New Stratigraphic and Palaeogeographic Results from the Palaeozoic and Early Mesozoic of the Middle Pontides (Northern Turkey) in the Azdavay, Devrekani, Kre and Inebolu Areas: Implications for the Carboniferous - Early Cretaceous Geodynamic Evolution an

Abstract

The KŸre Complex of the Middle Pontides, northern Turkey, is not a remnant of the Palaeotethys but consists of three different units with differing geological history, the KŸre Ridge Unit, the KŸre Ocean Unit and the ‚ala Unit. The KŸre Ridge Unit consists of the Serveay Group, a pre-Permian, low-grade metamorphic Variscan oceanic sequence, and the Soralok Group, a Lower and Middle Triassic shallow-water sequence of North Alpine facies and event succession which disconformably overlies the Serveay Group. Following a hiatus, the Soralok Group is overlain by marginal parts of the Akgšl Group with olistoliths of local origin which were derived mainly from the Soralok Group. The KŸre Ocean Unit consists mostly of the Akgšl Group (siliciclastic turbidites and olistostromes of the Karad agu tepe Formation, which is a middle Carnian to Middle Jurassic accretionary complex from the southern, active margin of the KŸre Ocean, and mainly Middle Jurassic molasse type shallow-water sandstones, siltstones and shales of an unnamed formation) and of thick oceanic basalts (Ipsinler Basalt). Tectonic slices of Middle Triassic to lower Carnian ophiolites and basalts are also present. The Karad agu tepe Formation contains numerous Middle Triassic exotic olistoliths and blocks of shallow-water and predominantly slope and basinal limestones, ocean-floor deep-sea sediments (shales and radiolarites), basalts and small clasts of ophiolites or ophiolitic detritus. The ‚ala Unit consists of deposits from the northern, passive margin of the KŸre Ocean with many Pelsonian to upper Norian Hallstatt Limestones and Rhaetian -Lower Jurassic (?Middle Jurassic) deep-water shales and marls. All three units are overlain following a period of non deposition by the Upper Jurassic BŸrnŸk Formation (red conglomerate, sandstone) and Inalto Formation (shallow-water platform carbonates). The KŸre Ridge Unit was split away from the Variscan Sakarya Continent by the opening of the Karakaya oceanic rift basin during latest Permian (Dorashamian) and became a continental splinter between the Karakaya oceanic rift basin and the KŸre Ocean (opened during the late Scythian). Southward subduction began in the KŸre Ocean during the middle Carnian (beginning of the Karadagu tepe siliciclastic turbidites), whereas at the northern passive margin the deposition of Hallstatt Limestones continued until the latest Norian. The deposition of siliciclastic turbidites and olistostromes (Diskaya Unit) began in the entire Karakaya oceanic rift basin during the middle Carnian, and ocean basin deposits (radiolarites, pelagic limestones) and slope deposits form the passive margin (e.g., Hallstatt Limestones) are no more present in the Karakaya oceanic rift basin indicating that this basin was very narrow (only a few hundreds of kilometres). During the late Norian, the Karakaya oceanic rift basin closed, whereas subduction at the southern (active margin) of the KŸre Ocean continued. At the northern margin of the (Upper Triassic?) Jurassic -Lower Cretaceous B e y k oz- ‚ agu layan turbidite basin (north of the KŸre Complex) the accretionary complex of an older ocean, the Late Palaeozoic Paphlagonian Ocean, was exposed that yielded clasts in the Beykoz -‚ agu l ayan turbidite basin. Among these clasts Carboniferous to Middle Permian (Capitanian) pelagic rocks (pelagic limestones, radiolarites) could be dated. A Middle to Late Permian southward-directed subduction is assumed for the Paphlagonian Ocean. Its closure occurred either at the end of the Permian or during the Scythian.