Benthonic foraminiferal mass extinction and survival assemblages from the Cenomanian-Turonian Boundary Event in the Menoyo section, northern 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 archacocretacea 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 archacocretacea 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 temporatily disappeared; Lazarus taxa (e.g. Tritaxia tricarinata (Reuss), nodosariids) and progenitor (e.g. Globoratalites sp. 1) taxa appcared. Disaster (e.g. Pracbulimina 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 archacocretacea 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 archacocretacea Zone.