Sequence Stratigraphy, Sea Level Change and Palaeoenvironments via Chemostratigraphy: Regional to Global Correlations*

Fourteen δ 13 C events are recognised in four Cenomanian sections in England and are isochronous with respect to biostratigraphic datums. Events in the Middle and Upper Cenomanian are readily identified in Italy. A δ 13 C correlation of Campanian sections in England, France, and Tunisia is demonstrated using 11 isotope events, which enable calibration of Boreal and Tethyan biostratigraphic schemes. Carbon isotope profiles predominantly follow eustatic sea-level, with rising δ 13 C accompanying transgression and falling δ 13 C accompanying regression. Significant positive carbon excursions are broadly associated with major transgressive events. Sr/Ca ratios and the Mn contents of pelagic carbonates vary systematically with respect to sea-level change. Increasing Sr/Ca ratios during periods of sea-level fall are attributed to the release of Sr from aragonite dissolution and replacement in subaerially exposed platform carbonates. Falling Sr/Ca ratios accompanied the re-establishment of shallow-water carbonate factories during sea-level rise. Mn flux increases with rising sea-level, with Mn reaching a maximum around each maximum flooding surface, before decreasing again through the overlying highstand systems tract, representing a period of relative constant carbonate supply. Correlations between variations in Sr/Ca ratios and Mn content with sequence stratigraphy in the English Cenomanian are consistent with published data from other Mesozoic successions. Elemental chemostratigraphy provides a means of developing a sequence stratigraphic framework in pelagic carbonate successions. This framework clearly needs to be constrained by geological evidence, but offers a powerful new tool for sequence analysis and correlation.