Palaeozoic Formations from Dobrogea and Pre-Dobrogea

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Palaeozoic Formations from Dobrogea and Pre-Dobrogea – An Overview

ANTONETA SEGHEDI

National Institute of Marine Geology and Geoecology, 23−25 Dimitrie Onciul Street, 024053 Bucharest, Romania (E-mail: [email protected])

Received 19 January 2011; revised typescript received 02 November 2011; accepted 11 December 2011

Abstract: An overview of lithological, palaeontological and geochronological evidence existing for the Palaeozoic formations from Dobrogea and Pre-Dobrogea has enabled a better understanding of the Palaeozoic history of these areas. Th e Lower Palaeozoic of Pre-Dobrogea, in places in continuity with the pelitic-silty facies of the underlying Vendian (Ediacaran) deposits, was one of the peri-Tornquist basins of Baltica, suggesting that the Scythian Platform in the Pre-Dobrogea basement represents the rift ed margin of the East European Craton. In North Dobrogea two types of Palaeozoic succession have formed in diff erent tectonic settings. Deep marine Ordovician–Devonian deposits, including pelagic cherts and shales, associated with turbidites, and facing Devonian carbonate platform deposits of the East European Craton, form northward-younging tectonic units of an accretionary wedge, tectonically accreted above a south-dipping subduction zone. South of the accretionary prism, the basinal to shallow marine Silurian–Devonian deposits of North Dobrogea, showing a similar lithology to the East Moesian successions, accumulated on top of low- grade Cambrian clastics with Avalonian affi nity indicated by detrital zircons. Late Palaeozoic erosion was accompanied by deposition of continental alluvial, fl uvial and volcano-sedimentary successions, overlying their basement above an imprecise Carboniferous gap. Th e low-grade metamorphic Boclugea terrane, showing Avalonian affi nity, and the associated Lower Palaeozoic deposits represent East Moesian successions, docked to Baltica by the Lower Devonian and subsequently involved in the Hercynian orogeny, being aff ected by Late Carboniferous–Early Permian regional metamorphism and granite intrusion. Th e Late Carboniferous–Early Permian syn-tectonic sedimentation, regional metamorphism of Palaeozoic formations and development of a calc-alkaline volcano-plutonic arc indicate an active plate margin setting and an upper plate position of the Măcin-type successions during the Variscan collision, when the Orliga terrane, with Cadomian affi nity, was accreted to Laurussia along a north-dipping subduction zone of the Rheic Ocean. Th e East Moesian Lower Palaeozoic succession, overstepping its Ediacaran basement, represents an Avalonian terrane, docked to the Baltica margin in the Early Palaeozoic. A narrow terrane detached from the Trans-European Suture Zone (TESZ) margin of the Baltica palaeocontinent forms a tectonic wedge within the East Moesian basement. Th e Palaeozoic sedimentary record of East Moesia shows a quartzitic facies in the Ordovician, graptolite shales in Upper Ordovician–Wenlock, black argillites in the Ludlow-Pridoli and fi ne-grained clastics in the Lower Devonian. Eifelian continental sandstones are followed by a carbonate platform from Givetian to Tournaisian times and coal- bearing clastics in the Carboniferous, indicating a foredeep basin evolution. By the Eifelian both East Moesia and Pre-Dobrogea were part of Laurussia, sharing the same old red sandstone facies. Th e Permian is a time of rift ing in Dobrogea and Pre-Dobrogea, although evidence for rift ing in the East Moesian sedimentary record is very limited. In the eastern basins of Pre-Dobrogea, Permian rift ing was accompanied by alkaline bimodal volcanism of the basalt- trachyte association, that aff ected also the northern margin of North Dobrogea. Late Permian within-plate alkaline magmatic activity emplaced plutonic and hypabyssal complexes along the south-western margin of North Dobrogea. Th e model proposed for the Palaeozoic history based on existing data for the north-western margin of the Black Sea records early Palaeozoic docking to Baltica of the Avalonian terrane of East Moesia, including the Boclugea terrane of North Dobrogea. Late Carboniferous–Early Permian accretion of the Cadomian Orliga terrane from North Dobrogea, accompanied by Hercynian metamorphism and granite intrusion, correlates with the closure of the Rheic Ocean. Subsequently, Avalonian and Cadomian terranes, together with a narrow terrane detached from the TESZ margin of Baltica palaeocontinent, were displaced southward along the strike-slip fault system of the TESZ.

Key Words: North Dobrogea Orogen, Moesian Platform, Scythian Platform, lithology, biostratigraphy

Dobruca ve Ön-Dobruca’nın Paleozoyik Formasyonları

Özet: Dobruca ve Ön-Dobruca’daki Paleozoyik formasyonlarının litolojik, paleontolojik ve jeokronolojik özelliklerinin gözden geçirilmesi bu bölgelerin Paleozoyik tarihçelerinin daha iyi anlaşılmasını sağlar. Ön-Dobruca’nın Alt Paleozoyik

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istifl eri, Ön-Dobruca’nın bazı bölgelerinde daha altta yer alan Vediyen (Edikariyen) pelitik-siltli fasiyeslerle devamlılık gösterir, ve Baltika’nın peri-Tornquist havzalarından birini oluşturur. Bu durum Ön-Dobrucayı da içine alan İskit Platformu’nun Doğu Avrupa Kratonu’nundan rift leşme ile ayrıldığına işaret etmektedir. Kuzey Dobruca’da farklı tektonik ortamlara işaret eden iki tip Paleozoyik istif bulunur. Çört ve şeyl ve bunlarla ilişkili türbiditlerden oluşan derin denizel Ordovisyen–Devoniyen çökelleri, ve bu çökellerin Doğu Avrupa Kratonuna bakan kenarında gelişmiş Devoniyen karbonat platformu, güneye doğru dalan bir dalma-batma zonunda gelişmiş bir eklenir prizma oluşturur. Eklenir prizmanın güneyinde, derinden sığ denize kadar değişen Kuzey Dobruca’nın Siluriyen–Devoniyen çökelleri, Doğu Moezya istfl erine benzerlik gösterir, ve kırıntılı zirkonlarla Avalonya’ya bağlı olduğu saptanan düşük dereceli Kambriyen kırıntılıları üzerinde çökelmiştir. Geç Paleozoyik’te gelişen erozyon ve bölgenin karalaşması sonucu karasal çökeller ve volkanik kayaları, arada bir Karbonifer boşluğu olmak üzere bu temel üzerinde yer alır. Düşük dereceli metamorfik kayalardan oluşan Bokluca mıntıkası Avalonya özellikleri gösterir, ve Bokluca’ya bağlı Alt Paleozoyik kayaları Doğu Moezya özellikleri taşır; bu birimler Erken Devoniyen’de Baltika ile çarpışmış ve daha sonra Geç Karbonifer–Erken Permiyen’de rejyonal metamorfizma ve granitik sokulumlar ile tanımlanan Hersiniyen orojenezi geçirmiştir. Bu özellikler ve Geç Karbonifer–Erken Permiyen yaşlı tektonizma ile eşyaşlı sedimentasyon, bölgenin bu dönemde aktif bir kıta kenarı konumunda olduğuna işaret eder. Kadomiyen özellikler gösteren Orliga mıntıkası, Reik Okyansu’nun kuzeye doğru dalıp yok olması sonucu Lavrasya’ya eklenmiştir. Doğu Moezya’nın Alt Paleozoyik istifl eri, Erken Paleozoyik’te Baltika’ya yamanan Avalonya tipi bir mıntıkaya aittir. Baltika’nın Trans-Avrupa Kenet Zonu (TESZ) kıta kenarınan ayrılmış ince bir mıntıka Doğu Moezya temeli içinde bir kıymık oluşturur. Doğu Moezya’nın sedimenter istifi, Ordovisyen’de kuvarsitik fasiyesler, Üst Ordovisyen–Venlok’ta graptolitli şeyller, Ludlov–Pridoli’de siyah çamur taşları, Alt Devoniyen’de ince taneli kırıntılılardan yapılmıştır. Efyeliyen yaşlı karasal kumtaşlarını takiben Givetiyen– Turnaziyen zaman aralığında platform karbonatları gelişmiş, ve daha sonra Karbonifer’de kömür içeren kırıntılılar, bir ön-ülke havzasında çökelmiştir. Eyfeliyen’de hem Ön-Dobruca hem de Doğu Moezya, Lavrasya’nın yamanmıştır ve benzer kırmızı kumtaşı fasiyesleri gösterirler. Permiyen’de Dobruca ve Ön-Dobruca’da rift leşme gözlenir, buna karşın Doğu Moezya’da rifitleşme ile ilgili çökel kayıtları çok kıtdır. Ön-Dobruca’nın doğu havzalarında Permiyen rift leşmesi ile beraber bazalt-trakit birlikteliğinden oluşan alkalin bimodal volkanizma gelişmiş, ve bu volkanizma Kuzey Dobruca’nın kuzey kenarını da etkilemiştir. Geç Permiyen levha-içi alkalin magmatizma sonucu Kuzey Dobruca’nın güneybatı kenarı boyunca derinlik ve yarı-derinlik kayaları yerleşmiştir. Burada sunulan model, Erken Paleozoyik’te Baltika’nın güney sınırı boyunca Doğu Moezya ve Kuzey Dobruca’nın Bokluca mıntıkasını içeren Avalonya kökenli kıta parçaçıklarının Baltika’ya eklenmesini içerir. Kuzey Dobruca’nın Kadomiyen kökenli Orliga mıntıkası Geç Karbonifer– Erken Permiyen’de kuzeye eklenmiş ve bu olay sonucu Reik Okyanusu kapanarak Hersiniyen metamorfizması ve granit yerleşimi gerçekleşmiştir. Bu olayları takiben Avalonya ve Kadomiyen kökenli mıntıkalar, ve Baltika’nın TESZ kenarından kopan ince bir mıntıka, TESZ boyunca gelişen doğrultu-atımlı faylar boyunca güneye doğru ötelenmiştir.

Anahtar Sözcükler: Kuzey Dobruca orojeni, Moezya Platformu, İskit platformu, litoloji, biyostratigrafi

Introduction runs through the southwestern part of Ukraine Th e western margin of the East European Craton, a and Moldavia, continuing to the Black Sea through major terrane boundary along the contact between the south-eastern Romania. stable Precambrian Fennoscandian-East European Th e northwestern margin of the Black Sea includes Craton and the younger structures of Western and three major structural units: the westernmost segment Southern Europe, was defi ned as the Trans-European of the Scythian Platform, the North Dobrogea Orogen Suture Zone or TESZ (Pharaoh 1999) (Figure 1). and the Moesian Platform. All these units include Along the TESZ, peri-Gondwanan terranes of Far Palaeozoic formations, concealed in the platforms East Avalonia are found, accreted to the former and exposed in North Dobrogea. In order to better Baltica palaeocontinent during the Lower Palaeozoic understand the geological evolution of this area and (Ziegler 1986, 1988; Pharaoh 1999; Winchester et improve palaeogeographic models, it is important to al. 2002, 2006), are mingled with proximal Baltican establish or update terrane affi nities. Due to limited terranes. All these terranes with Avalonian and reliable information and still poorly defi ned terrane Baltican affi nity are variously displaced together affi nities, most palaeocontinental reconstructions along the strike-slip faults of the TESZ (Winchester for Moesia and/or Dobrogea assume that each forms et al. 2002, 2006; Nawrocki & Poprawa 2006; Oczlon one single terrane (Mosar & Seghedi 1999; Stampfl i et al. 2007). Th e southeastern segment of the TESZ 2000; Kalvoda et al. 2002; Cocks & Torsvik 2005,

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Figure 1. Location of Dobrogea on a simplifi ed terrane map of Europe (modifi ed aft er the TESZ map of EUROPROBE project). US– Ukrainian shield, VM– Voronezh massif, EC– East Carpathians, SC– South Carpathians, SP– Scythian Platform, MP– Moesian Platform, NDO– North Dobrogea orogen.

2006; Nawrocki & Poprawa 2006; Winchester et al. comment on the evidence for Palaeogeographic 2006). However, from detailed analysis of various affi nities. Th e Palaeozoic record from Pre-Dobrogea existing data, terranes with both Baltican and presented here is the result of correlation of borehole Avalonian palaeogeographic affi nities were inferred data across state borders, based on the petrographic to make up the Moesian Platform and a model for studies of thin sections provided by the former Oil their displacement along the TESZ, together with Institute in Bucharest and the Geological Institute the North Dobrogea terrane, was proposed (Oczlon from Kishinev. Core samples stored at the Geological et al. 2007). Detrital zircon data enabled separation Institute from Kishinev and the Geological Institute of Avalonian and Cadomian terranes in the North of Romania have also been examined. For North Dobrogea metamorphic suites, brought together Dobrogea, the review of geological data is based on papers published in local journals, abstracts and fi eld following the closure of the Rheic Ocean (Balintoni guide books, as well as on unpublished reports and et al. 2010). PhD theses. Th e data on East Moesia are summarized Th e goal of this paper is to provide an according to the synthesis of the Moesian Palaeozoic overview of the lithological, biostratigraphical and from Romania (Seghedi et al. 2005a, b), to serve as a geochronological information from the Palaeozoic basis for comparison with North Dobrogea and Pre- formations in the northwest Black Sea area and Dobrogea.

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Geological and Tectonic Background part of Dobrogea belongs to Romania, except for its Th e north-western margin of the Black Sea is a southern margin that continues for some distance in highland area referred to as Dobrogea, a geographical Bulgaria. North of the Dobrogea highlands, the fl at- and historical province confi ned between the Black lying Pre-Dobrogea Depression is shared by three Sea shore, the Sfântu Gheorghe Distributary of the countries: Romania, Moldavia and Ukraine. Danube Delta and the lower reaches of the Danube Th e area consists of three main tectonic units, two River. Dobrogea is surrounded by the lowlands of Palaeozoic platforms (Moesian and Scythian) and the the Pre-Dobrogea Depression in the north and the Cimmerian Orogen of North Dobrogea (Săndulescu Romanian Plain in the west (Figure 2). Th e largest 1984) (Figure 3). While the Scythian Platform is

Figure 2. Th e main geotectonic units of the western Black Sea margin. Th e area with darker grey shading represents exposures of pre-Cenozoic rocks. EM– East Moesia; WM– West Moesia; SGF– Sfantu Gheorghe Fault; PCF– Peceneaga-Camena Fault; COF– Capidava-Ovidiu Fault; PF– Palazu Fault; EF– Eforie Fault; IMF– Intra- Moesian Fault.

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Post-tectonic cover (Babadağ Basin)

Palaeozoic

platform cover

Figure 3. Schematic map showing the main structural units of Dobrogea (modifi ed from Seghedi et al. 2005a). ND– North Dobrogea; CD– Central Dobrogea; SD– South Dobrogea; LCF– Luncaviţa-Consul Fault; other abbreviations as in Figure 2. entirely concealed by Quaternary deposits, the was part of the northern rift shoulder of the Western eastern parts of the North Dobrogea orogen and of Black Sea Basin, which sourced the kaolinite-rich the Moesian Platform are exposed in North Dobrogea Aptian syn-rift sediments preserved both in the Pre- and Central and South Dobrogea, respectively. Dobrogea depression and South Dobrogea (Rădan Separated from the Scythian Platform by the 1989; Ion et al. 2002). Sfântu Gheorghe Fault and bounded southward Surrounded by the Carpathians and the Balkans, by the Peceneaga-Camena Fault, North Dobrogea the Moesian Platform is an area with a heterogeneous represents the south-eastern part of the North and complex Precambrian basement overlain by a Dobrogea Cimmerian Orogen, where the Hercynian thick Palaeozoic to Cenozoic cover. West of the Black basement and its Mesozoic cover are exposed (Figures Sea, the eastern part of the platform (East Moesia) 2 & 3). Th e north-western part of the belt is covered consists of two tectonic provinces separated by the by Cenozoic deposits of the Carpathian foredeep. Capidava-Ovidiu Fault (Figure 3). Th e stratigraphic gap between the Late Jurassic Confi ned between the Peceneaga-Camena and and Cenomanian sediments which seal both the Capidava-Ovidiu crustal faults, Central Dobrogea Cimmerian structures of North Dobrogea, as well exposes the Neoproterozoic Moesian basement. as the Peceneaga-Camena Fault, suggests that Th e fl at-lying Palaeozoic cover, preserved only throughout the Early Cretaceous North Dobrogea west of the Danube, above the subsided part of the

673 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

Neoproterozoic basement, has been completely Pre-Dobrogea Depression. Other authors regard this removed from the uplift ed block of Central Dobrogea area as the southern passive margin margin of the during an unspecifi ed period of pre-Bathonian East European craton reworked by Late Proterozoic erosion. In the outcrop area, the Neoproterozoic (Early Baikalian) and younger tectonism (Kruglov & basement is unconformably covered by Bathonian– Tsypko 1988; Gerasimov 1994; Drumea et al. 1996; Kimmeridgian carbonate platform successions above Milanovsky 1996; Pavliuk et al. 1998; Poluchtovich local remnants of a pre-Bathonian weathering crust et al. 1998; Stephenson 2004; Stephenson et al. 2004; (Rădan 1999) (Figure 3). Saintot et al. 2006). South Dobrogea is a subsided Moesian block, Th e basement of the Pre-Dobrogea depression is along the Capidava-Ovidiu and Intramoesian faults. a highly tectonized area about 100 km wide, defi ned Th is block exposes only the Mesozoic–Cenozoic against the neighbouring units by the crustal faults Moesian cover with frequent discontinuities and Baimaklia-Artiz (or Leovo-Comrat-Dnestr) and gaps. West and north-west of the Danube River, the Sfântu Gheorghe, known from geophysical and corresponding parts of these main units of Dobrogea, drilling data (Figure 4). Th e structure of the pre- concealed by Cenozoic deposits, lie at depths of over Mesozoic basement is defi ned by the intersection 600 m in the footwall of the Danube Fault (Gavăt et of two major fault systems. A system of WNW– al. 1967) (Figure 2). ESE-trending, parallel faults has controlled the development of intrabasinal longitudinal ridges. Th is is intersected by a N–S-trending fault system, best Th e Pre-Dobrogea Depression developed east of the Prut River (Neaga & Moroz Th e Pre-Dobrogea depression represents a Mesozoic– 1987; Drumea et al. 1996; Ioane et al. 1996; Visarion Tertiary depression superimposed on a pre-Triassic & Neaga 1997). basement. According to Săndulescu (1984), the Pre- Beneath the fl at-lying Middle Jurassic –Tertiary Dobrogea basement is the westernmost segment of cover, the area of the Pre-Dobrogea Depression the epi-Variscan Scythian Platform. Running E–W is a Permian palaeorift (Neaga & Moroz 1987). A along the south-western corner of the East European longitudinal high, the Bolgrad-Chilia (or Lower Craton, the Scythian Platform is buried westward Prut) Horst (Neaga & Moroz 1987; Moroz et al. beneath the Tertiary molasse foredeep of the East 1997; Visarion & Neaga 1997), separates two Carpathians. depressions elongated E–W (Figures 4 & 5). Th e Both the age of cratonization and Variscan northern depression includes the Sărata-Tuzla history of this tectonic unit are quite controversial. and Aluat basins, separated by the Orehovka- Located between the East European Craton and Suvorovo basement high. Th e Sărata-Tuzla basin is the Alpine-Cimmerian folded belts on its southern complicated by a minor longitudinal intrabasinal border, the Scythian Platform is classically defi ned ridge. Th e Aluat basin continues into Romania in the as a wide Variscan belt referred to as the ‘Scythian WNW-elongated Bârlad depression; this basin shows orogen’ (Mouratov & Tseisler 1982; Milanovsky 1987; a staircase geometry, its bottom being progressively Zonenshain et al. 1990; Nikishin et al. 1996). With downthrown westward towards the East Carpathian active orogenesis supposed to have occurred from foredeep. Th is is accommodated by a system of N–S Early Carboniferous to Permian times (Nikishin et faults, reactivated as result of nappe stacking in the al. 1996, 2001; Stampfl i & Borel 2002), it has usually East Carpathians. Th e Sulina (or Lower Danube) been considered to represent the link between the basin, with its depocentre situated in the Danube Variscan orogen of western and central Europe Delta, developed south of the Bolgrad-Chilia high and the Uralian belt at the eastern edge of the East (Figure 4). European Platform. In the Mesozoic, the ‘Scythian Th e basement lies at depths of 1–1.5 km in orogen’ showed a platform stage of development areas of basement highs and at depths of 3–4 km (Mouratov 1979), its basement being concealed by in depressions (Mouratov & Tseisler1982). Th e the superimposed Mesozoic–Tertiary deposits of the basement of the Pre-Dobrogea consists of magmatic

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Figure 4. Distribution of the main basins of the Scythian Platform in the Predobrogea depression, with location of the main boreholes (compiled aft er Neaga & Moroz 1987; Paraschiv 1986; Pană 1997). Shades of grey represent grabens and highs, respectively. rocks (granites, diorites and gabbros), that yield of the magmatic basement rocks (Neaga & Moroz Neoproterozoic K-Ar ages (790, 640–620 Ma) (Neaga 1987). Th e Neoproterozoic Ediacaran (Vendian) age & Moroz 1987) (Figure 5). In the central part of the is derived from a phytocenosis with Vendotaenia Bolgrad-Chilia and Orehovka-Suvorovo highs, the antiqua Grujilov, identifi ed in the Orehovka borehole magmatic basement is unconformably overlain (Visarion et al. 1993). A K-Ar age of 600±20 Ma yielded by undeformed Vendian deposits. Th ese deposits by pelitic rocks is consistent with the palynological were intersected by the Orehovka and Suvorovo data. Th e Vendian succession (Avdărma Series) is boreholes for a thickness of over 2000 m. Remnants upward shallowing, including marine sediments of a palaeo-weathering crust were found on top (conglomerates, sandstones, volcanic sands, black

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Figure 5. Mesozoic subcrop map of the Scythian Platform, showing the distribution and structure of the Neoproterozoic and Palaeozoic formations (compiled aft er Visarion et al. 1993; Ioane et al. 1996 and Visarion & Neaga 1997). shales rich in phosphate nodules and grey siltstones, pebbly sandstones, with siltstone and mudstone sandstones and mudstones) grading upward into interbeds). With these features, the Vendian deposits continental deposits (conglomerates and purple of the Pre-Dobrogea resemble the Avdărma Series

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from the East European Platform cover, exposed All four major Cimmerian thrust bounded units along the Dnestr River, the only diff erence being the recognised in North Dobrogea have Hercynian lesser thickness of the latter (only 600–700 m). deformed basement and Triassic or Triassic–Jurassic Th e platform cover of the Pre-Dobrogea comprises cover (Mirăuţă, in Patrulius et al. 1973; Săndulescu mainly Cretaceous to Quaternary sediments with 1984) (Figure 7). Th e Cimmerian tectonic units are a total thickness of 2500 to 3500 m (Permyakov & interpreted either as low-angle nappes, based largely Maidanovich 1984). Due to the high mobility of the on geophysical data (Săndulescu 1984; Visarion et al. area, repeatedly subjected to oscillatory movements, 1993), or as high-angle thrusts, based on borehole the sedimentary cover shows stratigraphic gaps and information (Baltres 1993). Th e latter tectonic model unconformities, being characterized by the absence is fi gured in the transect VII of the TRANSMED of the Lower Jurassic and thin Lower Cretaceous Atlas (Papanikolaou et al. 2004). Th e Măcin deposits (Ionesi 1994). According to the synthesis Cimmerian tectonic unit (corresponding to the of Ion et al. (2002), the Mesozoic cover includes descriptive Măcin zone), exposes largely Palaeozoic formations, with only minor exposures of Triassic Callovian–Oxfordian black shales in the Danube deposits (Figures 3 & 6). In the Tulcea zone, exposing Delta and carbonates in the rest of the Pre-Dobrogea, mainly Triassic deposits and a few Palaeozoic and overlain by Oxfordian–Kimmeridgian carbonate Jurassic formations, are three Cimmerian tectonic platform limestone. Dolomites, clastics and units (Săndulescu 1984): the Consul, Niculiţel and evaporites develop in the Berriasian–Valanginian; Tulcea nappes. dolomites, dolomites and clastics in the Middle–late Aptian, while clastics occupy the northern half of Th e Triassic succession, unconformable on the the Delta in the Sarmatian followed by Late Meotian Hercynian basement, starts with lower Scythian shales, and the Quaternary is represented by sand (Werfenian) continental fanglomerates, followed and clay of marine, fl uvial and lacustrine origin. by sandstones and upper Scythian limestone turbidites (Baltres 1993). Rhyolites and basalts started to be emplaced in the late Scythian, with North Dobrogea the basaltic volcanism continuing up to Middle Th e narrow, NW-trending Cimmerian fold and Anisian (Baltres et al. 1992). Th e basaltic volcanism thrust belt of the North Dobrogea orogen (Figure 3) is partly coeval with deposition of nodular and is a basement with a Hercynian history of magmatism bioturbated limestones and cherty limestones. Th e and deformation. Th is basement was subsequently basinal succession terminates with Late Anisian– involved in early Alpine (Cimmerian) events, late Carnian Halobia marls (Baltres et al. 1988). experiencing extension during the Late Permian– Turbiditic deposits accumulated, starting in the late Middle Triassic, and compression (transpression) in Carnian and ranging up to the middle Jurassic, with the Late Triassic–Middle Jurassic (Seghedi 2001). A an upward coarsening trend of coarse members major high-angle reverse fault with a NW–SE strike (Baltres 1993; Grădinaru 1984). Shallow marine (Luncaviţa-Consul Fault, Savul 1935), represents carbonate sedimentation took place along the basin the contact between the Măcin and Tulcea zones margin from the Scythian to the Norian and in the (Mutihac 1964) (Figure 6). Th ese zones refer to Oxfordian–Kimmeridgian (Grădinaru 1981; Baltres areas with dominantly Palaeozoic and Triassic 1993). Apart from numerous unpublished reports, a exposures respectively; Jurassic deposits occur in detailed presentation of the Triassic–Jurassic deposits limited areas in both zones. Th e Măcin zone (Măcin of North Dobrogea is given in Grădinaru (1981, 1984, Nappe, Săndulescu 1984) is a Cimmerian tectonic 1988) and Seghedi (2001). unit exposing mainly Palaeozoic formations in the An early Cretaceous history is not preserved in western part of North Dobrogea. Th e Tulcea zone is the stratigraphic record, except for scarce remnants the larger, eastern part of North Dobrogea, exposing of a kaolinitic weathering crust, found in several mostly Triassic and Jurassic formations included in locations on top of the the Hercynian basement three Cimmerian thrusts (Săndulescu 1984). or the Triassic deposits. In one locality this crust

677 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

Figure 6. Quaternary subcrop map showing the outcrop areas of Palaeozoic formations and the main Cimmerian faults in North Dobrogea (modifi ed from Seghedi 1999).

is preserved beneath transgressive Cenomanian Histria Formation (Figure 3). Th e Upper Cretaceous calcarenites and was ascribed to the Aptian (Rădan succession includes Albian bioclastic limestones, 1989). Th e post-tectonic cover of the North Dobrogea Cenomanian–Turonian detrital limestones with orogen is represented by the shallow-marine Upper conglomerate interbeds in the eastern part, Coniacian Cretaceous sediments of the ‘Babadag basin’. Th ey detrital limestones with cherts, chalk and glauconite seal the deeply truncated Hercynian and Cimmerian and Santonian–Campanian nodular limestones structures, overstepping the easternmost segment developed only along the eastern margin of North of the Peceneaga-Camena Fault and overlying the Dobrogea (Ion et al. 2002 and references therein).

678 A. SEGHEDI s of s of exes; C-P– Carboniferous– C-P– exes; Predobrogea Depression. Predobrogea erentiated Hercynian basement basement Hercynian erentiated Seghedi of 2001). Location ed from Meidanchioi- 1993. MIF– er Baltres gured aft gured ’; J– Jurassic; T– Triassic; Pz– undiff Triassic; T– ’; J– Jurassic; – Late Cretaceous ‘Babadag basin ‘Babadag Cretaceous – Late 2 fi are structures Mesozoic data. borehole and based outcrops on drawn e sections are – Carboniferous–Early Permian Carapelit Formation; C– Carboniferous intrusives, C?– supposed Carboniferous cherts and turbidite and cherts Carboniferous C?– supposed intrusives, C– Carboniferous Formation; Carapelit Permian – Carboniferous–Early 1 -P 2 Permian granitoids; C granitoids; Permian including the Boclugea, Megina and Orliga metamorphic terranes and Silurian–Lower Devonian sediments; P– Permian alkaline compl Permian P– sediments; Devonian Silurian–Lower and terranes Orliga metamorphic and the Boclugea, Megina including the Tulcea type Palaeozoic; E– Ediacaran turbidites of Central Dobrogea; NP– Neoproterozoic basement of Central Dobrogea; PDD– PDD– Dobrogea; Central of basement Neoproterozoic NP– Dobrogea; Central of turbidites E– Ediacaran type Palaeozoic; the Tulcea sections is shown on inset map. Th inset map. on sections is shown K Cretaceous–Tertiary; K-T– Fault; Teliţa TF– Fault; Iulia Interpretative geological sections in North Dobrogea showing the Hercynian basement and the Cimmerian structures (modifi structures the Cimmerian and basement the Hercynian showing Dobrogea sections in North geological Interpretative Figure 7.

679 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

Central Dobrogea 1999). Palaeofl ow directions indicate a southern Th e Central Dobrogea basement consists of two source area which supplied both terrigenous and terranes with distinct lithologies and deformational volcanic clasts (Oaie 1999). Th e composition of history. Metapelites and metabasites of the Altin coarse members suggests that a major continental Tepe Group, with an initial amphibolite facies margin source delivered Palaeoproterozoic BIF and metamorphism, are ascribed to the Late Proterozoic gneisses into the basin; a second, volcanic source, based on K-Ar ages on biotite (696–643 Ma, Giuşcă yielded basalt and rhyolite clasts (Oaie et al. 2005). et al. 1967) (Figure 8). Metabasites are tholeiitic, Detrital zircon ages are consistent with Archaean and showing arc/back arc affi nities (Crowley et al. Palaeoproterozoic sources (Żelaźniewicz et al. 2009; 2000). Th e mesometamorphic rocks are exposed in Balintoni et al. 2011). Sedimentological, structural an antiform south of the Peceneaga-Camena Fault and mineralogical data suggest that the Histria and develop a wide greenschist facies mylonitic Formation accumulated in a foreland basin setting zone (Mureşan 1971) along their contact with the (Seghedi & Oaie 1995; Oaie 1999; Oaie et al. 2005), an overlying Histria Formation. Th is ductile shear interpretation consistent with results of geochemical zone in Altin Tepe rocks contrasts with the brittle and detrital zircon distribution data (Żelaźniewicz et deformation in the Histria Formation lithologies, the al. 2009). contact showing the main characteristics of a low- Th e Late Proterozoic–Early Cambrian angle detachment fault (Seghedi et al. 1999). depositional age of the turbidites is constrained Well exposed over the entire Central Dobrogea by palynological associations (Iliescu & Mutihac area, the Histria Formation is a succession up to 5000 1965). A medusoid imprint in the middle member m thick (O. Mirăuţă 1965, 1969; Visarion et al. 1988), of the Histria Formation, identifi ed as Nemiana consisting of two coarse members of sandstone simplex Palij, suggests an Ediacaria-type fauna (Oaie dominated, channelized midfan turbidites, separated 1992). In boreholes from the Romanian Plain, the by a thinner member (up to 500 m thick) of distal, turbidites are unconformably overlain by fl at-lying abyssal plain turbidites (Seghedi & Oaie 1995; Oaie quartzitic sandstones with Ordovician graptolites (E.

Figure 8. Schematic tectonostratigraphic charts for the metamorphic rocks of Dobrogea. K-Ar ages are taken from Ianovici & Giuşcă (1961); Giuşcă et al. (1967); Kräutner et al. (1988); Ar-Ar ages from Seghedi et al. (1999); monazite CHIME ages from Seghedi et al. (2003a); U-Pb detrital zircon ages from Balintoni et al. (2010, 2011).

680 A. SEGHEDI

Mirăuţă 1967; Iordan 1992, 1999). Neoproterozoic of basanites and trachybasalts showing intraplate deformation of the turbiditic succession in very- geochemical affi nities resulted through the rift ing low-grade metamorphic conditions occurred at 572 of the cratonic basement (Seghedi et al. 2000). Th e Ma (K-Ar WR) (Giuşcă et al. 1967) and resulted in Late Proterozoic deformation of the basaltic rocks, E–W-trending, open normal folds, with axial-planar dated at 547 Ma (K-Ar WR), is assumed to be slaty cleavages, penetrative only in fi ne-grained connected to northward thrusting of Archean and lithologies (O. Mirăuţă 1969; Seghedi & Oaie 1995). Palaeoproterozoic suites (Giuşcă et al. 1967; Kräutner Detrital zircon ages (Żelaźniewicz et al. 2001) are et al. 1988). interpreted to indicate an Avalonian affi nity for the According to the geological record, the Ediacaran turbidites (Oczlon et al. 2007) and a peri- undeformed sedimentary cover of South Dobrogea Amazonian provenance is suggested, based on the includes Ordovician to Quaternary formations age distribution pattern (Balintoni et al. 2011). separated by gaps. Several cycles have been separated: Th e platform cover exposed in Central Dobrogea Cambrian–Westphalian, Permian–Triassic, starts with Bathonian calcarenites rich in crinoidal Bathonian–Eocene and Miocene–Quaternary debris, transgressive on the Ediacaran basement, (Paraschiv 1975; Ionesi 1994). Th e Palaeozoic followed by Callovian–Oxfordian carbonates showing formations will be described in the next chapter. the same facies as in the Pre-Dobrogea depression Th e Mesozoic platform cover starts with and overlain by Oxfordian–Kimmeridgian carbonate unconformable, scarce Triassic red-beds, followed platform limestones (Ion et al. 2002 and references by Middle–Upper Triassic calcareous successions. therein). Only in the northeast does the Upper Th e Jurassic includes mainly carbonate platform Cretaceous cover of North Dobrogea overstep the sediments; strongly dolomitized limestones and Ediacaran basement (Figure 3). calcarenites prevail, unlike in the Central Dobrogea. Along the Capidava-Ovidiu Fault, the typical marine patch-reef facies of South Dobrogea is replaced by South Dobrogea regressive deposits, with alternating marine limy and In the subsurface of South Dobrogea, the cratonic evaporitic-lagoonal facies, partly coeval with those basement of the Moesian Platform is comparable to of the Oxfordian–Tithonian and Kimmeridgian– that of the Ukrainian Shield, containing Archaean Tithonian respectively (Avram et al. 1993). gneisses and an Lower Proterozoic banded iron Twelve distinct Cretaceous formations separated formation (BIF) (Palazu Mare Group) (Giuşcă et al. by stratigraphic discontinuities and established 1967, 1976; Giuşcă 1977) (Figure 8). Th e gneisses through detailed biostratigraphic studies on outcrops and the banded iron formation, correlated with and boreholes in South Dobrogea are presented in the Ukrainian shield of the East European Craton several papers (Avram et al. 1993; Ion et al. 2002 and (Giuşcă et al. 1967; Kräutner et al. 1988), have been references therein). Th e Berriasian–Valangianin– interpreted as the small, proximal Baltican Palazu Early Hauterivian includes an evaporitic-detrital terrane, displaced along the TESZ (Oczlon et al. succession; limestones with clayey interbeds, 2007). calcarenitic, dolomite-clayey, coarse siliciclastic, Th e BIF shows a Svecofennian HT-LP amphibolite calcareous-detrital and calcareous-marly successions. facies metamorphism, with andalusite-sillimanite Th e Middle–Upper Aptian has a fl uvio-lacustrine assemblages (Giuşcă et al. 1967, 1976). A later, facies with red beds, coal and kaolinite, while in the greenschist-facies retrogression was correlated Upper Aptian–Albian onshore clastics are followed with the very low-grade metamorphism of the by a marine marly-silty facies. Th e transgressive late Cadomian Neoproterozoic cover (Kräutner Lower Cenomanian consists of a basal conglomerate, et al. 1988). Neoproterozoic volcano-sedimentary glauconitic chalk and upper, massive chalky deposits (Cocoşu Formation) include volcanics and sandstone. Th e marl-dominated Upper Cenomanian volcano-sedimentary successions derived from a is overlain by clastic Turonian–Santonian– mafi c, alkaline volcanism (Figure 8). Basaltic fl ows Campanian chalky-glauconitic-quartzitic sandstone

681 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

with inoceramus shell-debris, followed by thick that terminate their evolution in the Ordovician chalk with chert. Th e Lower Maastrichtian includes (Conochitina brevis T. et de J., Rhabdochitina gracilis a lacustrine, variegated clayey and marly succession, Eis., Desmochitina urceolata B. et T., D. pellucida followed by Upper Maastrichtian interbedded chalky B. et J., Eremochitina sp., E. baculata B. et de J., marls and clays, chalky glauconitic sands/sandstones Siphonochitina sp. and acritarchs Baltisphaeridium and massive chalky limestones. Th e Palaeogene digitiforme Gorka, Lophosphaeridium papulatum includes glauconitic sands and sandy biocalcarenites, Martin, Multiplicisphaeridium continuatum rich in nummulites. Th e Miocene succession consists Kjellstrom.) and Silurian assemblages (Conochitina of normal marine Upper Badenian (Kossovian) and gordonensis Cramer, C. intermedia Eis., Rhabdochitina brackish Sarmatian clastics and bioclastic limestones, conocephala Eis, Desmochitina minor Eis., D. tinae separated by a break in sedimentation. Pliocene Cramer, the latter characteristic for the Llandovery) deposits include sands, conglomerates and silty clays, (Vaida & Seghedi 1997). Th e rest of the succession containing a mollusc fauna typical for the Upper (1954 m) belongs to the Vendian–Cambrian. Th e Pontian, Dacian and Romanian. Th e Quaternary situation in the Liman borehole suggests that the includes sands, clays and loess deposits. Ordovician–Middle Silurian deposits may be present in other areas of the Pre-Dobrogea Depression. Description of the Palaeozoic Formations Th e Palaeozoic Record of Pre-Dobrogea Depression Lower Devonian – Th e Lower Devonian (known Cambrian–Silurian – Th e areal distribution of east of the Prut River as the Iargara Series) includes Palaeozoic lithologies in Pre-Dobrogea is shown on fi ne-grained clastics showing the same facies as the the pre-Triassic subcrop map in Figure 5 and the coeval sediments from the western part of the East vertical succession of facies in Figure 9. A sequence of European Platform (Neaga & Moroz 1987). Th e reddish sandstones, siltstones and mudstones, 100– maximum thickness of deposits is 1200 m, attained in 300 m thick, intersected by boreholes in the Sărata- the Kazaklia borehole. Th e Iargara Series represents Tuzla grabens was ascribed to the Cambrian (Bogatzev a dominantly terrigenous, upward coarsening and 1971, in Belov et al. 1987), or to the early Cambrian– shallowing sequence. Its lower part (Cociulia Beds) Silurian interval (Belov et al. 1987). Orthoquartzitic consists of marine shales and argillites with thin sandstones from the Buciumeni borehole in Romania limestone interbeds, with a fauna of pelecypods, (Figure 4) yielded a palynological association of brachiopods and Orthoceratid fragments. Th e middle spores, acritarchs, leiosphaerids and algae specifi c to part (Lărguţa Beds) includes grey-greenish argillites, the Lower Ordovician, possibly including the Lower interbedded with sandstones, siltstones, detrital and Cambrian (Paraschiv 1986a). bioclastic limestones, the latter rich in brachiopods, pelecypods, bryozoans, ostracods and tentaculites Th e presence of the Ordovician and Lower– (Safarov & Kaptzan 1967). Th e upper part (Enichioi Middle Silurian was identifi ed, based on Chitinozoan Beds) comprises continental deposits, including assemblages in Liman borehole 1 from the southern quartzitic sandstones with thin red shale interbeds, margin of the Pre-Dobrogea Depression (Vaida & ascribed to the Lower Devonian on stratigraphic Seghedi 1997). Th e deposits, penetrated to a thickness criteria. West of the Prut River, purple quartzitic of 2674 m, had been previously assigned entirely to sandstones with Dictyonema sp., Umbellina bella and the Vendian. Th e lithofacies includes grey, bluish and Dentalina iregularis have been ascribed to the Lower purple siltstones and mudstones, with sandstones Devonian (Baltes 1969). Tuff s of andesitic, andesitic- interbedded in the middle part and limestones in the dacitic and dacitic composition are conformably upper parts of the succession. Only the upper part interbedded with the sandstones (Moroz et al. 1997). of the deposits (620 m thick) yielded palynological associations dominated by chitinozoans, with subordinate acritarcha and scolecodonts. Along Middle Devonian–Lower Carboniferous – Th e with the long range chitinozoans, there are species Middle–Upper Devonian includes evaporate-bearing,

682 A. SEGHEDI

Figure 9. Stratigraphic chart for the Palaeozoic deposits of the Scythian Platform (modifi ed from Neaga & Moroz 1987).

683 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

dark carbonate successions, oft en bituminous, with Carboniferous Terrigenous Facies – Th e terrigenous, thin siliciclastic interbeds. Th e lower part of this coal-bearing Carboniferous facies (Upper Visean– succession (Eifelian) consists of brecciated anhydritic Namurian) unconformably overlies Lower–Middle rocks interbedded with shales (300 m) (Neaga & Devonian sediments in the Aluat and Sărata-Tuzla Moroz 1987). Th e Upper Devonian is missing from basins. Th e sequence consists of grey sandstones and some areas, probably due to erosion. Th e Lower siltstones, with anthracite, interpreted as lacustrine Carboniferous, from the Tournaisian to the Namurian sediments (Neaga & Moroz 1987). Th ey are dated as (Serpuchovian), consists of massive limestones and late Visean–middle Namurian based on ostracods dolomites, rich in organic matter. Only the early recovered from thin limestone interbeds occurring at Late Visean is present in the eastern part of the Aluat the top of the succession. basin, while in the Tuzla borehole the succession is In the Bârlad depression, the equivalent of this preserved up to the base of the upper Serpuchovian coal-bearing succession is the Matca Formation. Th is (Vdovenko 1978, 1980a, b, 1986). For the Tournaisian is a sequence of black mudstones and grey sandstones, a correlation with coeval deposits from the East with local conglomerate layers. Pelitic intervals European Craton and Donbass Fold Belt is possible, contain thin spongolithic interbeds, indicating a based on the lithology and foraminifera-dominated shallow marine environment with depths of 60–100 microfaunal assemblages (Vdovenko 1986). m. Th e rocks are rich in pyrite and coalifi ed material, suggesting reducing conditions of the basin. A Petrographic studies (Baltres, in Roşca et proximal shelf facies developed at Matca, dominated al. 1994) indicate that the carbonate rocks are by conglomerates and sandstones (submerged delta), bioclastic and pelletal micrites, partly dolomitized, and a typical distal shelf succession, dominated by with anhydrite nodules, locally associated with clays and sandstones with sponges occurs at Burcioaia sandstones and mudstones rich in brachiopod (Pană 1991). Clast petrography includes volcanic bioclasts. Th e microfacies suggests tidal deposits, and vein quartz, plagioclase feldspars and various dominated by subtidal and intertidal sediments, the lithoclasts: basalts, rhyolites, spongoliths, siliceous initial sediments representing bioturbated, former shales, quartzites, seldom limestones; detrital micas limy oozes. Supratidal deposits are represented by are abundant, heavy minerals are tourmaline and evaporites and suggest formation in a warm, arid opaques; framboidal pyrite repaces Endothyra tests. climate, in a low energy environment (lagoon or Based on marine, nektobenthonic shelf fauna, embayment adjacent to the sea). with conodonts, endothyracae, ostracods, sponges, A very accurate biostratigraphy of the Devonian– fi sh bone fragments and teeth, the dark clastic Carboniferous carbonate sediments east of Prut River successions of the Matca Formation are assigned is based on microfauna (foraminifera, ostracods) to the Lower Carboniferous (Middle Tournaisian– (Vdovenko 1972, 1978, 1980a, b, 1986; Bercenko Lower–Middle Visean) (Pană 1991). Th e younger age & Kotliar 1980) and macrofauna (brachiopods, of the Carboniferous clastics in the Bârlad depression pelecypods, orthoceratids and bryozoans) (Safarov suggests that detrital Carboniferous sedimentation & Kaptzan 1967). Th e calcareous foraminifera has been established earlier in the western part of belong to the Fennosarmatian province of the the Pre-Dobrogea area than in the eastern part of North Palaeotethyan realm, characteristic of the Sărata basin, which might further suggest north- Avalonian terranes (Kalvoda 1999). Th e main eastward migration of the Carboniferous basin depocentre. diagnostic features of this province include: late Frasnian diversifi ed Multiseptida-Eonodosaria- Eogeinitzina association; late Famennian diversifi ed Permian – Continental red-beds, associated with Quasiendothyra association; late Tournaisian–early evaporites or volcanic-volcaniclastic rocks, represent Visean Kizel-Kosvin association, together with late the infi ll of the Aluat and Sărata-Tuzla basins. In the Visean taxa known from the southern margin of Sărata-Tuzla basin, the succession has a maximum Laurussia (Kalvoda et al. 2002). thickness between 2000 m to over 2500 m. In the

684 A. SEGHEDI

eastern part of the Aluat graben, east of the Prut fi ning cycles of alkali basalts, coarse tuff s, trachyte River, the Permian is dated by palaeontological and fl ows and ignimbritic rhyolites and rhyolitic tuff s, palynological data (a phyllopode association with separated by red sandstone intervals (Seghedi et al. Pseudoestheria, as well as assemblages of spores) 2001). (Kaptzan & Safarov 1965, 1966). Th e Permian age Th e dominant volcanic rocks are subalkaline: of the volcano-sedimentary successions from the subalkali basalts, hawaiites, mugearites, latites, Sărata-Tuzla basins is based on geochronological trachytes, trachy-dacites, trachy-rhyolites (Moroz & evidence (K-Ar ages) (Neaga & Moroz 1987), as well Neaga 1996), belonging to a basalt-trachyte bimodal as on facies and geometric criteria. association (Seghedi et al. 2001). Th eir subalkaline Th e Permian deposits, reworking Devonian and geochemical signature (Neaga & Moroz 1987; Moroz Lower Carboniferous limestones, show abrupt facies & Neaga 1996), as well as their interfi ngering with changes along and across the basin, with lateral facies red, continental sediments, indicate that they are variations, from coarsest breccias and fanglomerates products of continental, intraplate volcanism, related accumulated along the northern margin of the to extensional (possibly transtensional) rift ing. basin, to conglomerates and sandstones which grade Th e Permian syn-rift volcanism was subaerial, southward to evaporate-bearing thin laminated dominantly eff usive and subordinatly explosive, as siltstones and sandstones (Seghedi et al. 2003). indicated by the features of the preserved volcanic Th e deepest part of the Aluat basin is fi lled products. with thick successions of fi ne-grained continental In contrast to the Sărata-Tuzla graben, in the red-beds, rich in anhydrite and gypsum. Th ey eastern part of the Aluat basin intrusive rocks occur interfi nger with the coarse fanglomerates and (shonkinites, alkali syenites, syenites, monzonites, represent deposition in playa lake and coastal sabkha granodiorite porphyries, quartz-bearing porphyritic environments (Seghedi et al. 2001). In Romania, their syenites), as well as dyke rocks of the syenite group age was ascribed to the Permian, not precluding the (Moroz & Neaga 1996). possibility to include the Lower Triassic (Paraschiv 1986b). Below the Middle Triassic, a similar In the western part of the Bolgrad-Chilia sequence of evaporitic red-beds was intersected by high, magnetic anomalies represent ultrapotassic boreholes in the Danube Delta (Lower Prut Graben), magmatic bodies as confi rmed by boreholes. Such unconformably overlying Devonian dolomitic bodies vary from few metres to 20–30 m, or are limestones (Pătruţ et al. 1983). most probably stocks with thicknesses over 300 m. In the Sărata-Tuzla grabens, the Permian Tectonic control of emplacement is suggested by succession is largely dominated by volcanic and their location at the intersection of the two main volcaniclastic deposits, including lava fl ows and cross-cutting fault systems (Moroz & Neaga 1976; pyroclastic sediments, interbedded with continental Moroz & Neaga 1996). Th e Permian age of the red-beds. Based on geometric criteria, the volcanic ultrapotassic magmatic bodies was determined from successions are considered Lower Permian, while fi eld relations, as they intrude all their pre-Mesozoic the evaporitic, thin laminated red-beds represent the country rocks, producing considerable thermal Upper Permian, the Rotliegendes, possibly including and metasomatic eff ects, especially in carbonate the Lower Triassic. lithologies. Some magmatic rock samples yielded Th e Permian volcanic activity yielded thick Permian K-Ar cooling ages (248 Ma) (Moroz 1984). volcanic-volcaniclastic successions interbedded with continental red-beds. Volcanic products ascribed Palaeozoic Formations of North Dobrogea to the Lower Permian and consisting of lava fl ows and pyroclastic sediments are trapped in the Sărata- Th e Hercynian folded basement is exposed mainly in Tuzla basin, but they are known also along the the western, Măcin zone and forms isolated, smaller north-eastern margin of the Aluat basin. Detailed outcrop areas in the Triassic, Tulcea zone (Figure 3). facies analysis of cores recovered from borehole 1S Th e distribution of the Palaeozoic basement and its Furmanovka revealed several superimposed upward- Cimmerian structures are shown in the map from

685 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

Figure 6 and on the geological sections from Figure Two types of Palaeozoic successions were 7. In the Măcin zone, the Hercynian basement is distinguished (Seghedi & Oaie 1995; Seghedi 1999) exposed in the deeply eroded cores of several NW– (Figure 10), joined along the Teliţa Fault, a strike-slip SE-trending Cimmerian thrust folds. East of the fault concealed by the overlying Triassic deposits. Luncaviţa-Consul Fault, the basement crops out in Th is fault was also inferred from geophysical the cores of two E–W-trending Cimmerian folds – evidence (Visarion & Neaga 1997) (Figures 6 & 10). the Mahmudia anticline in the north and the Somova Th e vertical succession of facies is shown in Figure 11. anticline in the south (Murgoci 1914; O. Mirăuţă 1966b). Other smaller exposures of the pre-Triassic basement are scattered throughout the Triassic – Th e Tulcea-type Successions – Deep marine sediments, Jurassic deposits of the Tulcea zone. ascribed to the Ordovician–Devonian interval, have

Figure 10. Mesozoic subcrop map showing the distribution of the Palaeozoic formations in North Dobrogea, based on outcrop, borehole and geophysical information (modifi ed from Seghedi 1999). Note that the NW–SE structural grain of the Palaeozoic deposits and intrusions is the result of Cimmerian deformation.

686 A. SEGHEDI

Figure 11. Lithological chart for the Palaeozoic formations of North Dobrogea (modifi ed from Seghedi 1999).

687 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

been separated as the Dealul Horia, Rediu and based on a rich association of conodonts, identifi ed Beştepe formations (Patrulius et al. 1973, 1974) and by Elena Mirăuţă in grey limestones interbedded in dated using conodonts, chitinozoans and acritarcha. the black siliceous cherts (Table 1). Th e conodont Devonian deposits are exposed discontinuously in assemblage is associated with Glomospira sp., the core of the Cimmerian anticline, developed south Lituotuba sp., scolecodonts, ostracods and crinoids. of the Sfântu Gheorghe distributary between Tulcea Detailed palynological studies in the Movila Săpată and Mahmudia. Th e presence of the Ordovician borehole revealed an association of chitinozoans and Silurian deposits in the core of the Somova and acritarchs indicating a Lower Silurian age for Cimmerian anticline, beneath the Triassic deposits, the black slates (155 m thick) and a Middle–Upper is documented in the Movila Săpată and Marca Ordovician age for the underlying bedded cherts and boreholes (Seghedi, in Baltres et al. 1988) (Figure greenish siliceous slates (350 m thick). In the Movila 7). Th e Palaeozoic deposits form upward-coarsening Săpată borehole, the associations are dominated sequences of radiolarian cherts to turbidites, by Chitinozoans, with scarce Acritarcha (Table 1) representing northward younging, fault-bounded (Vaida & Seghedi 1996). Th e black slates from the successions (Figure 11). Th ey are supposed to have upper part of the Rediu Formation intercepted in the accumulated on oceanic crust or partly on passive Marca borehole yielded only Silurian palynological continental margin. associations (Vaida & Seghedi 1999), in good agreement with the conodont-dominated microfauna Dealul Horia Formation – A turbidite succession previously described in outcrops. Again chitinozoans is exposed in Dealul Horia, south-west of Tulcea, dominate the assemblage while Acritarcha are rare plunging eastwards beneath the black banded cherts (Table 1). of the Rediu Formation. Th ese sandstone-dominated turbidites represent a succession of coarse- and Th e Devonian Succession – Beştepe Formation – fi ne-grained, greenish sandstones and siltstones. Th e dominantly siliceous Devonian deposits are Sedimentological features indicate proximal discontinuously exposed on the southern bank of turbidites. Sedimentary structures are partly obscured the Danube in the core of the E–W-trending Triassic by an E–W-trending, steeply dipping penetrative anticline developed between Tulcea and Mahmudia. slaty cleavage and phyllosilicate foliation (Seghedi On the northern bank of the Danube, in Ukraine, this & Rădan 1989). Th e deposits are ascribed to the anticline continues in the Cartal-Orlovka area, where Ordovician based on their geometric position below the Devonian succession, separated as the Orlovka the Silurian Rediu Formation (O. Mirăuţă 1966b). series, was correlated with the Beştepe Formation Based on palynological assemblages dominated (Slyusar 1984). by acritarchs with subordinate chitinozoans, this formation was ascribed to the Upper Ordovician– Based on stratigraphical and palaeontological Silurian (Visarion, in E. Mirăuţă et al. 1986). studies, the stratigraphy proposed for the Devonian deposits from the Beştepe Hills includes a lower, fl ysch-type member, a middle member made of Rediu Formation – Both in outcrops and boreholes, limestones and schists and an upper member of two members could be identifi ed within the Rediu siliceous shales (O. Mirăuţă & E. Mirăuţă 1965a, b; O. Formation, corresponding to the stratigraphy Mirăuţă 1967). A diff erent stratigraphic succession is established by O. Mirăuţă (1966b): a lower, siliceous suggested by sedimentological and structural studies: member and an upper member of black or grey a lower member of siliceous rocks (cherts, siliceous slates. Th e siliceous pelagic rocks are rich in silicifi ed, shales with scarce, thin pelagic limestone interbeds) undeterminable radiolarians. Rocks are derived from and an upper member of distal turbidites (Oaie & the very low-grade metamorphism of a lithological Seghedi 1994). Th e structural style of these deposits association of black shales and radiolarian cherts is characterized by recumbent folds and thrusts (Seghedi et al. 1993). Th e age of the Rediu Formation (Figure 12a) formed as result of N–S compression. was ascribed to the Silurian (O. Mirăuţă 1966b), A slight southward increase in metamorphic grade

688 A. SEGHEDI sp. sp. sp. sp. Glomospira Lituotuba ostracods scolecodonts crinoids sp. LOEBLICH

Lophosphaeridium Multiplicisphaeridium radicosum

. EIS

. BOUCHE

PARIS PARIS er Elena Mirăuţă, in Mirăuţă 1966a, b; Mirăuţă 1971; Vaida & Seghedi 1971; Vaida 1966a, b; Mirăuţă in Mirăuţă er Elena Mirăuţă,

TAUG EIS.

elegans

sp Angochitina Conochitina fusiformisCyathochitina C. novempopulanica Cyathochitina campanulaeformis longicolla (EIS.) Angochitina Lagenochitina deunffi Lagenochitina

carnulus

sp. sp. denkmanni cf.

sp. sp. sp. sp. media recurvatur ia, P. foliata, P. kockeliana, kockeliana, P. foliata, ia, P. cf. . cf.

Oneotodus Acodus Oz. unicostatus Paltodus P Acodus walrathi Angulodus triangularis Belodella macrodentus B. devonicus, B. Briantodus H. austinensis, adunca, Hindeodella H. priscilla H. germane, multidens Ligonodina L. thoria curvatus Oistodus Ozarkodina congesta delicatulla Palmatodella unicostatus P. gracilis, Panderodus P. ang u st p e dobrogenis nnata P. decorosa, Polygnathus eifl P. pennata,P linguiformis, P. alternata P. alata, Prioniodina aurita Roundya fundamentata Ozarkodina Oz. typica Neoprionodus bicurvatoides Icriodus Carniodus 1999). Formation

et al. ed in the Tulcea-type Palaeozoic deposits from North Dobrogea (aft Dobrogea North from deposits Palaeozoic ed in the Tulcea-type

Rediu

Beştepe Formation Beştepe

Rediu Formation Rediu

D E V O N I A N A I N O V E D N A I R U L I S identifi record e fossil 1996; Vaida, in Seghedi 1996; Vaida, Th Stage Conodonts Chitinozoans Acritarcha Other LATE ORDOVICIAN Table 1. Table

689 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

from subgreenschist facies up to lower greenschist Th e ichnofaunal association with Helminthoides, facies was recorded in the siliceous shales (Seghedi Chondrites, Protopalaeodyction, etc., belongs to the 1999). Nereites ichnofacies and suggests accumulation at Th e ‘fl ysch-like member’ is represented by tightly the distal parts of the turbiditic fans, at water depths folded, fi ne grained, distal turbidites, fi lling small exceeding 800 m (Oaie 1989). Sedimentological synclines on top of siliceous rocks (Oaie & Seghedi features suggest that the turbidites accumulated in a 1994). Th ey are made of amalgamated thin beds sediment-starved, ponded basin. showing Tcde and Tde Bouma divisions (horizontal Th e siliceous member represents pelagic deposits, and ripple cross-laminated, fi ne-grained calcareous derived from radiolarian cherts and muds (Seghedi sandstones and dark mudstones) (Figure 12b), with et al. 1993). Th ey are interpreted to have accumulated abundant fl ute casts at the lower part of the sandstone on oceanic basement (Seghedi & Oaie 1994). lithofacies (O. Mirăuţă 1967). Ichnofauna is abundant Petrographic studies revealed that the lithological at the interface between d and e Bouma divisions and association is dominated by bedded radiolarian chert develops on top of the pelitic lithofacies (Figure 12c). (Figure 13) and siliceous slates, with minor bedded

(a) (b)

(c)

Figure 12. Views from the Tulcea-type Palaeozoic. (a) Outcrop-scale low-angle thrust in bedded cherts of Beştepe Formation (eastern part of the Beştepe Hills). (b) Tight normal folds in distal turbidites of Bestepe Formation (Pârlita abandoned quarry, Victoria). (c) Meandering trails on top of the pelitic lithofacies from distal turbidites of Beştepe Formation (Ilgani, Nufăru village). Th e trails indicate the deep water Nereites ichofacies.

690 A. SEGHEDI

(b)

(a) (c) Figure 13. Views from the cherts of the Beştepe Formation. (a) Borehole core of bedded chert (ch), consisting of white and dark siliceous layers rich in radiolaria (r). (b) Chert layer with radiolaria replaced by secondary silica. (c) Chert with ghosts of silicifi ed radiolaria, one individual still preserving spikes. iron carbonates and bedded iron sulphates and black few other outcrops (O. Mirăuţă 1967, 1971). Similar slates (Seghedi et al. 1993). Th ey show mineralogical micritic limestones, rich in more or less recrystallized evidence for deposition in anoxic conditions in a microfauna and upper Devonian conodonts (Asejeva basin below the CCD. Local interbeds of pelagic et al. 1981), are interbedded with siliceous deposits limestones suggest that for some time intervals, from the Orlovka quarry, on the northern bank of the deposition took place above the CCD level. Pelagic Danube (Slyusar 1984). Clastic deposits at Orlovka limestones form thin (1–5 cm) or thicker (10–40 yielded a Devonian palynological association cm) layers, interbedded locally in the siliceous rocks. (Velikanov et al. 1979), in good agreement with the Th ey have not been intercepted in any of the deep conodont ages. boreholes drilled in the core of the Tulcea-Mahmudia Th e Carboniferous is not documented in the anticline. deep marine sediments, although an indication for Th e Devonian age of the Beştepe Formation the Lower Carboniferous was given by palynological is based on the conodont fauna identifi ed in the data mentioned above. Considering the structure of interbedded limestones from the Beştepe Hills and a these successions, with northward younging tectonic

691 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

units formed by tectonic accretion beneath the upper Based on fi eld relations, metamorphic grade and plate, the presence of the Carboniferous cannot be K-Ar geochronology, the ages of the metamorphic precluded at depth, as shown in Figure 7. suites have been variously ascribed to the Devonian (Murgoci 1914; Rotman 1917), Cambrian and Ordovician (O. Mirăuţă 1966a; Seghedi 1980), or Th e Măcin-type Successions Late Precambrian (Ianovici & Giuşcă 1961; Giuşcă Th e largest area of Palaeozoic basement in North et al. 1967; Kräutner et al. 1988; Seghedi 1980, Dobrogea includes pre-Silurian metamorphic 1986a). An Early Cambrian age was assigned to formations, Silurian–Upper Palaeozoic the muscovite schists of the Boclugea group based anchimetamorphic rocks, as well as calc-alkaline on palynological data (Vaida & Seghedi 1999). Th e volcaniclastic suites and granitoids (Figure 11). microfl oral association, yielded by samples from Th e relationships between distinct metamorphic the Iulia borehole, consist of Acritacha, including terranes are tectonic, as well as their relations to the Micrhystridium sp., M. lanatum, Leiomarginata fossil-bearing Palaeozoic deposits (Seghedi 1980, simplex, Granomarginata prima, Uniporata nidius, 1986a). Th e Silurian to Upper Palaeozoic formations Tasmanites sp. were deformed in very low-grade metamorphic Th e youngest detrital zircon U-Pb ages (500–536 conditions, developing a slaty cleavage, penetrative in Ma) yielded by metamorphic rocks from the Măcin most lithologies (Seghedi 1985, 1986b). In Silurian– zone indicate that the maximum depositional age Lower Devonian lithologies, the steeply-dipping for the sedimentary protoliths of both the Boclugea penetrative cleavages strongly obliterate bedding. and Orliga sediments is Middle to Late Cambrian Th is deformation occurred prior to emplacement of (Balintoni et al. 2010). granitoid intrusions, which are surrounded by large Th ere are several lines of evidence indicating the areas of contact metamorphism. age of the Hercynian metamorphism. Single grain Metamorphic formations belong to three thrust- Ar-Ar dating of muscovites from Orliga samples has bounded groups, which vary in metamorphic grade yielded early Permian ages of 275±4 Ma on micaschist from middle-upper amphibolite facies (Orliga and 273±4 Ma on paragneiss (Seghedi et al. 1999) and Megina terranes) to lower greenschist facies (Figure 8). Monazite CHIME dating of metapelites (Boclugea terrane) (Figure 7). Th e lithology of the from the Orliga terrane yielded ages ranging between Orliga terrane is dominated by micaceous quartzites, 326±25 Ma and 282±38 Ma, indicating that the with subordinate metapelites, metabasic rocks and amphibolite facies metamorphic event took place in crystalline limestones, interpreted as an ancient the Late Carboniferous–Lower Permian time span accretionary complex (Seghedi & Oaie 1995; Seghedi (Seghedi et al. 2003a). Similar age ranges were yielded 1999). Metabasites in the Orliga Groups have the by monazites for the Megina metapelites (Seghedi, geochemical characteristics of ocean fl oor tholeiites Spear & Storm Hitchkock, unpublished data). (Crowley et al. 2000). Quartzites and phyllites make Th e Silurian – Cerna Formation – Th e succession up the Boclugea Group, a low-grade series of biotite includes a lower member of dark grey limestones grade metasediments. Th e Megina Group, dominated and shales, rich in pyrite and formed in an euxinic by amphibolites, with minor acid metavolcanics environment, and un upper member of black argillites and metapelites, is associated with orthogneisses. (O. Mirăuţă & E. Mirăuţă 1962; O. Mirăuţă 1966a); Geochemical features indicate that amphibolites the argillites show interbeds of quartz-muscovite represent ocean fl oor tholeiites associated with calc- sandstones and brown-yellowish limestones with alkaline rhyolitic volcanics (Seghedi 1999). REE rare organic debris (unidentifi ed gastropods, crinoid geochemistry suggests that mafi c volcanics of the ossicles). In their main outcrop area, the argillites Orliga and Megina terranes were generated by partial show highly discontinuous, lens-shaped bodies melting of a variably depleted mantle asthenosphere, of magmatic rocks with centimetric-decimetric with a contribution from a continental lithosphere thicknesses. Because these rocks are aff ected by component (Crowley et al. 2000). strong hydrothermal alteration, identifi cation

692 A. SEGHEDI

of their protoliths is extremely diffi cult. In most A review of the Lower Devonian fauna (Iordan outcrop areas, the Silurian deposits are overthrust 1999) revealed several features of the main faunal by quartzites and phyllites of the Boclugea group (O. assemblages presented in Table 2. Th e brachiopods Mirăuţă 1966a; Seghedi 1986a). Th e tight folding of form coquinas, along with corals, bryozoans, ostracods the deposits and superimposed deformation makes and trilobite fragments (Table 2). Tentaculitids also thickness estimation diffi cult. From bottom to top, form coquinas, sometimes exclusively covering the the facies succession indicates that basin shallowing rock surfaces and frequently associated with crinoids was accompanied by a transition from restricted to (Iordan 1974). normal marine conditions. Th e Cerna Formation was loosely ascribed Th e Late Palaeozoic – Carapelit Formation – to the Silurian based on macrofaunal remains, Continental deposits, reworking granites, quartzites like Cyathophyllum corals (Simionescu 1924), and phyllites (Murgoci 1914; Rotman 1917), were a Rastrites fragment (O. Mirăuţă & E. Mirăuţă separated as the Carapelit formation (Mrazec & Pascu 1962), the conodont Panderodus sp. and scarce 1896). Th eir primary relations with the metamorphic debris of tentaculites and corals (Iordan 1999). Th e basement are obscured due to subsequent Cimmerian identifi cation of the Lower Devonian conodont deformation. Th e oldest exposed conglomerates Icriodus woschmidti (O. Mirăuţă 1966a) in brown limestone interbeds within the argillitic succession rework limestone clasts that yielded Middle–Upper suggests an initial lithological continuity across the Devonian conodonts (O. Mirăuţă & E. Mirăuţă 1962), Silurian/Devonian boundary. while younger conglomerates rework quartzite and granite clasts, suggesting a reverse clast stratigraphy. Th e stratigraphic succession of the Carapelit Th e Lower Devonian – Bujoare Formation – Th e Formation (Figure 11) consists of lower, grey alluvial Lower Devonian deposits of the Măcin zone deposits, followed by continental red-beds and an show a thickness of 300–400 m (O. Mirăuţă & upper volcano-sedimentary succession (Oaie 1986; E. Mirăuţă 1962) and develop in Rhenish facies Seghedi & Oaie 1986; Seghedi et al. 1987). (Iordan 1974). Th e main lithological types are Alluvial deposits consist of grey alluvial fan- grouped into two members, representing the alluvial plain sequences, with debris fl ow and stream Geddinian and Coblenzian (O. Mirăuţă 1966a), respectively the Lochkovian–Emsian. According to fl ood conglomerates dominating the coarse members the stratigraphy of these authors, the lower part of and sandstone-siltstone cycles in the fl ood-plain the Lower Devonian succession includes white and deposits (Seghedi & Oaie 1986) (Figure 14c). grey limestones, overlying quartzitic sandstones Red beds (Martina red sandstones), up to 900 m (Figure 14a) interbedded with dark slates and brown thick, comprise a succession of pebbly red sandstones crinoidal limestones with Icriodus woschmidti. Th e (Figure 15a), showing both horizontal and planar upper part of the succession consists of discontinuous cross stratifi cation, and organized conglomerate beds, beds of quartzitic sandstones, black slates, calcareous with locally preserved clast imbrication; dessication limestones and crinoidal limestones (O. Mirăuţă & E. cracks and raindrop imprints are preserved in Mirăuţă 1962). Th e fauna frequently forms coquina places in thin, clayey, purple mud-drape facies (Oaie beds, suggesting deposition in an open shelf benthic 1986). Th ere is good fi eld evidence that the red beds environment (Iordan 1999). directly overlie wedge-shaped, alluvial fanglomerates Th e age of the clastics is indicated by a rich (Seghedi et al. 1987). Vertical facies distribution brachiopod-dominated fauna recovered from indicates an upward-coarsening sequence, deposited Bujorul Bulgăresc Hill (Cădere & Simionescu 1907; by a sandy braided river with fl uctuating discharge, Simionescu 1924), attesting the presence of the showing upward progradation of coarse, longitudinal Pragian–Emsian (Iordan 1974). Besides brachiopods bar deposits over sand dunes (Oaie 1986). Sandstone (Figure 14b), the Lower Devonian fauna contains petrography suggests that the onset of red bed crinoids and tentaculitids, with subordinate trilobites, deposition was related to a major climatic change, corals, bryozoans and ostracods (Iordan 1974). switching from a warm and humid climate which

693 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

(a)

(b)

(c)

Figure 14. Views from the Macin-type Palaeozoic. (a) Concentric folds deform decimetric orthoquartzite bed in the lower Devonian Bujoare Formation. Note cleavages fanning in anticline hinge. Only penetrative, steeply dipping cleavage planes are seen in mica-rich fi ne-grained sandstones overlying the orthoquartzite bed (Chior Tepe). (b) Brachiopod coquina in Bujoare Formation (Bujorul Bulgăresc Hill; aft er Iordan 1974). (c) Steeply-dipping slaty cleavage planes obliterating bedding in the alluvial plain member of the Carapelit Formation (Amzalar Hill). prevailed during alluvial fan sedimentation, to associations suggest that the style of sedimentation an arid, dry climate, that controlled the red bed was controlled by intermittent volcanic eruptions accumulation (Seghedi & Oaie 1986; Oaie 1986). (Seghedi et al. 1987). Overall volcanological Th e upper part of the Carapelit Formation features indicate that Hercynian volcanism in North is dominated by thick volcano-sedimentary Dobrogea was subaerial, characterized by calderas successions, consisting of superimposed cycles and plinian eruptions, while accumulation of the of pyroclastic deposits and coarse rhyolitic volcanic products was both subaerial and subaqueous epiclastic sequences. Pyroclastic rocks (Figure (in fl uvial and lacustrine environments). 15b) are dominated by large volumes of calc- Due to lack of fossils, the age of the Carapelit alkaline ignimbritic rhyolites (up to 1000 m thick), Formation is poorly constrained. It has been ascribed interbedded with air fall tuff s, rare base surge to the Permo–Carboniferous (Mrazec & Pascu 1986; deposits or accretionary lapilli tuff s and display the Rotman 1917), Carboniferous (Cantuniari 1913), geometry of superimposed fl ow units. Vertical facies Lower Carboniferous–Upper Devonian (Murgoci

694 A. SEGHEDI (Richt) sp. sp. sp. sp. ed gastropod gastropod ed cf. sp. unidentifi Palynomorphs Micrhystridium M. lanatum simplex Leiomarginata primaGranomarginata nidius Uniporata Tasmanites Trilobites Pilletina hammerschmidti Homalonotus Phacops Rastrites sp. sp. sp. sp. 1988) et al. Graptolites Bryozoans Eridotrypa Fenestella Hemitrypa

Ludw. Ludw. sp. sp. sp. sp. Tentaculitids Tentaculites scalaris Schl. durus Uniconus Crinoids typous Ctenocrinus bronn striatus Technocrinus (Hall) (Hall) Lophocrinus Conodonts Panderodus Entrochus Conodonts woschmidti Icriodus

C. dalmania ex gr. ex gr. cf. sp. sp. sp. Rom. er Iordan 1974; Mirăuţă 1965; Vaida, in Baltres in Baltres 1965; Vaida, 1974; Mirăuţă er Iordan radiculum Lindstroemia Paeck. Zaphrentis Cladochonus Corals Cyathophyllum Cyathophyllum ). (Vern.) (Vern.) (Arch.et (Arch.et (Oehlert) (Arch.et Vern.) (Arch.et (Schnur) (Maur (Scup.) (Buch) (Buch) (Schnur) (Schnur) (Schnur) (Stein.) (Phill.) (Phill.) (Vern.) (Schnur) (Schnur) (Roem.) (Schl.) (Schl.) (Sow), (Sow),

Kays. naranjoana sedgwicki . . minutus aff sp. Sow. Sow. . archiaci aff (d’Orb.) antiquus aff (Sow.) undulifer cf. Schnur cf. sp. ex gr. rhomboidalis (Wilch.) (Wilch.) rhomboidalis ex gr. sp. (Geib.) ’ cf. Spirifer Brachiopods Schizophoria provulvaria Dalmanella circularis D. fascicularis strigosa ‘Orthis’ Leptaena Pholidostrophia Rhenostrophia subarachnoidea Rhenostrophia Vern.) Stropheodonta S. explanata Douvillina interstrialis hipponix Schellwienella Chonetes sarcinulatus C. plebejus Strophochonetes tenuicostatus Retichonetes primaevus Acrospirifer A. pellico primaeviformis A. pellico Camarotoechia Meganteris Euryspirofer arduennensis Euryspirofer hystericusHysterolites Uncinulus Brachyspirifer carinatus bischofi Fimbrispirifer ‘ Cerna Cerna Bujoare Bujoare Boclugea Quartzites Formation Formation (Iulia borehole) (Iulia (aft formations Palaeozoic Măcin-type the of record e paleontological Th Lower Silurian Devonian Cambrian Ordovician Table 2. Table

695 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

(a) (b)

Figure 15. Views from the Carapelit Formation and Permian dykes. (a) Steep bedding in red sandstone and microconglomerate of the Carapelit Formation (Crapcea Hill). (b) Rhyolitic ignimbrite of the Carapelit Formation, showing pumice (dark) and crystalloclasts (light) in a welded tuff matrix. (c) Steep dykes of trachyte (left ) and alkali basalt (right) emplaced in turbidites of the Bestepe Formation (Pârlita abandoned quarry, Victoria). (d) Detail from the trachyte dyke, showing K feldspar phenocrysts in a pink, fi ne-grained matrix (Pârlita abandoned quarry, Victoria).

1914) and Lower Carboniferous (O. Mirăuţă & E. grained members, palynological data and microfaunal Mirăuţă 1962). Th e only fossil discovered so far is content of the reworked limestone clasts indicate that a plant, variously identifi ed by various authors as the Carapelit Formation is certainly post-Devonian. Calamaria, Asterocalamites or Archaeocalamites A Permo–Carboniferous (Late Carboniferous–early (Atanasiu 1940); these taxa indicate various Permian) age is favoured, based on the presence of time intervals – Upper Carboniferous or Upper red beds and volcaniclastic sedimentation (Mrazec & Devonian–Lower Carboniferous. A re-examination Pascu 1986; Rotman 1917; Oaie & Seghedi 1992). of this fossil is impossible, as the sample seems to be lost. Pelitic samples from Carapelit Hill yielded a poorly-preserved palaeontological content, Hercynian Calc-alkaline Intrusives – Field relations obviously reworked, including acritarchs, trilete demonstrate that two main phases of granitoid spores, chitinozoans, scolecodonts and microspores, emplacement took place in the Măcin Zone, before all suggesting the Silurian–Carboniferous interval and aft er the deposition of the Carapelit Formation (Vaida, in Seghedi et al. 1986). All existing (Rotman 1917). Older generation intrusives include information, derived from the petrography of coarse- mainly biotite granite, porphyritic biotite granite or

696 A. SEGHEDI

leucogranite, emplaced in Boclugea quartzites and Late Permian Alkaline-Sub-alkaline Magmatism phyllites and accompanied by contact metamorphic Dyke Swarms of the Basalt-trachyte Bimodal aureoles or metasomatic eff ects resulting in garnet- Association – Alkaline magmatic rocks are recorded diopside skarns. Such granites, along with their low- in two diff erent areas of North Dobrogea, forming grade metamorphic host rocks are reworked in the distinct petrological associations. A tectonic control Carapelit conglomerates. is suggested by their development south of the Sfantu Younger generation intrusives represented by Gheorghe Fault and north of the Peceneaga-Camena the Greci massif form a suite of highly diff erentiated Fault. I-type calc-alkaline rocks, ranging from dioritic and An E–W-trending dyke-swarm of the basalt- gabbroic facies to leucogranites, but dominated by trachyte bimodal association is emplaced exclusively biotite-hornblende granodiorites and tonalites. Th ese in the Upper Ordovician–Devonian deep marine massifs are emplaced in the Carapelit Formation as successions developed between the Sfântu Gheorghe high level, high temperature intrusives, with both and Teliţa Faults (Figure 9). Th e E–W- to ESE–WNW- cross-cutting and partly conformable contacts, trending, steeply-dipping dykes are known both from producing large contact metamorphic areas and local outcrop (Figure 15c), and from borehole drillings garnet-pyroxene skarns. Rocks are rich in xenoliths (Seghedi, in Baltres et al. 1988, 1991, 1992). Th e age of hornfelsed country rocks, as well as various types of the dyke-swarms is pre-Triassic, as documented by of cognate xenoliths. Geochemical data suggest a fi eld relations in outcrops at Hora Tepe (Monument mantle source for basic end members and a deep Hill), Tulcea (O. Mirăuţă 1966b). On the northern or mid-crustal environment for the genesis of the slope of Hora Tepe in Tulcea, steeply dipping trachyte granitic rocks, as well as evolution of a syn-collisional dykes intruding Devonian siliceous sediments of the geotectonic setting (Tatu & Seghedi 1999). Beştepe Formation are truncated by Lower Triassic K-Ar geochronological ages indicate Late (Werfenian) fanglomerates which rework clasts of Carboniferous (306, 320, 329 Ma) and early Permian the dyke rocks. ages (264 Ma) for the main intrusive bodies (Mînzatu Both in outcrops and boreholes, the subvolcanic et al. 1975). An apparent plateau age of 242.2±2.1 rocks display intense hydrothermal alteration Ma, yielded by biotite concentrate from the Greci that obscures their initial petrography (Seghedi granodiorite, indicates the Late Permian-Skythian et al. 1994). In basalts and olivine basalts, olivine interval (Seghedi et al. 1999). Considering that these and pyroxenes are replaced by dolomite and iron intrusives are cut by early Triassic dolerite and rhyolite carbonates, associated with various amounts dykes, this thermal event has been interpreted as the of chlorite and secondary silica. Trachytes are result of ductile mylonitization of the Hercynian porphyritic, with alkali feldspar phenocrysts in a basement during early Triassic rift ing. feldspar-dominated matrix (Figure 15d) showing Intrusives in the Tulcea Zone, dated as Middle weaker hydrothermal alteration, with only incipient Carboniferous by the K-Ar method (Mînzatu et replacement of feldspars by carbonates and illite. al. 1975) represent a suite of peraluminous, S-type Geochemical features of the dykes reveal the diff erentiated granites, emplaced as high temperature, bimodal character of the magmatism and suggest low level intrusions (Seghedi et al. 1994b). Th eir an intraplate setting (Seghedi et al. 1994a, b). Th e emplacement produced a high temperature-low bimodal association and the presence of high-K pressure metamorphism in their Lower Palaeozoic trachytes suggest magma generation in a complex host rocks. Th is suite consists of two mica granites, extensional setting, probably transitional between with hornblende in minor tonalitic facies and an active continental margin and extensional garnet in pegmatites, commonly rich in biotitic (transtensional) intraplate setting. Th e structural xenoliths and in zoned K-feldspar megacrysts. Th eir trend of the dyke swarm suggests generation in a geochemistry suggests formation by plagiclase and N–S-oriented stress fi eld. Th e bimodal association zircon fractionation from a magma formed by partial shows similar petrographic features and geochemical melting of the lower crust. signature and even the same type of extensive

697 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

hydrothermal alteration as the Permian volcanic Th e overall lithological succession and main rocks from the Scythian Platform, and therefore the biostratigraphic zones of the East Moesian Palaeozoic dykes are interpreted as connected with the Permian are shown in the synthetic lithological log from Figure rift ing of the Scythian Platform. 18. Detailed lithological logs of the main boreholes are presented in the review of the Moesian Palaeozoic (Seghedi et al. 2005a, b). Late Permian Sub-alkaline Magmatism – Along the south-western margin of North Dobrogea, parallel to Th e Palaeozoic succession begins with moderately the Peceneaga-Camena Fault, several small bodies of dipping Cambrian–Ordovician clastics and/or alkaline rocks have been emplaced in the Palaeozoic Wenlock to Lower Ludlow shales. It is considered country rocks, including the Carapelit Formation that the last folded member of this unit is the Lower (Cantuniari 1913; Întorsureanu et al. 1989) (Figures Ludlow, because in the 5083 Mangalia and 2881 6 & 7a). Th e most representative, Turcoaia massif, Călăraşi boreholes, the Lower Ludlow is overlain is made up of two distinct plutonic and hypabyssal above an angular unconformity by a fl at-lying associations which were intruded in a narrow succession starting with the Upper Ludlow (Răileanu time range as a concentric or ring-complex (Tatu et al. 1966, 1967; Paraschiv 1974). & Teleman 1997; Tatu 1999). From the core to the Th e Silurian deposits, with a maximum thickness periphery, quartz-syenites, monzogranites, alkali- of 700 m at Călăraşi, overstep the Ordovician granites and alkali-rhyolites occur. Values of the strata, directly overlying the Upper Neoproterozoic 87 86 Sr/ Sr ratio (Pop et al. 1985) suggest that crustal basement in the Romanian Plain. Th e largest part of anatexis took place in a continental, intraplate setting the Llandovery corresponds to a regional gap, only its (Tatu 1999). Mineralogical and geochemical data uppermost part being preserved in some boreholes indicate that the Turcoaia alkaline massif represents (Iordan 1981, 1982, 1984). An angular unconformity an A-type magmatic type with complex within-plate was recorded between the Lower and Upper Ludlow evolution. in the Călăraşi and Zăvoaia boreholes, accompanied Th e question of the emplacement age is not yet by a lithological change from graptolite shales to properly answered, as whole rock Rb-Sr radiometric argillites (Răileanu et al. 1967; Iordan 1981). dating has yielded a large age range from Permian Th e Silurian–Devonian boundary is continuous to Triassic (Mînzatu et al. 1975). However, a Late in the Zăvoaia and 2881 Călăraşi boreholes, marked Permian Ar-Ar age was yielded by riebeckites from the Turcoaia massif (Teleman, unpublished data). As by a change in facies from argillites to quartzitic the plutonic complex is cut by lower Triassic dykes sandstones. An angular unconformity was recorded of the basalt-rhyolite bimodal association, the Ar-Ar between the Silurian and Devonian in the 5083 age should be very close to the emplacement age of Mangalia borehole (Răileanu et al. 1966), similar to the Turcoaia massif. that recorded on the northern and western platform margin, in West Moesia (Paraschiv 1974). In East Moesia the Tournaisian–Lower Visean Palaeozoic Deposits of East Moesia corresponds to a regional stratigraphic gap (Iordan Th e Palaeozoic formations of East Moesia are 1999), unlike in West Moesia, where the Upper documented in 16 boreholes in South Dobrogea Devonian carbonate succession continues into and in 19 boreholes in the Romanian Plain (Figure the Carboniferous as far as the Namurian (Lower 16). Aft er penetrating thin Palaeozoic successions, Bashkirian) (Iordan 1988). several boreholes in the Romanian Plain bottomed in Ediacaran basement (Bordei Verde, Ţăndărei, Călăraşi, Zăvoaia boreholes etc.), which shows Cambrian–Ordovician – In South Dobrogea the similar facies with that from Central Dobrogea. Based presence of the Cambrian is not yet documented by on these data, the spatial distribution of the East fossils. It is assumed that the Cambrian represents Moesian Palaeozoic deposits and of their basement the lower part of the shallow marine quartzitic rocks are shown in Figure 17. sandstones over 500 m thick, intercepted in the 5083

698 A. SEGHEDI

Figure 16. Distribution of main boreholes intercepting Palaeozoic deposits in East Moesia (modifi ed from Seghedi et al. 2005).

Mangalia borehole, which in their upper part contain characterized by the hirundo graptolite zone (Iordan

Ordovician palynological assemblages (Paraschiv et 1992) and by O1 and O3 palynomorph zones (Beju al. 1983). 1972, 1973). In the Romanian Plain, an Arenig fauna was recorded in black argillites and grey-greenish Th e Ordovician succession consists of sandstones glauconitic siltstones from the Bordei Verde borehole. and orthoquartzites with shale interbeds, overlain Th e fauna includes the graptolites Didymograptus by glauconite-bearing shales (Murgeanu & Patrulius hirundo (Salt.) and the inarticulate brachiopods 1963; Beju 1972). Th e shales contain graptolites, Lingulella aff . davisii McCoy (Murgeanu & Spassov palynomorphs and brachiopods. Th e Ordovician is 1968).

699 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

Figure 17. Permian subcrop map showing the distribution of Precambrian basement rocks and Palaeozoic deposits in East Moesia (modifi ed from Seghedi et al. 2005).

Silurian – Th e Silurian sediments show the typical Iordan 1981, 1990; Paraschiv & Muţiu 1976). Th e graptolite shale facies, classical in the lower part maximum total thickness of the Silurian deposits (Wenlock–Lower Ludlow) and mixed in the upper from East Moesia is about 1000 m. In the Călăraşi part (Upper Ludlow and Přídolí) (Grigoraş 1956; and Zăvoaia boreholes, the limit between the Lower

700 A. SEGHEDI

Figure 18. Schematic lithological log of Palaeozoic formations from East Moesia (modifi ed from Seghedi et al. 2005a), showing the graptolites, tentaculites, trilobites, conodonts and brachiopod zones (aft er Răileanu et al. 1967; Iordan 1967, 1972, 1981, 1985, 1987b, 1988, 1992; Iordan & Rickards 1971; Iordan et al. 1985, 1987a) and chitinozoan zones (Beju 1972; Vaida et al. 2004).

701 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

and Upper Ludlow is marked by a change in facies Th e lithology refl ects various tidal-fl at environments, from black shales to argillites. In the mixed type of from supratidal to intertidal, as revealed by the graptolite shale facies, the fauna is represented microfacies studies (Vinogradov & Popescu 1984). by small bivalves (Cardiolidae, Lunulacardiidae Th e biostratigraphy of the Devonian was and Antipleuridae families), fl attened orthocone established in two boreholes in East Moesia, the 5082 cephalopods, microbrachiopods, corals (Favosites Mangalia and 2881 Călăraşi boreholes (Răileanu gothlandicus), crinoidal ossicles and scarce graptolites et al. 1967). Besides conodonts, tentaculites and (Table 3). trilobites, the Devonian biostratigraphy is based on Th e biostratigraphy of the Silurian is based on brachiopods, psilophytal plants, as well as placoderm graptolite zones: insectus-centrifugus, murchisoni and and ostracoderm fi shes. fi rmus zones for the lower Wenlock (Ţăndărei and Th e Lochkovian is indicated by the Icriodus Bordei Verde boreholes); radians and lundgreni for the woschmidti conodont zone (Răileanu et al. 1967). upper Wenlock (Iordan & Rickards 1971); nilssoni- Two global chitinozoan biozones of the Lochkovian scanicus and incipiens for the lower Ludlow (Tuzla- were identifi ed: Eisenackitina bohemica and Costineşti, 5083 Mangalia, Biruinţa, 2881 Călăraşi Urochitina simplex (Beju 1972; Vaida et al. 2004). Th e and Ţăndărei boreholes); bohemicus and inexpectatus Lochkovian assemblage also contains Bursachitina zones for the Upper Ludlow (Biruinţa, Ţăndărei, oviformis Eisenack (Lakova 1993; Vaida et al. 2005). Călăraşi and Zăvoaia boreholes) (Iordan 1981, 1990); ultimus-formosus for the Přídolí (Ţăndărei, Th e Pragian is indicated by the tentaculites zones 2881Călăraşi and Zăvoaia boreholes) (Table 4). Th e Nowakia acuaria and Voliynites velainii (Iordan 1967, Silurian chitinozoan associations are described in 1981; Iordan et al. 1985, 1987b). Besides tentaculites, the Ţăndărei borehole (Beju 1972; Iliescu 1976) and the assemblage includes brachiopods, bivalves, Zăvoaia (Vaida et al. 2004; Vaida & Verniers 2005), crinoids, ostracods, corals and gastropods (Table 4). the latter including the very short range top Přídolí Th e Emsian faunal assemblage is dominated Eisenachitina fi lifera and E. lagenomorpha. by trilobites and bivalves, with subordinate brachiopods, gastropods, orthoceratidae, corals, crinoids, bryozoans and ostracods. Th ree Emsian Devonian – Th e lower Devonian (Lochkovian – trilobite zones were identifi ed in the Mangalia and Emsian), up to 460 m thick, represents a continuation Călăraşi boreholes: Pseudocryphaeus prostellans, of the pelitic facies of the Silurian. It consists Pilletina asiatica and Dipleura fornix (Iordan 1967, of argillites, argillaceous shales, marly or sandy 1981, 1988). Th e trilobite assemblage is presented in argillites, dark siltstones with subordinate grey Table 4. quartzitic sandstones, showing coquina interbeds. Th e lower Devonian–Eifelian interval (Smirna Th e brachiopods recovered indicate a Lochkovian– quartzitic sandstones), 120 m thick, is dominated by Emsian age (Iordan 1999). Th e most representative quartzitic sandstones, orthoquartzites and quartzitic species, along with associated bivalves, are shown in conglomerates, with minor interbeds of black argillites Table 4. and dolomitic limestones. Red arkosic sandstones Th e Eifelian is characterized by the N. maureri occur toward the top of the sandstone facies in the tentaculites zone. Th e Eifelian clastic facies is rich in 5083 Mangalia and 2881 Călăraşi boreholes. psilophytal plants, placoderm and ostracoderm fi shes, Th e overlying Givetian–Famennian deposits while brachiopods, tentaculites, crinoids, bivalves, represent a carbonate-evaporite succession up to gastropods, corals, eurypterids, ostracods and 905 m thick in the Smirna borehole, separated conodonts are subordinate. Psilophital plants include as the Călăraşi Formation s. str. (Răileanu et al. Pseudosporochonus krejcii Pot. et Bern., Aneurophyton 1967; Iordan 1981). Th e bio- and lithofacies of the germanicum Kr. et Weyl., Calamophyton primaevum Călăraşi Formation include organogenic limestones, Kr. et Weyl. and Hyenia sp. (Răileanu et al. 1966; dolomites, as well as black limestones with evaporite Iordan et al. 1985). Th e placoderm and ostracoderm interbeds, with minor black argillites and sandstones. fi shes (Lunaspis broilii Gross, L. sp., ?Wijdeaspis sp.

702 A. SEGHEDI sp. sp. Mcoy Leptostrophia Scyphocrinites Scyphocrinites sp. sp. sp. sp. davisii davisii sp. . sp. aff Brachiopods/Crinoids Plectodonta Plectodonta Howellella Crotalocrinus Lingulella Orbiculoidaea Orbiculoidaea y Iordan (1999). y Iordan (Barr.) (Barr.) sp. primaevum sp. sp. sp. sp. cf. sp. ex. gr. ex. gr. sp. (Forbes) Nautiloids Cephalopods – Orthocone ‘Orthoceras’ ‘Orthoceras’ (Forbes) Parakionoceras Geisonoceras Geisonoceras Michelinoceras Geisonoceras Geisonoceras Michelinoceras ‘Orthoceras’ vertebratum vertebratum ‘Orthoceras’ Primaevum Geisonoceras rivale rivale Geisonoceras ‘Orthoceras’

Barr. Sow. Barr. (Barr.), (Barr.) Lunulacardium (Barr.) delis delis evolvens evolvens Barr. Barr. C. bohemica cf. D. fi C. interrupta C. interrupta . bohemica (Barr.) Barr. Barr. ex.gr. ex.gr. cf. sp. cf. sp. sp. aff sp. sp. fortis . cf. C Dualina Lunulacardium Cardiolita Cardiolita Cardiolita insolita‘Cardiola’ undulatum Dualina Butovicella migrans migrans Butovicella Cardiola sp. sp. Eis. Nich. Neodiversograptus Neodiversograptus Bouč. et Münch (Tullb.) (Gort.) (Barr.) (Barr.) (Barr.) (Barr.). (Jaeck.) (Bouč.) (Törnq.) Carr. (Salt.) (Richter) Iordan Iordan Tullb. (Richter) (Richter) (Salter) (Bronn) Barr. (Barr.) Graptolites Bivalves (Suess) (Suess) Tullb. (Lapw.) Eisel (Teller) Bouč. (Barr.) (Bouč.) umendosae umendosae (Hall) emingii (Tullb.) ex gr formosus Bouč. ex gr formosus Tullb. (Barr.) (Suess) (Tullb.) (Bouč.) Bouč. N. nilsoni N. nilsoni extensus extensus rmus rmus . dubius . dubius . sp. A . sp. cf . sp. 1 . sp. . cf. M. fi M Linograptus posthumus L ex .gr. ex .gr. M. incipiens M. incipiens Monograptus uncinatus uncinatus Monograptus Holoretiolites (Balticograptus) balticus balticus (Balticograptus) Holoretiolites macilentus Plectograptus Bohemograptus bohemicus grigoraşii Pristiograptus Linograptus posthumus Retiolites geinitzianus geinitzianus Retiolites pulchellus Barrandeograptus priodon Monograptus M. pseudocultellus M. pseudocultellus M. kolihai M. kolihai vomerinaMonoclimacis vomerina M. vomerina basilica M. linnarsoni praedubius Pristiograptus P. Cyrtograptus murchisoni C. sp.1. Didymograptus hirundo D Monograptus rarus Saetograptus grigoraşii Pristiograptus Pristiograptus dubius dubius Pristiograptus Saetograptus collonus S. chimaera Bohemograptus bohemicus Monoclimacis micropoma micropoma Monoclimacis scanicus Lobograptus nilssoni Neodiversograptus praemacilentus Plectograptus fl Monograptus Monoclimacis fl Monoclimacis dubius Pristiograptus pseudodubius P. trilleri Cyrtograptus C. lundgreni 1981, 1990), revised b (Iordan in East Moesia the Silurian facies of mixed shales and in the graptolite recorded faunas e main Th Lower Ludlow Boreholes Mangalia, Tuzla-Costineşti, Ţăndărei Călăraşi, Biruinţa and Upper Ludlow Călăraşi, Zăvoaia, Boreholes Biruinţa and Ţăndărei Lower Wenlock Bordei and Ţăndărei Boreholes Verde Ordovician Borehole Mangalia Přídolí Călăraşi, Boreholes Zăvoaia and Ţăndărei Upper Wenlock Upper Ianca-Berlescu and Boreholes Verde Bordei Table 3. Table

703 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA (Dahm.) Iordan . 1985; Iordan . 1985; Iordan Fuchs (Goldf.) Dienst. Dienst. (Maur) (Maur) Sandb. (Goldf.) et al

Mun. Ch. Mun. sp. sp. atum sp. sp. Iordan armorica . aff Actinopteria costata Leiopteria mandelensis Parallelodon Orthonota triplicata rugosa Paracyclas Carydium infl Cypricardinia Praectenodonta Praectenodonta Grammysia mangalica G. Grammysioidea inaequalis calatica ellipticus Nuculites Paleosolen costatus

(Hall) (Hall) (Barr.) (Conrd.) Kozl. Mcoy (Vern.) Dahm. Havl. davisii davisii (Stein.) . aff Brachiopods Bivalves/Foraminifera Plants/ . 1966; Patrulius & Iordan 1969, 1970; Iordan 1969, 1970; Iordan & Iordan . 1966; Patrulius et al Schelwienella umbraculum Schelwienella umbraculum (Schl.) unkelensis Chonetes trigeri Fimbrispirifer Leptostrophia index Schizophoria multistriata podolica Mutationela daleidensis F. najadum Najadospirifer arenosus Costispirifer sp. er Răileanu Răileanu er (Roem) Iordan Corniculina pectinata pectinata

(Eaton) Ljasch. Iordan Paris & Laufeld Paris Iordan Boumendjel (Roem.) . (Eisenack) Paris and Laufeld and Paris sp Haas lifera sp. răileanui

gyracanthus

Maill. (Sow.) Trilobites / Tentaculitids / / Tentaculitids Trilobites Conodonts / Chitinozoans Eisenachitina fi E. lagenomorpha Urnochitina urna kameli Urnochitina klonkensis Linochitina krizi Bursachtina Pseudocryphaeus prostellans hammerschmidtiP. gervilei rumaniana Parahomalonotus Burmeisteria Dipleura fornix Tentaculites straeleni T. ornatus T. Prolationus praelongus macarovici Multiconus plusquelleci Cingulochitina C. ervensis C. serrata, lata Fungochitina catenaria Margachitina Armoricochitina Ancyrochitina

Zones 2004) et al. rmus hirundo Lingulella ultimus-formosus inexpectatus bohemicus incipiens nilssoni-scanicus lundgreni radians fi murchisoni insectus-centrifugus Pseudocryphaeus prostellans asiatica Pilletina Dipleura fornix Nowakia acuaria acuaria Nowakia velainii Voliynites woschmidti Icriodus Eisenackitina bohemica simplex Urochitina (aft East Moesia of deposits the Ordovician–Emsian of faunas and zones e main Th 1999; Vaida 1999; Vaida Ordovician Upper Wenlock Upper Lower Wenlock Emsian Pragian Lochkovian Přídolí Upper Ludlow Lower Ludlow Table 4. Table

704 A. SEGHEDI

Obrucev, Drepanaspis sp., ?Kiaeraspis sp.) (Patrulius Lower Carboniferous carbonate rocks. Th e clastic & Iordan 1969, 1970), along with brachiopods and succession consists of clays, siltstones and sandstones crinoids are associated with the tentaculite Nowakia rich in plant debris, with limestone intercalations and maureri Zagora and Homoctenus cf. hanusi (Bouc. et coal layers. Th e lithofacies is deltaic in the Bashkirian Prantl.) (Iordan 1999) (Table 5). and sabkha-type in the Moskovian and Bashkirian Th e Givetian is indicated by the tentaculite (Pană 1997). In places, basic and acid volcanic rocks and brachiopod zones Tentaculites conicus and are associated with the clastics (Paraschiv 1986c). respectively Fimbrispirifer venustus and Mucrospirifer Plant remains are abundant (Calamites, Stigmaria, mucronatus. Th e faunal assemblage (Table 5) includes etc.) (Iordan 1999). tentaculites, brachiopods and stromatoporids (Iordan 1967, 1981, 1988; Iordan et al. 1985). Permian – Th e Permian deposits are little Th e Frasnian is documented by the Homoctenus represented in East Moesia, despite their large-scale krestovnikovi tentaculite zone and Mucrospirifer development in West Moesia. Sedimentary breccias bouchardi brachiopod zone. Th is assemblage (Table from the Dobromiru borehole, 54 m thick, lying 5) includes tentaculites and brachiopods (Iordan unconformably on top of lower Upper Carboniferous 1967, 1981, 1988). clastics and unconformably overlain by Jurassic Th e Famennian (Viroaga Limestones), identifi ed sandstones, have been ascribed to the Permian only in the Viroaga borehole from South Dobrogea, (Iordan et al. 1987b). Th e proximal clastic facies of is indicated by the brachiopod zone Cyrtospirifer the Permian suggest deposition next to a tectonic archiaci and the conodont zone Palmatolepis crepida uplift , very likely the rift shoulder referred to as the (Iordan et al. 1987a); the assemblage consists of North Bulgarian high. Th e typical Permian facies of brachiopods and conodonts, along with holothurian continental red-beds is widespread in West Moesia. sclerites, ophiuroids, Moravamminids and West of Mangalia, a Permian limestone facies was calcispheres (Table 5). identifi ed based on foraminifera (Pană 1997). It represents a continuation of the limestone facies of the Upper Carboniferous. Carboniferous – Th e Middle–Upper Visean reaches 268 m thick in the Dobromiru borehole from South Dobrogea. Th e facies succession in this borehole Palaeocontinental Affi nities consists of dark limestone intervals up to 11 m thick, During the Neoproterozoic, three accretionary interbedded with black and grey mudstones and dark orogens may be defi ned along continental margins sandstones rich in plant debris (Iordan et al. 1987b; (Ziegler 1990). Th e Baikalian-Timanian orogen Iordan 1999). is confi ned to processes at the edge of the Baltica In contrast with the Upper Devonian carbonate palaeocontinent (or East European Craton), while the succession, the limestones and dolomites of the Lower Pan-African and Cadomian are related to Gondwana Carboniferous facies are devoid of evaporites. Th eir margin. maximum thickness is 1580 m, attained in the 2881 Peri-Gondwanan terranes, originating from Călăraşi borehole. Th e Visean bio- and lithofacies the northern and western margins of Gondwana, includes endothyracee and algae (Paraschiv & are separated into 4 types, based on their detrital Năstăseanu 1976; Pană 1997); the outer platform zircon sources: Avalonian, Ganderian, Cadomian facies developed over large areas (Vinogradov & and Cratonic (Nance et al. 2008). Avalonian terranes Popescu 1984). represent oceanic volcanic arcs within the Panthalassa Th e upper part of the Carboniferous consists Ocean surrounding the Rodinia supercontinent, of a coal-bearing clastic succession about 350 m accreted to the Gondwana margin by 650 Ma. Th e thick (Vlaşin Formation, Namurian–Westphalian) main source for Avalonian detrital zircon was the (Paraschiv & Popescu 1980; Paraschiv et al. 1983), Amazonian craton. Th e Ganderian and Cratonic unconformably overlying the Middle Devonian or terranes have peri-Amazonian detrital zircon sources,

705 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

& . 1985; Iordan . 1985; Iordan et al Kr. et Weyl. et Kr. Pot. et Bern. Kr. et Weyl. Weyl. et Kr. . sp.? L Ostracoderm Fishes Gross primaevum

sp. sp. sp. Obrucev sp. Plants/ Bivalves / Foraminifera/ Placoderm Kiaeraspis Hyenia Pseudosporochonus krejcii krejcii Pseudosporochonus germanicum Aneurophyton Calamophyton Wijdeaspis Wijdeaspis Drepanaspis ? Lunaspis broilii Lunaspis broilii Calamites Stigmaria interstrialis Aviculopecten Endothyra bradyi . spp. C Rzhon. (Stuck.) (Conr.) (Conr.)

ﬁ (Hall) (Murch.) (Conr.) (Conr.) (Hall) (Dav.) Ivania (Hall) Bulb. . 1966; Patrulius & Iordan 1969, 1970; Iordan 1969, 1970; Iordan & Iordan . 1966; Patrulius (Murch.) (Havl.) Phill. demissa et al Cl. et Sw. martianof Havl. sp. bouchardi bouchardi mucronatus mucronatus sp. (S.) penelope marki

sp. aff. aff. Brachiopods/Stromatoporids rowei rowei

sp. Athyris vittata Janeia primaeva Mucrospirifer Mediospirifer audacula Spinocyrtia Devonochonetes scitulus kuzbasica Atrypa reticularis Fimbrispirifer venustus Mucrospirifer Amphipora ramosa Fimbrispirifer Rhipidomella rotunda Leptostrophia Markitoechia Cyrtospirifer archiaci Cyrtospirifer archiaci C. tchernychevi sibirica Productella Athyris Megachonetes Chonetes Strophodonta Strophodonta Daviesella llangolensis Dictyoclostus semireticulatus D. multispiniferus giganteus Gigantoproductus G. bisati Dictyoclostus retiformis carbonarius Productus Posidonia corrugate er Răileanu Răileanu er Maill. Ljash. Brans. et Mehl. (Pross.) T. straeleni T. (Bouc. et Prantl.) Sand. Roem.

Sand. Zagora hanusi . ortha Trilobites/Chitinozoans sp. A. stoppeli

cf. sp. Conodonts/ Tentaculitids/ cf conicus sp. F ex. gr. sp. F ex. gr.

cilis ﬁ Tentaculites Homoctenus Polygnathus linguiformis alveolus linguiformis gamma morph. P. xylus P. Icriodus norfordi I. orri expansa Panderodus Tentaculites Tentaculites Polygnathus webbi decorosus P. dubius P. xylus P. Ozarkodina congesta Dicricoconus T. bellulus potomacensis T. Homoctenus Icriodus brevis I. dif Polygnathus varcus, ansatus P. linguiformis weddigei P. parawebbi P. xylus P. Ozarkodina ballai O. lata Gnathodus symmetricusSyphonodella isosticha Quasiendothyra cobeitusana Megachonetes zimmermani Palmatolepis Icriodus cornutus Hibbardella Palmatolepis glabra lepta gracilis P. Zones Palmatolepis crepida Polygnathus nodocostatus

2004; Königshof & Boncheva 2005). 2004; Königshof et al. N. maureri Nowakia maureri Tentaculites conicus Fimbrispirifer venustus Tentaculites mucronatus Mucrospirifer Homoctenus krestovnikovi Mucrospirifer bouchardi Mucrospirifer Homoctenus krestovnikovi Homoctenus krestovnikovi Syphonodella isosticha Quasiendothyra cobeitusana Cyrtospirifer archiaci (aft East Moesia of deposits the Eifelian–Westphalian of faunas and zones e main 1999; Vaida 1999; Vaida Th Eifelian Givetian Namurian- Westphalian Frasnian Visean Tournaisian Famennian Table 5. Table

706 A. SEGHEDI

formed either of recycled crust, or from material not According to the ‘Scythian orogen’ model, the aff ected by Avalonian-Cadomian continental margin southernmost part of the East European Platform magmatism. Th e Cadomian terranes were supplied formed a passive margin of Baltica from the with detrital zircons derived from the African craton. Cambrian until the collision and docking of the Scythian Platform crust in the Late Palaeozoic, which Th e confi guration of palaeocontinents at the in this case would include terranes with both Baltican end of the Neoproterozoic is shown in Figure 19. and peri-Gondwanan affi nity. Th is model is based on Laurentia, which started to separate from West the assumption that the Scythian Platform represents Gondwana opening the Iapetus Ocean, includes an eastward prolongation of the Variscan orogen North America, Greenland and the British Isles north (or Palaeozoic platform) of central and western of the Iapetus Suture (Cocks & Torsvik 2005). Baltica Europe (Mouratov & Tseisler 1982; Milanovsky 1987; includes most of Scandinavia and Russia eastward Zonenshain et al. 1990; Visarion et al. 1993; Nikishin to the Urals. Peri-Gondwanan terranes of West and et al. 1996, 2001). However, there is no irrevocable East Avalonia include British Isles and NW Europe evidence that the basement crust of the Scythian south of the Iapetus Suture, Eastern Newfoundland, Platform includes a Late Palaeozoic (Variscan) most of the Maritime Provinces of Canada, parts of accretionary orogenic belt (Seghedi et al. 2003; the eastern United States (Cocks & Torsvik 2005). Stephenson et al. 2004). As observed in borehole Terranes forming the basement of Danubian Nappes cores, the Palaeozoic successions of the Scythian in the South Carpathians, as well as the East Moesian Platform do not show a penetrative deformation basement and the Boclugea terrane are included here related to folding (Seghedi et al. 2003b), as seen (Balintoni et al. 2010). Cadomia includes Armorica, in North Dobrogea. More steeply inclined dips of Iberia, Saxothuringia, Tepla-Barrandia, proto-Alps, bedding noticed in boreholes can be explained as Sakarya, Eastern Pontides, Menderes and Kırşehir result of block tilting and rotation connected to (Linnemann et al. 2008) to which the Carpathian and Permian rift ing (Seghedi et al. 2003b; Saintot et al. Orliga terranes were added (Balintoni et al. 2010). 2006).

Th e Scythian Platform – Considering the two main North Dobrogea – Results from detrital zircons from models proposed for its evolution, the Scythian 5 samples of Boclugea lithologies indicate several age Platform may show either Baltican or Avalonian/ groups, corresponding to the late Neoproterozoic– early Cambrian, the Mesoproterozoic, the 1.7 and 2.2 Cadomian affi nities. Discrimination between the two Ga interval of the Palaeoproterozoic and the 2.55– models is not possible yet based on detrital zircon 2.85 Ga interval of the Neoarchaean, with age gaps data, which are still lacking. or minima in the intervals 0.75–0.85 Ga, 1.65–1.7 Ga If the Scythian Platform represents the southern and 2.2–2.5 Ga (Balintoni et al. 2010). Considering margin of the East European Craton, involved in the signifi cant input from Mesoproterozoic and Neoproterozoic deformation, it was part of the Palaeoproterozoic sources and only minor zircon Baltica palaeocontinent. Evidence in favor of this contributions from Grenvillian sources, the authors affi nity comes from stratigraphical and geophysical conclude that an East Avalonian palaeogeographic data. As with the Neoproterozoic–Lower Palaeozoic affi nity seems likely for the Boclugea terrane. cover of the East European Platform, the undeformed Detrital zircon ages for the Orliga terrane show platform cover of the Scythian Platform starts with clusters at 0.5–0.75 Ga, 1.75–2.1 Ga, 2.3–2.5 Ga the Neoproterozoic clastics and contains Silurian and 2.55–2.85 Ga, with a gap covering the entire carbonates. Geophysical evidence also indicates Mesoproterozoic and the Grenvillian (Balintoni et that the lithosphere and crust of the southern East al. 2010). Because such patterns characterize the European Platform and Scythian Platform are Cadomian terranes that originated close to the thicker than those of the Phanerozoic Western West African craton (Samson et al. 2005; Nance & Europe terranes (Yegorova et al. 2004; Yegorova & Murphy 1994), the Orliga terrane is considered a true Starostenko 2002). Cadomian terrane (Balintoni et al. 2010).

707 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

Figure 19. Reconstruction of the Late Vendian (ca. 550 Ma) (modifi ed from Cocks & Torsvik 2005). Spreading centres are shown as black lines, subduction zones are shown as lines with ticks. Transform faults are accompanied by arrows. Black areas represent Grenville-Sveconorwegian mobile belts (about 1 Ga). Dark grey shaded areas are regions that show evidence of Avalonian-Cadomian-Pan-African-Baikalian-Timanian deformation, terrane amalgamation and magmatism. East Moesia (EM), Boclugea, Danubian, and other correlatives in the Balkans (DB) represent East Avalonian Peri-Gondwanan terranes (Balintoni et al. 2010). Cadomia (fi gured aft er Linnemann et al. 2008), includes Armorica (A), Iberia (Ib), Saxothuringia (ST), Tepla-Barrandia (TB), proto-Alps (PA), Sakarya, Eastern Pontides, Menderes and Kirshehir, with the Carpathian terranes (C) and Orliga (O) added by Balintoni et al. (2010). P represents Palazu terrane.

Based on U-Pb detrital zircon ages, a correlation two with Baltican and two with Avalonian affi nities of Orliga with the Cadomian Sebeş-Lotru terrane and have been separated in the entire Moesian Platform of Boclugea with the Avalonian Danubian terranes (Oczlon et al. 2007). According to these authors, East from the South Carpathians is possible (Balintoni Moesia consists of an Avalonian terrane comprising et al. 2010). Th is correlation suggests that the South Central and a large part of South Dobrogea, separated Carpathians and North Dobrogea were connected by the narrow Palazu terrane with a basement of during the Variscan orogeny. Th e continuity was Baltican affi nity. Th e review of terranes along the disrupted in the Early Cretaceous, by westward southwestern margin of the East European Craton, displacement of Moesia, related to the opening of the between the North Sea and the Black Sea, suggests western Black Sea basin (Balintoni & Baier 1997). that dextral strike-slip dominated the southwestern Baltican margin during Late Ordovician–Early Devonian accretion of Far Eastern Avalonia (Oczlon East Moesia et al. 2007). Southward displacement of some Evidence for the palaeogeographic affi nity of East Avalonian terranes, including East Moesia, occured Moesia is still controversial. Based on a detailed consequently to the Variscan indentation of the analysis of tectonostratigraphic, palaeontological Bohemian Massif, while current juxtaposition of the and geochronological data, four distinct terranes, Moesian terranes is the result of sinistral strike-slip

708 A. SEGHEDI

displacement during the opening of Mesozoic back- accretion of peri-Gondwanan terranes of Far East arc basins. Avalonia (Pharaoh 1999; Winchester et al. 2002, Palynological evidence based on Chitinozoans 2006); accretion to Laurussia during the Hercynian show a North Gondwanan affi nity of the East Moesian orogeny; rift ing and displacement along the TESZ, Lower Palaeozoic deposits (Vaida et al. 2004; Vaida & together with slivers of proximal Baltican terranes Verniers 2005), in good agreement with the affi nity accommodated along strike-slip faults (Winchester of the Lochkovian chitinozoans from West Moesia et al. 2006; Oczlon et al. 2007). (Northwest Bulgaria) (Lakova 1995; Yanev et al. Palaeogeographic affi nities proposed for the 2005). Th is however contrasts with the results from terranes presented here are based mainly on miospores (Steemans & Lakova 2004), which support lithology and palaeontological evidence derived a Baltican affi nity for Moesia at that time. from the Palaeozoic record. Detrital zircon ages are Lithology and macrofauna of the Lower Palaeozoic published only for the Central Dobrogea basement in the 5082 Mangalia borehole were previously used to (Żelaźniewicz et al. 2001, 2009; Balintoni et al. 2011) suggest an affi nity with the macrofauna identifi ed in and for the early Early Palaeozoic Boclugea and the Bosfor area (Bithynia), in basins with continuous Orliga terranes later aff ected by Hercynian regional marine sedimentation across the Silurian/Devonian metamorphism (Balintoni et al. 2010) (Figure 8). boundary (Iordan 1967). Th e macrofauna of Th e existing evidence indicates that terranes with trilobites and tentaculites is also comparable to that Baltican, Avalonian and Cadomian affi nities occur in from the Armorican and Bohemian Massifs that are the Dobrogea and Pre-Dobrogea area. considered part of Cadomia (Linnemann et al. 2008). Baltican affi nities are shown by the Palazu terrane Detrital zircon data exist so far for the Ediacaran and the Pre-Dobrogea basement. Th e Palazu terrane, basement of East Moesia. Detrital zircons yielded isolated in the basement of South Dobrogea between U/Pb SHRIMP ages of 1497±8 Ma, 1050±1 Ma, the Capidava-Ovidiu and Palazu faults, is a proximal 603±5 Ma and 579±7 Ma (Żelaźniewicz et al. 2001), Baltican sliver (Oczlon et al. 2007). It is made of interpreted as Avalonian (Seghedi et al. 2005a, b) or Archaean and Palaeoproterozoic crust, similar in Far East Avalonian sources (Oczlon et al. 2007). composition to the Ukrainian shield (Giuşcă et al. 1967, 1976), or the Sarmatia segment of Baltica (as Detrital zircons published by Balintoni et al. defi ned by Bogdanova et al. 1997). Ediacaran rift - (2011) show the following age concentrations: related volcano-sedimentary successions (Cocoşu the greatest age grouping of 2.65–3.0 Ga is Group) are preserved on top of the metamorphic Archean; Palaeoproterozoic ages show a very low crust. Th is geological association suggests an initial frequency around 1.8 Ga and between 2.2–2.6 Ga; location along the TESZ margin near the Volhyn- the Mesoproterozoic ages peak around 1.5 Ga; Orsha aulacogen, about 500 km north of the present Palaeoproterozoic ages cluster around 1.7 Ga and location of the Palazu terrane. Th e Volhynian series between 1.95–2.2 Ga; late Neoproterozoic ages from the Volhyn depression developed within the between 633–583 Ma., suggesting that the Brasiliano orgen (Nance et al. 2009) was the most important aulacogen includes lower Vendian fl ood basalts Neoproterozoic detrital zircon source for the Histria formed during continental rift ing that accompanied Formation. A detailed discussion of the zircon Rodinia breakup at about 750 Ma (Kumpulainen sources and their discrimination is found in Balintoni & Nystuen 1985; Torsvik et al. 1996; Nikishin et al. et al. (2011). 1996). Lithological, petrographic and geochemical features of the Volhynian basalts (Bakun-Czubarow et al. 2002; Białowolska et al. 2002) correlate well Discussion with those of the Cocoşu Group (Seghedi et al. 2000). Th e geological evolution of the Palaeozoic terranes In a series of palaeogeographic maps for the from Dobrogea and Pre-Dobrogea took place during East European Craton (Nikishin et al. 1996), the several events occurring at the south-western margin Pre-Dobrogea area is considered part of the Baltica of the East European Craton: Early Palaeozoic palaeocontinent. Fine-grained Vendian lithologies

709 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

from Pre-Dobrogea, with phosphate nodules and from the low-grade facies Boclugea rocks to the Vendotaenia antiqua, accumulated in the Dnestr very low-grade Silurian–lower Devonian deposits is basin of Baltica. Th is is one of the very large shelf obscured by subsequent thrusting, due to involvement basins, established along the western slope of the East in the Hercynian orogeny, following the accretion of European Craton during the Ediacaran and referred the Cadomian Orliga terrane. to as the Peri-Tornquist basin (Nikishin et al. 1996). Indirect evidence for an Avalonian provenance During the Cambrian, the Dnestr basin developed of the Lower Palaeozoic terranes in North Dobrogea into a passive continental margin, with shallow- can be derived from a critical analysis of their marine clastics overstepping the Vendian deposits. lithostratigraphy and from comparison with the Th is evolution is confi rmed in the Aluat and Bârlad Palaeozoic successions of East Moesia. basins, where Cambrian clastics have been identifi ed. In the Măcin zone of North Dobrogea, the basinal, Th e typical facies of Silurian carbonates from the anoxic Silurian lithofacies is shallowing upward to Moldavian and Baltic basins (Sliaupa et al. 2006) was Lower Devonian shelf sandstones and carbonates not found in Pre-Dobrogea. However, the Ordovician (Figure 11). Th e biostratigraphy of these successions and Silurian deposits, identifi ed by chitinozoans is ill-defi ned due to scarcity of fossil remains, the in the upper part of what had been considered a only exception being the Bujoare fossil site rich in Vendian succession, show a siltstone-mudstone Lower Devonian macrofauna. Th e entire Middle– facies with sandstone and limestone interbeds (Vaida Upper Devonian section is missing here due to & Seghedi 1997). Th is suggests that the transition erosion. Th is is indicated by the abundant limestone from the carbonate facies of the Peri-Tornquist Basin clasts reworked in the lowest fanglomerates of to the fi ne-grained clastic facies of the Peri-Caspian the Carapelit Formation exposed near the Lower basin (Nikishin et al. 1996) took place by lateral facies Devonian outcrops. As the Carapelit conglomerates changes in the Pre-Dobrogea area. are proximal deposits, provenance from more distal Th e Avalonian affi nity of East Moesian sources of conodont-bearing limestone clasts is Lower Palaeozoic successions is suggested by the precluded. Clast petrography and their fossil content unconformities within the Silurian and at the in the lower members of the Carapelit Formation base of the Silurian and Devonian, characteristic represent evidence that the middle and late Devonian of Caledonian displaced terranes along the TESZ in the Măcin zone developed in limestone facies, (Oczlon et al. 2007). Th e peri-Gondwanan, Avalonian similar to East Moesia and the Scythian Platform. provenance of Central Dobrogea is based on the Considering all lithological and structural detrital zircon spectrum in the Ediacaran turbidites information about the Silurian–Devonian successions presented so far (Żelaźniewicz et al. 2001, 2009; in the Măcin zone of North Dobrogea, lithological Balintoni et al. 2011) and on cold water acritarchs correlation with East Moesian coeval deposits from the East Moesian Palaeozoic cover (Oczlon et leads to a more reasonable lithostratigraphy, even if al. 2007). palaeontological evidence is scarce. Th e dark shales In North Dobrogea, terranes with both Avalonian of the Cerna Formation might be ascribed to the and Cadomian affi nities are indicated by detrital ?Wenlock–Lower Ludlow, based on their black shale zircon ages (Balintoni et al. 2010). Th e location facies. Th e overlying black argillites might represent of the Palaeozoic shelf facies south of deep marine the Upper Ludlow, as recorded in lithological logs Palaeozoic sediments indicates a north-northeast of several boreholes from East Moesia, where the facing continental margin of North Dobrogea, transition to upper Ludlow is marked by a change in consistent with a North Gondwanan provenance lithology from dark shales to argillites (Iordan 1999; (Oczlon et al. 2007). Th e Măcin-type Palaeozoic Seghedi et al. 2005a). Th e overlying argillites with successions overlie the Cambrian clastics of the thin interbeds of sandstones and calcarenites could Avalonian Boclugea terrane, so they might have represent the Pridoli. Discontinuous, thin layers of travelled together across the Tornquist sea. Initial volcanic tuff s are interbedded in the Upper Ludlow– relations, as well as the progressive metamorphism Pridoli succession in the Măcin zone, as with the Pridoli

710 A. SEGHEDI

lithofacies from the Zăvoaia borehole in East Moesia. that during the Palaeozoic, the basement of the Identifi cation of the conodont Icriodus woschmidti in Pre-Dobrogea Depression was part of the Baltican the same lithofacies marks the presence of the Lower foreland involved in the amalgamation of Avalonia/ Devonian, indicating the continuity of the argillite Baltica with Laurentia, and further evolved as part of facies into the Lochkovian. Th e Lochkovian, well- the Variscan foreland. dated on the brachiopod-dominated macrofauna Palaeozoic deposits of East Moesia show a well- from the Bujoare Hills, contains several beds of preserved palaeontological record and do not show mica-rich quartzitic sandstones, capped by a thin any structural elements indicative of metamorphism. orthoquartzite member, which might be lithologically Th e succession of Palaeozoic facies is well documented correlated with the Eifelian lithofacies of East Moesia. based on biostratigraphic zones: graptolites for the Th e shallow-marine limestones overlying the Eifelian Ordovician and Silurian, conodonts and chitinozoans quartzites, rich in crinoidal ossicles and silicifi ed for the Lochkovian, tentaculites and trilobites for the solitary corals, could be ascribed to the Givetian. Th e Pragian–early Givetian and spiriferids, conodonts rest of the Devonian shallow marine carbonate facies and foraminifera for the Givetian–Visean. Th e succession was probably removed by erosion during Namurian–Westphalian is dated on placoderm and deposition of the Carapelit Formation. ostracoderm fi shes, terrestrial plants, algae and Following this reasoning, it is possible to conclude foraminifera. Gaps in the succession correspond to that the Măcin-type Silurian–Devonian deposits of the Llandovery, Upper Wenlock and lower Upper North Dobrogea represent East Moesian successions. Ludlow. Based on these unconformities, a peri- Based on a previous palaeotectonic model (Mosar Gondwanan Avalonian affi nity is inferred for East & Seghedi 1999) (Figure 20) it is proposed that Moesia, considering also the Avalonian affi nity of the during the Cambrian–Silurian, the Avalonian part East Moesian Ediacaran basement. of North Dobrogea was part of the East Moesian Th e Precambrian basement of the Moesian terrane, docked to Baltica during the Silurian, and Platform between the Capidava-Ovidiu and Palazu experiencing a common history with the Scythian faults is a terrane with proximal Baltican derivation. margin of Baltica during the Devonian. Th e terranes Th is terrane, devoid of Palaeozoic deposits, was were further involved in the complex evolution probably detached from the northwestern slope of of the Hercynian orogen, when the Avalonian the Ukrainian shield (where Volhyn fl ood basalts North Dobrogea represented the upper plate where overlie the Palaeoproterozoic and Archaean Sarmatia regional metamorphism, crustal melting and granitic margin), and was displaced along the TESZ. plutonism and volcanism were taking place. Th e Cadomian Orliga terrane became part of North Ordovician to Devonian deep marine sediments Dobrogea in the Late Carboniferous, aft er the closure developed south of the Sfantu Gheorghe Fault (Figure of the Rheic Ocean. 10) show a strong contrast in facies and structural style with the Lower Palaeozoic passive margin successions of the Scythian Platform. Th e Tulcea- Synthesis and Conclusions type Palaeozoic sediments, dated on conodonts and As part of the Baltica palaeocontinent, the area of palynological assemblages, form several northward- the Scythian Platform was a shelf basin from the younging, upward-coarsening terranes, consisting Vendian until the Silurian. Early Devonian rift ing of radiolarian cherts, siliceous shales and distal disrupted the shelf basins that evolved further as a turbidites. Rocks show a southward increase in carbonate ramp during the Middle Late Devonian– metamorphic grade, from subgreenschist to lower Lower Carboniferous. Following the Middle–Late greenschist facies. Trace fossil assemblages and facies Carboniferous subduction in the areas of the West association indicate that turbidites accumulated in European Variscan and South European Scythian deep basins below the CCD. Lithological association orogens (as defi ned by Ziegler 1989), siliciclastic and upward-coarsening facies architecture from deposits with coal measures prograded on the passive siliceous pelagic rocks to turbidites suggests that these margin carbonates. Th e sedimentary record suggests terranes represent oceanic and trench sediments,

711 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

Figure 20. Plate tectonic reconstruction showing a possible scenario for the evolution of North Dobrogea, East Moesia and Pre- Dobrogea and surrounding oceanic realms in the Palaeozoic (modifi ed from Mosar & Seghedi 1999). Th e model is based on the constitution of North Dobrogea Palaeozoic basement, that includes an Ordovician–Devonian accretionary wedge separated from a Late Palaeozoic magmatic arc and retro-arc foreland basin by a strike-slip fault. Th e model shows accretion to Baltica of East Moesia (including the Boclugea terrane), following the closure of the Tornquist Sea and Variscan accretion of Orliga terrane upon closure of the Rheic Ocean. North Dobrogea shows south-dipping subduction in the Lower Palaeozoic and fi nally rather gently docks with the SE edge of Baltica and develops a strong syn- to post-collisional strike- slip deformation along the Teyssiere zone. Th is late Hercynian wrench tectonics is also related to the destruction of the Variscan Orogen and strongly aff ects the Dobrogea accretionary prism remnants, as well as the continental margin arc.

712 A. SEGHEDI

which record the trenchward movement of an oceanic and thrusting. Th is suggests an active margin setting plate. Th ey are interpreted as underthrust units of and upper plate position. Th e deep marine Palaeozoic an accretionary wedge, accreted to the upper plate pelagic cherts and distal turbidites, were part of the during southward subduction of the Scythian margin forearc wedge, tectonically accreted to the upper plate of the East European Craton (Mosar & Seghedi 1998; along a south-dipping subduction plane. Th e south Seghedi 1999). polarity of the subduction zone is indicated by the deep marine Palaeozoic of North Dobrogea facing Th e Upper Palaeozoic Carapelit Formation, the shallow-marine Devonian carbonate platform ascribed to the Upper Carboniferous–Early Permian, facies of the Scythian Platform. A north-dipping obviously represents a continental, volcanic molasse, subduction zone of Palaeotethys developed in the intruded by calc-alkaline granites. It contrasts in Late Palaeozoic as shown in Figure 20a, b. Th e trace composition and style with the Carboniferous of the Rheic suture runs through North Dobrogea, coal measures from the Scythian Platform of Pre- where both Avalonian and Cadomian terranes are Dobrogea. Th e Carapelit Formation strongly contrasts found, as in the Hercynian basement reworked in the in facies and explosive calc-alkaline volcanism with Alpine nappes of the South Carpathians (Balintoni et the Lower Permian continental red bed facies from al. 2010). the Pre-Dobrogea Depression, accompanied by eff usive-explosive alkaline bimodal volcanism. A Permian rift ing accompanied by bimodal alkaline model explaining the Upper Palaeozoic continental volcanism occurred both in North Dobrogea and the sedimentation and magmatism in North Dobrogea as Pre-Dobrogea. In North Dobrogea, Late Permian a result of thrust propagation in a retro-arc foreland rift ing is explained as a consequence of extensional collapse of the Variscan orogen, overthickenned basin (Seghedi et al. 1987; Oaie & Seghedi 1994; by thrusting and granite intrusion (Figure 20d). Seghedi & Oaie 1995) (Figure 20c) accounts for: the Th e transition from early Permian syn-collisional great thickness of fl uvial and alluvial continental calc-alkaline magmatism to Late Permian alkaline sediments of the Carapelit Formation, accumulated magmatism refl ects the changing stress regime from in active tectonic condition; mixed clast composition, compression to transtension and was explained as suggesting sediment recycling; very-low-grade result of slab roll-back (Figure 20d). Th e extensional metamorphism (anchizone metamorphism) of the (transtensional) regime propagated from the Palaeozoic sediments of the upper plate, connected Hercynian belt into its foreland, where rift ing was to retro-arc thrusting and progressive increase in accompanied by accumulation of thick volcano- metamorphic grade of Palaeozoic sediments toward sedimentary successions in the Sărata-Tuzla basin the thrusts footwalls. from the eastern part of the rift . Active rift ing of Compared to East Moesia, the Palaeozoic of the basement of the Pre-Dobrogea is suggested by North Dobrogea is loosely dated, due to the scarcity emplacement of the bimodal alkaline volcanism of of its fossil record. Th is can be explained by the the basalt-trachyte association. Th is volcanism was penetrative Hercynian deformation in amphibolite fed by the suite of the bimodal basalt-trachyte dykes to greenschist and subgreenschist facies conditions emplaced during the Permian along the northern and thermal metamorphism connected to granite margin of North Dobrogea, as well as by small bodies intrusion. Nevertheless, based on a vertical lithofacies of syenites and ultrapotassic alkaline rocks emplaced succession, the shallow-marine Lower Palaeozoic in the basement highs of the rift basin. In the of North Dobrogea correlates well with coeval meantime, alkaline volcanism developed from Late East Moesian deposits. On this basis, an Avalonian Permian to early Triassic times along the southern affi nity can be inferred for the Măcin-type Lower border of North Dobrogea, parallel to the Peceneaga- Palaeozoic, consistent with the Avalonian affi nity Camena Fault. of its basement, the Cambrian Boclugea terrane, as suggested by detrital zircons. Unlike East Moesia and Pre-Dobrogea, the continental Late Palaeozoic of Acknowledgements North Dobrogea was involved in Hercynian collision, Th is paper was written as result of the participation with metamorphism, volcano-plutonic development in the second ISGB conference in held in Ankara in

713 PALAEOZOIC FROM DOBROGEA AND PRE-DOBROGEA

2009 and supported from project PROMED, contract of Ayda Petek Üstaömer and an unknown reviewer 31-030/2007, fi nanced by the Ministry of Education are highly appreciated, considerably increasing and Research of Romania. Th e author is extremely the quality of this paper. Th e English language of grateful to Aral Okay for the strong support and the paper was greatly improved, thanks to Randell encouragement for writing this paper, as well as for Stephenson. his infi nite patience. Th e comments and suggestions

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