Benthonic foraminiferal response to the Cenomanian-Turonian boundary event in the Ganuza section, northern Spain.

Resumen

The studied interval comprises a 26.5 m thick section of the uppermost Cenomanian strata representing the uppermost Rotalipora cushmani and lowermost Whiteinella archaeocretacea Zones. Changes in the foraminiferal assemblages recorded in this interval may be summarized as follows:

l. P/B ratio fluctuates throughout the section; the highest values (78 %) are recorded in the lowermost part of the Whiteinella archaeocretacea Zone.

2. Benthonic diversity in the Ganuza section varíes from 9 to 27 with decreasing tendency up the section. Highest number of species (16-27) in the studied interval is observed in the Rotalipora cushmani Zone while 9 to 14 species are found in the Whiteinella archaeocretacea Zone.

3. Stepped extinctions of foraminiferal species were recorded - two planktonic Rotalipora greenhomensis and R. cushmani and several benthonic, e.g. Gavelinella baltica, Conorbina sp., rosalinids, Gubkonella graysonensis and Textularia chapmani went extinct during latest Rotalipora cushmani and earliest Whiteinella archaeocretacea chrons; several species disappeared temporarily, e.g. Praebulimina elata; they reappeared in the Lower Turonian; sorne others e.g. Lingulogavelinella globosa, Gavelinella plummerae appeared after the extinction of Rotalipora greenhomensis and become very abundant in the upper part of the studied interval; there is also a group of species present in the entire section which dominated assemblages in the middle and upper part of the studied section, e.g. Gaudryinella pusilla, Lenticulina rotulata or Gavelinella berlhelini.