Characterization of the salinity conditions of Cenomanian formations based on sedimentological and ichnological data of selected cores from Ivoirian offshore basin (septentrional Gulf of Guinea)

摘要

Detailed sedimentological and ichnological analysis of core material from selected wells were performed in order to fully characterize the range of facies encountered within Cenomanian formations of Ivorian offshore basin.Results indicate that the cored successions comprise four major groups of lithofacies: Pebbly (CS, PS), clean sandstone (S), muddy sandstone (S*M) and mudstone (HM, ML, MJ & M). These lithofacies groups were further sub-divided into component facies based mainly on sedimentary structures. The pebbly group comprises conglomerate sandy and pebbly sandstone. The clean sandstone group includes seven fades: massive sandstone, laminated sandstone, cross-bedded sandstone, bioturbated sandstone, deformed sandstone, wavy-bedded sandstone and rippled sandstone. The muddy sandstone group comprises bioturbated muddy sandstone, while the mudstone group comprises four main fades, namely wavy-bedded heterolithic/sandy mudstone, calcareous mudstone, silty mudstone and pure mudstone.A range of ichnofossils were identified in the cores including: Planolites isp, Palaeophycus isp, Lockeia isp, Phycosiphon isp, Thalassinoides isp, Rhizocorallium isp, Cylindrichnus isp, Chondrites isp and Teichichnus isp. Among these, the Phycosiphon isp Chondrites isp and Rhizocorallium isp reveal fully marine salinities in some intervals of these cores, although Chondrites isp usually used as proxy for disoxia and Rhizocorallium isp were sometimes associated with Glossifungites isp ichnofossils. Integration of the sedimentary data (lithofacies) and trace fossil ichnofossils data revealed several depositional environments ranging from coastal/deltaic to shallow marine settings within the Cenomanian cores.