Radiolarians of the uppermost Oxfordian (Hypselum Zone) of the Wieluń Upland (central Poland)

Radiolarian assemblages from the uppermost Oxfordian (Hypselum Zone) deposits of two sections (Katarowa Góra and Bobrowniki) in the Wieluń Upland (central Poland) are studied for the first time. The overall composition of the assemblages is characterized by low taxonomic diversity, with many individuals of spherical morphotypes, with dominance of the family Williriedellidae and Gongylothoracidae, among the nassellarians. The radiolarians show features mostly of the Northern Tethyan fauna. Additionally, more cosmopolitan forms consisting of spumellarians and of cold water representatives of the family Parvicingulidae appear in the middle and upper parts of the Hypselum Zone. This change in the character of the radiolarian assemblages suggests Boreal influences into the Submediterranean basin related to activity of sea currents, which have been stimulated by climatic changes during the latest Oxfordian.