Two main thrust slices in the Camdag area (NW Anatolia), were informally named the Southern and Northern Camdag units. New micropaleontological and palynological data about the Ordovician, Silurian and Devonian in the Northern Camdag have allowed a better understanding of the Early Palaeozoic evolution of this critical area between the Istanbul Terrane in the west and the Zonguldak Terrane in the east. The Middle Ordovician age obtained from the conodont-bearing limestone band within the Aydos Formation in this study is in agreement with the data from the Zonguldag Terrane. Acritarch evidence suggests a Late Ordovician age of the upper part of Aydos Formation. This paper concerns the Northern unit. Three members are distinguished in the Findikli Formation and dated biostratigraphically. The lower member (Black Shale Member) of the Findikli Formation is absent from the Kabalak Dere section, but was assigned elsewhere to the Llandovery on the basis of graptolites. The middle member (Shale-Siltstone Member) is dated as Wenlock and Ludlow on the basis of acritarchs. The upper member (Shale-Limestones Member) spans a continuous upper Silurian - Lower Devonian succession. The overlaying Ferizli Formation is assigned to the Middle Devonian on the basis of conodonts. The new stratigraphic data indicate that the Southern Camdag unit corresponds to the Istanbul Terrane and the Northern Camdag unit to the Zonguldak Terrane. The tectonic contact between the Northern and the Southern units is a steep south-verging thrust-fault.