The reasons for the enlargement of Congo River at Malebo Pool are still unclear at present, but various assumptions have been made to date. Moreover, the geological maps produced on both sides of the border remain partially incompatible. The study of the geological context of the cross-border region of the Malebo Pool (Kinshasa and Brazzaville) is conducted in order to harmonize the geological interpretations and to improve the understanding of the Pool formation . On the basis of the new field data and new comparisons on both sides of the Congo River , the study will have to allow to validate or on the contrary to question some current assumptions. This study is carried out with the CRGM in Kinshasa and the Marien NGOUABI University in Brazzaville. A geological map will be produced at the end of the project. It will be the fruit of two complementary lines of research: a structural study and a study of sedimentological processes.