Integrated stratigraphy of the La Vedova section (Conero Riviera, Italy) and implications for the Burdigalian/Langhian boundary

Abstract

We present a high resolution integrated stratigraphy (calcareous plankton biostratigraphy and magnetostratigraphy) of the upper Burdigalian to lower Langhian interval in the La Vedova section (Conero Riviera, Italy). The succession of planktonic foraminifer and calcareous nannofossil events and their relative position in the La Vedova section are comparable with those recorded in other Mediterranean sections suggesting a continuous deposition across the Burdigalian/Langhian boundary interval. The high resolution magnetostratigraphic record, integrated with calcareous plankton events, has been correlated to the ATNTS2004 and ranges from sub-chrons C5Cn.1n to C5Bn.2n. In addition, the integrated magnetobiostratigraphic record of the La Vedova section provides a new magnetostratigraphic calibration of calcareous plankton events, thereby improving the existing Mediterranean biochronology for the upper Burdigalian to lower Langhian. On the basis of our magnetobiostratigraphic results, the deep marine La Vedova section could be considered a suitable succession for defining the Langhian GSSP (Global Stratotype Section and Point). The recommended guiding criteria to identify the base of the Langhian stage (the Praeorbulina datum and the magnetic reversal C5Cn/C5Br) are recorded in the section. In this work the Praeorbulina datum is represented by the first occurrence of P. glomerosa curva following Blow (1956; 1969). In the La Vedova section, this bioevent postdates the Acmea End of the planktonic foraminifer Paragloborotalia siakensis and the Paracme End of the calcareous nannofossil Sphenolithus heteromorphus, approximates the C5Br/C5Bn.2n reversal boundary and is dated at 15.23 Ma. The top of Chron C5Cn, dated at 15.974 Ma, is better approximated by the Last Common Occurrences of the calcareous nannofossil Helicosphaera ampliaperta and the planktonic foraminifer Paragloborotalia bella. At La Vedova the first occurrence of P. glomerosa curva is about 740 kyrs younger than C5Cn /C5Br reversal boundary, which represents the provisional guiding criterion to define the base of the Langhian (Lourens et al. 2004). The age difference between the Praeorbulina datum and the top of C5Cn implies that the Langhian GSSP cannot be located in a position close to both Chron C5Cn and the Praeorbulina datum (Lourens et al. 2004) and that the selection of either of these guiding criteria to identify the base of the Langhian will strongly affect its duration.