Planktonic foraminiferal and calcareous nannofossil biostratigraphy and magnetostratigraphy of the uppermost Campanian and Maastrichtian at Zumaia, northern Spain

Juan C Larrasoaña,Jacqueline A Lees,Ignacio Arenillas,José A Arz,Irene Pérez-Rodríguez

doi:10.1016/j.cretres.2012.03.011

Abstract

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 (UC15eTP? to UC20dTP) 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.

Highlights

The Maastrichtian Stage records significant palaeobiological, climatic and oceanographic changes, as well as a meteorite impact event (e.g., Huber and Watkins, 1992; MacLeod et al, 1997; Lees, 2002; Frank et al, 2005; Schulte et al, 2010)
Grey marls and whitish limestones from Units 2e6 are characterised by a weak natural remanent magnetization (NRM), which is typically lower than 0.2 mA/m (Fig. 4B)
240e300 C, and up to 460 C, a characteristic remanent magnetization (ChRM) can be identified in about 90% of the samples, despite their overall weak intensities (Table 1)

Summary

Introduction

The Maastrichtian Stage records significant palaeobiological, climatic and oceanographic changes, as well as a meteorite impact event (e.g., Huber and Watkins, 1992; MacLeod et al, 1997; Lees, 2002; Frank et al, 2005; Schulte et al, 2010). Zumaia exhibits alternating limestones and marls, representing orbitally controlled deposition of great interest to cyclostratigraphy (e.g., ten Kate and Sprenger, 1993). These features have potential for use in Maastrichtian astronomical tuning (e.g., Husson et al, 2011), and for more rigorous calibration of the low-latitude fossil datums with the geological time-scale (GTS of Gradstein et al, 2004; Ogg et al, 2008). Previous multidisciplinary research has been performed on the Maastrichtian of Zumaia, documenting the stratigraphy (e.g., Mount and Ward, 1986; Wiedmann, 1988), ammonites and inoceramids (Ward et al, 1991; MacLeod and Orr, 1993; Ward and Kennedy, 1993), foraminifera (Herm, 1965; Lamolda, 1983; Arz and Molina, 2002), nannofossils (Burnett et al, 1992a; Lamolda and Gorostidi, 1994), carbon and oxygen stable isotopes (Mount et al, 1986; Paul and Lamolda, 2007) and orbital cyclicity (ten Kate and Sprenger, 1993)

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Discussion

Conclusion