Sedimentology, geochemistry and depositional environments of the 1175-570 Ma carbonate series, Sankuru-Mbuji-Mayi-Lomami-Lovoy and Bas-Congo basins, Democratic Republic of Congo: new insights into late Mesoproterozoic and Neoproterozoic glacially- and/or tectonically-influenced sedimentary systems in equatorial Africa

The one of the most important Eras of the Earth history, i.e. Neoproterozoic (1000-542 Ma),was an enigmatic period characterized by the development of the first stable long-lived ~1.1-0.9 Ga Rodinia and 550-500 Ma Gondwana supercontinents, global-scale orogenic belts,extreme climatic changes (cf. Snowball Earth Hypothesis), the development of microbialorganisms facilitating the oxidizing atmosphere and explosion of eukaryotic forms toward thefirst animals in the terminal Proterozoic. This thesis presents a multidisciplinary study of twoNeoproterozoic basins, i.e. Bas-Congo and Sankuru-Mbuji-Mayi-Lomami-Lovoy, in and around the Congo Craton including sedimentology, geochemistry, diagenesis, chemostratigraphy and radiometric dating of carbonate deposits themselves.The Mbuji-Mayi Supergroup sequence deposited in a SE-NW trending 1500 m-thick siliciclastic-carbonate intracratonic failed-rift basin, extends from the northern Katanga Province towards the centre of the Congo River Basin. The 1000 m-thick carbonate succession is related to the evolution of a marine ramp submitted to evaporation, with ‘deep’ shaly basinal and low-energy carbonate outer-ramp environments, marine biohermal midramp (MF6) and ‘very shallow’ restricted tide-dominated lagoonal inner-ramp (MF7-MF9) settings overlain by lacustrine (MF10) and sabkha (MF11) environments, periodicallysubmitted to a river water source with a possible freshwater-influence. The sequence stratigraphy shows that the sedimentation is cyclic in the inner ramp with plurimetric ‘thin’ peritidal cycles (± 4 m on average) recording a relative sea level of a maximum of 4 m, with fluctuations in the range of 1-4 m. The outer/mid ramp subtidal facies are also cyclic with ‘thick’ subtidal cycles characterized by an average thickness of ± 17 m, with a probable sealevelfluctuations around 10 to 20 m. The geochemistry approach, including isotopic and major/trace and REE+Y data, allows to infer the nature of the dolomitization processes operating in each carbonate subgroup, i.e dolomitization may be attributed to evaporative reflux of groundwater or to mixing zones of freshwater lenses. The latest alteration processes occured during the uplift of the SMLL Basin. New ages, including LA-ICP-MS U-Pb laser ablation data on detrital zircon grains retrieved in the lower arenaceous-pelitic sequence (BI group), combined with carbon and strontium isotopic analyses, yielded a new depositional time frame of the Mbuji-Mayi Supergroup between 1176 and 800 Ma reinforcing the formerly suggested correlation with the Roan Group in the Katanga Province.In the Democratic Republic of Congo, the Sturtian-Marinoan interglacial period was previously related to pre-glacial carbonate-dominated shallow marine sedimentation of the Haut-Shiloango Subgroup with stromatolitic reefs at the transition between greenhouse (warm) and icehouse (cold) climate periods, commonly marked by worldwide glacigenic diamictites and cap carbonates. This thesis highlights that these deposists record as a deepening-upward evolution from storm-influenced facies in mid- and outer-ramps to deepwater environments, with emplacement of mass flow deposits in toe-of-slope settings controlled by synsedimentary faults. In absence of diagnostic glacial features, the marinoan Upper Diamictite Formation is interpreted as a continuous sediment gravity flow deposition along carbonate platform-margin slopes, which occurred along tectonically active continental margins locally influenced by altitude glaciers, developed after a rift–drift transition. The maximum depth of the deepening-upward facies is observed in the C2a member. Theshallowing-upward facies exibit a return of distally calcareous tempestites and semi-restricted to restricted peritidal carbonates associated with shallow lagoonal subtidal and intertidal zones submitted to detrital fluxes in the upper C2b to C3b members.The geochemistry highlights (i) the existence of a δ13C-depth gradient of shallow-water and deep-water carbonates; (ii) the carbonate systems were deposited in oxic to suboxic conditions; and (iii) all samples have uniform flat non-marine shale-normalized REE+Y distributions reflectingcontinental detrital inputs in nearshore environments, or that the nearshore sediments werereworked from ’shallow’ inner to mid-ramp settings in deep-water slope and outer-rampenvironments, during the rift-drift transition in the basin. The pre-, syn- and post-glacialcarbonate systems could record a distally short-lived regional synrift freshwater-influencedsubmarine fan derived from nearshore sediments, including gravity flow structures, which areattributed to regional tectonic processes due to a sudden deepening of the basin caused bydifferential tilting and uplifting of blocks, related to the 750-670 Ma oceanic spreading of thecentral-southern Macaúbas Basin.Combining sedimentology, isotopes and trace elemental geochemistry, the thesis highlightsthat the δ13C variations in the Neoproterozoic carbonates are complex to interpret, and can berelated to: (i) the existence of a δ13C-depth gradient; (ii) the exchange between isotopicallylight carbon in meteoric waters and carbonate during lithification and early diagenesis; and(iii) isotopic perturbations due to regional metamorphism. Considering the possible englaciation of the Earth (Snowball Earth hypothesis), the Mbuji-Mayi Supergroup and WestCongolian Group seem reflected the intimate relationship between glaciations and tectonicactivity during the break-up of the Rodinia supercontinent, followed by the rift–drifttransition, and finally the pre-orogenic period on the passive continental margin.Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

Hydrocarbon reservoir potential of Neoproterozoic carbonates in the Mbuji-Mayi Supergroup (Sankuru-Bushimay area), Democratic Republic of Congo: stratigraphy, sedimentology, geochemistry, petrophysics

Final Report presented at Paris, March 2012info:eu-repo/semantics/publishe

Early and late neoproterozoic c, o and sr isotope chemostratigraphy in the carbonates of west congo and mbuji-mayi supergroups: A preserved marine signature?

The carbon, oxygen and strontium isotope geochemistry is the most widely applied chemostratigraphic tool in the reconstruction of paleoenvironments and indirect regional or global correlations for the Neoproterozoic times. Relatively good preserved carbonate rocks of the West Congo Supergroup, i.e. the Schisto-Calcaire Subgroup of the Democratic Republic of Congo and Gabon, and the Mbuji-Mayi Supergroup, i.e. the BII group from the Democratic Republic of Congo, make these Neoproterozoic successions unique for chemostratigraphical studies. In this paper, we propose to discuss on the fidelity of δ13Ccarb and Sr signatures in Neoproterozoic carbonates on the basis of a severe diagenetic control, using trace and major geochemistry, combined with C and O stable isotope analysis. Our result highlights that the δ13Ccarb fluctuations of the Schisto-Calcaire Subgroup reflect (i) facies variations, (ii) exchanges between isotopically light carbon in meteoric waters and carbonate during lithification and early diagenesis, and/or (iii) regional metamorphism grades rather than temporal signals of ocean chemistry, while in the unmetamorphosed carbonates of the Mbuji-Mayi Supergroup, reported to the Bitter Springs anomaly (~810Ma), the use of δ13C ratios are worldwide applicable for inter-basin correlations. © 2013 Elsevier B.V.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Les réservoirs carbonatés (sédimentologie, diagenèse…) du Méso-Néoprotérozoïque de la Cuvette du Congo (Mbuji- Mayi, République Démocratique du Congo)

Janvier 2010, également présenté les 7 et 8 Février 2011info:eu-repo/semantics/publishe

Hydrocarbon reservoir potential of Neoproterozoic carbonates in the Democratic Republic of Congo (DRC): stratigraphy, sedimentology, diagenesis, microbial influence

info:eu-repo/semantics/nonPublishe

Sedimentology and sequential stratigraphy of the Mbuji-Mayi Supergroup (Neoproterozoic, Democratic Republic of Congo)

info:eu-repo/semantics/nonPublishe

Paleoenvironments of the Neoproterozoic carbonates in the Schisto-Calcaire Subgroup (C2 and C3) in Democratic Republic of Congo: lithostratigraphy and diagenesis

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Neoproterozoic uppermost Haut-Shiloango Subgroup (West Congo Supergroup, Democratic Republic of Congo): Misinterpreted stromatolites and implications for sea-level fluctuations before the onset of the Marinoan glaciation

The middle Neoproterozoic carbonate-dominated uppermost Haut-Shiloango Subgroup (Sh8h and Sh8i members) in the Lower-Congo Province of the Democratic Republic of Congo is considered as recording pre-glacial shallow-marine sedimentation with stromatolitic reefs overlain by the Upper Diamictite Formation. We investigated these stromatolitic carbonates in order to highlight their biogenicity. Newly defined lithofacies and geochemical analyses (stable isotopes, major, trace and REE+Y elements) are used to provide insights into the origins of the depositional events that occurred immediately before Marinoan global glaciation. These insights should in turn provide constraints on the models developed for this glaciation event.The series consists of three shaly and carbonate lithofacies: (i) alternating limestones and claystones (lithofacies 1); (ii) nodular wackestones (lithofacies 2); and (iii) clast-supported conglomerates and breccias (lithofacies 3). Lithofacies 1 is an open marine low-energy mid/outer ramp system with hummocky cross-laminations and distal tempestites; lithofacies 2 is a distal slope facies with synsedimentary contorted structures, slided and slumped semi-consolidated limestone beds; lithofacies 3 consists of debris flows deposited in a basinal setting controlled by synsedimentary faults. None of the facies exhibits petrographic evidence of biogenicity such as stromatolitic laminar-reticulate fabrics and/or associated sediments (e.g. peloids, oncoids, ooids) or typical features such as mudcracks or clotted fabrics. The uppermost Haut-Shiloango Subgroup is made up from the stratigraphic succession of the three lithofacies and corresponds to a deepening-upward evolution from storm-influenced lithofacies in mid- and outer-ramp to deep-water environments, with emplacement of mass flow deposits in toe-of-slope settings. These processes occurred along tectonically active continental margins locally influenced by altitude glaciers, developed after a rift-drift transition.Uniform flat non-marine shale-normalized REE+Y patterns indicate freshwater-influenced signatures in the Sh8h carbonates. Moderate Y, Zr and Rb values reflect continental detrital inputs in nearshore environments rather than in deep-water environments. These nearshore sediments have been reworked from shallow inner- to mid-ramp settings into deeper outer-ramp and deep-water slope environments as a consequence of the tilting and uplifting of blocks. The blocks belonged to a graben-like basin related to the 750-670. Ma oceanic spreading in the central-southern Macaúbas Basin. © 2013 Elsevier Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Microstructures in the Neoproterozoic tillites around the Congo River Basin (CRB), Democratic Republic of Congo (DRC): Comparison with the Karoo tillites from the Dekese borehole in the CRB

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The Neoproterozoic record in Gabon and Democratic Republic of Congo: A stable isotope sudy.

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