Upper Cretaceous (upper Turonian – lower Campanian) calcareous nannofossils and carbon isotopes from Seaford Head (southern England): critical appraisal of biozones and correlation to GSSPs

This study presents a revised calcareous nannofossil biostratigraphy and a new high-resolution carbonate carbon isotope record (δ13Ccarb) for the Seaford Head section in southern England, a key reference section for the Upper Cretaceous of NW Europe. A new sedimentary log for the uppermost Turonian – lower middle Coniacian section is drawn and combined with previously published logs for the upper Coniacian to lower Campanian. The compiled isotopic record incorporates 713 new sample data along with recently published δ13Ccarb values from the section, and the calcareous nannofossil biostratigraphy is supported by the detailed analysis of 68 samples, using both semi-quantitative and quantitative abundance data. The local confidence in the record of biohorizons in the section and their supra-regional reliability are addressed. These include the highest and lowest occurrences of index species, but we additionally critically assess the stratigraphic use of highest and lowest consistent occurrences and the Base and Top of taxon acme levels. Three commonly used zonal and two subzonal markers are shown to be unreliable but 10 secondary events show high reliability for correlation. Carbon isotope stratigraphy, supported by macrofossil and microfossil biostratigraphy, allows for precise correlations to other European sections like Trunch, eastern England, and Salzgitter-Salder and Lägerdorf, northern Germany. Our integrated stratigraphic approach thus allows for a more accurate assessment of biozonation schemes and chemostratigraphy. In particular, this study provides a valuable resource for the refined stratigraphic expression of Coniacian, Santonian and Campanian stage boundaries and large-scale correlation of southern England to Global Stratotype Sections and Points (GSSPs).