The first record of the Mid-Barremian Oceanic Anoxic Event and the Late Hauterivian platform drowning of the Bilecik platform, Sakarya Zone, western Turkey

The late Hauterivian platform drowning has been recorded in the Hauterivian/Barremian boundary beds in western Turkey. This drowning event recorded by presence of hardgrounds, glauconite- and phosphate-bearing facies over the platform carbonates is followed up by pelagic carbonates. Ammonitico Rosso like reddish colored, thick-bedded limestones include multiple hardgrounds, abundant ammonites, belemnites and bivalves just below the Hauterivian/Barremian boundary. The hardground surfaces contain macro and micro-scale manganese and iron encrustations, micro- and macro-boring structures, calcite mineralization and glauconite minerals. Geochemical analysis indicates that Mn encrustation in the hardground is related to hydrothermal and/or hydrogenetic-detrital and associated with continental margin occurrence. A red pelagic limestone succession with planktonic foraminifera overlies the last hardground surface at the Hauterivian-Barremian boundary and is followed up by the alternation of gray colored bioturbated sandy/silty limestones with radiolaria and black shales or sandy/silty mudstones. A black shale level including ammonite, manganese, iron, pyrite and glauconite minerals takes place around the early Barremian-late Barremian boundary. At the top of the sections, there is a succession composed of alternation of thicker sandy limestone and shale/marl covering the black shale interval. The record of mid-Barremian black shale interval over the platform carbonates and the overlying pelagic succession with radiolaria indicate that the mid-Barremian Oceanic Anoxic Event took place after the drowning of the platform. Stable delta C-13 and delta O-18 isotope excursions have been detected within black shale zone and display parallel pattern with European sections. This study presents the first record of the mid-Barremian anoxic oceanic event on the Sakarya Zone of Pontides in Turkey. (C) 2012 Elsevier Ltd. All rights reserved.