Biostratigraphy constraints on Chemostratigraphy of the Mbuji-Mayi Supergroup, Democratic Republic of Congo: Evidence for a Late Mesoproterozoic-Early Neoproterozoic age (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.
A well preserved and diversified microfossil assemblage is reported from the Meso–Neoproterozoic Mbuji-Mayi Supergroup in the Kasai oriental Province, central part of Democratic Republic of Congo. A total of 49 taxa belonging to 27 genera were identified, including 11 species of unambiguous eukaryotes, 10 species of possible eukaryotes or prokaryotes and 28 species of probable bacteria. This assemblage is more diverse than previously reported but includes taxa reported in coeval worldwide assemblages. It is characterized by abundant sphaeromorphs, filamentous colonial aggregates and filamentous forms, as well as a relatively low diversity of acanthomorphs including the Late Mesoproterozoic and Early Neoproterozoic index fossil – Trachyhystrichosphaera aimika – reported for the first time in Central Africa. This species co-occurs with other taxa also reported for the first time in Africa: Trachyhystrichosphaera botula, Jacutianema solubila, cf. Tappania sp., Valeria elongata and numerous other taxa. Correlation with other geochronologically constrained successions that contain Trachyhystrichosphaera confirms T. aimika as promising index fossil to define the Late Mesoproterozoic–Early Neoproterozoic interval. The available biostratigraphic data enable to suggest a minimum Tonian age for the Mbuji-Mayi Supergroup. This age is consistent with the published and new geochronological data. Comparison with worldwide Proterozoic assemblages permits to define microfossil assemblages useful for biostratigraphy. This study significantly improves our understanding of the diversity of the Late Mesoproterozoic–Early Neoproterozoic biosphere, and in particular the diversification of early eukaryotes, preserved in the Democratic Republic of Congo rock record and more broadly in Africa where micropaleontological investigations are sparse.
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.
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.
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.
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.
Chemical Geology, 2000
Application of the 207 Pb-204 Pb double-spiking technique to correct for mass-fractionation led to marked improvement in the quality of Pb isotope data and resulting ages obtained on low-grade metamorphosed Neoproterozoic carbonate rocks from the Pan-African Gariep and Saldania Belts in southern Namibia and South Africa. Carbonate rock powders were Ž . dissolved using 1 N acetic acid. Residue fractions were separated from the supernatant carbonate fractions and analysed separately. Marbles from the lower Pickelhaube Formation, Gariep Belt, yielded distinctly different 207 Pbr 206 Pb isochron Ž . Ž . ages of 728 " 32 MSWDs 1.5 and 545 " 13 Ma MSWDs 7.4 for the carbonate and residue fractions, respectively. The former is interpreted as dating early diagenesis, whereas the latter is in excellent agreement with the timing of regional metamorphism. In contrast, both the carbonate and residue fractions from the Bloeddrif Member, Holgat Formation, Gariep Belt, and from the Kombuis Member, Matjies River Formation, Saldania Belt, yielded indistinguishable 207 Pbr 206 Pb isochron ages. The isotope data from both fractions combined define an isochron age for the Bloeddrif Member marbles of Ž . Ž . 555 " 28 MSWDs 22.8 . A whole rock isochron age of 553 " 30 Ma MSWDs 14.3 is given by the weighed sums of separately analysed carbonate and residue fractions data of the Kombuis Member. Both ages are interpreted to reflect early diagenesis. Our novel approach to double-spike 207 Pbr 206 Pb dating of carbonate rocks highlights not only the importance of dating carbonate and residue fractions separately, but also led to a major revision of stratigraphic correlation between the Gariep and Saldania Belts. q
Journal of African Earth Sciences, 2014
The Turonian-Coniacian series of Bireno and Douleb Members (carbonate Members of the Aleg Formation) have been examined on their sedimentology, stratigraphy and faunistic contents to provide new insights into the paleoenvironment evolution and sea-level changes in the Gafsa basin. At this scale, both the Turonian-Coniacian series are mainly made of marls and limestones and locally include evaporites. In this paper, ostracods together with benthonic and planktonic foraminifers, collected from the Upper Cretaceous series of Berda and Chemsi mountains, are used to provide some chronostratigraphic precisions (age and limits) of these lithostratigraphic units. Accordingly, four lithostratigraphic units, belonging to the Aleg Formation, were recognized following an ascending order; the Annaba Member (Lower Turonian), the Bireno Member (Lower Turonian-Middle Turonian), the Lower Aleg Marls (Middle Turonian-Upper Turonian, Jebel Chemsi and Upper Turonian-Lower Coniacian, Jebel Berda) and the Douleb Member (Coniacian). These units are overlaid by the Upper Aleg marls Santonian in age. The recognized microfacies are interpreted as a shallow marine deposit of a lagoonal environment, shallowing upward from supratidal to subtidal settings with scattered rudistic patch reefs. The corresponding carbonate sediments were affected by several diagenetic stages starting at the sea floor (early diagenesis), continuing near the surface (meteoric diagenesis) and ending in the subsurface (burial diagenesis).
Geology and Resource Potential of the Congo Basin, 2014
During the Messinian Salinity Crisis (MSC), between 5.97 and 5.33 Ma, the marine connections between the Atlantic Ocean and the Mediterranean Sea were temporarily restricted. The post-MSC reflooding of the Mediterranean Sea by the Atlantic waters and its sedimentary record are debated. The Boudinar basin (North-Morocco) provides an exceptional record of this period between ca 5.32-5.27 and 4.37 Ma at youngest (Zanclean-Zone PL1). The sedimentary succession of this basin comprises seven facies associations corresponding to depositional settings ranging from continental to open marine environments. We provide a new sequence stratigraphic framework, based on twelve stratigraphic sections. Two orders of depositional sequences (4 th , 3 rd order), related to base-level changes during the Late-Messinian Early-Pliocene time interval, are correlated at the basin scale. According to our reconstruction, the post-MSC base level rise and the Zanclean reflooding lasted from a minimum of several tens up to hundreds thousands years, suggesting a gradual, not catastrophic event indicative of a progressive transgression.