Sequence Stratigraphy, Sea Level Change & Palaeoenvironments Via Chemostratigraphy: Regional to Global Correlations

Mabrouk, Amina¹, Ian Jarvis², Habib Belayouni³, R. TJ Moody⁴, Ross Sandman⁵ (1) Faculty of Sciences of Tunis, Tunis, Tunisia (2) Kingston University, Kingston Upon Thames, United Kingdom (3) Faculté des Sciences de Tunis, Tunis, Tunisia (4) Kingston University, Hants, United Kingdom (5) Moody-Sandman Associates, London, United Kingdom

Fourteen δ¹³C events are recognised in four biostratigraphically well-constrained 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 δ¹³13C 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 δ¹³13C accompanying transgression and falling δ¹³13C accompanying regression. Significant positive carbon excursions are broadly associated with major transgressive events, but other factors such as changing rates of sea-level rise and fall, complicate relationships. Correlations between variations in Mn content and sequence stratigraphy in the English Cenomanian are consistent with published data from other Mesozoic successions. High Mn values associated with the large positive δ¹³13C excursion spanning the Cenomanian/Turonian boundary are not related directly to the oceanic anoxic event that caused the carbon isotope event, but may be explained by normal marine processes. Consistent Cenomanian Sr/Ca ratio trends are demonstrated in England and Italy, which are tied to a detailed sequence stratigraphic framework for NW Europe. 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. Furthermore, A provisional chemostratigraphic framework is presented for Upper Cretaceous-Eocene pelagic carbonate formations in NE Libya. These display distinct geochemical signatures that hold great potential for correlation, sequence stratigraphic analysis and palaeoenvirenmental interpretations.