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Mesozoic |
1 Institute of Paleobiology, Polish Academy of Sciences, Al. Zwirki i Wigury 93, 02-089 Warsaw, Poland
2 Facultad de Ciencias, Universidad del Pais Vasco, Apdo 644, 48080 Bilbao, Spain
Foraminiferal response to the Cenomanian-Turonian Boundary Event was studied from a 50 m thick section in Menoyo, northern Spain, representing the uppermost Rotalipora cushmani and Whiteinella archaeocretacea Zones. Taxonomic and stratigraphic studies on benthonic foraminiferal assemblages indicate that the studied section represents mass extinction and survival intervals, with the mass extinction boundary in the lowermost part of the Whiteinella archaeocretacea Zone.
Stepped extinction within benthonic foraminifers was observed in the uppermost Rotalipora cushmani Zone. In the late phase of mass extinction several species became extinct (e.g. Gavelinella intermedia-cenomanica-baltica group, Tritaxia pyramidata (Reuss)), some others temporarily disappeared; Lazarus taxa (e.g. Tritaxia tricarinata (Reuss), nodosariids) and progenitor (e.g. Globoratalites sp. 1) taxa appeared. Disaster (e.g. Praebulimina elata) species along with opportunistic taxa (e.g. Gyroidinoides praestans (Magniez-Jannin), Ammobaculites parvispira Ten Dam) colonized vacated ecospace in the middle part of the survival interval, i.e. in the topmost part of the Rotalipora cushmani Zone. Opportunistic taxa dominated assemblages in the Whiteinella archaeocretacea Zone, i.e. in the higher part of the survival interval.
The recorded changes in benthonic foraminiferal assemblages most likely reflect the decline in oxygenation level of the bottom waters at the end of the Rotalipora cushmani Zone and the persistence of these unfavourable conditions in the Whiteinella archaeocretacea Zone.