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

Abstract

The Kre Complex of the Middle Pontides, northern Turkey, isnot a remnant of the Palaeotethys but consists of three different unitswith differing geological history, the Kre Ridge Unit, the KreOcean Unit and the ala Unit. The Kre Ridge Unit consists of theServeay Group, a pre-Permian, low-grade metamorphic Variscanoceanic sequence, and the Sõralõk Group, a Lower and Middle Triassicshallow-water sequence of North Alpine facies and event successionwhich disconformably overlies the Serveay Group. Following ahiatus, the Sõralõk Group is overlain by marginal parts of the AkglGroup with olistoliths of local origin which were derived mainly fromthe Sõralõk Group. The Kre Ocean Unit consists mostly of theAkgl Group (siliciclastic turbidites and olistostromes of the Karadagù tepe Formation, which is a middle Carnian to Middle Jurassicaccretionary complex from the southern, active margin of the KreOcean, 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 Karadagù tepe Formation contains numerous Middle Triassic exotic olistolithsand blocks of shallow-water and predominantly slope and basinallimestones, ocean-floor deep-sea sediments (shales and radiolarites),basalts and small clasts of ophiolites or ophiolitic detritus. Theala Unit consists of deposits from the northern, passive margin ofthe Kre Ocean with many Pelsonian to upper Norian Hallstatt Limestonesand Rhaetian -Lower Jurassic (?Middle Jurassic) deep-watershales and marls. All three units are overlain following a period ofnon deposition by the Upper Jurassic Brnk Formation (red conglomerate, sandstone) and Inaltõ Formation (shallow-water platformcarbonates).The Kre Ridge Unit was split away from the Variscan SakaryaContinent by the opening of the Karakaya oceanic rift basin duringlatest Permian (Dorashamian) and became a continental splinterbetween the Karakaya oceanic rift basin and the Kre Ocean (openedduring the late Scythian).Southward subduction began in the Kre Ocean during the middleCarnian (beginning of the Karadagù tepe siliciclastic turbidites),whereas at the northern passive margin the deposition of HallstattLimestones 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 oceanbasin deposits (radiolarites, pelagic limestones) and slope depositsform the passive margin (e.g., Hallstatt Limestones) are no more present in the Karakaya oceanic rift basin indicating that this basin wasvery narrow (only a few hundreds of kilometres). During the lateNorian, the Karakaya oceanic rift basin closed, whereas subduction atthe southern (active margin) of the Kre Ocean continued. At thenorthern margin of the (Upper Triassic?) Jurassic -Lower CretaceousB e y k oz- agù layan turbidite basin (north of the Kre Complex) theaccretionary complex of an older ocean, the Late Palaeozoic Paphlagonian Ocean, was exposed that yielded clasts in the Beykoz - agù 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 subductionis assumed for the Paphlagonian Ocean. Its closure occurredeither at the end of the Permian or during the Scythian.