Upper Cretaceous volcaniclastic complexes and calcareous plankton biostratigraphy in the Western Pontides, NW Turkey

Authors : Katharina BOEHM, Michael WAGREICH, Erik WOLFGRING, Okan TÜYSÜZ, Susanne GIER, İsmail Ömer YILMAZ

Pages : 187-206

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Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :This study describes and interprets Upper Cretaceous volcaniclastics interbedded with hemipelagic to pelagic limestones, marls, and turbidites from the Western Pontides, northwestern Turkey. The Dereköy Formation, the Unaz Formation insert ignore into journalissuearticles values(red pelagic limestone unit);, and the Cambu Formation can be distinguished, overlain by the turbiditic Akveren Formation. Biostratigraphic ages from the predominantly volcaniclastic Dereköy Formation indicate Turonian insert ignore into journalissuearticles values(Dicarinella concavata planktonic foraminifera zone, CC13/UC8-9 nannofossil zones); to middle/late Santonian ages up to CC17/UC13. The Unaz Formation, deposited during the late Santonian insert ignore into journalissuearticles values(UC13, Dicarinella asymetrica Zone);, is overlain by the volcaniclastic Cambu Formation of latest Santonian insert ignore into journalissuearticles values(CC17b/UC13); to early/middle Campanian insert ignore into journalissuearticles values(CC20/UC15a); age. However, turbidite intercalations are already present diachronously from CC19/UC14d onwards, and the turbiditic Akveren Formation ranges up into the late Maastrichtian insert ignore into journalissuearticles values(Abathomphalus mayaroensis Zone);. Geochemistry of the volcaniclastic units reveals information about the volcanic series and tectonic setting, although element mobility has to be considered. An overall trend of calc-alkaline to high-K calc-alkaline series and basaltic to basalt-andesitic rock types was identified. A negative Nb anomaly with respect to Th and Ce in all samples confirms the existence of a volcanic arc, also indicated by a negative Ti anomaly. Biostratigraphic age constraints give evidence for volcanic arc activity mainly between Turonian and early Campanian, ca. 91 - 79 Ma. Various geochemical data, especially element variations normalized to N-MORB, show two types of volcanic arc basalts insert ignore into journalissuearticles values(VAB);: insert ignore into journalissuearticles values(1); Calc-alkaline to high-K calc-alkaline VAB have increased Nb and Zr values, insert ignore into journalissuearticles values(2); more tholeiitic VABs are depleted in Nb, Zr, Ti, V. The volcaniclastics successions were deposited in an arc setting triggered by different stages of subduction of the Neotethys Ocean to the south and contemporaneous spreading in the Western Black Sea Basin to the north. An extensional regime caused formation of small but deeper-water sedimentary basins along the southern shore of the Black Sea where volcaniclastic complexes interfingered within short lateral distances with pelagic and mass-flow deposits.
Keywords : Western Pontides, Turkey, Upper Cretaceous, volcaniclastics, geochemistry, biostratigraphy, nannofossils, foraminifera