REASSESSING THE BARTONIAN UNIT STRATOTYPES: AN INTEGRATED APPROACH
The base of the Bartonian Stage in the type area is defined by the Nummulites prestwichianus bed, which provides a locally distinctive level, however is not widely correlatable outside of the Hampshire basin. Only a single, long-ranged, planktonic foraminifera has been identified, Dipsidripella danvillensis, and so correlation of this bed with planktonic foraminiferal biostratigraphy has not been possible. The dinoflagellates do show a taxonomic turnover with Rhombodinium draco occurring a few centemeters above the level of the N. prestwichianus bed at several localities in the Hampshire basin, however, this is not consistant outside of this region. Calcareous nannofossils from the site were relatively impoverished, with NP zones being largely recognized by secondary markers. However, Aubry (1983, 1986) recognized Reticulofenestra umbilica, which is a primary marker within the CP zonation, and suggests further correlation potential for calcareous nannoplankton. Palaeomagnetic studies have also been carried out at the Alum bay section; Dawber et al., (2011) identified C18n with the NP16-17 boundary and the Nummulites prestwichianus bed as being within the underlying reversed interval, but there are problems with their interpretation with the nannofossil record.Improvement in the stratigraphy is essential to better define this interval and provide a globally useful datum. In order to resolve this issue, we present a new assessment of the Alum Bay section using integrated smaller and larger benthic foraminiferal, dinoflagellate and nannofossil stratigraphy.