Instituto Geologico y Minero de Espana, Spain

The well-exposed and continuous uppermost Cretaceous in the coastal section of Zumaia (northern Spain) crops out as cyclic, deep-water, hemipelagic carbonate-rich sediments of significant geological interest. We present a new, high-resolution calibration of planktonic foraminiferal and calcareous nannofossil biostratigraphic datums, alongside new magnetostratigraphy. Six planktonic foraminiferal zones (Rugoglobigerina rotundata to Pseudoguembelina hariaensis) and nine nannofossil (sub)zones (UC15e (super TP) ? to UC20d (super TP) ) have been identified, encompassing the uppermost Campanian through uppermost Maastrichtian. Magnetostratigraphic data were obtained from the lower half of the section, where chrons C31r and C31n have been identified; the lithological nature of the upper part of the section provided spurious palaeomagnetic results. According to these data, the Campanian/Maastrichtian (C/M) boundary lies in Chron C31r at Zumaia. Differences between the planktonic foraminiferal and nannofossil datums at Zumaia and those from the Tercis boundary stratotype section (France) suggest that the biostratigraphic criteria used to identify the C/M boundary are problematic. We propose, therefore, two alternative, key biostratigraphic datums with which to determine the stratigraphic position of this boundary: the stratigraphic base occurrence datum (BO) of the planktonic foraminifer Pseudoguembelina palpebra and the top occurrence datum (TO) of the nannofossil Broinsonia parca subsp. constricta. The C31r/C31n magnetic polarity reversal, and the BOs of the planktonic foraminifer Racemiguembelina fructicosa and the nannofossil Lithraphidites quadratus are events that may prove useful in formally defining the lower/upper Maastrichtian boundary. Abstract Copyright (2012) Elsevier, B.V.