Thermal maturation of carbonaceous material from Mbuji-Mayi Supergroup (Kasai, Democratic Republic of Congo) (original) (raw)
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Palaeogeography, Palaeoclimatology, Palaeoecology, 2013
The late Mesoproterozoic-middle Neoproterozoic period (ca. 1300 Ma-800 Ma) heralded extraordinary climatic and biological changes related to the tectonic changes that resulted in the assembly (~1.0 Ga) and the break-up of Rodinia (880 Ma-850 Ma). In the Democratic Republic of Congo, these changes are recorded in the Mbuji-Mayi Supergroup which was deposited in the SE-NW trending siliciclastic-carbonate failed-rift Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. New LA-ICP-MS U-Pb laser ablation data on detrital zircon grains retrieved from the lower arenaceous-pelitic sequence (BI group) together with C and Sr isotopic data on carbonates from the upper dolomitic-pelitic sequence (BII group) and an 40 Ar/ 39 Ar age determination on a dolerite give a new depositional time frame between 1174 ± 22 Ma and ca. 800 Ma for the Mbuji-Mayi Supergroup. The upper age limit is based on the assumption that the transition between the BIIb and BIIc subgroups recorded the Bitter Springs anomaly. In terms of tectonic and paleoclimatic settings, the BII group was deposited in the eastern passive margin of the Congo Craton during warm periods interlaced with temporarily dry and wet seasons, suggesting greenhouse conditions during the fragmentation of Rodinia.
Journal of African Earth Sciences, 2018
New detailed lithological, sedimentological, chemostratigraphic data were obtained from exploration drilling samples on the C5 carbonate-dominated formation of the Neoproterozoic Lukala Subgroup (former Schisto-Calcaire Subgroup) from the West Congo Belt (WCB) in the Democratic Republic of Congo. This formation records the last post-Marinoan sea-level events that occurred in the whole basin, followed by the development of the Araçuaï-West Congo Orogen between 630 and 560 Ma. The C5 Formation consists of back-reef lagoonal and peritidal/sabkha cycles of~2.0 m in thickness, that record a short-time marine regression, rapidly flooded by a marine transgression with deposition of organic-rich argillaceous carbonates or shales under dysoxia and anoxia conditions. These dysoxic/anoxic waters were rapidly followed by a regional-scale marine transgression, favouring mixing with well-oxygenated waters, and the development of benthic Tonian to Cambro-Ordovician Obruchevella parva-type 'seagrasses' in the nearshore zones of the lagoons. New d 13 C and 87 Sr/ 86 Sr isotopic data in the C5 Formation of the Lukala Subgroup are used in the frame of a correlation with the Sete Lagoas Formation in Brazil. Relatively comparable negative to positive d 13 C excursions point to marine flooding of the whole basin and allow extension of the debatable Late Ediacaran age of the uppermost Sete Lagoas and C5 formations. Sr isotope "blind dating" failed due to low Sr concentration related to a dolomitization event close 540 Ma. Several tentative datings of the C5 Formation converge to a Late Ediacaran age ranging between 575 and 540 Ma. As the overlying Mpioka folded Subgroup, the C5 series suffered the Pan African deformation, dated at 566 ± 42 Ma. Unlike the previously generally accepted interpretation, our data suggests that the Mpioka Subgroup was deposited in the Early Cambrian.
Approximately 1000 m of strata in the Upper Paleozoic Lukuga Formation in the Dekese core in the central Congo Basin provide lithostratigraphic, mineralogical, and isotopic evidence for substantial climatic variation within a long-lived lacustrine basin. Lithostratigraphic indicators of cold climate include polymictic strata (dropstone deposits) and coupled laminations of fine clay-size material and coarse silt (glacial varves). Dropstones are concentrated in three stratigraphic zones in the lower ~ 425 m of the Lukuga Formation, and varved strata occur in two broad stratigraphic zones in the lower ~ 700 m of the formation. These sedimentological indicators suggest that the lower ~ 2/3 of the Lukuga Formation was strongly influenced by frigid conditions and glacial-like processes. The clay-size fraction of 97 samples is dominated by detrital minerals, including quartz, feldspar, chlorite, illite, and poorly ordered expansible 2:1 phyllosilicates. Based on variation in the mineralogy of these samples, the Lukuga Formation is divisible into three Clay Mineral Zones (CMZs), numbered in ascending stratigraphic order. CMZ 1 and CMZ 3 include several horizons of expansible 2:1 phyllosilicates that represent warmer/wetter intervals. Intervening CMZ 2 is a long (~ 500 m) zone of chlorite and illite with no expansible phyllosilicates and is interpreted as a continuous cold/frigid interval. There are numerous calcite-cemented layers, including spar-filled veins that cross depositional bedding and represent postburial alteration, radiaxial fibrous cements that displace detrital grains, and micrite that crystallized near the time of deposition. Eighty-two stable isotope analyses of micrite yield δ13C values that range from –44.6‰ to –4.1‰ and δ18O values that range from –20.0‰ to 5.0‰ (VPDB). The carbon isotope data likely reflect a range of local carbon sources derived from bacterial activity and are unrelated to paleoclimatic conditions. In contrast, stratigraphic patterns in the oxygen isotope data suggest five or six intervals of frigid conditions conducive to glacial processes.
Journal of African Earth Sciences
Isotope chemostratigraphy (d 18 O and d 13 C) a b s t r a c t The Ediacaran Schisto-Calcaire Group is a~1300 m-thick succession belonging to the West Congo Supergroup in Central Africa. In the Comba Basin, it consists of three carbonate-dominated units defined as formations (SCI to SCIII) that are unconformably overlain by clastic deposits (Mpioka Group) interpreted as a molassic formation associated with the Panafrican Orogen. The underlying Upper Tillite and Cap Carbonate (SCI a) units, considered as markers of the Snowball Earth event were studied in three sections. We investigated the carbonates of the Schisto-Calcaire Group by defining new microfacies (MF1-MF7) and we performed C and O isotopic analyses in order to constraint the depositional and diagenetic events directly after the Marinoan interval. Stratigraphic variations of the stable isotopes are important in the series with lighter d 18 O values (>1.5‰) than those of the Neoproterozoic ocean in the SCI c unit. According to regional stratigraphy a temperature effect can be dismissed and a freshwater surface layer is the origin of such negative d 18 O values in this unit. The negative d 13 C anomaly (À3.5‰ on average) of the Cap Carbonate is similarly to the d 18 O values (À6.4‰ on average) in the range of the marine domain during postglacial sea level rise. The sample suite as a whole (SCII and SCIII formations) displays heavier d 18 O and d 13 C than those of the lower part (SCI unit) of the Schisto-Calcaire Group. The comparison with the Lower Congo (Democratic Republic of Congo) and Nyanga (Gabon) basins shows that the meteoric flushing in SCI c unit of the Schisto-Calcaire Group was regional and not local, and could be derived from a climatic evolution. Although an overall overprint is present, our isotopic relationships argue against overall diagenetic resetting of primary compositions and suggest that with careful examination combined with detailed petrographic analysis general depositional and diagenetic controls can be discerned in oxygen and carbon isotopic data in the Schisto-Calcaire Group.
Precambrian Research, 2017
In this paper, we present new age constraints for the lower part of the Meso-Neoproterozoic sedimentary Mbuji-Mayi Supergroup (Democratic Republic of Congo, DRC). This Supergroup preserves a large diversity of organic-walled microfossils, evidencing the diversification of early eukaryotes for the first time in Central Africa. We use different methods such as in situ U-Pb geochronology by LA-ICP-MS and U-Th-Pb chemical datings by Electron Microprobe on diagenetic and detrital minerals such as xenotimes, monazites and zircons. We attempt to better constrain the provenance of the Mbuji-Mayi sediments and the minimum age of the Mbuji-Mayi Supergroup to constrain the age of the microfossils. Results with LA-ICP-MS and EMP provide new ages between 1030 and 1065 Ma for the diagenesis of the lower part of the sedimentary sequence. These results are consistent with data on biostratigraphy supporting the occurrence of worldwide changes at the Mesoproterozoic/Neoproterozoic boundary.
The stratiform Cu mineralisation at Lufukwe, Lufilian foreland, Democratic Republic Congo
PROGRAM Thursday September 7th 8H00-9H00: WELCOME OF PARTICIPANTS 9H00-9H10: Opening of the meeting: the word of the president (D. Laduron) CLIMATE AND ENVIRONMENTAL GEOLOGY 9H10-9H30: Yans J., Dupuis C. Dating of the weathering processes in the Ardenne area (Belgium) 9H30-9H50: Quinif Y. U/Th dating of a near water-table speleothem in the cave of Han-sur-Lesse -Implications on geodynamics evolution of Ardenne 9H50-10H10: Petermans T., Rosset P., Foriers E., Camelbeeck T. Evaluation and mapping of local site effects and seismic hazard: case studies in Mons Basin and Brussels region 10H10-10H30: Petit J., Taillez A., Verheyden S., Chou L., Mattielli N. First steps towards Cu and Zn isotope geochemistry in estuarine environments 10H30-10H50: COFFEE BREAK AND POSTER SESSION 10H50-11H10: Missiaen, P., Van Itterbeeck, J., Folie, A.,. Markevich, V.S., Van Damme,D., Dian-Yong, G., Smith, Th. The Subeng mammal site (Late Paleocene, China): evidence for a unique woodland on the dry Mongolian Plateau 11H10-11H30: De Vleeschouwer F., Van Vliët-Lanoé B., Fagel N., Richter T., Boës X., Gehrels M. High resolution petrography of impregnated peat columns containing tephras. Principle, applications and perspectives 11H30-11H50: Renson V., De Vleeschouwer F., Fagel N., Mattielli N., Nekrassoff S., Streel, M. Contribution of elemental and lead isotopes geochemistry to archeology in a Belgian peat bog (Hautes Fagnes) the CRIMEA project members The "Clathrate Gun" did not fire bubbles… 12H10-12H30: Van Rooij D., Blamart D., Foubert A., Henriet J-P. Offshore record of British-Irish ice sheet fluctuations during the last glacial cycle: implications for deep-water sedimentation POSTERS Berger J., Ennih N., Demaiffe D., Liégeois, J.P. Reactivation of a cratonic boundary in an intraplate setting: the Cenozoic alkaline lavas from Djbel Sahro (anti-Atlas, Morocco) Bertola C., Boulvain F. Poty E. Magnetic susceptibility and high resolution correlation in Belgian Tournaisian Bolle O., Diot H. Magmatic fabrics in Sveconorwegian postcollisionnal magmatic bodies (southern Norway) revealed by their anisotropy of magnetic susceptibility (AMS) Active faults and fault segmentation in the Ufipa plateau, SW-Tanzania Mathys M., Baeteman C., De Batist M. The Quaternary geological evolution of the Belgian Continental Shelf: a sneak preview Missiaen T., Henriet J.P., Halleux L., Martens R. High resolution geophysical investigations of an old WW1 munition dump site Missiaen T., Slob E., Versteeg W., Donselaar M.E. Comparing different geofysica methods in the Verdronken land van Saeftinge
Neues Jahrbuch für Mineralogie - Abhandlungen, 2009
Th-U-Pb dating of metamorphic monazite by electron microprobe (EMP) and P-T path reconstruction from sillimanitebearing garnet-biotite gneisses provide new insight into the Pan-African structural and metamorphic evolution in the Kekem area in the Central African Fold Belt of Cameroon. Two events can be distinguished: (1) crystallization of garnet-bearing assemblages and monazite during a Pan-African high temperature metamorphism and (2) subsequent deformation with pervasive mylonitisation. Geothermobarometry based on cation-exchange and net transfer reactions in garnet-bearing assemblages in low-strain domains (Ca-and Mg-rich garnet core compositions and enclosed plagioclase and biotite) yielded 720 °C/12 kbars. The Mg-rich and Capoor garnet rims crystallized at 750 °C/7 kbars. The mylonitic foliation was formed during subsequent cooling and decompression. Two groups of monazite ages have been recognized; an older group of monazite grains is preserved in low-strain domains and defi nes ages from 580 to 570 Ma. A slightly younger group of grains situated in high-strain mylonitic domains displays ages between 564 and 552 Ma. The data imply Pan-African high-temperature amphibolite-facies metamorphism along a clockwise P-T path. The recorded P-T evolution involves a marked variation in pressure, which is typical of collisional crustal thickening.
Journal of African Earth Sciences, 2006
Lithogeochemical, chemostratigraphic, Rb-Sr and Sm-Nd isotope as well as U-Pb single zircon age data from the principal stratigraphic units of the West Congolian Group (West Congo Supergroup) in the West Congo Belt, Democratic Republic of Congo, presented in this reconnaissance study provide new insights into regional stratigraphic correlation and sediment provenance. The oldest unit (Sansikwa Subgroup) is a continental rift basin fill that culminated in a marine glacial diamictite (Lower Mixtite Formation), which is correlated with the global 750-720 Ma Sturtian glaciation. This is followed by a post-glacial, marine carbonate-dominated succession (Haut Shiloango Subgroup), a second diamictite unit (Upper Mixtite Formation) for which a syn-Marinoan (636 Ma) age is favoured, a post-glacial carbonate succession (Schisto-Calcaire Subgroup) and finally molasse sediments that experienced orogenic deformation at c. 566 Ma, as indicated by new 40 Ar-39 Ar data. The youngest unit (Inkisi Group) is post-orogenic, derived from the West Congo Belt, and thus not part of the same supersequence. The proposed regional to global correlation of the various units is in line with progressively younger detrital zircon age spectra upsection. Overall, these age spectra indicate a Neoarchaean basement source (Congo Craton) and a Palaeoproterozoic source from the known Kimezian Supergroup to the west of the belt, which corresponds in age with the Eburnean of southern Africa. In addition, we identified a hitherto unknown late Mesoproterozoic source to the west of the belt, the age of which is comparable to the Espinhaço Supergroup of the Araçuai Belt in Brazil.
Journal of African Earth Sciences, 2017
The origin of breccias in the Neoproterozoic Katanga Supergroup in D.R of Congo is still a matter of debate. At the Shangoluwe Cu deposit located in the Kambove mining district (central part of the Lufilian arc), the sedimentary breccias bearing Cu mineralisation have been investigated for lithological and sedimentological study, quantitative analysis of the breccias fragments and fault kinematic analysis in order to understand the origin of the breccias, their lithostratigraphic position and the timing of mineralisation. At Shangoluwe, three sedimentary breccias sequentially deposited within the Kundelungu rocks can be identified on the basis of the nature of the matrix and fragments; from bottom to the top, the Ferruginous Breccias, the Dolomitic Breccias and the Siliceous Breccias. These breccias were deposited as lenses. The presence of debris and grain flows, a finely laminated matrix, pseudo-stratification, normal and reverse graded-bedding, and the presence of interbedded siltstone, sandy shale, dolomitic shale, shale and dolomite, are considered as evidence of a sedimentary origin of the breccias. The log normal distribution of the fragments indicates that gravity flow was the main deposition mechanism. The Ferruginous and Dolomitic Breccias are regarded as contemporaneous with the Kundelungu Group. They were deposited as lenses interbedded in the Kanianga and Mongwe formations, both affected by the Lufilian orogeny (D1-Kolwezian and D2 e Monwezian phases). The Siliceous Breccias are post-orogenic as shown by the presence of an erosional and angular unconformity respectively on the Dolomitic Breccias and the Kundelungu formations. Therefore, the Siliceous Breccias are attributed to the Lower Palaeozoic Biano Subgroup and the lithostratigraphy of the Biano Subgroup is proposed for revision accordingly. Copper mineralisation postdates the deposition of the breccias, the dissolution of dolomite fragments and in-situ fragmentation. This mineralisation occurred during late-to post-orogenic extension of the Lufilian orogeny, and was remobilised during the Cenozoic.