Development of the Middle Devonian-Mississippian carbonate platform in Zonguldak Terrane (NW Anatolia, Türkiye) with special emphasis on the Devonian-Carboniferous Boundary

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2025-01-01

Author

Okuyucu, Cengiz
Boncheva, Iliana
Sachanski, Valeri
Saydam-Demiray, D. Gülnur
Göncüoğlu, Mehmet Cemal

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The Zonguldak Terrane in the northwestern Türkiye is one of the continental micro-plates representing the eastern prolongation of the Variscan belt in Eastern Europe. Its distinguishing feature from the neighboring Variscan terranes (e.g. Istanbul Terrane) is the presence of a well-developed Middle Devonian–Mississippian carbonate platform. This platform carbonate succession, named as Yılanlı Formation, was sampled in detail for conodonts and foraminifera along six measured sections for a better understanding of its geological evolution. In the studied sections, the lowermost limestone bands alternating with green-yellow shales and marls are dated by conodonts to latest Emsian–late Eifelian. This interval is interpreted as the onset of the carbonate platform deposition. The following limestone-shale intercalations yielded an Eifelian–lower Givetian succession, conformably overlain by upper Givetian–? lower middle Frasnian strata. This series is covered by shallow marine, medium to thick-bedded grey limestones with five to twenty cm thick K-bentonite bands. Scarce foraminifera findings only suggest a Late Devonian age. The upper part of this thick-bedded carbonate package with cm-thick black chert bands, which are named as the “transitional D-C beds” as they yielded foraminifera (including the new taxon: Laxoendothyra parakosvensis gracilis subsp. nov.) ranging from latest Famennian to earliest Tournaisian. Upwards the cherty limestones are replaced by cherts and nodular limestones with conodonts of the Siphonodella mehli Zone indicating a change from platform to slope conditions during the early Tournaisian. The following package of dark grey, thick-bedded to massive limestone with conodonts of the Si. isosticha Zone marks the restoration back to shallow platform conditions during the middle Tournaisian, frequently observed in Variscan terranes. The uppermost part of the Yılanlı Formation comprises a thick package of grey to pink nodular limestones alternating with shales and mudstones. The Yılanlı Formation is transitional to the Alacaağzı Formation, which comprises siltstones and plant-bearing sandstones with calcarenite nodules including early Serpukhovian conodonts. This change from carbonate platform to deltaic and fluvial conditions is typical along the Variscan belt and ascribed to the drowning of the Middle Devonian–Mississippian carbonate platform. Biostratigraphic data recovered from the studied sections of the Yılanlı Formation from the Zonguldak Terrane in NW Anatolia suggest that the Yılanlı Formation was deposited during latest Emsian-late Eifelian to late Viséan.

Subject Keywords

Conodonts, Devonian–Carboniferous Boundary, Foraminifera, NW Türkiye, Stratigraphy, Zonguldak Terrane

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https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=105001481518&origin=inward
https://hdl.handle.net/11511/114264

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Department of Geological Engineering, Article