Silurian Graptolite, Conodont and Cryptospore Biostratigraphy of the Gülüç Section in Ereğli, Zonguldak Terrane, NW Anatolia, Turkey

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.