6 research outputs found
Geological study of the Mpioka subgroup in the Nionga massif. (Bas-congo, DRC)
No full textThe massif of Nionga is located in the province of Bas-Congo in the Democratic Republic of the Congo. The subgroup of Mpioka is lithostratigraphiquement to Group West-Congolien (566 Ma). And Zadinien, Mayumbien and West-Congolien together form what is called the supergroup West Congo (L. Tack et al., 2001).
This work objectives were to determine: the petrographical types of rocks of this subgroup of Mpioka, the area source of debris, the mechanism and the physico-chemical conditions of the medium of filing.
The interest of this study resided in the fact that the massif of Nionga is located in the Mayumbe ditch where manifestations lithologic and tectonic chain West-Congo are recorded. And into this ditch, extending south of Gabon to northern Angola from Congo-Brazzaville and the Democratic Republic of Congo, the massif of Nionga is the only sector where the subgroup of Mpioka outcrops in low vertical and lateral extension. As such, this massif was clear to understand, after the chemical stage schisto-limestone, the dynamics of the basin during the filing of the detrital episode of Mpioka in Bas-Congo.
This study allowed us to conclude that the subgroup of Mpioka located in the Nionga massif is formed of clay and sandstone lithofacies, and that it is a rythmite deposited on a flat tidal where driveways come tides have alternately deposited sand (bench of sandstone and sandstone beds - average energy) and sludge (shoals of shales and clay beds - low energy). A medium scale, observed the intercalation of sandstone in shale and on a small scale, the alternation of the quartz-clay laminae. The slump structures resulting rupture and the transport of sediment layers thus producing intertidal sediments in the flats mixtures chaotic types and channels of rivers; rolled sludge have a zonation that would be the result of differences; in the texture, composition and colouring of rocks solid bedding would be due to a very rapid sedimentation in the flats intertidal. Oxidizing conditions from the middle of deposit are translated by the red hue of these rocks. And this colour is due to the presence of ferric iron (hematite) which is common in this massif. Apart from the neoformations chloritic, ironstone, and calcite, quartz sediments of the Mpioka subgroup come from erosion of metamorphic rocks, very rugged, Transmazonien and Kimezien.
Correlated with the Pi of the subgroup of Mpioka term in Bungo basin (Angola), this sub-group flush in the massif of Nionga testifies to the existence of a shoal during the filing of Pc, Pe, Pk and Pm and a deflection crustal during the filing of Pi. This subgroup is also between two sedimentary gaps, and is transgressive on Schisto-limestone in the Mayumbe ditch where the level passed successively (from Pc to Pe) regression to a breach (of Pe to Pi) and finally to a regression (of Pi in Pm).Le massif de Nionga est situé dans la province du Bas-Congo en République Démocratique du Congo. Le Sous-groupe de Mpioka appartient lithostratigraphiquement au Groupe Ouest-Congolien (566 Ma). Et l’ensemble Zadinien, Mayumbien et Ouest-Congolien forme ce qu’on appelle le Supergroupe West-Congo (L. Tack et al., 2001).
Ce travail avait pour objectifs de déterminer : les types pétrographiques des roches de ce Sous-groupe de Mpioka, la zone-source des débris, le mécanisme de mise en place ainsi que les conditions physico-chimiques du milieu de dépôt.
L’intérêt de cette étude résidait dans le fait que le massif de Nionga est situé dans le fossé de Mayumbe où toutes les manifestations lithologiques et tectoniques de la chaîne West-Congo sont enregistrées. Et dans ce fossé, s’étendant du Sud du Gabon jusqu’au Nord de l’Angola en passant par le Congo-Brazzaville et la République Démocratique du Congo, le massif de Nionga est le seul secteur où le Sous-groupe de Mpioka affleure en faible extension verticale et latérale. A ce titre, ce massif était bien indiqué pour comprendre, après la phase chimique schisto-calcaire, la dynamique du bassin pendant le dépôt de l’épisode détritique de Mpioka au Bas-Congo.
Cette étude nous avait permis de conclure que le Sous-groupe de Mpioka localisé dans le massif de Nionga est formé des lithofaciès argileux et gréseux, et que c’est une rythmite déposée sur une flat tidale où les allées et venues des marées ont alternativement déposées du sable (banc de grès et lits gréseux – moyenne énergie) et des boues (bancs de shales et lits argileux – faible énergie). A moyenne échelle, on observe l’intercalation du grès dans les shales et à petite échelle, l’alternance des laminations gréso-argileuses. Les structures en slump résulteraient de la rupture et du transport de couches de sédiments produisant ainsi des types chaotiques de mixtures de sédiments dans les flats intertidales et les chenaux de rivières ; les boues laminées présentent un rubanement qui serait le résultat de différences dans la texture, la composition et la coloration des roches ; le litage massif serait dû à une sédimentation très rapide dans les flats intertidales. Les conditions oxydantes du milieu de dépôt sont traduites par la teinte rouge de ces roches. Et cette teinte est due à la présence du fer ferrique (hématite) qui est fréquente dans ce massif. Hormis les néoformations chloriteuse, ferrugineuse et calcitique, les sédiments quartzeux du Sous-groupe de Mpioka proviennent de l’érosion des roches métamorphiques, à relief très accidenté, des Transmazonien et Kimézien.
Corrélé au terme Pi du Sous-groupe de Mpioka dans le bassin de Bungo (Angola), ce Sous-groupe affleurant dans le massif de Nionga témoigne de l’existence d’un haut-fond durant le dépôt de Pc, Pe, Pk et Pm et d’un fléchissement crustal au cours du dépôt de Pi. Ce Sous-groupe est également compris entre deux lacunes sédimentaires, et est transgressif sur le Schisto-calcaire dans le fossé de Mayumbe où le niveau passe successivement d’une régression (de Pc à Pe) à une transgression (de Pe à Pi) et enfin à une régression (de Pi à Pm)
Petrographic characterisation and paleoenvironmental reconstruction of the Kipala shales (Central Basin, DRC, Kwilu Province)
No full textIn order to fill the glaring gaps in geological data for the Kipala region, in the Kwilu province of the Democratic Republic of Congo, geological studies were carried out. The results identified four different lithofacies in the study area: dark greasy shale, feldspathic microgres, clayey sandstone and bituminous shale. The petrographic compositions and palaeoenvironmental conditions of the deposit are presented for the first time in this work. From a petrographic point of view, the rock samples analysed differ in the nature of their constituent minerals and/or matrix or cement. Similarly, there is a close relationship between local lake and river sediments. The size and degree of rounding of the clayey sandstones in the rocks studied suggest that they were transported over a long period under strong hydrodynamic conditions
Petrographic Characterisation and Paleoenvironmental Reconstruction of the Kipala Shales (Central Basin, DRC, Kwilu Province)
No full textIn order to fill the glaring gaps in geological data for the Kipala region, in the Kwilu province of the Democratic Republic of Congo, geological studies were carried out. The results identified four different lithofacies in the study area: dark greasy shale, feldspathic microgres, clayey sandstone and bituminous shale. The petrographic compositions and palaeoenvironmental conditions of the deposit are presented for the first time in this work. From a petrographic point of view, the rock samples analysed differ in the nature of their constituent minerals and/or matrix or cement. Similarly, there is a close relationship between local lake and river sediments. The size and degree of rounding of the clayey sandstones in the rocks studied suggest that they were transported over a long period under strong hydrodynamic conditions
Magmatic-hydrothermal evolution of Sn-W granites in the Kibara belt, Democratic Republic of Congo: ⁴⁰Ar-³⁹Ar dating and LA-ICP-MS microanalysis of cassiterites and cassiterite-hosted fluid inclusions
No full textISSN:1872-7360ISSN:0169-1368ISSN:0169-136
Granulometric and Mineralogical Characterization of Sands from the Middle Course of the Kasai River (Ilebo Territory, Kasai Province, DRC)
No full textThis study addresses sediment dynamics within the fluvial system of the middle Kasai Basin, specifically between Ilebo town (pk605) and the confluence with the Loange River (pk525). The primary aim is to characterize the granulometric and mineralogical evolution of sand bars in the Kasai River, which pose navigational challenges in this section of the basin. The study seeks to answer the following question: How do the granulometric and mineralogical characteristics of sands transported by the middle course of the Kasai River evolve? The research employs laboratory granulometric techniques. Twenty sand samples were collected from sand bars along the middle and navigable course of the Kasai River during the flood recession period, ranging from upstream to downstream. Sieving was conducted using an AFNOR-type sieve column, followed by sedimentometric analyses and the calculation of various Folk & Ward textural parameters using the Excel program Gradistat. Additionally, six samples underwent automated mineralogical analysis using a QEMSCAN FEG Quanta 650. Granulometric analysis revealed that the sands from the middle course of the Kasai River are unimodal, with fine to medium grains in the granulometric fraction ranging from 186.2 µm to 426.8 µm. Most of these sands are moderately to well graded, with grains showing granulometric symmetry and, less commonly, fine asymmetry. Their kurtosis is largely mesokurtic, with occasional leptokurtic and platykurtic characteristics, indicating multiple depositional environments. The study demonstrates that the evolution of these granulometric parameters is uneven along the middle course of the Kasai River, though overall, the parameters exhibit limited variation. This suggests minimal and regular sediment inputs, consistent with the relative regularity of granulometric variations in environments characterized by free sedimentation. Automated mineralogical analysis identified a diverse mineralogical assemblage, dominated by quartz, followed by calcite, iron oxides, orthoclase, plagioclase, and kaolinite. Additionally, a group of minerals that do not exceed the 0.55% threshold—such as illite, apatite, ilmenite, muscovite, chlorite, biotite, montmorillonite, rutile, pyrophyllite, siderite, zircon, and dolomite—was identified. Consequently, the mineralogical evolution is not uniform throughout the middle course of the Kasai River, showing a sawtooth variation. This study clarifies the evolution of the granulometric parameters of Kasai River sands, which are influenced by the river's hydrodynamic regime. It also elucidates the mineralogical evolution, linked to the petrographic nature of source areas, which are distributed based on their mechanical resistance to abrasion, chemical alteration, and the morphology of the riverbed. The findings from this research contribute significantly to the field of sedimentology and integrated river managemen
Dissipative time-domain one-dimensional model for viscothermal acoustic propagation in wind instruments.
No full textCopyright 2021 Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America.The following article appeared in Thibault, A., & Chabassier, J. (2021). Dissipative time-domain one-dimensional model for viscothermal acoustic propagation in wind instruments. The Journal of the Acoustical Society of America, 150(2), 1165-1175 and may be found at https://doi.org/10.1121/10.0005537 .International audienceAccurate modeling of acoustic propagation in tubes of varying cross-section in musical acoustics must include the effect of viscous and thermal boundary layers. Models of viscothermal losses are classically written in the frequency domain. An approximate time-domain model is proposed, where all the physical parameters of the instrument as the bore shape or the wave celerity are explicit coefficients. The model depends on absolute tabulated constants which only reflect that the pipe is axisymmetric. It can be seen as a telegrapher’s equations augmented by an adjustable number of auxiliary unknowns. A global energy is dissipated. A time discretization based on variational approximation is proposed along with numerical experiments and comparisons with other model
