The Pontides formed the southern active margin of Laurasia during the Mesozoic. They became separated from mainland Laurasia during the Late Cretaceous, with the opening of the Black Sea as an oceanic back-arc basin. During the Early Cretaceous, a large submarine turbidite fan complex developed in the Central Pontides. The turbidites cover an area of 400 km by 90 km with a thickness of more than 2 km. We have investigated the provenance of these turbidites-the Çağlayan Formation-using paleocurrent measurements, U-Pb detrital zircon ages, REE abundances of dated zircons and geochemistry of detrital rutile grains. than 2% of the total zircon population, which implies lack of a coeval magmatic arc in the region. This is compatible with the absence of the Lower Cretaceous granites in the Pontides. Thus, although the Çağlayan Basin occupied a fore-arc position above the subduction zone, the arc was missing, probably due to flat subduction, and the basin was 3 largely fed from the Ukrainian Shield in the north. This also indicates that the Black Sea opened after the Early Cretaceous following the deposition of the Çağlayan Formation.

Before the Late Cretaceous opening of the Black Sea, the Central Pontides constituted part of the southern margin of Laurasia. Two features that distinguish the Central Pontides from the neighbouring Pontide regions are the presence of an extensive Lower Cretaceous submarine turbidite fan (the Çağlayan Formation) in the north, and a huge area of Jurassic–Cretaceous subduction–accretion complexes in the south.The Central Pontides comprise two terranes, the Istanbul Zone in the west and the Sakarya Zone in the east, which were amalgamated before the Late Jurassic (Kimmeridgian), most probably during the Triassic. The basement in the western Central Pontides (the Istanbul Zone) is made up of a Palaeozoic sedimentary sequence, which ends with Carboniferous coal measures and Permo-Triassic red beds. In the eastern Central Pontides, the basement consists of Permo-Carboniferous granites and an Upper Triassic forearc sequence of siliciclastic turbidites with tectonic slivers of pre-Jurassic ophiolite (the Küre Complex). The Küre Complex is intruded by Middle Jurassic granites and porphyries, which constitute the western termination of a major magmatic arc.Upper Jurassic–Lower Cretaceous shallow-marine limestones (the İnaltı Formation) lie unconformably over both the Istanbul and Sakarya sequences in the Central Pontides. Two new measured stratigraphic sections from the İnaltı Formation constrain the age of the İnaltı Formation as Kimmeridgian–Berriasian. After a period of uplift and erosion during the Valanginian and Hauterivian, the İnaltı Formation is unconformably overlain by an over 2 km-thick sequence of Barremian–Aptian turbidites. Palaeocurrent measurements and detrital zircons indicate that the major part of the turbidites was derived from the East European Platform, implying that the Black Sea was not open before the Aptian. The Çağlayan turbidites pass northwards to a coeval carbonate–clastic shelf exposed along the present Black Sea coast. In the southern part of the Central Pontides, the Lower Cretaceous turbidites were deformed and metamorphosed in the Albian. Albian times also witnessed accretion of Tethyan oceanic crustal and mantle sequences to the southern margin of Laurasia, represented by Albian eclogites and blueschists in the Central Pontides.A new depositional cycle started in the Late Cretaceous with Coniacian–Santonian red pelagic limestones, which lie unconformably over the older units. The limestones pass up into thick sequences of Santonian–Campanian arc volcanic rocks. The volcanism ceased in the middle Campanian, and the interval between late Campanian and middle Eocene is represented by a thick sequence of siliciclastic and calciclastic turbidites in the northern part of the Central Pontides. Coeval sequences in the south are shallow marine and are separated by unconformities. The marine deposition in the Central Pontides ended in the Middle Eocene as a consequence of collision of the Pontides with the Kırşehir Massif.

mentioned Permo-Triassic accretionary complexes, which include greenschist-to blueschist-facies rocks with lenses of eclogites, indicating the presence of a coeval subduction zone. The Permo-Triassic subduction and deformation events in the Pontides are commonly attributed to the Cimmeride Orogeny, leading to closure of the Paleo-Tethys Ocean and opening of the Neo-Tethys (e.g., Şengör, 1984;Stampfli and Borel, 2002). A Permo-Triassic magmatic arc related to coeval subduction has not been documented. However, beneath the Tertiary sedimentary rocks of the Scythian Platform, deep wells indicate the presence of Triassic igneous rocks (details in Okay et al., 2013;Okay and Nikishin, 2015) and were interpreted as parts of the possible Triassic magmatic arc. The Triassic Cimmeride Orogeny was followed by the development of a Jurassic magmatic arc, which can be traced along the Sakarya Zone, Crimea, and the Caucasus (

The Lower and Upper Cretaceous turbidites cover large areas in the central Pontides (north-central Turkey). The Lower Cretaceous turbidites are over 2 km thick and are exposed in an area of 400 × 90 km. The Upper Cretaceous (Campanian-Maastrichtian) forearc turbidites are up to 1,200 m thick and crop out in NW-SE trending elongate basins about 40 km wide, extending along the central and eastern Pontides. We present new detrital zircon U-Pb ages, petrography, and paleocurrent measurements from the Campanian-Maastrichtian turbidites and compare them to those from the Lower Cretaceous turbidites. The Campanian-Maastrichtian sandstones are dominated by carbonate and magmatic lithic grains. The paleocurrents indicate paleoflow directions parallel to the axis of the basin. The sandstones are dominated by Late Cretaceous zircons indicating derivation mainly from the coeval magmatic arc. In contrast, the Lower Cretaceous sandstones are dominated by quartz and feldspar, and paleocurrents indicate southward transport. The detrital zircons in the Lower Cretaceous sandstones are mainly Archean and Paleoproterozoic, indicating that in the Early Cretaceous, the source of turbidites was from the Archean-Paleoproterozoic Ukrainian Shield to the north. After the opening of the Black Sea in the Late Cretaceous, the connection between the Pontides and the East European Platform was severed and the Campanian-Maastrichtian turbidites were sourced principally from the magmatic arc in the Pontides. Our results indicate that the Campanian-Maastrichtian turbidites represent the first turbiditic sequence deposited after the opening of the Black Sea.