.Green-gray clays with purple and yellow-brown spots mostly prevail,however the layers of lignite and lignite clays can be found here aswell. The thickness of the series is undeterminable due to the erosionsurface.

Between the Coal and Variegated series in the central part of theMCD, some intercalation of the gray clay and silt appear in the lower

part of the Variegated series (variegated clays). Southwards, theirproportion increases and the lower part of the Variegated series getfrom the bottom to the topmore andmore character of the Coal series(Fig. 7, cross-section 4–4′). In the transgressive cycle parts, extra coalseams appear from the south until the ninth roof seam. Thus, thesesediments are called the Transitional series, or transitional blue claylayers (Janoschek, 1943).

The main rocks of the Transitional series are gray and blue-grayclays. Sands and silts form less thick layers and lens. Honěk et al.(2001) claimed that the Transitional series intercalations progres-sively split into the variegated intercalations towards the eastern andwestern margins of the MCD.

The thickness of the Transitional series is variable. In its northernpart (the central part of theMCD) it varies from about 7 to 15 m. In thedeepest parts of the MCD eastwards Břeclav the thickness is up to60 m. The rock complex with the character of lignite series (i.e. Coaland Transitional series together) in this particular part of the MCDreaches a thickness of up to 150 m (Fig. 7, cross-section 4–4′).

According to Harzhauser et al. (2004) in the Slovakian part of theVB the lignite-bearing Čáry Formation is overlain by a 450 m thicksuccession of marl, clay, and silt with intercalations of sand, gravel,rare lignites, and sporadic freshwater limestone in the top. In thecentral and northern part of the Austrian VB the top of the lower partof the Gbely Formation consists of an up to 40 m thick layer of sand(so-called “Zwischensand”). To zone G Brix (1989) also classified asthe “Blaue Serie” (=blue series), which consists of up to 350 m thickblue-green clays, with layers of yellowish sand and very rare ligniticclays. The roof of the blue series is according to Harzhauser et al.(2004) represented by “Bunte Serie” (=variegated series) byJanoschek (1943) and “Gelbe Serie” (=yellow series) of zone H byPapp (1951) [Fig. 3].

4. Character of used data

This study is based on tens of thousands analyses of samples frommore than 3300 boreholes and many channel samples. The boreholerecords were collected between the years 1952 and 1990. Thereliability of these records had to be verified before their usage(Honěk et al., 2009). The data were divided into three categoriesaccording to their credibility, accuracy, and completeness.

The borehole records collected during geological surveys in the1970s and the 1980s as well as data coming from channel samplingrepresent the most reliable, complete, and extensive (with respect tothe number of the analyses carried out) category. The drilling grid is1000×1000 m. The drill coreswere taken from the boreholes. However,these data only cover the central and northern parts of the MCD.

When drilling and sample collecting the focus was mainly placedon the lignite seam. In case of losing the seam core, the missing part ofthe seam profile was supplemented according to the logging measure(gamma-gamma-carotage). In other cases the logging was executedonly for the purpose of determining the water-bearing and imper-meable horizons. The density of the drilling grid was high enough forcarrying out the seam correlation.

The determination of chemical and technological parameters wasmainly focused on the Dubňany seam. For completeness of the wholeseam profile one sample was taken from the roof and the seat-earth ofthe seam. The coal seamwas divided according to its coal petrographycharacter. From each of the beds thicker than 5 cm one sample wastaken. From the thicker beds the samples were taken on the basis ofmacro-petrographic evaluation seam structure (usually according tothe visibly increased amount of inorganic admixtures). With all thesamples the following basic analyses were carried out: the ash yield[Ad — ash (dry, %)], net calorific value [Qi

r — as received, MJ·kg−1],gross calorific value [Qs

daf — dry, ash free, MJ·kg−1], volatile matter[Vdaf — dry, ash free, %], sulfur content [Sd — sulfur (dry, %)], andmoisture [Wt

r — as received, %] analyses.

Fig. 7. Correlation scheme of the Moravian Central Depression (cross-section 4–4′). The location of the cross-sections is shown in Fig. 4.

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The second data category contains borehole records from the 1950sand the 1960s. The data come from all parts of the SMLC. The drillinggrid was mostly 2000×2000 m. Around the mining areas the griddecreased to 500×250 m, sometimes even to 250×250 m (Fig. 4).Therefore, the data suffer from inaccuracies in determining the coalseam base (the average error is approximately 0.5 m). The errorswerecaused by the drilling method used, the so-called “counterflush”. Thismethod is based on the elevation of the drilled rock and coalfragments to the surface by drilling mud through drill pipes. Thedifferences in the size and density of the drilled out rock and coalfragments caused the gravity separation of these fragments in theborehole. This separation precluded creation of a reliable lithologicallog. Because the geophysical well logs were not measured, it wasimpossible to determine the seam base boundaries with sufficientaccuracy.

At the beginning of the 1950s, no analyses were carried out withinthis category. Later, only the basic analyses of all coal benches and allintercalations from coal seam mixed into one sample (“mixedsample”), were conducted. During the 1960s, analyses of petrograph-ically different types of coal beds and intercalations in the seamstarted.

The third data category contains the borehole records obtainedduring petroleum explorations realized between the years 1930 and1960. In this data category no coal analysis was carried out and theerror in determining the coal seam base varies from 2 to 3 m. Thisrelatively high error is partially caused by the counterflush drillingmethod, but mainly by human factors (The lignite seams were not thegoal of the measurements and, therefore, many measurement errorswere encountered). Moreover, no loggings were carried out for thesedata. The data of this category were used to model the Dubňany seamin the parts where the data of previous two categories were missing.

The deposit database was created on the basis of the extracted dataafter their verification. On the basis of this database the structural-tectonic reconstruction of the bases of the individual seams wascarried out. Moreover, the database gave rise to a most-likelyhypothesis of the tectonic evolution of the SMLC (Jelínek et al.,2009). Consequently, a digital model of the deposit was created(Staněk et al., 2006).

5. Characteristics of the coal

The Kyjov and Dubňany coal seams, including the seams in the roofrocks, are formed by humic, low rank brown coal. The color of the coalis mainly brown with yellow, red and black shades. From thepetrographic viewpoint, there are well-distinguishable xylite anddetritus components. The degree of gelification varies, from ungelifiedparts to strongly gelified parts. According to the international coalclassification it belongs to the ortho-lignite (UN-ECE, 1998).

The most common lithotype of the South Moravian lignite is thexylite-detritus coal. Less frequent are the detritus, the semi-detritus,and detritus-xylite coals. The least frequent is the xylite coal. There arespatial differences among different lithotypes. In the northern andeastern parts of the MCD and in the HKP the xylite component (xylitecoal, detritus-xylite coal, and semi-detritus coal) dominates. Theoccurrence of these lithotypes indicates relatively dry environment ofthe arboreous mire (Honěk et al., 2001).

In addition to the low-ash coal (with the ash yield Ad≤30%), theseams also contain layers with increased ash contents (high-ash coal:30%bAd≤50%) and partings of the coaly rocks (50%bAd≤70%) androcks with coal addition (AdN70%). The inorganic admixture is almostwithout exception clay, much less silt or even sand. Generally, with anincreasing proportion of inorganic admixture the xylite content in thelithotype decreases. Hence, in the high-ash coal only the clay xylite-detritus and clay detritus contents prevail, while the coaly rockscontain a little amount of xylite. Consequently, the partings can beformed by the coaly–silty clay or the coaly–clay silt. The layers of the

coaly silt, coaly sand, or sand with the coal addition commonly occurin the seat-earth of the Kyjov seam.

During the deposit exploration in the SMLC extensive chemical–technological analyses to determine the ash yield, net calorific value,gross calorific value, volatile matter, sulfur content, and moisturewere carried out. In the following overview of the chemical–technological parameters we restrict ourselves to information aboutthe most important qualitative variables.

The coal in the SMLC has low net calorific value and high contentsin volatile matter and moisture. The maximal net calorific valueQr

i [MJ·kg−1] (with the ash content Adb10%) is about 12 MJ·kg−1.However, within the entire Dubňany seam, the Qr

i value decreasesfrom 11.1 MJ·kg−1 (eastern part) to 2.1 MJ·kg−1 (western part). Ingeneral, the Qr

i values are around 9.2 MJ·kg−1 in the eastern part ofthe MCD and around 6.8 MJ·kg−1 in the western part of the MCD.However, in the RBSP the Qr

i values are considerably lower, with themean 4.3 MJ·kg−1, as a consequence of a massive parting, splittingthe seam into two separated benches (Fig. 5, cross-section 3–3′). Inthe Kyjov area (the Hovorany–Kyjov Part) the mean value of Qr

i

equals to 9.1 MJ·kg−1. In addition to the Qri values, the calorimetric

testing also determines the values of the gross calorific valueQSdaf [MJ·kg−1]. From the existing information we can conclude that

the QSdaf values usually range between 25 and 27 MJ·kg−1.

For the MCD the volatile matter Vdaf [%] content usually variesbetween 56 and 64%. The Vdaf values are higher in the RBSP, in somesamples even extending 70%. Spatial distribution of the volatile matterVdaf within the SMLC depends more likely on changing of the organicmaterial distribution than on the seam depth (Sivek et al., 2008).

As a consequence of a low degree of coalification, the lignite hashighmoisture in its original conditionWt

d. In the lignite with a low ashcontent (up to 15% Ad) the Wt

d value varies between 40 and 50%,occasionally attaining values above 60%. The Wt

d value decreases withincreasing value of Ad.

In this study we focused especially on the description of spatialdistribution of the ash yield and sulfur content.

5.1. Ash yield

The ash yield (dry) Ad [%] was determined for all the analyzedsamples (the first and second data categories). On the basis of thesedata, the correlation schemes for the Dubňany seam were created(Fig. 6). The data of the second category include information from theindividual parts of the entire seam “mixed samples”. The distributionof the ash yield (Ad) was determined for data of both categories(Fig. 9A). The ash yields were calculated for the entire geological seamthickness.

No significant differences of the ash yields between the Dubňanyseam and the Kyjov seam can be observed. In the studied samples theminimum coal ash yield is mostly between 8 and 10% Ad, only rarelyreaching lower percentages. The minimum ash yield below 5% isabnormal. The ash yield is also influenced by the petrographic coalcomposition. The lowest ash yield values were found in the xylite coalsamples with a well-preserved wood structure. In general, the xyliteparts of the coal contain less ash than the detritus parts. The highestquality seam parts, belonging to the seam vertical geological profile,have the ash yield of about 10–12% Ad. Mostly the yield in the seamparts range between 15 and 28% (Fig. 6). The minimum values of theash yield for the entire seam are 12–15% Ad (Fig. 9).

The spatial distribution of the ash yield in the seam is related to itsgeological development. Increased ash yield in the Kyjov seam can beseen in the northern part of the HKP west of Kyjov. The ash yield andthe number and thickness of the intercalations increase northwards(Fig. 5, cross-section 2–2′). This phenomenon can be observed in theprofiles in the Kyjov seam (Fig. 8). In the M171 profile the seam isunsplit, however in the M164 and M339 profiles situated in the northintercalations occur. Intercalations are formed by coaly rocks, clays, or

Fig. 8. Profiles of the Dubňany and Kyjov seams with the vertical distribution of the ash yield Ad and sulfur content Std in the Hovorany–Kyjov Part (M339, M164 and M171), in theKelčany–Domanín Part (P8), and in the Moravian Central Depression (C1, D237, HO399 and N8). The location of the profiles is shown in Fig. 9.

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even silts. This fact indicates an influence of the river, flowing into thecoal-forming area from the north. In the KDP the ash yield in the Kyjovseam increases eastwards. This fact corresponds to the increased seamthickness (Fig. 4). Therefore, in accordance with Jiříček (1985), it canbe assumed that the fluvial sedimentation in the Hradiště Graben hadan influence on coal deposition in the KDP.

In the Dubňany seam the increased ash yields can be seen mainlyin the RBSP and in the western and southern parts of the MCD.

Generally, the higher ash yields are caused by the massiveintercalation, splitting the Dubňany seam into two coal benches.The ash yield in the entire seam increases due to the high thickness ofthe intercalations, which we included into the analysis. However, it isstill possible to observe the changes in the spatial ash distribution. Inthe central part of the RBSP, the thickness of the dividing intercalationis the smallest and the coal quality is the highest. In some places, wecan see an interconnection of both coal layers. Towards the RBSP

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margins the coal quality decreases, while the ash yield increases andin several places thinning of the coaly layers can be observed. The ashincrease towards the NE can be explained by the material input fromthe NNE. Jiříček (1985) presumes that the parting composition in theseam is an evidence of its river origin. A paleoriver of the HradištěGraben probably flowed into this area.

The lowest ash yields of the Dubňany seamwithin the MCD can befound in its central part west of Hodonín. Very exceptionally, in thisarea the yields in the coal layers exceed values of 20% (Fig. 5, cross-section 4–4′). Towards the west and south the values graduallyincrease and in the area around Břeclav they reach over 80% (Fig. 9A).Westwards the coal quality in the individual coaly layers decreaseseven to the level comparable with coaly rocks (Fig. 5, cross-section 4–4′). In the same direction, both the number and thickness ofintercalations increase and at the western margin only one of thethree seam benches is commercial. A similar situation can be observedin the southern part of the MCD (Fig. 5, cross-section 4–4′).Southwards both the geological thickness of the seam and thicknessof the dividing intercalations increase, the thickness of the coal layersdecreases, and the ash yield increases. In the southern part of theMCDthe coal with the ash yield between 40 and 60% dominates even in thecoal layers (Fig. 5, cross-section 4–4′).

Northeastwards from the central part of the MCD the ash yieldreaches up to 40% (Fig. 9). This fact reflects the increase of both thenumber and thickness of intercalations in the seam. Northwards ofHodonín the seam is divided into two coal benches. This trendcontinues further to the RBSP, where the seam is split into twobenches in its entire volume.

5.2. Sulfur content

While the ash yield was determined for almost all samples, thesulfur content Std [%] was determined only in their small portion. Forinstance, only five analyses in total of the sulfur content were carried

Fig. 9. Spatial distribution of the ash yield Ad (A) and the sulfur content Std (B) in the i

out in the RBSP. For this reason, the sulfur data of the RBSP were notincluded in Fig. 9B.

Sulfur in the coal seams occurs in two forms: the sulfate sulfur andthe pyritic sulfur. Rarely, higher sulfur content occurs in some seamparts, as a consequence of pyrite concretions. Mostly, such a pyrite isof the indigenous type. The mean sulfur content in the Dubňany seamranges from 1.8 to 2.1% (Fig. 9B). Higher sulfur content values can befound in the northern part of the MCD and along its northeasternmargin. Here, the values exceed 2.5%. Additionally, in the RBSP theaverage sulfur content is higher, reaching 2.4%. However, this averagevalue was computed from only 5 analyses.

Much higher values of the sulfur content can be found in the Kyjovseam. In the HKP the mean sulfur content is 3.2% and in the KDP it ismore than 4.0%. The sulfur vertical distribution Std of the Kyjov seam isvery variable. In the KDP the values of Std are high in the entire seamprofile (4.7–4.9%). Only at the seam base the values reach 3.5% andapproximately in the middle part of the seam the value is 2.7% (Fig. 8,profile P8). Similar is the situationwith theM171 profile from the HKP(Fig. 8), the values of Std do not differ much throughout the entireseam. They range between 3.0 and 3.2%. Only in the bottom andmiddle parts of the seam do the Std values reach from 4.2 to 4.9%.Concordance of the vertical distribution of Std in the HKP can beobserved in the M339 and M164 profiles (Fig. 8). From the initialvalues 4.9% at the seam base the values decrease to 3.5 to 1.9% in theupper parts of the seam. In the middle part of the seam, a gradualincrease of the values up to 5.4 to 6.0% can be observed within bothprofiles. The upper part of the seam is uniform, with Std reaching thevalues of 4.0 to 4.3%.

The vertical distribution of Std in the Dubňany seam has a similarcharacter in all of the studied profiles (Fig. 8). At the base of the seamthe coal layers Std are the lowest (0.9–1.9%). Towards the upper partsof the seam the value of Std slightly increases in all profiles. Thisincrease is in the magnitude of only the tenths of 1%. In the middlepart of the seam Std in the coal reaches maximally 2.1% (Fig. 8, profileD267). A slight increase of Std in the coal continues towards the upper

ndividual parts of the SMLC with localization of the vertical profiles of the seams.

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parts of the seam, where its values are the highest (2.2 to 3.8%). Fig. 9Bdepicts the average values of Std for the entire geological seamthickness. Thus, the maximal values of Std in the MCD do not exceed3%.

In the roof seams of the Dubňany seam the sulfur content in thecoal was calculated only exceptionally. Few data are from the first andsecond roof seams. In the first seam in the roof rocks of the Dubňanyseam the sulfur content is higher than 4.3%. In the second roof seamthe sulfur content Std is 2.0–4.5% and the average value is 3.2%.

6. Discussion

In this research we have found that the spatial distribution of thestudied primary chemical–technological coal parameters in theDubňany and Kyjov seams follows the geological evolution of thisarea. The values of studied parameters reflect different developmentconditions of the coal seams in zone B and zone F in the Late Miocene.

The sedimentation in the SMLC in the Early Pannonian wasinfluenced by both the reactivation of the faults in the VB pull-apartstructure (Strauss et al., 2006) and a sea transgression into the basin(Magyar et al., 1999). In the marginal parts of the VB, characteristicdelta-associated facies were created (Harzhauser et al., 2003).According to Harzhauser et al. (2004) these facies document aphase during which fluvial facies penetrated far into the VB. Jiříček(1985) presumed that the river sediments of the Mistelbach delta(Fig. 1) reached even to Břeclav, where they mixed with the fluvial

Fig. 10. Spatial view on the Kyjov seam base – Pannonian age, zone B (the Hovorany–KyjovMoravian Central Depression and Rohatec–Bzenec–Strážnice Part) with the contour map ofLegend: 1— fan delta with outlined direction of the clastic material inflow to the basin in Panthe basin in the Pannonian zone F, 3 — direction of the clastic material inflow coming frommigration of the clastic material from the Rohatec–Bzenec sedimentary area into MCD Pann

sands of the Hradiště Graben. The subjacent sandy horizons of theKyjov seam are according to Jiříček (1985) of fluvial origin and weretransported to the area from the Hradiště Graben. In the southern andsouthwestern direction these sandy deposits turn into the fine-grained silty sands or even fully clay deposits. In the central part of theSMLC the sandy horizons occur only occasionally.

The origin of the Kyjov seam that directly overlies the sandyhorizon of the Gray series (zone B) is connected with thetransgressive stage (Kováč et al., 1998; Magyar et al., 1999). Accordingto Kováč et al. (1998), brackish-water andmolasses of the lagoon typewere forming in the northern part of the SMLC. On the basis of fluvialfauna findings in the lignite Jiříček (1985) assumed the freshwaterdevelopment of the Kyjov seam. According to the studies of thePalaeogene coal (Casagrande, 1987 and Shimoyama et al., 1990), highsulfur contents suggest a brackish environment.

It is probable that during the Kyjov seam forming the sedimentaryenvironment changed a few times. In both studied areas (the HKP andKDP) the sedimentary environment was first brackish (Kováč et al.,1998). This fact is supported by the high content of sulfur at the seambase (Fig. 8). Due to river flows coming into the area from the northand northeast (Fig. 10), the environments slowly changed into thefreshwater ones (lower sulfur content in the bottompart of the seam—

Fig. 8). The sulfur increase in the middle part of the seam in the HKPand the upper part of the seam in theKDP indicates a transgression anda slow increase of the salinity in the sedimentary environment (Fig. 9).In the KDP the sulfur content keeps the same level which gives an

and Kečany–Domanín Parts) and the Dubňany seam base – Pannonian age, zone F (thethe Ad content. Direction of the clastic material inflow during the Pannonian is shown.nonian zone B, 2— fan delta with the outlined direction of the clastic material inflow tothe northern branch of the Mistelbach delta, 4 — direction and position of episodic

onian zone F, 5 — main fault zones, 6 — state borders.

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evidence of the stable sedimentary environment. In the HKP aconsequent slight decrease of the sulfur content can be observed,probably due to the river flow.

The influence of river flows on the salinity change differs in thetwo studied areas. On the basis of the average value of the sulfurcontent (Fig. 9B) and differences in the sulfur vertical distribution inthe seam profiles (Fig. 8), we can claim that the KDP was under asmaller river influence than the HKP. The coal-forming swamp of theHKP was influenced mainly by the river flow coming from the north(Fig. 10). Jiříček (1985) called it the Kelčany River. Its existence isproven by the increased ash content in the northern part westwardsof Kyjov (Fig. 9A) and a greater occurrence of the silty or even sandyintercalations, the thickness of which is raising northwards (Fig. 5,cross-section 2–2′). In the KDP the intercalations have the character ofcoal clays. This indicates a lesser influence of the river flows. Theincreased ash yield (Fig. 9A) and the presence of the silty in-tercalations in the eastern part of the KDP show the significance of oneof the Hradiště Graben benches. This corresponds to the Jiříček's(1985) opinion of the fluvial character of the intercalations.

A slightly different development in the studied areas can be relatedto the tectonic development of the region. According to Decker (1996)and Fodor (1995) the stress field in the VB had in this period a N–Scompressive component and an E–W extensive component (Fig. 2).Activation of movements on the faults of the pull-apart structure ofthe VB took place especially northeastwards and southwestwards.Harzhauser et al. (2003) described a tectonic activity and thedisplacement of tectonic blocks along the Steinberg fault system inthe Austrian part of the VB in the period of the Early Pannonian. TheSteinberg fault zone divided both studied areas in the SMLC (Fig. 10).Thus, it is possible that at the end of the Kyjov seam development theseparation of both areas and local descent of the KDP took place.

After the Kyjov seam formation the relative sea level fell. This fact issupported by the existence of the river channel confirmed by mining(Fig. 4). It is probably the same flow bringing the river sediments into acoal-bearing swamp of the HKP (the Kelčany River) and influencing itssalinity whilst Kyjov seamwas forming. In the southern part of the HKPthe river channel split into two benches, reaching in some parts to theseat-earth of the seam. This river channel was filled by sends of Yellow-sand series (zone C), situated in the direct overlying rock of the Kyjovseam.Weare referring to a complex of cyclically changing sand, silts andclay bedswith lignitic layers (Fig. 5, cross-section 2–2′). Altogether ninecycles were described in the HKP.

According toHarzhauser et al. (2004) the cyclic structure of the EarlyPannonian is not always related with the local tectonic movements. Hepresumed that the cyclical structure reflects the oscillations in therelative lake level. He also claimed that in the marginal parts of the VBthese cycles capture a regular changing of the lacustrine environmentsand phases of river progradationwith thedeposition of gravels and sandin channels (Harzhauser et al., 2004).

Zones C and D are regarded as a part of the transgressive systemstract which culminated in the maximum flooding surface within zoneE (Harzhauser et al., 2003). The subsidence accelerated and deltasediments were replaced by shallow-water basin deposits (Kováčet al., 1998). The tectonic phase with the N–S compression stress fieldculminated (Fig. 3). The VB was opening on the sigmoidally bendingsinistral strike–slip faults in the NE–SW direction. On the accompa-nying faults in the N–S direction, the tectonic blocks descended intothe open space of the VB (Decker et al., 2005). In the SMLC thesubsidence in the area between the Steinberg and Lužice–Lanžhotfault zones linked with the Polešovice fault zone took place (Fig. 10).The MCD and RBSP were formed.

The sedimentation of zone F in the SMLC startedwith transgressivesandy–clay deposits. Coal series with the Dubňany seam on the basiswas formed. Both the geological thickness (Fig. 4) and ash yield of theDubňany seam (Fig. 9A) in theMCD significantly increasedwestwardsand southwestwards.

In the same directions the number of the partings, which dividethe Dubňany seam into four benches, and their thickness increased(Fig. 6). Moreover, the coal benches gradually changed into the coalyrocks. Simultaneously, the grain size of the parting rocks increased.Jiříček (1985) explained that this phenomenon was caused by riversthat were bringing the clastic material into the MCD through thechannels in the swamp vegetation from the northwest and westdirections. This material flowed into the basin northwestwards fromBřeclav and was further spread (Fig. 10). From the south the clasticmaterial was brought into the area by the northern branch of theMistelbach delta (Fig. 1).

According to Jiříček and Seifert (1990), the ash yield increase in thenortheast of the eastern part of the MCD (Fig. 9B) could be explainedin a similar way. In the central part of the profile (Fig. 6, cross-section5–5′), the Dubňany seam is divided into two benches by a parting,which consists of the coaly clay. Thickness of the seam parting nearbythe northeastern boundary of the MCD increases eastwards. Splittingof the coal seam into two individual benches is characteristic for theRBSP (Fig. 5, cross-section 3–3′). One could conclude that in the timeof the Dubňany seam origin both parts were connected bysedimentation. The RBSP could be also of a liman environment(Jiříček and Seifert, 1990), into which the river material wastransported from the Hradiště Graben. The major amount of theclastic material stayed in the RBSP behind the forming tectonic ridgeof the Polešovice fault zone. Only rarely did this material crossthrough the ridge into the MCD (Fig. 10). The connection of the twoareas is evident from the behavior of the axis of the northern part ofthe VB (Fig. 4). This behavior suddenly changes from the NNE–SSWdirection into the ENE–WSW direction. Further eastwards the axis isinterrupted, but in the RBSP it continues in the ENE–WSW directionand even further it bends into the NE–SW direction. The behavior ofthe axis corresponds to the main faults zones of the pull-apart systemthat formed the sedimentary area in the northern part of the VB(Fig. 7). The two parts were connected during the Late Pannonian(zone F).

The different seam thickness (Fig. 4), ash yield (Fig. 9A), andinterrupted axis of the basin (Fig. 4) are evidences of the reactivationof the tectonically active fault zone (Polešovice fault zone) betweenthe MCD and RBSP. The movements of the individual faults of thistectonic zone from the Middle Pannonian until the Late Pannonian(Strauss et al., 2006) gradually caused splitting of the seam into thetwo parts.

The petrographic character of the parting material in the RBSPsupports Jiříček's (1985) hypothesis that the environment was of acalm liman or a lagoon type of sedimentation with the coarse rivermaterial rarely being transported from the Hradiště Graben (Fig. 10).Kováč et al. (1998) presumed the low salinity (0–15‰) of thesedimentary environment in the whole northern part of the VB.

On the basis of the sulfur content in the coal substance of theDubňany seam (Fig. 8) we assume that at the beginning of seamformation the sedimentary environment in the MCD was thefreshwater swamp one. Low sulfur contents in the bottom part ofthe seam (0.9–1.9%) indicate this fact. In the middle part of the seam,the values increase by tenths of a percentage. In the upper part of theseam, the sulfur contents of the profiles situated further to the northare 3.0–3.8%. The profile of the central part of the MCD shows thesulfur content of 2.2% in its upper part. We presume this increase ofsulfur to be caused by the beginning of transgression and by a slightrise of the salinity when creating the upper parts of the seam. Thisparticular transgression, represented in the MCD by thick sand layers(Fig. 7), ended forming of the Dubňany seam.

In the Coal series (zone F) together with the Dubňany seam thecoal-forming conditions were renewed several times. The Coal seriesis formed by a rock complex with an apparent cyclic structure andwith occurrence of other seams or their equivalents in the Dubňanyseam roof. In the transgressive sand layers of the individual cycles the

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portion of the fine and clay components increases, followed by thepure clay and by the coal seam. Honěk et al. (2001) described sixcycles in the Coal series in the Dubňany seam roof, with three large,but economically unimportant coal seams and with other coal layers.The thickness of the Coal series is in the northern part of the MCDabout 32–35 m, southwards it increases up to 70–80 m (Fig. 7, cross-section 4–4′).

After the significant transgression over the Coal series (zone F) thesediments of zone G — the Variegated series, composed of gray claycomplex with layers of greenish, yellow-gray, reddish, and yellow-brown or even red clays, were deposited. In the clays there are non-continuous layers and strays of freckled silts and fine-grained sands.In the entire Variegated series the layers of the white-gray silty–clayfreshwater limestone can be found.

In the northern part of the SMLC the sedimentary environment inzone G was not suitable for forming of seams. The forming areasmoved to the center of the basin. This fact is proven by theTransitional series deposit occurrence (zone G) in the middle part ofthe MCD. Southwards, further coal layers up to the ninth overlyingrock are situated (Fig. 7, cross-section 4–4′). The development of theTransitional series in zone G with the occurrence of further ligniteseams and the increasing thickness up to 60 m shows transformationof the suitable conditions for swamp forming to the south and to theoverlying rocks. Kováč et al. (1998) also mentioned further gradualtransgression that did not inundate the northern parts of the VB.

According to Harzhauser et al. (2004) the sedimentation oflacustrine facies in the Late Pannonian might reflect hydrologicallyconditioned transgressive phases. This hypothesis is based on the fact(Decker and Peresson, 1996) that in this period the VB underwent avery strong change in the large-scale stress field. Instead of the N–Scompression and E–W extension, an E–W compressive stress fieldevolved, resulting in the basin inversion and ceasing of the pull-apartkinematics. The deposition is thus extremely unlikely (Harzhauser etal., 2004). The lake level decrease in the period between zones F and Gwas according to (Harzhauser et al., 2004) related to the minimum ofthe 2.35-myr eccentricity cycle.

The thickness of the Dubňany seam shows that the sedimentationat the beginning of zone F took place in the tectonically relatively calmenvironment. Only evidence of the tectonic activity is the Polešovicefault zone, which gradually separated the sedimentary environmentof the MCD from the RBSP in zone F. A distinct tectonic deformation ofthe lignite seam in the SMLC started only in the Pliocene, when theextensive component of the stress field in the NE–SW directiondominated (Decker et al., 2005). In the SMLC, rejuvenation of thetectonic zones of the pull-apart system took place in the directions ofNE–SW and NW–SE to NNW–SSE.

7. Conclusion

On the basis of both chemical and technological parameters andlithological characteristics of the Pannonian deposits from theboreholes and many channel samples, we showed that the VB in thePannonian period gradually developed into a freshwater bay of thePannonian Sea. Brackish environment with the typical delta sedi-mentation in the marginal areas in zone A subsequently evolved intoan offshore (zone B). During deposition of the upper part of zone Bconditions enabling coal forming were established in the northernparts of the SMLC. The sedimentary environment, in which the Kyjovseam was formed, was under the influence of the river flows, whichdecreased its salinity.

From the ash-yield study of the body of coal it follows that theKelčany River and the Hradiště Graben flow brought the clasticmaterial into the forming seam from the north and northeast,respectively. The sulfur increase in the middle and upper parts ofthe seam indicates a light salinity increase of the sedimentaryenvironment and the coming transgression.

Cyclic sedimentation was typical for zones C to E. The subsidenceaccelerated and the delta deposits were replaced by shallow-waterbasin deposits (Kováč et al., 1998). The VB opened and in the SMLC thesubsidence of the area between Steinberg fault zone and the Lužice–Lanžhot fault zone, which is interconnected with the Polešovice faultzone (Fig. 10), occurred.

The MCD and RBSP were forming. After transgression at thebeginning of zone F a swamp environment occurred. The Dubňanyseam was forming. The sedimentary environment in this period wasfreshwater palustrine. Main sources of the clastic material for theMCD were streams flowing into the area from the west and thenorthern branch of the Mistelbach delta (Fig. 10). In the western andsouthwestern part of the MCD this material flowed into the basin andby rippling it further spread eastwards and northeastwards.

The clastic material was drifted into the RBSP from the north— theHradiště Graben (Fig. 10). The sedimentary environment waschanging slowly. A slight sulfur increase in the vertical profile of theDubňany seam indicates the starting transgression which terminatedcoal-forming sedimentation. The coal-forming conditions wererestored several times in zone F. This fact is proven by the existenceof the six cycles with lignite or coaly layers in the Coal series. Thesedimentary cycles with the coal-forming sedimentation occurredalso in zone G — the Transitional series; however only in the centraland southern parts of the MCD. An increasing thickness of the grayclays in the Transitional series and the growing number of the cycleswith the coal layers in the southern part of the MCD show a shift ofsuitable conditions for the coal-bearing swamps towards the southand into the overlying rocks.

The Upper Pannonian was tectonically a rather calm time. Onlyduring the Dubňany seam formation a gradual splitting of the RBSPand MCD took place, as a consequence of the activated movements onthe Polešovice fault zone. The significant tectonic deformation of thelignite seams in the SMLC took place in the Pliocene, when the changeof the stress field in the VB rejuvenated tectonic zones of the pull-apart system towards the NE–SW and NW–SE to the NNW–SSE.

Acknowledgements

This research has been carried out within the project GA CR105/09/1090 financed by the Grant Agency of the Czech Republic, theproject ICT CZ.1.05/2.1.00/03.0082 (Institute of Clean Technologies formining and utilization of raw materials for energy use) supported bythe European Union, from the state budget of the Ministry ofEducation, Youth and Sports, and the project VEGA 1/02222/08 bythe Grant Agency of the Slovak Republic.

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