Middle to Upper Tournasian Radiolaria of the Baltalimani Formation, Istanbul, Turkey

Abstract Radiolarians collected from five localities of the Baltalimani Formation in the Istanbul region are described in detail, and the local stratigraphic ranges and persistence of biostratigraphically important radiolarian species are documented. The spumellarian component is published for the first time, and four new species are described: Albaillella kayai n. sp., Ceratoikiscum jucundum n. sp., Meschedea akcetensis n. sp., and Stigmosphaerostylus istanbulensis n. sp. Two assemblages are recognized: the A. paradoxa and the A. sp. aff. A. undulata-A. deflandrei assemblage. The older A. paradoxa assemblage contains Traenosphaera sicarius, Pararchocyrtium serrensis, Cyrtisphaeractenium mendax, and common to abundant A. paradoxa and Popofskyellium. Albaillella paradoxa is not restricted to the older assemblage but is the only species of Albaillella present. The younger A. sp. aff. A. undulata-A. deflandrei assemblage contains either A. sp. aff. A. undulata or A. deflandrei. Albaillella indensis ambigua, ...