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The Cenomanian–Turonian carbonate ramp in the Adıyaman Region of SE Turkey (Northern Arabian Platform) records an abrupt shift from benthic carbonate deposits to pelagic deposits near the Cenomanian–Turonian boundary event (CTBE) in the İnişdere stratigraphic section and surrounding borehole sections. A positive δ13C excursion of up to 2.15% is recorded in carbonate and organic carbon deposited around the CTBE and provides evidence of a direct link between the CTBE and oceanic anoxic events and the demise of the shallow carbonate production in the Derdere Formation. The microfacies analyses, biostratigraphic dating and palaeoenvironmental interpretations suggest that the platform was drowned near the CTBE as a result of changing environmental conditions. The microfacies indicating significant deepening show a contemporaneity to equivalent surfaces globally and thus strongly support an isochronous formation of Cenomanian–Turonian facies by eustatic sea-level changes. Anoxia spreading over the platform drastically reduced the carbonate production as observed in the studied sections and, therefore, resulted in a reduction in carbonate accumulation rates. Regional/local subsidence and a coeval sea-level rise during the late Cenomanian to early Turonian interval were the cause of the drowning of the platform, including regional anoxia at the northern Arabian platform linked to the Cenomanian–Turonian oceanic anoxic event (OAE2).

Abstract. The micropalaeontology of the mid-Cretaceous Derdere Formation (Mardin Group) from outcrops close to the town of Derik in south-eastern Turkey is described here. In thin sections from the carbonates that form the majority of this formation, rich and diverse micropalaeontological assemblages are present. These include larger benthonic foraminifera, planktonic foraminifera, and other microfossils, including calcareous algae. Alveolinid foraminifera are particularly common and include a new species – Simplalveolina mardinensis. In contrast to some previous studies, the majority of the section can be demonstrated to be Cenomanian (notably middle Cenomanian) in age with no confirmation of extension into the Albian or Turonian. Deposition took place on a carbonate ramp within a range of discrete deposition settings ranging from peritidal to outer ramp. A notable feature is the small-scale (a few metres) shallowing-up cycles within the inner-ramp facies that may be allocyclic or autocyclic in origin. Three major deepening events are recognised within the succession, characterised by more open marine microfauna and microfacies. These occur at the base of the formation, within the mid-Cenomanian lower part, and towards the top of the formation. These may correlate with three Cenomanian deepening phases seen in other parts of the Arabian Plate.

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