Calcareous nannofossils from the Late Jurassic‐Early Cretaceous of Northwest Anatolia, Turkey

Abstract

AbstractWithin the framework of an integrated stratigraphy, a detailed biostratigraphic study of Late Jurassic‐Early Cretaceous (Tithonian‐Valanginian) calcareous nannofossils was carried out in north‐west Anatolia, Turkey.Samples were collected from nine sections spanning the Yosunlukbayiri and Sogukçam Limestone formations. The Yosunlukbayiri Formation consists of alternating green to cream coloured marl and micritic limestone that becomes detrital (calciturbidites) in the upper part. The Sogukçam Limestone Formation, which overlies the Yosunlukbayiri Formation, consists of white to pink, porcellaneous micritic limestone. A semi‐quantitative analysis of calcareous nannofossils was performed mainly 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 mexicana mexicana Zone, Microstaurus chiastius Zone, Nannoconus steinmannii steinmannii Zone, Retecapsa angustiforata Zone, Calcicalathina oblongata Zone) and 37 biohorizons were recognized from the Tithonian to Valanginian and calibrated to the Calpionellid (Altiner and Özkan 1991) and the foraminiferal‐algal zonation schemes (Altiner 1991).