Late Permian fluvio-lacustrine successions of the Çakraz Formation in the Zonguldak Terrane between the regions of Akçakoca and Ereğli were investigated in order to describe the litho- and biostratigraphic properties and explain the depositional environment. The studied succession with black, dark-grey to greenish-grey shales, siltstones and limestones is named the Alaplı Member to distinguish it from the classical red clastic successions, which are tentatively named the Ereğli Member of the Çakraz Formation. The organic-rich black shales, mudstones and limestones of the Alaplı Member yielded palynological assemblages suggesting a Lopingian (Tatarian) age. The lack of any marine macro- or microfossils, the fine-grained character of the lithofacies with abundant plant material and the association of poorly sorted conglomerates in the middle part of the succession indicate possible deposition in a broad range of fluvial and lacustrine environments. Successions of similar age and depositional environment are known from the East European Variscan Belt in Bulgaria and Romania. Common successions were also developed in actively extending shallow-marine platforms on the NW Palaeotethyan margin at the end of the Permian Period.

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