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Earliest studies on the Silurian System in Bulgaria are associated with the names of Dimitar Allahverdzhiev and Stefan Bonchev. Allahverdzhiev was the first to find Silurian graptolites in this country; his specimens are housed in the Laboratory of Geocollections of the Geological Institute (Bulgarian Academy of Sciences). Bonchev laid the foundations of the lithostratigraphic subdivision of Palaeozoic sediments in the West Balkan Mts. by distinguishing all their lithologic variations. In terms of regional tectonic zonation, the study area is a part of a first-rank Late Alpine unit, the Srednogorie Zone, represented by the Svoge Unit. The lithostratigraphy of the Palaeozoic marine successions in the Svoge Unit consists of nine formal units (Grohoten, Tseretsel, Sirman, Saltar, Mala Reka, Yabukov Dol, Ogradishte, Romcha and Katina formations) and one informal unit (silty-clayey metaformation). Their distribution is illustrated in a geologic map. The biostratigraphic subdivision of the Silurian System in Bulgaria is based on graptolites. Herein, the latest two “standard” zonal schemes are shown: the Generalized graptolite zonation and the Graptolite zonation for the peri-Gondwana (Europe). About 25% of these graptolite zones have not yet been recognized in Bulgaria; the extent of the others is plotted against a generalized section of the Silurian System for the region.

The graptolite-bearing interval in well A1-NC101, Libya indicates a Hirnantian age (persculptus graptolite Zone) for the lowermost Tanezzuft Fm based on the presence and stratigraphical distribution of N.? pseudovenustus. In the C1-NC101 core, the presence of N. inazaouae (recognised for the first time outside Algeria) and M. parvulus indicates either the uppermost Ordovician or the lowermost Silurian, but the revised total stratigraphical range of N. targuii (ascensus-acuminatus graptolite Zone) suggests an earliest Rhuddanian age. Several specimens of N. targuii are longer than those previously recorded.Pure quartz arenites of the uppermost Mamuniyat Fm (well A1-NC101) were deposited during the end-Hirnantian deglaciation probably in a nearshore marine environment. Their provenance was associated with sedimentary recycling of mature sands that were formed across North Gondwana in Cambrian and pre-glacial Ordovician times.

WOS: 000346296000008, The Karadere area to the east of Safranbolu in NW Anatolia is one of the very few localities in Turkey where the contact between the Cadomian basement and the Lower Palaeozoic transgressive succession is well exposed. The Ordovician graptolite Rhabdinopora flabelliformis (Eichwald) ssp. was found in the basal part of the Bakacak Formation, indicating an Early to early Late Tremadocian age for the beginning of the Palaeozoic transgression in the Zonguldak terrane. A few metres above this occurrence, another horizon contains Paradelograptus cf. antiquus (T. S. Hall), which mainly ranges into the Late Tremadocian. Higher up in the Ordovician succession, a new graptolite bed confirms an early Darriwilian (Dw1) age for the middle part of the Karadere Formation with the occurrence of the biozonal index Levisograptus austrodentatus (Harris & Keble) and the first record of Tetragraptus cor (Strandmark) in the area. The palaeobiogeographic distribution of these Karadere fossils is in agreement with a peri-Gondwanan affinity of the Zonguldak Terrane of the Pontides, NW Anatolia, during the Early-Middle Ordovician., teams of the TUBITAK-BAS joint-projectTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [102Y157]; Spanish MINECO [CGL2012-39471]; IGCP project [591], The authors gratefully acknowledge Iskra Lakova for her contributions to a former version of this study with a divergent content. The members of the Turkish (G. Saglam, I. Gedik, N. Ozgul) and Bulgarian (I. Boncheva, S. Yanev and Y. Maliakov) teams of the TUBITAK-BAS joint-project No. 102Y157 are acknowledged for their involvement during the field studies. Participation of J. C. G.-M. was possible through the project CGL2012-39471 of the Spanish MINECO. This paper has benefited from the review of P. S torch (Prague) and J. Maletz (Berlin) and is a contribution to IGCP project 591.

The studied Guluc section of the Silurian Findikli Formation is situated on the western bank of Guluc Creek in Eregli, NW Anatolia, Turkey, in the eastern part of the Zonguldak Terrane. The Guluc section consists of 3 sedimentary packages: greenish grey limy siltstones, 5-7 m thick (1), overlain by an irregular alternation of black shales and clayey limestones, about 15 m thick (2), and a 6-7 m thick succession of mainly siltstones and sandy limestones (3). A combined biostratigraphy based upon graptolites, cryptospores and conodonts indicates that Package 1 is of Llandovery (Rhuddanian, Aeronian and/or early Telychian) age, Package 2 and Package 3 are of late Wenlock-early Ludlow (Homerian and Ludfordian) age. Graptolites in packages 2 and 3 indicate the presence of the Cyrtograptus lundgreni, Neodiversograptus nilssoni and Lobograptus scanicus graptolite biozones. The Ozarkodina crassa Biozone occurs in the lower Gorstian (Ludlow). The specific features of the Guluc section (lithological changes, condensation, stratigraphic gap, change in graptolite diversity) are related to the global model of Silurian T-R cycles. The Silurian Findikli Formation in the Guluc section, about 20 m thick, represents a condensed lithological succession which differs significantly from the coeval thick, stratigraphically widespread black shales and siltstones of the same formation in the Zonguldak and Istanbul terranes. Sixteen cryptospore species are described and their stratigraphic and geographic distributions are summarised.