Stratigraphy and the upper Jurassic lower Cretaceous radiolarians from thecarbonate-siliceous deposits, Ankara Region, Turkey

In the Ankara region, the Jurassic-Cretaceous Alacaatli key section spans t he stratigraphic interval from the Oxfordian to the Valanginian (but not al l the three Jurassic Series, as it was believed earlier). Abundant and dive rse radiolarian assemblages are used for the detailed subdivision of these deposits and their correlation with the sections in the West Mediterranean region. Three units were distinguished and dated by radiolarians: (1) the m iddle Oxfordian-lower Tithonian (cherts and limestones, including the "ammo nitico rosso" facies of the latter), 35-40 m; (2) the upper Kimmeridgian-Lo wer Berriasian (limestones and marls), 33 m; (3) the upper Tithonian-upper Valanginian (micritic limestones and calcarenites), 59 m.