Striking Variation in the Provenance of the Lower and Upper Cretaceous Turbidites in the Central Pontides (Northern Turkey) Related to the Opening of the Black Sea

摘要

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 x 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.