Geochemical Characterisation and Correlation of Cenomanian Turonian Sediments in Central-eastern Tunisia

Geochemical analysis of 254 core and cuttings samples from three petroleum exploration and development wells (Well 1, 2, and 3) in the Sfax area of eastern Tunisia, has successfully characterised the Cenomanian Fahdene Formation, and the Turonian Annaba, Bireno and Douleb members of the Aleg Formation. The cored mid-Turonian Bireno Member in the Well 3 is subdivided into two lithostratigraphic units: (i) Unit 1, attributed to a shallow subtidal environment; (ii) Unit 2, believed to represent an intertidal to supratidal sabkha environment. Vertical geochemical profiles were established for each well for 11 major elements and 7 trace elements. Chemostratigraphic correlation based on marker geochemical shifts that reflect member boundaries and the two Bireno Member sub-units has been successfully established between the three wells. Porosity seems to be strongly correlated with Ca and Mg, reflecting the importance of peri-reefal limestones and sabkha dolostones as important reservoir horizons, while clay minerals provide the main source of gamma ray response, and clay-rich beds typically represent relatively tight intervals. Chemostratigraphic studies of shallow-marine sediments such as the Bireno Member, offer considerable potential for the characterisation, subdivision and correlation of strata in petroleum basins.