Pyroclastic kaolin coal–tonsteins of the Upper Carboniferous of Zonguldak and Amasra, Turkey

Ž .International Journal of Coal Geology 45 2000 39–53www.elsevier.nlrlocaterijcoalgeo

Pyroclastic kaolin coal–tonsteins of the Upper Carboniferous ofZonguldak and Amasra, Turkey

Kurt Burger a, Friedrich K. Bandelow b,), Gerd Bieg c,1

a Lothringenstrasse 8, D-45259 Essen, Germanyb Deutsche Montan Technologie GmbH, Am Technologiepark 1, D-45307 Essen, Germany

c DSK-Zentrallaboratorium, Wilhelmstrasse 98, D-44649 Herne, Germany

Received 7 March 2000; accepted 16 August 2000

Abstract

Ž .The existence of pyroclastic kaolin coal–tonsteins tonsteins, smectites from Upper Carboniferous strata of the coalmining region of Zonguldak and Amasra, north-western Turkey is reported. In the area of Zonguldak, tonsteins were

Ž . Ž .discovered within the seams Pic II and Piric Asma 5 Mine of the Kozlu Formation Westphalian A . In the area of Amasra,Ž . Ž .tonsteins occur in the seams Kalin and Tavan Tarlaagzi Mine of the Karadon Formation Westphalian B, C . Thin sections

were prepared to investigate mineral composition and texture; detailed descriptions are presented. Kaolinite is thepredominant mineral. In the Tavan tonstein montmorillonite–illite is also present. Pyrogenic phenocrysts prove that thetonsteins are alteration products of volcanic ashes. Therefore, a wide lateral distribution of these layers can be expected.These tonsteins represent very suitable stratigraphic markers in the Upper Carboniferous strata of northwestern Turkey.q 2000 Elsevier Science B.V. All rights reserved.

Keywords: Carboniferous; tonstein; tuff; chronostratigraphy; Turkey

1. Introduction

Ž .Over many years, kaolin coal -tonsteins havebeen discovered in various coal basins world-wide.

Ž . Ž .The papers of Hoehne 1964 and Burger 1985apresent overviews of these findings. Meanwhile, nu-merous authors have reported additional occurrences.

) Corresponding author. Fax: q49-201-172-1967.Ž .E-mail addresses: [email protected] F.K. Bandelow ,

Ž [email protected] G. Bieg .1 Fax: q49-2325-593-596.

In most cases, the tonsteins can be described as thinŽrock layers in the range of millimetres to several

centimetres, rarely exceeding more than a few.decimetres with wide lateral distribution and very

specific mineralogical–petrographical characteristics.They occur in coal beds, as well as in the surround-ing clastic beds, and commonly represent alteredvolcanic ash layers. It was demonstrated that theycan be used as perfect chrono-stratigraphic markersin order to identify and correlate coal seams in thecourse of exploration as well as exploitation activi-

Žties in the mining industry Burger, 1982, 1985b;

0009-2541r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.Ž .PII: S0166-5162 00 00021-5

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Ž .Fig. 1. Geological map of the Zonguldak–Amasra area simplified after Konyali, 1978 .

( )K. Burger et al.r International Journal of Coal Geology 45 2000 39–53 41

Zhou et al., 1989; Lyons et al., 1992; Tschernow-.janz, 1992; Bohor and Triplehorn, 1993; etc. . There-

fore, in the coal mining industry, tonsteins serve asan important basis for mine planning, in general, andfor production management, in particular.

Moreover, from a geo-scientific point of view,tonsteins are also of great importance as, in manycases, pyrogenic sanidine or zircon is included intheir mineral composition. Hence, radiometric agedeterminations can be carried out, provided these

Žminerals comply with certain prerequisites Burger et.al., 1997 . In comparison to litho-stratigraphic

andror bio-stratigraphic methods, radiometric resultsprovide absolute age data for chrono-stratigraphiccorrelation within the globally accepted geologic

Žtimetable Lippolt et al., 1984; Kunk and Rice, 1994;Claoue-Long et al., 1995; Burger et al., 1997; Hess´

.et al., 1999 .Tonsteins have been known from the Upper Car-

Žboniferous of NW Turkey since 1956 Pickhardt,.1956, 1957a,b . In the meantime, additional occur-

rences were discovered in the area. However, there isno detailed information published regarding theseimportant chrono-stratigraphic markers from themining region of Zonguldak and Amasra. This paperreports briefly about these findings.

2. Geological and stratigraphical overview

Structurally, the Carboniferous strata belong tothe Istanbul Zone, which is bounded in the west bythe West Black Sea Fault and in the east by the West

Ž .Crimean Fault Okay et al., 1994 . The strata occurcommonly in structurally isolated areas along thecoastline of the Black Sea, a belt stretching from thetown of Eregli in the west to the town of Cide in the

Ž .east Fig. 1 . Mining of the coal seams is mainlyconcentrated in the area around Zonguldak and to alimited extent in the Amasra–Bartin and Pelitova–Kurucasile areas.

The coal seams are part of the Upper Carbonifer-ous, which is subdivided into three stratigraphicstages: the Alacaagzi Formation, the Kozlu Forma-

Ž .tion, and the Karadon Formation Fig. 2 . Detailedinformation regarding the stratigraphy may be ob-

Ž .tained from the papers of Konyali 1978 , KereyŽ . Ž .1984 , Karayagit and Orhan 1997 .

The stratigraphic sections with the litho- and bio-stratigraphic correlation for the Zonguldak andAmasra–Bartin mining areas were adapted from

Ž . Ž .Kerey et al. 1986 Fig. 2 . About 90% of the UpperCarboniferous of these areas belongs to a limnicfacies whereas marine fauna were found only in thelower part of the Alacaagzi Formation. The strati-graphic correlation is based on characteristic rock

Ž .layers conglomerate, sandstone , on fossil flora andŽ .non-marine fauna Kerey et al., 1986 , on palynolog-

Žical findings Nakoman, 1978; Akgun and Akyol,¨. Ž1992 , and on coal petrographic results Karayigit et

.al., 1998 . Furthermore, the bio-stratigraphic investi-Ž .gations of Kerey et al. 1986 are also used as the

basis for the correlation with the international strati-graphic table of Western Europe. As a result, theUpper Carboniferous of NW Turkey comprises the

Ž .Namurian, Westphalian A, B, C, D and minorŽ .Stephanian, Fig. 2 .

3. Methods

The prominent petrographic properties of ton-steins provide a reliable basis to distinguish suchtonsteins macroscopically andror microscopicallyfrom common, detrital claystone beds in coal-bearingsequences. Principally, samples of tonsteins weretaken in order to undertake microscopic investiga-tions.

For this investigation, thin sections were producedperpendicularly to the bedding for the identificationof the mineral components. All samples were investi-gated by means of a polarizing microscope.

The available sample material was insufficient fordetailed XRD analyses. However, in order to provethe existence of tonsteins, semi-quantitative micro-scopic identification of mineral components is astandard tool in tonstein research. This method pro-vides sufficient qualitative information about rele-vant phenocrysts, which allows the characterisation

Ž .of tonstein types Bohor and Triplehorn, 1993 .The term tonstein refers to volcanic ashes, which

were deposited, altered, and conserved in coal seamsandror in fine clastic sediments of the roof and floorstrata.

( )K. Burger et al.r International Journal of Coal Geology 45 2000 39–5342

Ž .Fig. 2. Lithological and stratigraphical table of the Carboniferous of the Zonguldak–Amasra area after Kerey et al., 1986 showing thestratigraphic positions of the tonsteins.

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Ž . ŽFig. 3. Seam sections with the position and thickness of the tonsteins in the seams Pic II and Piric Zonguldak, Asma 5, Kozlu Formation as well as Kalin and Tavan Amasra,.Tarlaagzi, Karadon Formation .


4. Results

4.1. Stratigraphic position of kaolin coal–tonsteins

Petrography has shown that the newly identifiedtonsteins are pyroclastic tonsteins. They can be usedfor the identification and correlation of coal seams aswell as for the detailed stratigraphic classification ofthe strata in the coal mining area of NW Turkey. Fig.2 depicts the stratigraphic positions of the newlyintroduced kaolin coal–tonsteins.

In the Zonguldak area, samples of tonsteins wereŽtaken from the Kozlu Formation boundary zone of.Upper NamurianrWestphalian A . In the Amasra–

Bartin area they are located within the KaradonŽ . Ž .Formation Westphalian B to D Fig. 2 .

As far as we know, the first tonstein was discov-Ž .ered by Pickhardt 1956, 1957a,b in seam Kalin at

Tarlaagzi Mine, Amasra, in the course of a micro-scopic investigation of seam profiles. This tonsteinwas resampled during this investigation.

4.2. Petrographic examinations

4.2.1. ZonguldakrAsma 5 coal mineCoal seams of the Kozlu Formation are exposed

at Mine Asma 5 along the cross-cut to the south onthe y250 m level. The simple macro-petrographicdescription of the seams Pic II and Piric proved theexistence of tonsteins. Fig. 3 shows the position ofthe tonsteins within the seams. Table 1 provides anoverview of the mineral components and matrix on asemi-quantitative basis.

Due to the limited time available underground anddue to the mining conditions, only one sample from

Ž .each seam was collected by Bandelow 1989 . Else-where, tonsteins are extensive, which means thatfurther findings of tonsteins in the strata of theAlacaagzi, Kozlu, and Karadon Formations are likely,provided systematic investigations are performed.

4.2.1.1. Pic II — kaolin coal–tonstein. The finelygrained band is 5 mm thick and of dark grey colour

Table 1Mineral composition of the pyroclastic coal–tonsteins of the Zonguldak and Amasra coal fields

Mineral-composition Area pyroclastic tonsteins

TarlaagzirAmasra Asma 5rZonguldak

Tonstein Tavan Tonstein Kalin Tonstein Piric Tonstein Pic II

Ž .Thickness of tonsteins cm 20 2–3 3 0,5Ž .Kaolinite after biotite

Crystals, tablets, colums, fragments XX XXXX XXX XGraupen X O XX XX

Ž .Biotite fresh O XX XXX OŽ .Pseudomorphs of kaolinite after feldspar X XX XXX X

FeldsparAlbite XX O XX XXSanidine X XX O OPlagioclase X O O O

QuartzFragments X X XX Xa-, b-Quartz X X X O

Ž .Volcanic glass pseudomorph X O O OApatite X O X XZircon X X X O

Ž .Carbonate siderite XX O XX XPyrite X O O OMatrixKaolinitic XXXX O O XXMontmorillonitic–illitic XXXX O O OHumic O XXX XXX XX

Ž .Mineral constituents: XXXXsabundant dominant , XXXs frequent, XXssome, Xssporadic, Osnot detected.


Ž . Ž .Fig. 4. Pic II-tonstein, Kozlu Formation Westphalian A , Zonguldak Area, Amasra Mine 5, cross-cut south, y250 m level: A KaolinizedŽ .biotite, fragments of biotite, feldspar pseudomorphs, scattered quartz in kaolinitic matrix. One-fourth nicols. B Kaolinite graupen,

Ž .fragments of biotite and feldspar pseudomorphs, quartz in kaolinitic and humic matrix. One-fourth nicols. C Fragments of biotite andŽ .pseudomorphs of feldspar, fresh feldspar with marginal carbonatization, humic matrix. One-fourth nicols. D Fragment of feldspar

Ž . Ž .sanidine? . One-fourth nicols. E Apatite. One-fourth nicols.


Ž . Ž .Fig. 5. Piric-tonstein, Kozlu Formation Westphalian A . Zonguldak-Area, Asma Mine 5, cross-cut south, y250 m level: A Pleochroicbiotites, fragments of pseudomorphs of biotite and feldspar, microcristalline kaolinite graupe, sporadic quartz, microcristalline kaolinitic

Ž . Ž .matrix. One-fourth nicols. B Biotite as above. Feldspar pseudomorphs and magmatic quartz with inclusions. One-half nicols. C DifferentŽ . Ž .cutting positions of biotite, biotite with apatite inclusion right , scattered pseudomorphs of feldspar. One-fourth nicols. D Finely spotted

Ž .quartz left and right below , fresh feldspar and fragments of feldspar pseudomorphs in kaolinitic and humic matrix. One-half nicols.


Ž .Fig. 6. Kalin-tonstein, Karadon Formation Westphalian B, C, D . Amasra Area, Tarlaagzi Mine, Gallery — 35 m, cross-cut south at 520 mŽ . Ž . Ž .sample 2 : A Slightly bent column of kaolinite surrounded by kaolinized fragments of biotite in humic matrix. One-half nicols. B

Ž . Ž .Kaolinized biotites and feldspar pseudomorph centre in humic matrix. Longitudinal splitting of the kaolinite crystal right . One-fourthŽ . Ž .nicols. C Fragments of kaolinized biotite and sanidine crystals in humic matrix. One-half nicols. D Sanidine crystal with pronounced

cleavage cracks. One-fourth nicols.


with sharp contacts to the coal. It is a pyroclastickaolin coal–tonstein of pseudomorphic type afterfeldspar and after biotite with kaolin graupen. Pri-mary phenocrysts are feldspar, quartz, biotite, andapatite. The dominant phenocryst is kaolinized and

Žfresh feldspar in the form of angular fragments Fig..4C,D . Fragments of quartz in similar shape and size

Ž .occur less frequently Fig. 4A,C . The microscopi-cally fine-granular brown matrix is interstratified

Ž .with minute coal streaks and silica bands Fig. 4 .

4.2.1.2. Piric — kaolin coal–tonstein. The 3-cm-thick layer is a pyroclastic kaolin coal–tonstein, typepseudomorphic tonstein after biotite and feldsparwith sharp contacts to the coal. Phenocrysts areidentified as biotite, feldspar, quartz, apatite andzircon; b-quartz occurs sporadically. Biotites withcharacteristic lamellar structures are kaolinized vari-ably and frequently include minute apatite and zirconcrystals. Fragmental and idiomorphic apatite reachsizes of max 0.24 mm. The microscopically fine-grained brown matrix is interstratified with minutecoal streaks, carbonates, and lenticulated silica bands

Ž .predominantly at the coal–tonstein contact Fig. 5 .

4.2.2. AmasrarTarlaagzi coal mineTonsteins were sampled in the Kalin and Tavan

Ž .seams by Pickhardt 1956, 1957a,b . He traced thebands in the Kalin seam and he stated the followinglocations:

1. Gallery — 35 m NN, 150 m north-east,2. Gallery — 35 m NN, cross-cut south-east at 520

m,3. Gallery — 7 m NN, cross-cut south-east at 730

m.

The tonstein sample from seam Tavan was takenin an opening located at the north-eastern main roadof the underground coal mine. It was not practicableto map the seam section due to its thickness and the

Ž .roadway supports. Karayigit et al. 1998 refer to this20–25-cm-thick layer as a Aschieferton-like partingB.

4.2.2.1. Kalin — kaolin coal–tonstein. The fine-grained, grey-brown band, 2–3 cm thick, is a pyro-clastic kaolin coal–tonstein, type crystal tonstein af-ter biotite and feldspar. Phenocrysts are biotite,feldspar, and sporadic zircon. Fresh brown biotitewith lamination and clear sanidine with cleavagetraces are characteristic for this layer. The phe-nocrysts are embedded in humous matrix. The rela-

Ž .tive abundance approximately 3% of sanidine givesthe option for isotopic age-determination, providedan appropriately sized sample can be taken in the

Ž .coal mine Fig. 6 .

4.2.2.2. TaÕan — kaolin coal–tonstein. The 20 cmthick, massive layer is of light brownish to beigecolour and shows bedding due to clay balls in thecentre and difference in colour. Microscopic investi-gations have been carried out on thin sections per-pendicular to the bedding and on separated grainsamples because the layer disaggregates when itcomes in contact with water due to the dominating

Ž . Ž .proportion 90% of the clayey matrix Figs. 7–9 .The pyroclastic, mixed-layered kaolin coal–ton-

stein of the dense, low-grade crystal type depictsphenocrysts of biotite, feldspar, quartz, apatite, andzircon; siderite and apatite are of secondary origin.The cryptocrystalline matrix still shows remnant vit-

Ž .roclastic texture Fig. 8 . Thin coal streaks, cuticules,and kaolin-impregnated plant relics are striking. Thehigher birefringence of some kaolin crystals in theupper part of the band as well as at the margins ofsome albite feldspars indicates an incipient stage ofillitization. Fig. 9 shows further magmatic mineralsof the Tavan tonstein.

4.2.3. Mineral components and genetic interpreta-tion

Mineral composition of the investigated tonsteinsdemonstrate their volcanic origin and are conformingwith numerous markers, which have been investi-gated in coal basins all over the world. There is nodoubt that the kaolin coal–tonsteins Pic II, Piric,

Ž . Ž .Fig. 7. Tavan-tonstein, Karadon Formation Westphalian B, C, D . Amasra Area, Tarlaagzi Mine, main road north-east: A KaolinizedŽ .biotite with adsorption of iron in direction of the lamellae. Kaolinitic–montmorillonitic matrix with humic matter. One-fourth nicols. B

Ž .Crystals of kaolinite in columnar and fragmentary forms. Kaolinitic–montmorillonitic matrix with humic matter. One-half nicols. C AlbiteŽ .in kaolinitic–montmorillonitic matrix with carbonates and minute coaly particles. One-fourth nicols. D Oblique cut of a plant relic with

Ž .accumulated spores right , kaolinitic–montmorillonitic matrix. One-fourth nicols.


Kalin, and Tavan are altered volcanic ashes. Theauthors dispense with a renewed discussion about the

origin of these tonsteins and refer to Zhou et al.Ž . Ž . Ž .1989 , Lyons et al. 1992 , Tschernowjanz 1992 ,


Ž . Ž .Fig. 8. Tavan-tonstein, Karodan Formation Westphalian B, C, D . Amasra Area, Tarlaagzi Mine, main road northeast: A GlomeratedŽ .crystals of kaolinite derived from recrystallized volcanic glass. Kaolinitic–montmorillonitic matrix. One-fourth nicols. B Partly well

Ž .preserved vitroclastic stucture. Minute particles of glass were altered to kaolinite. One-fourth nicols. C Sanidine showing magmaticŽ .corrosion. Kaolinitic–montmorillonitic matrix with interspersed humic particles and carbonates. One-fourth nicols. D Magmatic quartz and

feldspar. One-fourth nicols.


Ž . Ž . Ž .Fig. 9. Tavan-tonstein, Karadon Formation Westphalian B, C, D . Amasra Area, Tarlaagzi Mine, main road north-east: A and B CrystalsŽ . Ž .of albite in vitroclastic and microcristalline–kaolinitic matrix. One-half nicols. C Magmatic quartz. One-fourth nicols. D Idiomorphic

Ž . Ž .zircon. One-fourth nicols. E Fragment of sanidine. One-fourth nicols. F Sanidine showing well developed cleavage cracks. One-fourthnicols.


Ž .Bohor and Triplehorn 1993 , and others. Volcanicashes have a widespread distribution and hence, theauthors expect that the layers may reach importancefor the local and regional stratigraphy and for thecorrelation of beds in the Zonguldak and Amasra–Batin coal fields.

4.3. Tuff layers in the coal-bearing strata

Beside the described tonsteins, three tuff horizonswith thicknesses of up to 7 m exist within the clasticsediments of the Karadon Formation of Zonguldak

Ž . Žand Amasra–Bartin Fig. 2 Karayagyit et al., 1998,.Fig. 2 . These pyroclastics have been known gener-

ally in the area for a long time, and referred to by theGerman term: ASchiefertonB.

The term Schieferton in the German mining in-Ždustry is used to address claystone and shale limnic

.andror paralic facies as described in the GermanŽStandard DIN Deutsches Institut fur Normung e. V.,¨

.1985 . Therefore, it is recommended that the termSchieferton in the mining region of ZonguldakrAmasra is relinquished and the general term tuff is

Ž .used instead Fig. 2 .A detailed petrographic investigation of these tuff

layers is strongly needed in order to achieve a reli-able chrono-stratigraphic correlation between themining areas of Zonguldak and Amasra. This elabo-ration, however, is reserved for later scientific ef-forts.

5. Conclusion and recommendation

Petrography has shown that the newly identifiedtonsteins are pyroclastic tonsteins. They can be usedfor the identification and correlation of coal seams aswell as for the detailed stratigraphic classification ofthe strata in the coal mining area of NW Turkey.

It is recommended that these pyroclastic layersshould be investigated systematically in order toimprove the stratigraphic table and the seam correla-tion in Zonguldak and Amasra. A detailed investiga-tion of the Upper Carboniferous strata could yieldmore tonstein findings. The proof of a precisechrono-stratigraphic marker would allow the correla-tion of the northwestern Turkish Upper Carbonifer-ous with the western Germanrwestern European

ŽUpper Carboniferous strata Lippolt et al., 1984;.Burger et al., 1997 with reliable data.

The presence of approximately 3% of the high-temperature feldspar Sanidine in the Kalin tonsteinfrom Amasra offers a good chance to tackle this task.However, particular efforts to obtain further samplematerial from Amasra in order to separate Sanidinefor the 40Arr39Ar age determination in the laboratoryof Geochronology of the University of Heidelbergfailed, so far. The quantity of sanidine in the sample

Ž .from Asma Zonguldak was not sufficient for anabsolute age dating. However, a larger sample masswould allow the separation of sufficient sanidine foran absolute age determination.

We like to recommend that Turkish coal geolo-gists in cooperation with the mining companiesshould initiate a new tonstein investigation cam-paign.

Acknowledgements

We like to express our thanks to W. Pickhardt,Essen, for his valuable information regarding hisformer investigations in TarlaagzirAmasra as wellas for the micro-photos shown in Fig. 6. Thanks toA.I. Karayigit, Beytepe–Ankara, for his informationand publications. Thanks to the management of Tar-laagzirAmasra for their permission to allow thesampling of tonsteins, which was carried out by K.Karakok, Gelsenkirchen.¨

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Pyroclastic kaolin coal–tonsteins of the Upper Carboniferous of Zonguldak and Amasra, Turkey