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).

Geochemistry of Cretaceous Sea Rocks from the LEO-3X Well in the Eastern Abidjan Margin, Côte d’Ivoire Offshore Basin

In this study, we apply geochemical and statistical analyses to evaluate the source rocks and kerogen type of Cretaceous sediments from the Cote d’Ivoire sedimentary basin. The geochemical analysis includes pyrolysis data such as total organic carbon (TOC%), generation source potential (S2) and hydrogen index (HI). The results of the cluster analysis separated the source rocks in the study area into two main groups. 1) Source rocks characterized by HI > 300 (mg/g), TOC from 1.76% to 3.19% by weight, and S2 from 6.55 to 14.46 (mg/g), indicating good to excellent source rocks with type II kerogen and are capable of generating oil. 2) Source rocks characterized by HI between 200 and 300 (mg/g), TOC from 1.6 to 2.02 wt%, and S2 from 3.45 to 5.36 (mg/g) indicating medium to good source rocks with type II-III kerogen and capable of generating a mixture of oil and gas.

Chemostratigraphic Characterization Tests on Sedimentary Formations in the Côte D’Ivoire Offshore Basin: Case of A-X and B-X Wells

The tests performed with two hundred and thirty-nine (239) samples from the A-X and B-X drillings help to know their sedimentological and chemostratigraphic characters. In sedimentological term formations are composed of sand, sandstone, limestone, siltstone and argillite that alternate along the drill. In chemostratigraphic term two megasequences (MS1 and MS2) have been identified. A correlation of chemostratigraphic data completed by the lithology results allowed a subdivision of oil wells that shows two main types of deposits environments. First, a proximal marine environment to continental and to Albian marked by a detrital flow deducted from the concentrations evolution of indicator elements of terrigenous material that are K, Mg, and Rb. On the other hand, a deep to shallow marine environment of Cenomanian to Paleocene marked by the presence of predominantly clay sediments and abundant glauconite in the lower Senonian. Nevertheless, there is a transition or intermediate environment that is characterized by the presence of glauconite and detrital flows.