Iliana Boncheva

Stratigraphy, correlations and palaeogeography of Palaeozoic terranes of Bulgaria and NW Turkey: a review of recent data

Abstract Within the Alpine tectonic units SE of the European Variscan Orogenic Belt in Bulgaria and NW Turkey several crustal blocks are identified. Although their contact relations with surrounding units are obscured by Alpine events, the differences in the succession of events, stratigraphy, sedimentology and palaeobiogeographical distribution within them permits recognition of the Moesian, Balkan, Istanbul and Zonguldak Terranes. The Moesian terrane corresponds to the pre-Variscan Palaeozoic and Neoproterozoic rocks of the Moesian microplate in north Bulgaria and south Romania. The Balkan Terrane in Bulgaria incorporates Neoproteozoic and Palaeozoic sequences in the Western Balkanides (part of the Carpathian-Balkan orogen) and another three allochthonous units (Kraishte, Central Balkanides and Strandzhides). In NW Anatolia in Turkey, the Caledonian basement and Ordovician to Carboniferous sedimentary succession are divided into the Istanbul Terrane and the Zonguldak Terrane. With the exception of the Moesian Terrane in the Bulgarian area, they all comprise a Cadomian basement with relicts of oceanic lithosphere, volcanic arc and a continental crust of unknown affinity. Based on characteristic features within their Palaeozoic successions, there terranes are correlated with the main terrane assemblages in Central and Eastern Europe. It is suggested that they all are of peri-Gondwanan origin but behaved independently while drifting towards Laurussia. During the Early Devonian the Zonguldak Terrane docked to Baltica, whereas the others were still at similar palaeolatitudes to the Central European terranes (e.g. Saxo-Thuringian). This was followed by the successive accretion of the Moesian Terrane to Laurussia along the Rhenohercynian suture at the end of Devonian-Early Carboniferous and of the Balkan and Istanbul Terranes the Early and Late Carboniferous.

FIRST DISCOVERY OF MIDDLE TOURNAISIAN CONODONTS IN THE GRIOTTE-TYPE NODULAR PELAGIC LIMESTONES, ISTANBUL AREA, NW TURKEY

The uppermost layers of the Ayineburnu member of the Buyukada Formation in the Istanbul-Gebze area are represented by Griotte-type pelagic nodular limestones. They yielded conodont elements (Bispathodus stabilis and Siphonodella lobata) that can iden- tify the interval from the upper part of the sandbergi Zone through the isosticha- Upper crenulata Zone - middle Tournaisian - Early Carbonif- erous. This is the first middle Tournaisian conodont record published from an autochthonous succession in the Istanbul Terrane, NW Tur- key. This level characterizes the very last carbonate deposition and is followed by lydites and black siliceous shales and finally by the accu- mulation of flysch-type deposits during the late Tournaisian and early Visean, that mark the onset of Variscan events to the north of the Is- tanbul Terrane. A correlation with the Lower Carboniferous succes- sions in the easterly-located Zonguldak area suggests that Istanbul and Zonguldak terranes were in quite different palaeogeographic positions during this time interval.

CARBONIFEROUS CONODONT BIOSTRATIGRAPHY AND LATE PALAEOZOIC DEPOSITIONAL EVOLUTION IN SOUTH CENTRAL IRAN (ASADABAD SECTION - SE ISFAHAN)

Asadabad section in Central Iran is one of the most complete sequences so far described across the Carboniferous of Iran. The stratigraphic and biostratigraphic data on the sediments overlying the Devonian carbonate platform give evidence about the duration of shallow water depositional evolution. There are thirty productive levels with conodonts in the Carbonifeous section ranging in age from early Tournaisian to the top of Bashkirian (Lower expansa - s ulcata to sinuosus zones). There is scarce evidence about the elongatus Zone presence - Late Pennsylvanian. S ulcata to anchoralis-latus conodont zones in Shishtu Formation and muricatus to sinuosus Zone and a possible elongatus Zone in Sardar Formation have been indentified. These conodont zones are reported for the first time in that area. A crinoidal limestone - key bed horizon, is traceable in the studied area as well as in other parts of Iran. It is Early Pennsylvanian-Bashkirian in age and is correlated to sinuatus-minutus Zone. The studied Shishtu and Sardar Formations (Carboniferous) as well as Vazhnan and Surmaq Formation (Permian) in the section belong to marine near shore sedimentation with many macrofaunal remains.

New age data from the tectonostratigraphic units of the Istranca “Massif” in NW Turkey: a correlation with SE Bulgaria

Abstract The Istranca Crystalline Complex in NW Anatolia and SE Bulgaria includes structural units that differ in lithostratigraphy, metamorphism, age and structural position. They are collectively named as the “Istranca nappes” comprising from bottom to top the Sarpdere, Mahyadağ and Doğanköy Nappes. The Sarpdere Nappe consists of Lower Triassic arkosic metasandstones with slate interlayers, followed by Middle to Upper Triassic carbonates and an alternation of Upper Triassic clastics and carbonates. The Mahyadağ Nappe comprises a low-grade metamorphic Late Paleozoic- Triassic carbonate-siliciclastic sedimentary succession. The Doğanköy Nappe includes Precambrian?-Paleozoic metasediments, intruded by Late Carboniferous-Early Permian calc-alkaline granitoids. Its Triassic cover comprises metaclastics and metacarbonates. The Istranca nappes were juxtaposed at the end of the Triassic and transgressively covered by Lower Jurassic coarse clastics, followed above by Middle to Late Jurassic carbonates, black shales and carbonate-siliciclastic sedimentary succession. The phosphate concretions in black shales yielded radiolarian assemblages indicating Late Bajocian-Early Bathonian, Early Bathonian and Early Kimmeridgian ages. These nappes and their Jurassic cover are unconformably overlain by the Cenomanian-Santonian volcano-sedimentary successions intruded by Santonian-Campanian Dereköy-Demirköy intrusive suite. The preliminary data suggest that the Variscan basements of the Mahyadağ and Sarpdere Nappes were juxtaposed prior to the Triassic and overridden by the Doğanköy Nappe of possible Rhodopean origin from S to N during the Cimmerian compressional events

Palaeoenvironmental study of the Palaeotethys Ocean: the Givetian-Frasnian boundary of a shallow-marine environment using combined facies analysis and geochemistry (Zefreh Section/Central Iran)

The Zefreh section in central Iran represents a carbonate ramp succession with a general shallow-marine palaeoenvironment. This section represents most of the Bahram Formation (Givetian to at least Middle falsiovalis Zone) and consists of a very heterogeneous succession of medium- to coarse-grained sandstones, skeletal pack- to grainstones with local biostromes, massive or laminated dolostones, and shales. Microfacies analysis allowed the discrimination of 12 microfacies reflecting supratidal to open marine palaeoenvironments. The shallow-marine environment was investigated using facies analysis and geochemical proxies. Redox conditions in the Zefreh section appear to be primarily oxic and support the facies and sedimentological results. The provenance of the Zefreh sediments using La, Sc, Zr, and Th indicates that they are most likely derived from continental arc volcanics which is consistent with the preliminary tectonic interpretations. Conodonts and brachiopods were used for establishing the biostratigraphical framework. The lack of important zonal index taxa of the widely applied conodont standard zonation requires the application of an alternative shallow-marine conodont zonation. Based on conodont and brachiopod data, the Zefreh section covers sediments ranging from the upper Givetian to lower Frasnian.

Middle Devonian (Givetian) conodonts from the northern margin of Gondwana (Soh and Natanz regions, north-west Isfahan, Central Iran): biostratigraphy and palaeoenvironmental implications

Four sections of mainly Middle Devonian (Givetian) shallow-marine rocks at the northern margin of Gondwana (Central Iran) were investigated with a special focus on the Bahram Formation, as the stratigraphic range of the Bahram Formation is uncertain and still under discussion. Generally, the Bahram Formation is discontinuously underlain by the Lower Devonian Padeha Formation and disconformably overlain by the Permian Jamal Formation. Conodont communities from the four sections in the Soh area (Najhaf and Neqeleh sections) and the Natanz area (Varcamar and North Tar sections) were investigated. The most widely applied conodont standard zonation of the Upper Givetian contain taxa characteristic of deeper shelf facies whereas conodont fauna of the investigated sections mainly show affinities to shallow-marine environments. Shallow-water conodont associations corresponding to the expansus Zone and subterminus Zone are described from Central Iran for the first time, whereas the vast majority of icriodontid and polygnathid faunas were reported from shallow-marine carbonates around Laurussia (e.g. North America, and Europe). Thirty-six species and subspecies were assigned to five genera (Ancyrodella, Bipennatus, Icriodus, Polygnathus and Pandorinellina). The sedimentological record is characterised by remarkable lateral facies changes, but in the upper part of the Givetian, a general transgressive trend is obvious due to the dominance of limestones and small biostromes.

A Late Devonian (Frasnian) bryozoan fauna from central Iran

A bryozoan fauna from the Late Devonian (Frasnian) of the Bahram Formation of the Zefreh section in central Iran contains four species: three trepostomes and one rhabdomesine cryptostome. Two species are new: the trepostome Coeloclemis zefrehensis sp. nov. and the rhabdomesine cryptostome Euthyrhombopora tenuis sp. nov. The trepostome species Cyphotrypa definita Morozova, 1960 and Anomalotoechus ramosus Morozova, 1960 were recorded previously from the Upper Devonian (Frasnian) of the Kuznets Basin. The genera Coeloclemis and Euthyrhombo-pora are recorded from the Devonian for the first time. The fauna is dominated by the erect ramose Euthyrhombopora tenuis sp. nov., with rare occurrences of the massive Cyphotrypa definita Morozova, 1960. The bryozoans indicate low to moderate water energy environment of middle to outer ramp position.

Conodont biostratigraphy of the Kesheh and Dizlu sections, and the age range of the Bahram Formation in central Iran

Conodont fauna from the Kesheh and Dizlu sections in the North Isfahan province were investigated. Shallow-water and/or near-shore conodonts, mainly belonging to the icriodid–polygnathid biofacies, dominate the conodont fauna. Due to the depositional setting which is characterised by predominantly shallow-water palaeoenvironments and the lack of some important zonal index taxa (e.g. Palmatolepis species), a precise conodont biostratigraphy is difficult to establish. The Kesheh section covers sediments ranging from the Givetian hermanni Zone to disparilis Zone whereas in the Dizlu section, the ranges of Middle triangularis to Uppermost crepida, the marginifera to Upper trachytera, and the Lower and Middle expansa Zones indicate a Famennian age. The stratigraphic range of the Bahram Formation is discussed, and according to literature and new conodont data presented herein, it is likely that the age of the Bahram Formation in central Iran has a stratigraphical range from the Givetian (hermanni Zone) to the late Famennian (Middle expansa Zone).