Chemostratigraphy of Upper Cretaceous Chalk, Tunisia

Chalk deposition characterised most of the Late Cretaceous period in many areas of the world. In Tunisia it occurred predominantly during the Campanian - Maastrichtian stages. The facies, characteristic of the Abiod Chalk Formation, was sampled in four wells from the Miskar Gas Field (SE Tunisia), and at Le Kef section (NW Tunisia). A geochemical investigation of 19 elements in the Miskar wells and 12 elements at Le Kef has permitted to constrain vertical geochemical profiles suited for correlation. Eight chemostratigraphic units are defined in the offshore wells. Nine geochemical sequences (GCS) and eight isotope sequences (IsS) were correlated between Le Kef and Miskar. The 13C/12C curve for the Abiod Formation at Le Kef is correlated to other Tethyan, Boreal and NW Pacific Ocean sections. Fourteen correlation sequences (CC) are identified, two of which are considered to be major isotopic events: The correlation confirms that carbon isotope trends reflect global rather than local processes. Correlations can be used to test the validity of Campanian global biostratigraphic frameworks, and improve our understanding of the nature and timing of Late Cretaceous sea-level change.