In NW Turkey, a generally anchizonal metamorphic, well-developed and continuous Palaeozoic sequence crops out. The basement of this Palaeozoic sequence is presumed to be a Pan-African basement which crops out only farther east of İstanbul. The Palaeozoic sequence starts regressive with the turbiditic arkosic clastics and continue with fluvial conglomerates. This regressive part of the sequence is considered to be filling a deep lake basin under the influence of Gondwanian periglacial conditions. The transgressive part of the sequence starts during the Silurian with shallow marine clastics. After this period the depositional basin received passive continental margin deposits; the fossiliferous early Devonian thick shelf-type limestones, middle Devonian shales and late Devonian-early Carboniferous nodular limestones, cherts and shales. The early Carboniferous flysch, which was probably related to the Hercynian (or Scythide?) Orogeny, covers the whole transgressive sequence. The Palaeozoic sequence of İstanbul is cut by numerous west vergent thrust faults. The main structural style of the Palaeozoic rocks suggests that there is a main décollement underneath the sequence and they are deformed in a thin-skinned mode. Restoration of the cross-sections show that there is almost 50% shortening along an east-west direction. Considering the paleontological resemblance and the zircon ages from various previous studies, this margin is thought to belong to Gondwana-Land. However the İstanbul Palaeozoic differs from the European Hercynides in the absence of medium to high grade metamorphism and pre-Permian volcanism.
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