Evidence of the Albo-Cenomanian Unconformity Using Chemical Elements Case Study of Sediments from the Eastern Abidjan Margin

Sedimentological and chemostratigraphical studies using accessory elements on 322 samples of cuttings from oil wells located in the submerged sedimentary basin (offshore) of Côte d’Ivoire. This basin covered the chronostratigraphic interval from the Upper Albian to the top of the Maastrichtian. The aim of this study was to determine the major accident, the Albo-Cenomanian unconformity, using chemical elements. To achieve this goal, we had to count the accessory elements glauconite, pyrite and carbonaceous debris, and identify all the chemical elements present in each cuttings sample. The results clearly indicate that: the sediments are essentially composed of carbonaceous debris and pyrite, with a high potassium content for sediments dating from the Abian period;and glauconite, carbonaceous debris, pyrite, and a sharp decrease in potassium content for sediments dating from the Cenomanian to the Maastrichtian period. Threshold values for ratios of source-indicating chemical elements (Zr, Ti, Y, Th) and paleoenvironmental elements (K, Rb, Mg, Al,) highlighted the MS1 and MS2 mega-sequences in the study area. The difference observed in the threshold values of these ratios can be explained by changes in sedimentary dynamics. The depositional environment varies from an inner continental shelf with strong littoral influence (Upper Albian) to an increasing subsidence outer continental shelf (Cenomanian-K/Pg boundary).