Palaeozoic terranes of the Balkan Peninsula in the framework of Pangea assembly

Palaeogeography, Palaeoclimatology, Palaeoecology 161 (2000) 151–177 www.elsevier.nl/locate/palaeo

Palaeozoic terranes of the Balkan Peninsula in the framework of Pangea assembly Slavcho Yanev * Geological Institute, Bulgarian Academy of Sciences, G. Bonchev Str. Bl. 24, BG-1113 Sofia, Bulgaria

Abstract The presence of three Gondwanan Palaeozoic terranes in the basement of the eastern part of the Balkan Peninsula is revealed by sedimentological, palaeoclimatological, biogeographical and magnetic data. The terranes are, from north to south, the Moesian, Balkan and Thracian terranes. They originate from different parts of Gondwana and Perigondwana. Regional data indicate an en echelon movement of the Moesian and Balkan (incl. Thracian?) terranes from the southern humid zone (in the Ordovician), through the southern arid zone (Moesian terrane during the Devonian) and the equatorial zone (during the Carboniferous), to the northern arid zone (in the Permian). Devonian convergence brought the Moesian terrane and the Dobrudgea periphery of Palaeo-Europe into collisional contact. The collision between the Moesian and Balkan (incl. Thracian) terranes took place during the Late Carboniferous and Permian and was related to the formation of the Variscan orogeny. Upper Palaeozoic molasse sediments blanket a palaeo-relief in predominantly continental environments. Both the collision of the Perigondwanan Moesian and Balkan terranes as well as their accretion to Palaeo-Europe are confirmed by the presence of a megaflora and palynomorphs, similar to those in other Pangea land areas of similar climatic and hypsometric conditions. This study attempts to improve the understanding of the palaeogeographic evolution of the Balkan area. It further tries to explain the regional processes and stages of formation of Pangea. © 2000 Elsevier Science B.V. All rights reserved. Keywords: collision; Gondwana; Palaeo-Europe; palaeogeography; Palaeozoic; Pangea

1. Introduction Until recently, data on the formation of Pangea from the Balkan Peninsula were entirely absent. The first recognition ( Yanev, 1989) of the presence of Gondwana Palaeozoic sediments in Bulgaria was later supplemented by further sedimentological, palaeoclimatic, palaeobiogeographical and palaeomagnetic data from Bulgaria and Yugoslavia ( Yanev, 1990, 1991, 1993b, 1997; Milicevic, 1992, 1993, 1994; Lakova, 1995; Yanev * Fax: +359-2-72-46-38. E-mail address: [email protected] (S. Yanev)

and Boncheva, 1997). These studies established the presence of three Gondwanan Palaeozoic terranes in the basement of the eastern part of the peninsula (from north to south) called the Moesian, Balkan and Thracian terranes ( Figs. 1–3).

2. Gondwanan origin of the Early Palaeozoic terranes U–Pb dating of zircons from Precambrian– Cambrian ophiolitic massive gabbro has yielded an age of 563±5 Ma, indicating Pan-African

0031-0182/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S0 0 3 1 -0 1 8 2 ( 0 0 ) 0 0 12 1 - 8

Fig. 1. Morphotectonic and palaeotectonic subdivision of Bulgaria and palaeogeography during the Permian. (A) Balkan Peninsula with geographic position of Bulgaria (crosshatched ). (B) Morphotectonic subdivision (after Bonchev, 1982). (C ) Early Palaeozoic terranes in the basement of the present-day territory of Bulgaria. (D) Permian palaeogeography: 1—zones without Permian sediments (source areas); 2—zone of the continental coarse clastic Lower Permian deposits and fine clastic Upper Permian sediments (Northern continental basin); 3—sabkha (halite-bearing) and lagoon (anhydrite-bearing) sedimentation; 4—Variscan orogen with very limited intramountain Lower Permian continental sediments; 5—zone of the Southern Upper Permian continental basin (5a—certain, 5b—probable); 6—distribution of Lower Permian volcanic and pyroclastic rocks; 7—marine sedimentation (after Malyakov and Bakalova, 1978), probably in allochthonous position or present as olistostroms; 8—cross sections.

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affiliation characteristics of the development of Gondwana ( Van Quadt et al., 1998). A number of lithologic and palaeoclimatic data indicate that the Balkan and Moesian terranes were within the palaeolatitudal range of Gondwana and Perigondwana during the respective periods. The Upper Ordovician succession in the Balkan terrane contains diamictites that are interpreted as glacialmarine deposits ( Yanev, 1989). They originated from latitudes south of 40°S. Chamosites and goethitic iron oolites are found in Ordovician and Devonian deposits of the Stara Planina Mountain in the Balkan terrane ( Yanev, 1991) and in Silurian rocks of the Istanbul zone ( Ketin, 1983). Their presence indicates deposition in the humid zone of intermediate latitudes. Middle Devonian to Lower Carboniferous turbiditic sediments from the Balkan terrane contain psilophytic plant fragments that indicate a humid climate. During the Middle Devonian–Early Carboniferous, however, gypsum and anhydrite, indicating an arid climate, were formed along the eastern margin of the Moesian terrane (in Bulgaria and Romania). Recently, the palaeobiogeographical affiliations of a number of fossils from both terranes with the Gondwanan provinces have been clarified. They include: $ Llanvirnian acritarchs from the Balkan terrane: Dicrodiacrodium normale Burmann; Veryhachium sartbernardense Martin; V. valiente (Cram. et al.), etc. ( Kalvacheva, 1986); $ Late Arenigian acritarchs from the Balkan terrane: Acanthodiacrodium cf. intercalarae Burmann; A. cf. uniforme Burmann; A. cf. vavrolorae Cramer and Diez; Coryphidium cf. milada Cramer and Diez; C. cf. mimitum Cramer and Diez; Striatotheca cf. principalis Burmann; S. cf. queta (Martin), etc. ( Kalvacheva, 1984); $ Llandoverian–Wenlockian acritarchs from the Balkan terrane: Neoverytachium carmine Cramer, etc. ( Kalvacheva, 1978); $ Llanvirnian–Llandeillian trilobite association: Cyclopige prisca Barr.; C. prisca var. longicephala Klonc.; C. rediviva (Barr.); Ectillaenus cf. highesi (Hicks) (Spassov, 1960); $ Pridolian chitinozoans from the Moesian terrane: Ancyrochitina lybiensis (Jaglin); A. floris (Jaglin); A. regulatis ( Taug. and Jekh.);

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Bursachitina gordonensis (Cramer); B. krizi (Paris and Laufeld ); Angochitina crassispina pelosa (Schweinberg); Fungochitina kosovensis (Paris and Kriz); Kalochitina lorensis (Schweinberg); Margachitina saretensis (Boumenjel ) (Lakova, 1995); $ Lochkovian chitinozoans from the Moesian terrane: Angochitina chlupaci Paris and Laufeld; Fungochitina lata (Taug. and Jekh.); Eisenakitina tougourdeavi (Rausher and Doubinger); Cingulochitina plusquellechi Paris; Ancyrochitina asterigis Paris; Lagenochitina naviculata Taug. and Jekh.; Bursachitina cf. oviformis Eis. (Lakova, 1995); $ Lochkovian molluscs from the Balkan terrane: Hercynella cf. bohemica Barr.; H. sp. aff. nobilis Barr.; Neklania obtusa Barr.; N. resecta (Barr.); Patrocardium aff. seminotum (Barr.); Stylonema aff. solvens Per.; Plectodonta sp. ex gr. Pl. comitans (Bar.) and the tentaculite Novakia intermedia (Barr.) (Pribyl and Spassov, 1960); $ Middle Devonian miospores from the Moesian terrane, more precisely Geminospora lemurata (Boncheva et al., in press). The Ordovician and Silurian acritarchs clearly relate to the cold-water peri-Gondwanaland (Mediterranean) palaeoplankton province ( Kalvacheva, 1990). The Middle Ordovician trilobite association is typical for the Bohemian province ( Yanev, 1991). The Upper Silurian and Lower Devonian chitinozoan assemblages from the Moesian terrane are interpreted as belonging to the Afro-South American province (Lakova, 1995). The molluscan fauna correlates with Bohemian genera and species (Pribyl and Spassov, 1960). Similar Bohemian trilobite and molluscan faunas of the Ordovician and Devonian were assigned to the peri-Gondwanaland province (Chlupac, 1982; Gutierrez Marco and Rabano, 1987 and other authors). The Middle Devonian association of miospores with Geminospora lemurata shows that the Moesian terrane is located in the West-Gondwana province, as indicated by Loboziak and Street (1995). Palaeomagnetic data exist only for the Balkan terrane. The investigations by Milicevic (1994) of the Serbian part of the terrane indicate a position between 50 and 29° south (with an average of 39°)

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Fig. 3. Palaeozoic stratigraphy of the Moesian terrane (after Yanev, 1993a,b).

during the Tremadocian and an average of 38° south for the Late Ordovician (Caradocian– Ashgilian). Milicevic (1992) located the formation of the Palaeozoic turbiditic sediments of the Belava, Vlasina, and Greben Mountains within a zone of 10–15±3° southern palaeolatitude, and

data from the Suva Planina Mountains show that similar sediments were formed close to the palaeoequator. The age of the flysch section in the Balkan terrane is latest Middle Devonian to Visean. According to Krstic and Maslarevic (1989), the turbiditic sediments become progressively younger

Fig. 2. Pre-Palaeozoic lithostratigraphy of the Thracian (‘Rhodope’) terrane (after Kozhoukharov, 1991, in Yanev, 1993a). Symbols for Figs. 3 and 4: 1—glaciomarine sediments (dropstones); 2—continental clastics; 3—pelites; 4—sandstones; 5—conglomerates; 6—carbonates; 7—evaporites; 8—volcanics; 9—coal; 10—turbidites; 11—silicites; 12—olistostroms; 13—red beds.

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from the Southeast to the Northwest (from Belava, Vlahina and Greben Mountains to Suva Mountain). Therefore, it is believed that the palaeomagnetic data from the first area characterise the Devonian part of the section, while those from the Suva Mountain are from the Carboniferous portion. Some data from the confirmed marine Lower Carboniferous sediments also indicate palaeolatitudes close to the palaeoequator or slightly south of it (Milicevic, 1993). The palaeomagnetic data suggest that sedimentation during the Permian occurred in the northern arid zone at about 8–14°N (Nozharov et al. 1980; Milicevic, 1993).

3. Differences between the Early Palaeozoic terranes Non-metamorphosed Lower Palaeozoic rocks are absent from the Thracian terrane. The most important differences between the Palaeozoic sedimentary rocks from the Moesian and Balkan ter-

ranes are: 1—The presence of Arenigian olisthostromes in the Balkan terrane, and the large total thickness of the Ordovician succession reaching up to 4700 m in contrast to 510 m of quartzites and argillites in the Moesian terrane; 2—Chertyshaly sedimentation during Silurian in the Balkan terrane and limely-shaly in the Moesian terrane; 3—Completely different lithology of the Devonian section in the two terranes: in the Balkan terrane, the sequence begins with calcareous and cherty rocks and ends with siliciclastic rocks, whereas in the Moesian terrane, siliciclastics in the lower part are overlain by calcareous rocks. Calcareous and pelitic–siliciclastic Lower Carboniferous rocks (up to 2800 m thick) are present in the Moesian terrane, whereas these rocks are absent in the Balkan terrane (see Figs. 4 and 5). Although the Moesian, Balkan, and Thracian terranes were all part of Gondwanaland, their different lithologies indicate an origin from different parts of Gondwana and Perigondwana. The undoubtedly Gondwanan terranes in Europe (Bohemia, Spain, Sardine, etc.), North Africa, and

Fig. 4. Palaeozoic lithological columns of the Moesian terrane (after Haydoutov and Yanev, 1997).

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Fig. 5. Palaeozoic lithological columns of the Balkan terrane (after Haydoutov and Yanev, 1997).

South America have been found to show lithological features similar to the Lower Palaeozoic of the Moesian and Balkan terranes ( Yanev, 1997). However, lithological and fossil similarities to sec-

tions of Baltic origin are lacking, for example, between the Lower and Middle Palaeozoic in the Moesian Gondwanic terrane and the nearby Lavrassian Scythian platform (Gorak et al., 1985).

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4. Migration of Early Palaeozoic terranes and collisional processes The sedimentological, palaeoclimatologic and palaeomagnetic data show en echelon movement

of the Moesian and Balkan (incl. Thracian?) terranes from the southern moderately humid zone in the Ordovician, through the southern arid zone—the Moesian terrane during the Devonian— and the equatorial zone during the Carboniferous

Fig. 6. Palaeozoic lithological columns of the Moesian terrane (after Haydoutor and Yanev, 1997).

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Fig. 7. Scheme of the position of the East European (‘Russian’) Craton (RC ), Moesian terrane (MT ) and Balkan terrane (BT ) with respect to the equator during the Ordovician, Silurian, Devonian, Carboniferous and Permian (after Yanev, 1993a,b).

to the northern arid zone in the Permian (see Figs. 6 and 7). Late Devonian convergence put the Moesian terrane and the Dobrudgea at the periphery of Palaeo-Europe in a collisional contact. Evidence for this tectonism is some marginal facies, variations in the rock thickness in the Devonian and in the Lower Carboniferous successions of the Moesian terrane. Furthermore, some well data indicate folding and thrusting ( Yanev and Boncheva, 1997). The collision between the Moesian and Balkan (incl. Thracian) terranes postdates the Early Carboniferous and continued during the Late Carboniferous and Permian based on sedimentological and palaeontological evidence ( Tenchov, 1975; Janev, 1988; Yanev and Dimitrova, 1997) and supported by synchronous acid, collisional type magmatism ( Tchounev and Bonev, 1975). The Late Palaeozoic evolution of the region is closely related to the Variscan collisional orogeny, which was the result of the prolonged intercontinental collision between fragments of the Gondwanaland and Laurussian continental massifs. Accretion of the Moesian, Balkan and Thracian terranes to each other and to Laurussia is supported by the occurrence of megaflora and palynomorphs similar to those in Germany, France, Turkey, and all Pangaea land areas of similar climatic and hypsometric conditions (see Schirmer, 1960; Tenchov, 1966, 1975; Nikolov et al., 1988; Yanev and Dimitrova, 1997 with Hoffmann et al., 1989; Cassinis et al., 1992; Van Adrichem Boogaert et al., 1995). The Upper

Fig. 8. Distribution of selected Upper Palaeozoic schematic stratigraphic sections and columnar sections, and symbols for Figs. 9– 11. Symbols: 1—breccia; 2—conglomerates; 3—sandstones; 4— siltstones; 5—shales; 6—limestones; 7—dolomites; 8—anhydrites; 9—halites; 10—coal; 11—volcanics; 12—volcanoclastics; 13—carbonate concretions; 14—anhydrite concretions; 15— unconformity; 16—stratigraphic gaps; 17—erosional surface; 18—30—sedimentary structures: 18—massive; 19—lamination; 20—large-scale cross-stratification; 21—small-scale cross-stratification; 22—cross-wave stratification; 23—flaser bedding; 24— lenticular bedding; 25—channels; 26—vegetal palaeosol; 27— mud cracks; 28—bioturbation; 29—ripple marks; 30—drop marks; 31—41—fossil content: 31—macroflora; 32—microflora; 33—plant branches; 34—foraminifer benthonic; 35—algae; 36— bryozoans; 37—crinoids; 38—echinoderms; 39—conodonts; 40—brachiopods; 41—goniatites; 42—anchimetamorphism; 43— borehole data. Depositional environments: 1—continental: 1a— fluvial; 1ap—alluvial plain; 1br—braided river; 1c—coarsegrained; 1f—fine-grained; 1p—proluvial; 1pf—proluvial finegrained; 1pl—proluvial lake; 1b—continental basin; 1l—lacustrine; 1m—marshland; 2–3—transitional: 2a—lagoonal sulfates, etc.; 2h—sabkha-halite; 3—deltaic; 4–6—marine; 4–5—shallow marine, clastics; 5—shallow marine, carbonates.

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Table 1 Distribution of sporomorphs in the different Upper Permian formations from North Bulgaria (after Schirmer, 1960; Yanev, 1993a) Formations

Microphytofossils

1

2

3

+

+ + + + + + +

+

+ + + +

+ + + +

+ +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

4

+

+ + + + +

+ +

+

+ + + + + + + +

+ + + + + +

Lueckisporites virkkiae (pot. et Kl.) Gr. Lueckisporites globosus Kl. Lueckisporites platysuccoides Schaar. Lueckisporites hialinus Schaar. Taeniaesporites noviaulensis Lesch. Taeniasporites alatus Kl. Taeniasporites ortisei Kl. Taeniasporites samoilovichii pantii ( Kl ) Jons. Striatites richteri ( Kl ) Jons. Striatites minor Kl. Illinites unicus Kosan. Illinites delassaucei (Pot. & Kl.)Gr. Limitisporites latus Lesch. Limitisporites rectus Lesch. Platysaccus papilionis Pot. et Kl. Klausipolenites schlaubergeri (Pot & Kl.) Jons. Klausipolenites vestitus Jons. Caytonipolenites latus Maedl. Claytonipolenites reductus Maedl. Falcisporites zapfei Lesch. Nuskoisporites klausi (Greb.) Gardenosporites heisseli Kl. Gardenosporites moroderi Kl. Paravesicaspora splendens (Lesch) Kl. Alisporites ovatus (Blame & Hen.) Jons. Vittatina cinninnata Lub. Vittatina zaneri Efr. Vittatina costabilis Wills. Vittatina vittifer Lub. Striatodiplopinites sp. Azonalettes sp. Pityosporites sp. Sphedripites sp. Chozdonsporites sp. Decussatisporites sp. Ginkgocycadophytes sp. Cordaitina sp. Potoniesporites sp. Calamospora sp. Nuskoisporites gondvanensis Pot. & Kl. Taeniasporites antegnus Lesch. Labisporites granulatus Lesch. Vittatina striata Lub. Protodiploxypinus elongatus Pemphygaletes striatus Jugosporites sp. Ginctaceapollenites sp. Gnetaceapollenites sp. Vittatina sp. Striatites sp. Nuskoisporites sp. Lueckisporites sp. Kraeuselisporites sp.

Formations: 1: Mirovo 2: Vetrino 3: Targovishte 4: Totleben

Fig. 9. Selected columnar sections of the Upper Palaeozoic of North Bulgaria (distribution and symbols as in Fig. 8).

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Fig. 10. Selected columnar sections of the Upper Palaeozoic of Stara Planina Mountain ( Variscan orogen zone) (distribution and symbols as in Fig. 8).

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Fig. 11. Selected columnar sections of the Upper Palaeozoic of South Bulgaria (distribution and symbols as in Fig. 8).

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Palaeozoic sediments rest on a palaeo-relief and are predominantly continental deposits (Maslarevic, 1961; Janev, 1964, 1989; Protic, 1967; Yanev, 1981, 1983). Upper Palaeozoic sediments are characterised by orogenic and postorogenic molasse ( Yanev, 1981; Nastaseanu, 1987). These sediments cover large portions of the suture zone between the two former megacontinents during the formation of Pangea (Lu¨tzner, 1988; Pokorski, 1988b; Ziegler, 1989; Yilmaz et al., 1996).

5. Upper Palaeozoic changes The available biostratigraphic data from the Upper Palaeozoic succession in the Balkan area are scarce, due to the continental character of the sediments ( Yanev, 1981, 1982, 1983). The known mega- and microfossils (for the Upper Permian palynomorphs, see Table 1) are, however, comparable to the associations from Central and West Europe (Hoffmann et al., 1989; Cassinis et al., 1992; Van Adrichem Boogaert et al., 1995). The characteristics of the sedimentary succession allow reconstruction of the overall framework of this part of the Pangea, including changes in sedimentation and tectonic style in the region ( Figs. 8–11). 5.1. Carboniferous The Carboniferous sediments of Bulgaria show considerable facies variations (Fig. 12). In SW Bulgaria, the very incomplete upper Tournaisian succession (column 1) consists of interbedded shales, subordinate sandstones and rare limestones, with a chert horizon in the middle of the succession. The sediments reflect deposition in marine shelf environments. In NW Bulgaria (column 2),

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the Middle Devonian is overlain by polydetrital and algal-foraminifer limestones of shallow mainly infralittoral origin. Similar sediments and depositional conditions persisted until the Middle Visean, gradually advancing to NE Bulgaria (column 3) where they overlie a prominent Middle–Late Devonian erosional surface. During the Late Visean, tectonic activity in the Balkan and Moesian terranes caused subaerial exposure and subsequently a depositional break in the Balkan terrane. This became a source area that supplied terrigenous material to the depositional basins of the Moesian terrane. The marine environments retreated to the east at the end of the Visean, and a very thick siliciclastic succession was formed in a delta system located in the southern Dobrudgea ( Fig. 12, columns 3 and 4; Fig. 13). Swampy delta plains persisted while the system prograded to the west. In the southern Dobrudgea, an initially paralic and, from the Namurian to the Westphalian, limnic siliciclastic and coal-bearing sediments were deposited in fluvial and lacustrine environments ( Yanev, 1982). From the middle Carboniferous, the Variscan mountain chain crosses the Balkan Peninsula. In intramountain valleys, limnic, clastic and coal-bearing sediments were deposited on river plains and in lake systems during the Namurian and Westphalian ( Fig. 12, column 5). According to some reconstructions, similar sediments continued to be deposited until the Late Stephanian ( Fig. 12, columns 6 and 7). 5.2. Permian After a reorganisation of the basins during the earliest Permian, partly uplifted molasse sediments became eroded to various degrees and formed a siliciclastic source area. New areas of deposition

Fig. 12. Carboniferous System in Bulgaria (after Janev, 1996) I. Lithological columns: 1—Kraishte; 2—Gomotartsi; 3—South Dobrudgea; 4—Svogue; 5—Lyutadzhik; 6—Belogradchik (for the distribution, see scheme IV ). Symbols: 1—lydites (cherts); 2— limestones; 3—argillaceous limestones; 4—wave-shaped and nodular limestones and marls; 5—conglomerates; 6—breccia; 7—sandstones; 8—sandstones with fragments of coal; 9—siltstones; 10—argillites and shales; 11—coal. II—IV. Lithological and palaeogeographic schemes of Bulgaria during the Carboniferous: II—Upper Tournaisian: 1—dry lands; 2—zone of chert-carbonate-clayey sedimentation; 3—zone of shallow water marine carbonate sedimentation; III—Upper Visean: 1—dry land; 2—zone of fine clasticclayey marine sedimentation; IV—Upper Carboniferous: 1—outcrops; 2—zone of continental intramountain sedimentation; white— absence of Upper Carboniferous deposits or Meso-Cenozoic cover; C1—Lower Carboniferous; N+W—Namurian and Westphalian; S+P—Stephanian and Permian.

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Fig. 13. Carboniferous in North Bulgaria. (A) Scheme showing equal thicknesses of Carboniferous sediments in North Bulgaria based on geological and seismic data (after Yanev et al., 1991). (B, C ) Palaeogeography of South Dobrudgea: (B) during the Late Visean; (C ) during the Westfalian (after Yanev, 1985). Symbols. A: 1—absence of Carboniferous sediments; 2—lines of equal thickness; 3—boundary between the Balkan and Fore-Balkan; 4—boundary between the Fore-Balkan and the South Moesian periplatform area; 5—faults with strike and dip; 6—faults (certain and uncertain); 7—cryptoruptures. B and C—depositional environments: 1—marine; 2—shallow marine, coastal; 3—deltaic; 4—continental (fluvial, alluvial plain over the former delta); 5— lowland (sediment bypass, partially sediment source); 6—Dobrudgea coal basin; 7—supposed direction of the palaeoriver; 8— supposed boundary between the sea and delta during the Namurian (N ) and Westphalian ( W ).

were formed, each with their own specific character reflecting the palaeogeographic situation ( Figs. 1D and 18). In many localities, deposition persisted from Late Stephanian to Early Rotliegend times. However, there is no evidence of such sediments in wells drilled at the borders of the Moesian terrane, suggesting that the main part of the terrane

was uplifted and eroded during the Stephanian. In the Balkan terrane two types of Stephanian— Lower Rotliegend molasse are known: (1) in the internal part and at the immediate peripheries of the orogen forming intramountain deposits ( Fig. 14, columns 11–15, 20–23, 27); and (2) between the Variscan orogen and the uplifted

Fig. 14. Schematic geological columns of the Permian System in Bulgaria (based on outcrops and borehole data). Symbols: 1— conglomerates; 2—breccia; 3—concretions: a—limy, b—anhydritic; 4—gravelites; 5—sandstones; 6—siltstones; 7—argillites; 8— coal; 9—argillaceous limestones; 10—dolomites; 11—anhydrites; 12—halites (salt); 13—andesites; 14—trachytes; 15—latites; 16— dacites; 17—xenotuffs; 18—tuffs; 19—tuffites; 20—ignimbrites. Sketch: distribution of sections.

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Rhodope terrane ( Fig. 14, columns 24–26, 28). Some of the occurrences of the first group are located at the periphery of the collisional orogen where the limiting faults provided channels for volcanogenic materials (see also the cross-sections in Fig. 1). The siliciclastics of the molasse successions are dominated by material from the Balkan terrane, which was the more uplifted part of the accretional prism. Limited quantities of carbonate material from the Moesian terrane also indicate that a system of foreland depressions was developed along parts of the suture zone between the terranes.

6. Lithostratigraphy of the Permian System In the Moesian terrane, two lithostratigraphic groups, corresponding to the Lower and Upper Permian, have been defined according to the requirements of the International Stratigraphic Code ( Yanev, 1992a, 1993a). The lower group, named the North-Bulgaria Group ( Fig. 15), consists (from below) of an unnamed variegated claydominated formation, the Nanevo and Komunari Formations (Lower Rotliegend), the Severtsi Formation ( Upper Rotliegend), and the Bdin and Dolna Zlatitsa Formations (undivided Rotliegend). The Nanevo Formation is further subdivided into the Kamen Bryag, Bayachevo, and Balgarevo Members and the Bdin Formation into the Bononia, Deleyna and Rasovo Members ( Yanev, 1992a). The variegated clay-dominated formation at the base comprises red and grey– green sandstones, siltstones and shales ( Fig. 14, the bottom of column 10). The Nanevo Formation, from the base to the top, consists predominantly of various medium-acid volcanics and tuffs, the Kamen Bryag Member, conglomerates and small amounts of siltstones with tuffs and redeposited volcanic material, named the Bayachevo Member, and argillaceous shales with some mixed gravelsandy rocks, the Balgarevo Member ( Fig. 14, column 10 and 17). Polygenetic breccia-conglomerates, conglomerates, red and black–greyish sandstones and siltstones alternate in the Komunari Formation (psephitic rocks laterally pinch out) (Fig. 14, column 18). The Bdin

Formation is dominated by conglomerate with carbonate fragments (with some admixture of volcanic fragments, mainly in the Bononia Member) with the Deleyna Member (Fig. 14, columns 2 and 3) being of poorly sorted shale composition. The Dolna Zlatitsa Formation consists of brown–reddish, mainly massive argillites and clayey siltstones with rare interbeds of siltstones and fine-grained sandstones (Fig. 14, column 16). Breccia conglomerates, sandstones and siltstones (small amount of argillites), psephite-bearing clasts (including coal ), low-metamorphic and volcanic rocks alternate in the Severtsi Formation (Fig. 14, column 6). The Severtsi Formation overlies an erosional surface, whereas the other formations interdigitate laterally with a correlation between the three separate members (Fig. 15). The Komunari Formation occurs along the southern margin of the eastern part of North Bulgaria, the Dolna Zlatitsa Formation occurs in the Tarnovo Depression and the areas around it, the Nanevo Formation lies in the Bulgarian Coastal Dobrudgea and around the NorthBulgarian Swell, and the Severtsi Formation occurs in NE Bulgaria. The following five formations form the Upper Permian Lower Danube Group: Mirovo Formation, Vetrino Formation (with the Zhitnitsa and Hrabrovo Members), Targovishte Formation (with the Trastikovo and Bezvoditsa Members), Totleben Formation, and Sokolare Formation. The Mirovo Formation consists of greyish black shales and some siltstones, marls, dolomites, and anhydrites (Fig. 14, the bottom of column 19). The Vetrino Formation is composed of alternating argillaceous sediments and evaporites (mainly halite, anhydrite, and dolomite), with a few silty psammites and limestones. The Hrabrovo Member comprising mainly evaporites and abundant halite–agillite breccia ( Fig. 14, column 19) interdigitates laterally with the Zhitnitsa Member consisting predominantly of fine-grained siliciclastic sediments and some evaporites (Fig. 14, column 18). The Targovishte Formation consists of massive and poorly sorted red silty-shaly sediments (mudstones) and fine-grained sandstones, and contains some anhydrite and carbonate concretions ( Fig. 14, column 2, 4, 9, 10, 16, 17 and 18). A

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Fig. 15. Relationship between the different lithostratigraphic units in North Bulgaria: (A) generalised; (B) between the formations and members in the Lower Permian.

sequence of layered anhydrites and dolomites is defined as the Bezvoditsa Member ( Fig. 14, column 18). Sections composed entirely of chemical sediments are included in the Trastikovo Member. The Totleben Formation is an alternation

of thin-bedded, well-sorted shales, siltstones and sandstones of various colours—whitish, reddish brown, grey–greenish, etc.—changing from one bed to the other (Fig. 14, column 4, 9 and 10). The Sokolare Formation differs in its coarser but

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better sorted rocks: sandstones, gravellites, immature conglomerates with subordinate interbeds of hyporocks ( Fig. 14, column 7). The Mirovo, Vetrino, Targovishte and Totleben Formations are in superpositional relationship without being ubiquitously spread. The Trastikovo and Bezvoditsa Members interdigitate laterally, and in some places, the Bezvoditsa Member is stratigraphically located at a higher level within the Targovishte Formation ( Figs. 1 and 15). At present, the Mirovo and Vetrino Formations are known from the Provadia area (Moesian terrane, NE Bulgaria near the Black Sea coast). The Totleben Formation extends to the east of the Vit River, and the Sokolare Formation is ubiquitous in the eastern part of Dobrudgea. The laterally most widespread unit is the Targovishte Formation extending from the town of Vidin to the Black Sea coast (Fig. 16). In North Bulgaria, variations in facies and palaeogeography were rather large during the early Permian, whereas the Upper Permian sections show a more simple picture: a continental basin developed with lateral transitions into lagoonal or sabkha environments (Fig. 1, columns 2, 3 and 4 in Fig. 9). Lower Permian sedimentation along the southern periphery of the Moesian terrane started in isolated, oxygen-rich lakes. Volcanic and pyroclastic material was locally deposited. Later, more

widespread but still spot-like proluvial and proluvial-basin sedimentation took place. Isolated subbasins were filled with material supplied from the calcareous Lower Carboniferous and Devonian rocks (Bdin Formation, especially in its NW part). Zones of more uniform continental-basin deposition of fine-grained sediments persisted between the Targovishte–Popovo area and the eastern part of the Tarnovo district (see the thicknesses in Fig. 17). The North-Bulgarian Uplift is surrounded by a zone of pyroclastic and coarse terrigenous sediments. From the south, coarser clastic material derived from low-metamorphic and Lower and Middle Palaeozoic siliciclastic sediments of the Balkan terrane were brought into the continental basin. The Upper Permian deposits along the southern periphery of NW Bulgaria consist of psammitic rocks of the Rikovska Formation that were formed in a delta adjacent to the continental basin in the north. The distribution of the Targovishte Formation documents an arid continental basin at least in one third of North Bulgaria including the area to the east and to the west of the North-east Bulgarian dryland. During the deposition of Totleben Formation, the basin persisted and probably prograded laterally within a more humid climate. The coarser clastic Sokolare Formation marks the north-eastern periphery of the basin (the neighbourhood of the Dobrudgea palaeo-dryland ) at the end of the Permian.

Fig. 16. Palaeogeographic scheme showing the distribution of the different lithostratigraphic formations in North Bulgaria. Symbols: 1—Pre-Permian basement; 2—Lower Permian basement; 3–9 Distribution of different Upper Permian units: 3—Targoviste Formation; 4—Bezvoditsa Member; 5—Vetrino Formation; 6—Hrabrovo Member; 7—Totleben Formation; 8—Sokolare Formation; 9— Rikovska Formation.

Fig. 17. Scheme showing the main lithostratigraphic units of the Permian in Germany, compared in the text with the Bulgarian units (after Hoffmann et al., 1989).

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7. Comparison of continental Permian sedimentation in Bulgaria and Western Europe Similarities exist between the Upper Palaeozoic successions in Bulgaria and in Germany, Italy, Austria, France, Spain, Poland, and Yugoslavia. Distinct similarities are obvious in sections from the orogenic zone of the Balkan and Moesian terranes in Bulgaria ( Tenchov and Yanev, 1963; Yanev and Tenchov, 1976, 1978; Yanev, 1981) and the Thu¨ringer Wald in Germany (Lu¨tzner, 1988) and betwen sections from the Moesian terrane and the North-German depression and the Polish Lowland (Parasciv, 1982, 1989; Pokorski, 1988a,b, 1989; Hoffmann et al., 1989; Yanev, 1992a, 1993a; Van Adrichem Boogaert et al., 1995). Comparable successions include the Gehren Formation in Thu¨ringer Wald, Germany, and the pre-Stephanian formations at the villages of Granichak and Zverino in Bulgaria (Fig. 10), the Manebach Formation in Germany and the Zelenigrad and Buk Formations in Bulgaria, the Goldlauter Formation in Germany and Vranska and Smolyanovtsi Formations in Bulgaria ( Yanev, 1981), the Rotterode Formation in Germany and the section north of the town of Sliven, Bulgaria (Zhukov et al., 1976), and the Tambach and Brauchwitz Formations in Germany and the Vranskikamak and Midzhur Formations in Bulgaria. Areas of the Moesian Plate situated far from the orogen show similarities to the Northern German Depression. The Altmark Subgroup (the so-called ‘volcanic Autunian’) of Germany may be compared with the Nanevo Formation, the Mueritz Subgroup (the ‘sedimentary Autunian’) with the Komunari Formation, the Parachim Formation with the Severtsi Formation, the Mirow Formation with the upper part of the Dolna Zlatitsa Formation, and the Elbe Subgroup with the Targovishte Formation. There is also some resemblance between the Zechstein succession in Germany and the Upper Permian salt-bearing sediments around Provadia in Bulgaria. Evaporitebearing sediments are, however, quite limited, being known only from the subsurface areas north of the town of Varna ( locality 9 in the inset of Fig. 14) and near of the town of Provadia ( locality

18 in the inset of Fig. 14). It is suggested that marine Permian sediments exist further to the east in the Black Sea area (Malyakov and Bakalova, 1978; Trifonova and Boyanov, 1986). There are several unsolved problems concerning the correlation between the Bulgarian and European sections. Bulgarian sediments of proposed Late Permian age based on limited palaeontological data show lithological similarities to the so-called ‘Upper Rotliegend II’ or ‘Saxon II’ in Germany. Although the similarity in trends of sedimentation of the compared regions is obvious, it remains unclear as to whether it occurred synchronously or reflects the incomplete biostratigraphic information. However, it should be noted that part of the Upper Rotliegend II (Saxon II ) in Central Europe has been referred to the Kazanian and Tatarian (Hoffmann et al., 1989; Van Adrichem Boogaert et al., 1995) and then the terms Rotliegend and Zechstein have largely a facial meaning.

8. Palaeotectonics Palaeotectonic events are documented by certain discordances related to Caledonian (?) and Variscan structures, stratigraphic gaps, and several specific features in siliciclastic rocks ( Yanev, 1981, 1992b, 1996). Ten major hiati have been recognised in the dated non-metamorphosed Palaeozoic sections: near the end of the Ordovician, pre–Late Devonian, pre-Late Tournaisian, Late Visean, preLate Carboniferous, Westphalian–Stephanian boundary, at the beginning of Early Rotliegend, Early Rotliegend–Late Rotliegend boundary, between Early Rotliegend I and Late Rotliegend II (sensu Van Adrichem Boogaert et al., 1995), and at the Early–Late Permian boundary. Besides these, in North-east Bulgaria (Moesian terrane), six intraformational erosional events have been identified in the Devonian, two in the paralic Upper Visean deposits and three in the continental Late Carboniferous of the South Dobrudgea (see column 3, Fig. 12). Four regional erosional events in the continental Namurian–Westphalian north of Sofia in the Balkan terrane are also known (see column 4, Fig. 12).

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The Ordovician sediments in the Balkan terrane underwent some folding and shallow erosion at the end of the Ordovician. The overlying sandstones were deposited with a slight angular (10– 15) and azimuthal unconformity, which suggests rather weak Caledonian movements. However, the composition and thickness of the Upper Devonian

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turbidites show deep erosion in other areas, indirectly indicating synsedimentary tectonic events. A substantial sedimentary hiatus between the Lower and Upper Carboniferous in the Balkan terrane is documented from a lack of deposition or complete erosion of Lower Carboniferous sediments and deposition of very coarse-grained siliciclastic rocks

Fig. 18. Comparative palaeogeographic schemes for part of South-eastern Europe during the Westphalian, Lower Permian and Upper Permian (1a, 2a, and 3a—after Yilmaz et al. (1996), 1b, 12b, and 3b—after the data of Yanev in this paper). Legend: 1—continental highlands (zones without deposition, sediment source); 2—continental lowlands (sediment bypass); 3—continental highland with intramountain (very limited ) sedimentation; 4—continental intermountain deposition; 5—continental, fluvial, lacustrine deposition; 6—continental basin deposition; 7—deltaic and coastal plain deposition; 8—marine shelf deposition; 9—basin or slope deposition; 10—deep ocean deposition; 11—equator; 12—state boundaries; 13—block and coastline.

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Fig. 19. Additional new distribution of the palaeomagnetic data. (p. 5) Symbols: 1—Thracian terrane; 2—Balkan terrane; 3—Moesian terrane; palaeomagnetic data from Ordovician (O); Devonian (D); Carboniferous (C ) and Permian (P).

in the Late Carboniferous. This is related to a very strong tectonic event during the Sudetian phase. The Upper Carboniferous continental sediments rest with a marked angular unconformity on a variegated, intensively folded substrate. The tectonic collision occurred in a complicated manner and also intermittently from Namurian to the Late Permian. Various stages of the collision and related changes of the palaeogeographic environments are marked by erosion and migration of the areas of accumulation and source provinces, as well as by unconformities with the preceding Carboniferous and older deposits (see Fig. 12—I.4, 5 and 6 and IV; Fig. 14, columns 4, 5, 6, 8–10, 13, 16, 17, etc.). In NE Bulgaria, the Middle and Upper Devonian mixed carbonate-siliciclastic successions overlie an erosional surface of the Dobrudgea palaeo-dryland, indicating a tectonic event during the accretion of the Moesian terrane to the periphery of Laurussia. For a short period of time, thick

carbonate deposits underwent erosion in some blocks, representing uplifted areas of the accretionary relief, whereas in subsiding blocks, the process was compensated by the deposition of about 200 m of calcareous conglomerates. Subsurface data and abnormal faunal successions further support an interval of folding and thrusting. In North Bulgaria, seismic data show a structural unconformity between carbonates of Devonian age and the Lower Carboniferous carbonate platform rocks. Major tectonic and facial changes occurred during the Late Visean. Due to uplift, the subsequent erosion locally persisted until the Middle Devonian (220–780 m of Upper Devonian, Lower and Middle Visean sediments are lacking). The Late Palaeozoic tectonic movements in the two terranes show some correlation in time but a different spatial intensity. Their effects decrease from the south ( Variscan orogen) to the north (young mobile platform). It is possible to correlate

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the recorded tectonic events in Bulgaria and Germany. The best examples are the Saalian unconformity and the Altmark movements. The main stages of the palaeogeodynamic evolution of the studied area are: (1) individual development of different parts of the epicontinental sea during the Ordovician, Silurian, and partly Devonian; (2) Middle Devonian transformation of the Moesian terrane into a passive segment of a marginal sea, and of the Balkan terrane into an active segment of a marginal sea (a system including a frontal arc, an interarc turbidite basin, and a back arc, probably corresponding to the Moesian segment); and (3) Late Palaeozoic formation of the collisional Variscan orogen in the southern area, and the young mobile platform in the northern area.

9. Conclusions During the last two decades, much effort has been made to improve the palaeogeographic syntheses of Western and Central Europe, including the development of Pangea ( Ziegler, 1986, 1988, 1989, 1993; McKerrow and Scotese, 1990; Vai, 1994, 1997; Yilmaz et al., 1996). These reconstructions rely only to a limited degree on data from the East Balkan region (Spassov et al., 1978; Yanev, 1981, 1990, 1997; Tenchov, 1987; Janev, 1988, 1989; Krstic et al., 1992; Janev, 1996). The columns and sketches (Figs. 9–14, 17 and 18) of the distribution, facies, palaeogeographic zones and thicknesses of the Carboniferous and Permian sediments in Bulgaria can be used to improve the Balkan part of global reconstructions (see variants 1b, 2b and 3b in Figs. 18 and 19). In addition, the facies and lithologic similarities to terranes from other European parts of the Pangea can be used to outline the relations of Balkan with regions of comparable palaeogeography. This study is an attempt to explain the processes and stages of the formation of Pangea in that part of the world as a merger of Laurussia with fragments of Gondwana and Perigondwana. The investigation has not only scientific, but also practical, aspects, which involve the exploration for oil, gas and sedimentary copper-polymetallic and rare-metal ores.

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Acknowledgements The author is grateful for the valuable remarks and comments on the manuscript made by the reviewers Prof. P.A. Ziegler, Prof. P. Bankwitz, and to Drs. Jo¨rg Trappe and Lars Stemmerik for the English revision of the text. This paper is a contribution to the GSGP-program Pangea and IGCP Project 351 ‘Early Palaeozoic Evolution of NW Gondwana’. The support of the National Science Found of Bulgaria (Project NZ 602) is gratefully acknowledged.

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