The uppermost layers of the Ayineburnu member of the Buyukada Formation in the Istanbul-Gebze area are represented by Griotte-type pelagic nodular limestones. They yielded conodont elements (Bispathodus stabilis and Siphonodella lobata) that can iden- tify the interval from the upper part of the sandbergi Zone through the isosticha- Upper crenulata Zone - middle Tournaisian - Early Carbonif- erous. This is the first middle Tournaisian conodont record published from an autochthonous succession in the Istanbul Terrane, NW Tur- key. This level characterizes the very last carbonate deposition and is followed by lydites and black siliceous shales and finally by the accu- mulation of flysch-type deposits during the late Tournaisian and early Visean, that mark the onset of Variscan events to the north of the Is- tanbul Terrane. A correlation with the Lower Carboniferous succes- sions in the easterly-located Zonguldak area suggests that Istanbul and Zonguldak terranes were in quite different palaeogeographic positions during this time interval.