First evidence of the Cenomanian/Turonian boundary event (CTBE) in the Alakırçay Nappe of the Antalya Nappes, southwest Turkey

Abstract

The Doyran section in the Alakırçay Nappe of the Antalya Nappes includes the organic carbon-rich black shales within radiolarian-rich pelagic sediments that were deposited in an off-margin abyssal environment. A biostratigraphical analysis, based on radiolarian assemblages, indicates that the rock units studied encompass the Cenomanian/Turonian boundary (CTBE). The total organic carbon contents of the black shales in this horizon vary from 7.89 to 42.19% wt with an average value of 22.0% wt. The calculated values of the hydrogen and oxygen indexes indicate that the organic carbon originated from marine organic matter (type I/II kerogen). The black shales include thin-bedded and laminated layers deposited at low sedimentation rates with little terrestrial input. Lamination, no bioturbation and abundant pyrite occurrences indicate that the anoxic conditions prevailed on the depositional environment and favoured the preservation of organic matter. Lithological features and the radiolarian fauna of the CTBE in the Doyran section are in keeping with each other and correlate with the CTBE at other localities in the Atlantic and Tethyan realms.