1. Introduction
The formation of the Variscan Belt in Europe occurred as a result of the closure of the Rheic Ocean. In western and central Europe, the rock units of the Variscan Belt (Variscan Terrane assemblage/Variscan successions) and their stratigraphic properties have been studied in detail (Martinez Catalan et al. Reference Martinez Catalan, Fernandez-Suarez, Jenner, Belousova and Diez Montes2004; Mazur et al. Reference Mazur, Aleksandrowski, Kryza and Oberc-Dziedzic2006; Seghedi, Reference Seghedi2012). The coeval occurrences of Variscan successions towards eastern Europe can be followed in the Balkan (Yanev, Reference Yanev1993, Reference Yanev, Göncüoğlu and Derman1997, Reference Yanev2000) and Moesian and Caucasian (Yanev & Adamia, Reference Yanev and Adamia2010) terranes (Fig. 1). In NW Anatolia, the Ordovician–Carboniferous Variscan successions on both sides of Bosphorus have been known as the ‘Palaeozoic of İstanbul’ since the mid-nineteenth century (Verneuil, Reference Verneuil1836–Reference Verneuil1837; Strickland, Reference Strickland1840; Tchihatcheff, Reference Tchihatcheff1854), also known as the İstanbul zone (Şengör, Yılmaz & Sungurlu, Reference Şengör, Yılmaz, Sungurlu, Dixon and Robertson1984). This tectonic unit (Fig. 2a) was described in the sense of Howell (Reference Howell1989) as a Variscan Terrane by Göncüoğlu, Dirik & Kozlu (Reference Göncüoğlu, Dirik and Kozlu1997). Later, Göncüoğlu & Kozur (Reference Göncüoğlu, Kozur, Linnemann, Heuse, Fatka, Kraft, Brocke and Erdtmann1998), Göncüoğlu & Kozlu (Reference Göncüoğlu and Kozlu2000) and Yanev et al. (Reference Yanev, Göncüoğlu, Gedik, Lakova, Boncheva, Sachanski, Okuyucu, Özgül, Timur, Maliakov, Saydam, Robertson and Mountrakis2006) suggested that the northwestern Black Sea region including NW Anatolia actually comprises a terrane assemblage consisting of two different Gondwana-derived microplates. The İstanbul Terrane (IT) in the west covers İstanbul, Gebze and South Çamdağ areas and the Zonguldak Terrane (ZT) is located (Fig. 2b) in Çamdağ, Zonguldak and Safranbolu areas in the east and NE (e.g. Göncüoğlu, Reference Göncüoğlu2010). The differences in lithostratigraphy, structural and metamorphic features and palaeobiogeography of these terranes was discussed in earlier studies in considerable detail (Göncüoğlu & Kozur, Reference Göncüoğlu, Kozur, Linnemann, Heuse, Fatka, Kraft, Brocke and Erdtmann1998; Göncüoğlu & Kozlu, Reference Göncüoğlu and Kozlu2000; Kozur & Göncüoğlu, Reference Kozur and Göncüoğlu2000; Dojen et al. Reference Dojen, Özgül, Göncüoğlu and Göncüoğlu2004; Yanev et al. Reference Yanev, Göncüoğlu, Gedik, Lakova, Boncheva, Sachanski, Okuyucu, Özgül, Timur, Maliakov, Saydam, Robertson and Mountrakis2006; Bozkaya, Yalçin & Göncüoğlu, Reference Bozkaya, Yalçin and Göncüoğlu2012 a, b; Sachanski et al. Reference Sachanski, Göncüoğlu, Lakova, Boncheva and Saydam-Demiray2012; Okuyucu, Vachard & Göncüoğlu, Reference Okuyucu, Vachard and Göncüoğlu2013). In contrast to the detailed evaluation of the Ordovician – lower Carboniferous marine deposition in the IT and ZT, our knowledge of the stratigraphy, ages and depositional environment of the Permian – Lower Triassic overstep sequences are very scarce. These overstep sequences mainly comprise red continental clastics with a few volcanic inlayers, named the Çakraz Formation in NW Anatolia (Akyol et al. Reference Akyol, Arpat, Erdoğan, Göğer, Güney, Şaroğlu, Şentürk, Tütüncü and Uysal1974).
Figure 1. Position of the İstanbul and Zonguldak terranes within the Western and Central European Variscan Belt (IT – İstanbul Terrane; ZT – Zonguldak Terrane) (Bozkaya, Yalçin & Göncüoğlu, Reference Bozkaya, Yalçin and Göncüoğlu2012 b).
Figure 2. (a) The main tectonic units of Turkey and the position of the İstanbul and Zonguldak terranes (Göncüoğlu, Dirik & Kozlu, Reference Göncüoğlu, Dirik and Kozlu1997). NAFZ – North Anatolian Fault Zone; EAFZ – East Anatolian Fault Zone. (b) The distribution of the Palaeozoic outcrops in the İstanbul and Zonguldak terranes (modified from Bozkaya, Yalçin & Göncüoğlu, Reference Bozkaya, Yalçin and Göncüoğlu2012 b).
Recently, we discovered (Göncüoğlu, Okuyucu & Dimitrova, Reference Göncüoğlu, Okuyucu and Dimitrova2011) dark-coloured fluvio-lacustrine deposits of Tatarian age in the Ereğli area (Fig. 1), which were erroneously taken for Silurian black shales in previous studies (e.g. Timur & Aksay, Reference Timur and Aksay2002).
The aim of this study is to describe the litho- and biostratigraphic properties of this recently discovered Tatarian chronostratigraphic unit of Çakraz Formation from the Ereğli area, and to discuss and correlate this succession and its biostratigraphic features with the coeval occurrences in IT and the other Laurasian margin successions. We have attempted to explain the depositional environment of this succession while considering the results of recent biostratigraphic studies (e.g. Alişan & Derman, Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995; Dimitrova & Stolle, Reference Dimitrova and Stolle2010; Stolle, Reference Stolle2011, Reference Stolle2014; Gand et al. Reference Gand, Tüysüz, Steyer, Allain, Sakinç, Sanchez, Şengör and Şen2011) carried out on this formation in the region.
2. Geological framework
In NW Anatolia the Çakraz Formation occurs as discontinuous outcrops from the İstanbul-Gebze to Kastamonu-Inebolu areas (Fig. 1). The type locality is the Çakraz village to the east of Amasra (Akyol et al. Reference Akyol, Arpat, Erdoğan, Göğer, Güney, Şaroğlu, Şentürk, Tütüncü and Uysal1974; Tüysüz, Aksay & Yiğitbaş, Reference Tüysüz, Aksay and Yiğitbaş2004) in the ZT. The ZT and IT share the same late Neoproterozoic (Cadomian) basement. In both terranes Ordovician siliciclastics disconformably overlie this Cadomian basement. The oldest sediments dated by fossils are the early – early late Tremadocian black shales (Göncüoğlu et al. Reference Göncüoğlu, Sachanski, Gutierrez-Marco and Okuyucu2014) in the ZT. The Early Devonian unconformity above the middle Silurian very-low-grade metamorphic black shales (Bozkaya, Yalçin & Göncüoğlu, Reference Bozkaya, Yalçin and Göncüoğlu2012 a, b), a well-developed Emsian–Visean carbonate platform succession (Fig. 3) and the Namurian coal-bearing fluvial sediments are the distinguishing features of the ZT. The Çakraz Formation unconformably overlies the Namurian flysch-type deposits in IT (e.g. Özgül, Reference Özgül2012). In the ZT it overlies the Stephanian fluvial sediments (e.g. Kerey, Reference Kerey, Dixon and Robertson1984).
Figure 3. Generalized columnar section of the Zonguldak Terrane (Bozkaya, Yalçin & Göncüoğlu, Reference Bozkaya, Yalçin and Göncüoğlu2012 b).
The lower part of the Çakraz Formation is dominated by poorly sorted red to violet conglomerates, whereas the upper part is characterized by cross-bedded red sandstones with alternations of conglomeratic sandstones (Güvenç et al. Reference Güvenç, Demirel, Meşhur, Gül and Tekin1994; Alişan & Derman, Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995). The thickness of the formation varies over the range 1000–3500 m in the Upper Sakarya valley. Upwards, the Çakraz Formation grades into a light-coloured succession with lacustrine marls and mudstones that are attributed to the Çakrazboz Formation of Late Triassic age (Alişan & Derman, Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995).
Field work undertaken in the area between the Ereğli and Alaplı (Fig. 4) and palynological samples collected in 2004 and 2010 have revealed for the first time the presence of a >1000 m thick succession with black, dark-grey to greenish-grey shales, siltstones and limestones to the south of Alaplı (Fig. 4). This lithostratigraphic unit is named the Alaplı Member of the Çakraz Formation (Göncüoğlu, Okuyucu & Dimitrova, Reference Göncüoğlu, Okuyucu and Dimitrova2011) and will be evaluated in detail. To distinguish the red clastic successions of the Çakraz Formation from the newly discovered fluvio-lacustrine unit, we tentatively named the classical red fluvial succession the Ereğli Member of the Çakraz Formation.
Figure 4. Geological map of the study area and the distribution of the Alaplı Member in the Ereğli and Alaplı regions (modified from Aydın et al. Reference Aydin, Serdar, Şahinturk, Yazman, Cokuğraş, Demir and Özcelik1987). Undiff. – undifferentiated.
3. The Alaplı Member of the Çakraz Formation
3.a. Lithostratigraphy
The recently determined succession of the Alaplı Member in Ereğli region and its conformable upper contact to the main body of Çakraz Formation (Ereğli Member) was not described or included in previous studies (e.g. Yazman & Çokuğraş, Reference Yazman and Çokuğraş1983; Altun & Aksay, Reference Altun and Aksay2002). Moreover, the Alaplı Member was considered as the equivalent of the upper Silurian black shales and Lower Devonian black limestones of the Yılanlı Formation.
In Ereğli area the Alaplı Member rests directly on the pre-Permian basement (Fig. 5). Locally, the contact is faulted. The lowermost part of the Alaplı Member includes an alternation of thin- to medium-bedded greenish-grey siltstones and sandstones with thin black mudstones, very rich in plant remains (Figs 5, 6a, b). The overlying part of the unit comprises thin-bedded violet and green laminated mudstone and green shale alternation at base and thin- to medium-bedded dark grey-black limestone with green-grey shale and siltstone interlayers at the top. The middle part of the member is represented by thin- to medium-bedded dark-grey grey-red-violet conglomerates with thin-bedded limestone, dolomitic limestone and shale interlayers (Fig. 6c, d). The black shales and limestones in this part are rich in organic matter and include miospore assemblages but lack any macrofossils (Fig. 6e, f). The pebbles of the conglomerates are mainly from the Kurtköy (Ordovician), Fındıklı (Silurian) and fossiliferous Upper Devonian – lower Carboniferous limestones of the Yılanlı formations (Fig. 6c, d). The conglomerates continue upwards as thin- to medium-bedded dark grey-black limestone with green-grey shale alternations. The uppermost part of the Alaplı Member is represented by thin-bedded black shale with siltstone interlayers. The black shales are very rich in organic matter but lack any macro- or microfossils (Fig. 6a). The occurrences of black shales (mainly laminated) are occasionally accompanied by pyritic shales.
Figure 5. Generalized lithostratigraphic section of the Çakraz Formation in Ereğli area.
Figure 6. Field photos of the Çakraz Formation from the Ereğli and Alaplı regions. (a) General lithological characteristics of the Alaplı and Ereğli members and the contact between them and their post-Triassic cover (near to Erdemir Beach, Ereğli district); (b) alternation of thin- to medium-bedded greenish-grey siltstones and sandstones with thin black mudstones; (c, d) thin- to medium-bedded dark-grey grey-red-violet conglomerates; (e, f) organic-matter-rich black shales and limestone levels which include miospore assemblages. Photograhs (b–f) were taken on road between Oluce and Kasımlı districts.
The Alaplı Member of Çakraz Formation is conformably overlain by the Ereğli Member, which starts with the thin- to medium-bedded red-pink, grey, sandstone, mudstone and siltstone alternations with shale interlayers at the bottom (Fig. 6a). The upper part of member is represented by thin- to medium-bedded red-pink sandstone and siltstone alternations. The main body of the member is represented by an alternation of red, violet, occasionally massive, moderate- to thick-bedded conglomerate, sandstone, siltstone and mudstone with mud cracks, rain drops and cross-bedding. The uppermost part of the formation is typically a greenish-yellow-colored marl, siltstone and claystone alternation (Fig. 6a) (Altun & Aksay, Reference Altun and Aksay2002).
Late Cretaceous volcanic and volcanoclastic rocks unconformably overlie the Çakraz Formation in the Ereğli area (Fig. 6a) (e.g. Altun & Aksay, Reference Altun and Aksay2002).
3.b. Depositional features
The Alaplı Member, described here for the first time in detail, is represented by sandstone shale alternation at the base, conglomerates with limestone, dolomitic limestone interlayers at the middle and shale with siltstone interlayers at the top. The predominantly fine-grained character of the lithofacies, mainly the occurrences of laminated mudstones associated with shales and sands with abundant plant material, represents the deposits of lacustrine deltas formed at lake margins, which were related to the river systems (Newell, Tverdokhlebov & Benton, Reference Newell, Tverdokhlebov and Benton1999; Cassinis, Durand & Ronchi, Reference Cassinis, Durand and Ronchi2007; Newell et al. Reference Newell, Sennikov, Benton, Molostovskaya, Golubev, Minikh and Minikh2010; Opluštil et al. Reference Opluštil, Šimunek, Zajic and Mencl2013). The limestone levels in between conglomerates and the overlying units in the Alaplı Member probably represent lacustrine carbonates deposited in shallow lakes. The association of poorly sorted conglomerates in the middle part of the succession with shale interlayers indicates a possible influx of the river channel to the lacustrine system. It is probable that the Alaplı Member and underlying units were deposited in an interior continental basin that was closed to the marine shelves and deposited in a broad range of fluvial and lacustrine environments. This is also supported by the lack of any marine macro- or microfossils in the formation.
3.c. Palynological data and age
The upper Permian sediments from the Ereğli area in north Turkey is scarcely represented in outcrop and still very little studied. From four samples (Fig. 5) taken from the freshest outcrops, only two samples (10-AK-13 and 10-AK-19) contain relatively well-preserved material for palynological determination and illustration.
Pollen and spores from the rocks were recovered by dissolving in hydrofluoric acid, in nitric acid (40%) and zinc chloride, then cleared in potassium hydroxide (5%). The maceration material (in Geological Institute, Sofia) was mounted in glycerin jelly, or only jelly, for microscopic study. The dark colour of the spores and pollen can be used to assess the degree of thermal alteration that organic material in sediments has been subjected to. The dominant study material is generally poorly preserved palynomorphs.
The palynological assemblage of the samples include various taxa (48 pollen grains and spores). The common genera such as Lueckisporites and other species and genera such as Limitisporites lepidus, Vitreisporites sp., Cedruites sp., Platysaccus sp., Vittatina persecta, Illinites sp., Striatites cf. ovalis, Hamiapollenites sp., Lunatisporites sp., Jugasporites sp., Falcisporites sp., Alisporites sp., Striatopodocarpites sp., Nuskoisporites sp. and Protohaploxypinus sp. are depicted in Figure 7.
Figure 7. Selected palynological taxa from the Alaplı Member of the Çakraz Formation in the Alaplı-Ereğli region, NW Turkey. All magnifications ×700. (a) Limitisporites lepidus (Valts) Hart Reference Hart1963, 10-AK-13; (b) Limitisporites sp., 10-AK-13; (c)? Vitreisporites sp., 10-AK-19; (d) Cedruites sp., 10-AK-19; (e) Platysaccus sp., 10-AK-13; (f) Vittatina persecta Zauer Reference Zauer1960, 10-AK-13; (g) Illinites sp., 10-AK-13; (h) Verrucosisporites sp., 10-AK-13; (i) Striatites cf. ovalis Schaarschmidt, Reference Schaarschmidt1963, 10-AK-19; (j, k) Lueckisporites sp., 10-AK-19; (l) Namiapollenites sp., 10-AK-19; (m) Lunatisporites = Taeniasporites sp., 10-AK-19; (n) Lueckisporites nyakapendensis Hart Reference Hart1963, 10-AK-13; (o) Jugasporitres sp., 10-AK-13; (p) Falcisporites sp., 10-AK-19; (r)? Alisporites sp., 10-AK-19; (s) Striatopodocarpites sp., 10-AK-13; (t) Nuskoisporites sp., 10-AK-13; (u, v) Protohaploxypinus sp., 10-AK-13.
The entire sequence is characterized by the dominance of striate bisaccate genera that includes Striatites, Striatopodocarpites, Striatopollenites and taneiate taxa as Lueckisporites and Lunatisporites. The palyno-assemblage (Fig. 7) is also described by specimens from the genera Limitisporites lepidus, bisaccate form genera Cedruites sp., Lueckiesporites sp., Illinites sp., spores (Verrucosisporites), cf. Alisporites sp., Jugasporites sp., Limitisporites sp., Striatopodocarpites sp., Nuskoisporites sp., Protohaploxypinus sp. and genus Vittatina.
International palynological correlations are not well established for the Permian at present. The palynological zonal scheme (Fijalkowska, Reference Fıjalkowska1994; Stephanson, Osterloff & Fılatoff, Reference Stephenson, Osterloff and Fılatoff2003) used by several authors (Jin et al. Reference Jın, Glenıster, Kotlyar and Sheng1994; Utting et al. Reference Uttıng, Esaulova, Sılantıev and Makarova1997; Hochuli et al. Reference Hochuli, Hermann, Vigran, Bucher and Weissert2010; Stolle, Yalçin & Kavak, Reference Stolle, Yalçin and Kavak2011) is based on many stratigraphic ranges of the forma genera.
The stratigraphic range of selected species such as Lueckisporites, Alisporites, Lunatisporites and Hamiapollenites (Fig. 7) allow the assemblage to be dated to the upper Permian rocks, and the same age was given to the studied formation at this locality.
The assemblage from north Turkey is correlated with and indicates Zechstein assemblages which have been described from many European countries (see Visscher, Reference Visscher1971) and also in Bulgaria (Dimitrova, Petrunova & Yanev, Reference Dimitrova, Petrunova and Yanev2006) and Turkey (Stolle, Yalçin & Kavak, Reference Stolle, Yalçin and Kavak2011; Stolle, Yalçin & Kozlu, Reference Stolle, Yalçin, Kozlu, Yalçın, Corbacıoglu, Aksu and Bozdogan2012). Important genera in the deposits with similar age are Lueckisporites (12 specimens of this genus), Lunatisporites and Illinites-Limitisporites complex. Other important genera include Hamiapollenites, Protohaploxypinus, Alisporites and Podocarpites. Taeniate and non-taeniate disaccates are dominant and include the species Protohaploxypinus spp. and Striatopodocarpidites spp.
At the end of the Permian Period, the worldwide collapse (Visscher et al. Reference Vısscher, Looy, Collınson, Brınkhuıs, van Konıjnenburg-van Cıttert, Kurscher and Sephoton2004) of the terrestrial and marine ecosystems resulted in major perturbation. The situation in the studied material suggests that conifers with large sacci (Lunatisporites, Hamiapollenites) were starting to dominate the flora. Reworked palynomorphs are identified in the maceration material as genera of early Carboniferous age and one specimen of Late Devonian age.
The established microflora is dominated by striate pollen grains, which would represent xerophytic floras mainly related to the Pteridospermaphyta. Other genera, such as Alisporites, Vitreisporites (two very dark, badly preserved specimens from different taxa), Vittatina and Cycadopites, could correspond to groups of Coniferophyta (Cordaitales and Coniferales) and Cycadophyta (e.g. Balme, Reference Balme1995). Ornamented forms are mainly represented by Verrucosisporites and Lucidisporites, characteristic of a variety of late Palaeozoic ferns (Balme, Reference Balme1995). Nuskoisporites conifers (Walchiaceae; Ortiseia), prepollen of the late Permian conifer species (Florin, Reference Florın1927), was present in the samples only with one taxon. Lueckisporites virkkiae conifers (Majonicaceae; Majonica), known from the late Permian conifer Majonica alpine (Clement-Westerhof, Reference Clement-Westerhof1987), includes two specimens. The assignable forms of Voltziaceaesporites conifers (family unknown; Yuccites), known from coniferous cones (Willsiostrobus), have also been described as Alisporites (Balme, Reference Balme, Kummel and Teichert1970) and are seen in the assemblage with less well-preserved forms. Jugasporites (one specimen) conifers (probably Ullmanniaceae; genus unknown) forms are morphologically similar. Multitaeniate pollen Pteridosperms (Peltaspermales; family and genus unknown) identified form-genera include Lunatisporites and Protohaploxypinus. Cycadopites spp. cycads (family and genus unknown) monosulcate pollen is known from a variety of Palaeozoic and Mesozoic gymnosperms (Balme, Reference Balme1995). Considering the megafossil record, late Permian and Early–Middle Triassic forms from Europe are likely to represent cycads (Balme, Reference Balme1995). The disaccate striate, taeniate pollen is prominent for the assemblages of late Permian and Early Triassic age (Traverse, Reference Traverse1988).
The Tatarian period is characterized by a decrease in Vittatina and spore specimens (species of the Lycopsida). The dominant conifer taxa of the late Permian Euramerican floral realm became extinct at, or close to the Permian–Triassic (P-Tr) border. The long-ranging Carboniferous–Permian Walchiaceae also became extinct close to the P-Tr boundary (Poort et al. Reference Poort, Clement-Westerhof, Looy and Visscher1997) and Cycadopites and Lueckisporites virkkiae (it is easy to recognize this slightly diploxylonoid autline species, where sacci are less than semi-circular in shape) present with very common taxa belong to maceration material. In fact, after the P-Tr crisis the prepollen condition never appeared in gymnosperm evolution (Florin, Reference Florın1927; Taylor & Taylor, Reference Taylor and Taylor1993). On the other hand, the temporary reappearance of Jugasporites Leschik could indicate that the Ullmanniaceae survived outside Europe.
The early Permian Period is dominated by polyplicate pollen and the regular appearance of monosaccate pollen (Dimitrova et al. Reference Dimitrova, Broutın, Yanev and Petrunova2005). The late Permian assemblages of the studied material include bisaccate pollen and commonly appear in association with Cycadopites and Lueckisporites virkkiae, such as the forma species from NE Bulgaria (Dimitrova, Petrunova & Yanev, Reference Dimitrova, Petrunova and Yanev2006) and Turkey (Dimitrova & Stolle, Reference Dimitrova and Stolle2010).
Palynological assemblages from the rocks of the Alaplı Member in north Turkey are broadly synchronous throughout with similar interregional comparison of deposits within NW Turkey. Part of the Çakraz Formation with successions from Europe (Southern Alps, Germany) was correlated and discussed by Stolle (Reference Stolle2014). This correlation also supports our conclusion that the studied deposits of the Çakraz Formation in Alaplı-Ereğli area are late Permian (Tatarian) in age.
4. Discussion
4.a. Regional geological correlation
There are some lithological differences in Çakraz Formation considering the regional distribution in Çamdağ, Zonguldak (Ereğli, Alaplı) and Çakraz areas of the ZT. The Çakraz Formation in the Çakraz-Amasra region is represented mainly by red sandstone and mudstones with green, grey mudstone and sandstone interlayers. Poorly sorted and grain-supported conglomerates represent the lowest stratigraphic level of the formation. The grain size decreases upwards from pebble to sand and mud to clay. The overlying deposits consist of red, reddish, purple sandstone, mudstone and shale (Güvenç et al. Reference Güvenç, Demirel, Meşhur, Gül and Tekin1994; Alişan & Derman, Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995; Tüysüz, Aksay & Yiğitbaş, Reference Tüysüz, Aksay and Yiğitbaş2004; Gand et al. Reference Gand, Tüysüz, Steyer, Allain, Sakinç, Sanchez, Şengör and Şen2011) (Fig. 8). In Çamdağ region, the Çakraz Formation is composed of reddish sandstone and siltstone with fine-bedded claystones (Alişan & Derman, Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995; Gedik & Önalan, Reference Gedik and Önalan2001; Stolle, Reference Stolle2014) (Fig. 8). In one locality only, a relatively thin conglomerate level was observed (e.g. Stolle, Reference Stolle2014). The Çakraz Formation in the Zonguldak-Ereğli area is represented by an alternation of red, violet, occasionally massive, moderate- to thick-bedded conglomerate, sandstone, siltstone and mudstone with mud cracks, raindrops and cross-bedding (Altun & Aksay, Reference Altun and Aksay2002). Generally, this part of the formation is overlain by the recently discovered Alaplı Member (Fig. 5).
Figure 8. Generalized columnar sections of the Çakraz Formation in Çamdağ, Zonguldak (Ereğli, Alaplı) and Çakraz areas of the ZT, highlighting the lithological differences (Alişan & Derman, Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995; Altun & Aksay, Reference Altun and Aksay2002; Gedik & Aksay, Reference Gedik and Aksay2002; Timur & Aksay, Reference Timur and Aksay2002; Tüysüz, Aksay & Yiğitbaş, Reference Tüysüz, Aksay and Yiğitbaş2004; Stolle, Reference Stolle2012, Reference Stolle2014).
In the IT, the Permo-Triassic succession is known as the Kapaklı Formation (e.g. Özgül, Reference Özgül2012). The Kapaklı Formation has been subdivided to several informal lithostratigraphic units by Altınlı (1968). The lowermost unit (Unit A) is up to 1000 m thick and consists of red, thick-bedded, poorly sorted conglomerates with large (5–30 cm) boulders. They are locally interbedded with olivine basaltic-andesitic lava flows. This unit has been compared with the Permian Verrucano facies of the Alps (e.g. Arthaber, Reference Arthaber1915; Derman, Reference Derman, Göncüoğlu and Derman1997). Similar interregional comparison of deposits within NW Turkey and correlation of part of the Çakraz Formation with successions from Europe (Southern Alps; Germany) has been carried out and discussed by Stolle (Reference Stolle2014), using data from the Camdag area.
Further NW in the Balkan area, the Permian system is well defined based on the sedimentary cycles (groups) which are separated by a marked unconformity (Yanev, Reference Yanev1981; Yanev, Maslarevic & Krstic, Reference Yanev, Maslarevic and Krstic2001). The first group, generally including upper Stephanian – lower Permian strata (Yanev, Reference Yanev2000; Yanev & Adamia, Reference Yanev and Adamia2010), is characterized by lacustrine, fluvial and proluvial fan deposits as well as volcanic rocks. The second group of upper Permian deposits (?Tatarian to the P-Tr boundary) consists of deltaic and continental clastics and halite evaporates, which is limited to the southeastern part of the Moesian Terrane (Yanev, Reference Yanev1993; Yanev, Maslarevic & Krstic, Reference Yanev, Maslarevic and Krstic2001; Yanev & Adamia, Reference Yanev and Adamia2010).
The lower Permian deposits of Bulgaria and Romania show molasse-type features in the Balkan, the Prebalkan, the Sredna Gora, the Kraishte, the south Carpathians, the Apuseni Mountains and the Carapelit Basin (Seghedi et al. Reference Seghedi, Popa, Oaie and Nicolae2001; Yanev, Maslarevic & Krstic, Reference Yanev, Maslarevic and Krstic2001). The Moesian and Scythian platforms, as well as in the Kraishte region, the upper Permian units are not typically molassic in character compared to the lower Permian parts of successions, which are mainly represented by continental and transitional facies units (Seghedi et al. Reference Seghedi, Popa, Oaie and Nicolae2001; Yanev, Maslarevic & Krstic, Reference Yanev, Maslarevic and Krstic2001). The sequences in Moesian and Scythian platforms are fault-related (tectonically controlled) and the deposition occurs in shallower grabens and half-grabens (Yanev, Maslarevic & Krstic, Reference Yanev, Maslarevic and Krstic2001; Yanev & Adamia, Reference Yanev and Adamia2010). The similarity of the Permian deposits, mainly those of late Permian age in the Moesian Platform both in Romanian and Bulgarian parts, is caused by their mirrored position in the foreland of the Variscan chain. The other control on Permian sedimentation in Bulgaria and Romania is explained by active subaerial volcanism (the lower part of Rotliegend facies) for the former, and by bimodal volcanism, which continued during Triassic time, for the latter in the Moesian platform (Yanev, Maslarevic & Krstic, Reference Yanev, Maslarevic and Krstic2001).
The depositional environments of the Permian successions in both regions corresponds to a variety of continental environments such as fluvial, proluvial, playa, colluvial and alluvial-plain to palustrine, lacustrine, continental basin and sabkha conditions (Yanev, Reference Yanev1970, Reference Yanev1989; Seghedi et al. Reference Seghedi, Popa, Oaie and Nicolae2001; Yanev, Maslarevic & Krstic, Reference Yanev, Maslarevic and Krstic2001; Yanev & Adamia, Reference Yanev and Adamia2010).
4.b. Changes in the depositional environment and age of the Çakraz Formation
Overall, there is general agreement over the deposition of the Çakraz Formation in a continental environment being mainly related to a fluvial system. The depositional conditions of Çakraz Formation in Çamdağ region is described by Alişan & Derman (Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995) as continental and the depositional environment is proposed as river-channel and floodplain, possibly related to an alluvial fan with small lakes. This is also supported by the composition of the microfloras (mainly bisaccate pollen from hinterland conifers) of Stolle (Reference Stolle2011) in Çamdağ region. Tüysüz, Aksay & Yiğitbaş (Reference Tüysüz, Aksay and Yiğitbaş2004) provided a detailed lithological description of the Çakraz Formation in the Çakraz-Amasra region. In this area the base of the succession mainly consists of reddish conglomerates which are overlain by irregular braided fluvial sediments. Towards the top of the unit, more regular meandering river-floodplain sediments dominate. Gand et al. (Reference Gand, Tüysüz, Steyer, Allain, Sakinç, Sanchez, Şengör and Şen2011) suggested a palustrine floodplain environment for the Cisuralian (early Permian) red-bed levels including mud cracks and raindrops from the Çakraz Formation near Çakraz village. The fluvial system and its sub-environments are assumed to be the depositional environment of Çakraz Formation in Gand et al. (Reference Gand, Tüysüz, Steyer, Allain, Sakinç, Sanchez, Şengör and Şen2011), based on the horizons of Grancy (Reference Grancy1938); this level is the equivalent of member p2 of Grancy (Reference Grancy1938).
Biostratigraphic and fossil data to help determine the age of the Çakraz Formation are rare. It was informally declared as Permo-Triassic in age by Altun & Aksay (Reference Altun and Aksay2002), Gedik & Aksay (Reference Gedik and Aksay2002), Timur & Aksay (Reference Timur and Aksay2002) and Tüysüz, Aksay & Yiğitbaş (Reference Tüysüz, Aksay and Yiğitbaş2004). The age of the Çakraz Formation has also been proposed as early Permian (Grancy, Reference Grancy1938; Wedding, Reference Wedding1970), Permian (Tokay, Reference Tokay1962), Triassic (Jongmans, 1939) and Permian-Triassic (Akyol et al. Reference Akyol, Arpat, Erdoğan, Göğer, Güney, Şaroğlu, Şentürk, Tütüncü and Uysal1974; Kaya, Wiedmann & Kozur, Reference Kaya, Wiedmann and Kozur1986; Yergök et al. Reference Yergök, Akman, Tekin, Karabalik, Arbas, Akat, Armağan, Erdogan and Karakullukçu1987) in previous studies. In Çamdağ region (NW Anatolia), Alişan & Derman (Reference Alişan, Derman, Erler, Ercan, Bingöl and Örçen1995) dated the lake deposits of Çakraz Group as Late Triassic. The Çamdağ Formation, the equivalent of the Çakraz Formation in the Ereğli region, was dated as late Permian in age based on palynological findings. This study is the first palynological data revealed from the red beds of the Çakraz Formation.
Recently, Stolle (Reference Stolle2011) studied the pollen-dominated assemblages of the Permian part of Çakraz Formation in Çamdağ region and indicated that the assemblages are characterized by a high proportion of Lueckisporites; the Çamdağ assemblage also shows similarities to the upper Permian successions of the palaeogeographically adjacent regions of northeastern Bulgaria and western Europe. Gand et al. (Reference Gand, Tüysüz, Steyer, Allain, Sakinç, Sanchez, Şengör and Şen2011) have proposed a Cisuralian (early Permian) age for the Çakraz Formation near the Çakraz village (NW Anatolia), based on tetrapod footprints in the red beds of the lower part of formation (member p2) where coniferophyte Walchia (discovered by Grancy, Reference Grancy1938) was previously recorded. The finding of ichno- and macrofloral remains, together with the sedimentological data (mud cracks, raindrops), suggest a palustrine floodplain environment for these red-bed levels of the formation. Stolle (Reference Stolle2014) has recently proposed an early Kungurian – Capitanian age for the palynomorph-bearing sections of the mainly reddish-coloured deposits of the Çakraz Formation in the Çamdağ region (NW Anatolia).
According to previously published results and this study, which mainly corresponds to the black shale, mudstone and a conglomeratic level in the middle part of the formation, the stratigraphic ranges of reddish-coloured Çakraz Formation are limited to Permian age (Fig. 9). A Cisuralian (Gand et al. Reference Gand, Tüysüz, Steyer, Allain, Sakinç, Sanchez, Şengör and Şen2011) age is reported from the tetrapod-footprint-bearing level in Çakraz region. Stolle (Reference Stolle2014) recently specified an age range of late Cisuralian – Guadalupian (early Kungurian – Capitanian) for the palynomorph-bearing strata in Çamdağ region based on corelations with new palynological and radiometric data.
Figure 9. Stratigraphic ranges of the biostratigraphically investigated different parts of Çakraz Formation according to the previous studies of Gand et al. (Reference Gand, Tüysüz, Steyer, Allain, Sakinç, Sanchez, Şengör and Şen2011), Stolle (Reference Stolle2014) and this study.
In brief, our recent findings from the succession, including miospores in black shale, and from mudstone from the south of Alaplı region (Fig. 9) suggest a Lopingian (Tatarian) age based on bisaccate pollen with the association of Cycadopites and some of the species including Lueckisporites virkkiae, Falcisporites sp. and Alisporites sp. The Russian name Tatarian was used for the equivalent of late Permian (Lopingian and partly Guadalupian) as proposed by Tverdokhlebov et al. (Reference Tverdokhlebov, Tverdokhlebova, Benton and Storrs1997, Reference Tverdokhlebov, Tverdokhlebova, Minikh, Surkov and Benton2005), Benton, Tverdokhlebov & Surkov (Reference Benton, Tverdokhlebov and Surkov2004), Taylor et al. (Reference Taylor, Tucker, Twitchett, Kearsey, Benton, Newell, Surkov and Tverdokhlobov2009), Kotlyar, Golubev & Sılantıev (Reference Kotlyar, Golubev, Sılantıev, Gladenkov, Zakharov and Ippolitov2013) and Golubev et al. Reference Golubev, Sılantıev, Balabanov, Kotlyar, Mınıkh, Molostovskaya, Nurgaliev, Silantiev and Urazaeva2014 (Fig. 9).
5. Conclusions
The >1000 m thick organic-rich dark-coloured successions in the Zonguldak Terrane between Akçakoca and Ereğli, which were classified as being of early Palaeozoic (Ordovician–Devonian) age in previous studies, has been shown by palynological evidence to be late Permian (Tatarian) in age. The unit is the first finding of anoxic sediments of late Permian age in NW Anatolia. Because of its distinctive lithostratigraphy, the successions are described as a new lithostratigraphic unit and named the Alaplı Member of the Çakraz Formation.
The Alaplı Member is transitionally overlain by dysoxic, red, pink and violet sandstones and conglomerates with rare bands of silt- and mudstone and rare tuffaceous layers (Ereğli Member of the Çakraz Formation).
The black shales, mudstones and limestones of the Alaplı Member are very rich in organic matter but lack any macrofossils. The plant-bearing siliciclastics of the member yielded palynological assemblages including bisaccate pollen, and mainly appear in our studied section in association with Cycadopites and Lueckisporites virkkiae that are considered to indicate a late Permian (Tatarian) age. The overlying conglomerates in the middle part of the succession are dominated by pebbles of Kurtköy (Ordovician), Fındıklı (Silurian) and fossiliferous Yılanlı (Lower Devonian – lower Carboniferous) formations.
The Alaplı Member was very probably deposited in an intra-platformal basin that was closed to the marine shelves in a broad range of fluvial and lacustrine environments. Basins similar in age and depositional features are described from the East European Variscan Belt in Bulgaria and Romania, which were also developed in actively extending shallow-marine platforms on the NW Palaeotethyan margin at the end of the Permian Period.
Acknowledgements
This paper is the product of a joint project (102Y157) between BAS (Bulgaria) and TUBITAK (Turkey). The authors acknowledge both institutions and MTA (Turkey) for their financial support. The members of the Turkish (D. G. Saydam and N. Özgül) and Bulgarian (I. Boncheva, V. Sachanski, I. Lakova, S. Yanev and Y. Maliakov) teams are also acknowledged for their involvement and contributions during the field studies. Dr E. Stolle is gratefully acknowledged for her scientific comments, which improved the manuscript.
