Biostratigraphie, paléoécologie et évolution thermique du Supergroupe Mésoprotérozoïque de Mbuji-Mayi, RdCongo.

Understanding the origin, evolution and distribution of life in Universe - the subject of astrobiology - requires unambiguous knowledge of the different stages of evolution of life on Earth, the only planet where, for the moment, the existence of life is an absolute evidence. This requires the contribution of several scientific disciplines (biology, geology, geochemistry, geophysics, micropaleontology ...) in the production of data relating to the Precambrian, period during which life appeared on Earth and knew its first stages of evolution.
This study focusses on a key period of life evolution, and in particular the diversification of early eukaryotes, during the Proterozoic. It presents the results on the micropaleontology, palaeoecology, chemostratigraphy and geothermometry of the Mbuji-Mayi Supergroup, located in the Democratic Republic of Congo. This sedimentary sequence is dated between 1065 and 1000 Ma (late Mesoproterozoic).
The results obtained using conventional analyzes (optical microscopy, mass spectrometry, Raman microspectroscopy, XRD, solid bitumen reflectance and TAI) reveal: (1) a well-preserved assemblage of organic-walled microfossils, consisting of 49 taxa of which 11 unicellular and multicellular eukaryotes. This assemblage is similar to other contemporaneous assemblages known elsewhere in the world, impliyng a connection with the other oceanic basins, and permitting to improve Proterozoic biostratigraphy ; (2) a redox stratification of ocean water into oxic, anoxic iron-rich and anoxic sulfidic-rich zones during the deposition of the Mbuji-Mayi Supergroup; (3) an abundance and better preservation and perhaps habitats of eukaryotes in proximal anoxic and iron-rich environments; (4) δ13Ccarb variations similar to contemporaneous variations elsewhere in the world; (5) a similarity between the different ranges of temperature estimates from Raman geothermometers, solid bitumen reflectance or Kübler index obtain on clays. This has shown that extraction of kerogen by acid attack does not alter its chemical signal. This moderate diversity of eukaryotes at ~ 1065 Ma makes it possible to set back the great diversification of the first eukaryotes which is generally estimated at 800 Ma, and to show that it also happened in Africa.