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.