CALCAREOUS NANNOFOSSILS FROM THE LATE JURASSIC EARLY CRETACEOUS OF NORTHWEST ANATOLIA, TURKEY

Within the framework of an integrated stratigraphy, a detailed biostra tigraphic study of Late Jurassic-Early Cretaceous (Tithonian-Valangini an) calcareous nannofossils was carried out in north-west Anatolia, Tu rkey. Samples were collected from nine sections spanning the Yosunlukb ayiri and Sogukcam Limestone formations. The Yosunlukbayiri Formation consists of alternating green to cream coloured marl and micritic lime stone that becomes detrital (calciturbidites) in the upper part. The S ogukcam Limestone Formation, which overlies the Yosunlukbayiri Formati on, consists of white to pink, porcellaneous micritic limestone. A sem i-quantitative analysis of calcareous nannofossils was performed mainl y using light microscopy. This revealed the first and last occurrences of important marker species, together with fluctuations of abundance and species diversity. Nannofossil assemblages are generally dominated by the most abundant and solution resistant taxa, such as Conusphaera spp., Faviconus multicolumnatus, Nannoconus spp. and Watznaueria spp. , and occur in rock-forming quantities. Five zones (Conusphaera mexica na mexicana Zone, Microstaurus chiastius Zone, Nannoconus steinmannii steinmannii Zone, Retecapsa angustiforata Zone, Calcicalathina oblonga ta Zone) and 37 biohorizons were recognized from the Tithonian to Vala nginian and calibrated to the Calpionellid (Altiner and Ozkan 1991) an d the foraminiferal-algal zonation schemes (Altiner 1991).