Thermal maturity estimation of carbonaceous material from proterozoic organic-walled microfossils assemblages (DRCongo, Mauritania and Australia) by using Raman spectroscopy

Biostratigraphie, Chémostratigraphie et caractérisation de la matière organique du Supergroupe de Mbuji-May

Surveillance of FAP: a prospective blinded comparison of capsule endoscopy and other GI imaging to detect small bowel polyps

Background: Familial adenomatous polyposis (FAP) is a hereditary disorder characterized by polyposis along the gastrointestinal tract. Information on adenoma status below the duodenum has previously been restricted due to its inaccessibility in vivo. Ca

Etude géochimique de la matière organique sédimentaire par pyrolyse: caractérisation des roches à kérogène et des bitumes par pyrolyse comparative et analyse cinétique, application au secteur pétrolier du Bas Zaïre-Angola

dissertn: Diss. Doct

Tectonic evolution of the Congo Basin using geophysical data and 3D numerical simulations

The Congo basin (CB) is an intracratonic basin that occupies a large part of the Congo Craton (1.2 million km2) covering approximately 10% of the continent [1]. It contains up to 9 km of sedimentary rocks from the Mesoproterozoic until Cenozoic age. The formation of the CB started with a rifting phase during Mesoproterozoic with the amalgamation of the Rodinia supercontinent (1.2 Gyr). Afterwards, the main episodes of subsidence occurred during the subsequent Neoproterozoic post-rift phases, which were followed by phases of compression at the end of the Permian and during the Early Jurassic age and other sedimentation episodes during Upper Cretaceous and Cenozoic [2]. We reconstruct the stratigraphy and tectonic evolution of the basin by analyzing seismic reflection profiles. Furthermore, we estimated the velocity, density, and thickness of the sedimentary layers in order to calculate their gravity effect. Afterwards, we calculate the gravity disturbance and Bouguer anomalies using a combined satellite and terrestrial data gravity model. The gravity disturbance obtained from the EIGEN-6C4 gravity model [3] shows two types of anomalies. One with a long wavelength (~50 mGal) that covers the entire area of the Congo basin and a second one with a short wavelength (~130 mGal), having a NW-SE trend, which corresponds to the main depocenters of sediments detected by the interpretation of seismic reflection profiles. These results have been used as input parameters for 3D numerical simulations to test the main mechanisms of formation and evolution of the CB. For this aim, we used the thermomechanical I3ELVIS code [4] to simulate the initial rift phase. The numerical tests have been conducted considering a sub-circular weak zone in the central part of the cratonic lithosphere [2] and applying a velocity of 2.5 cm/yr in two orthogonal directions (NS and EW), to test the hypothesis of the formation of a multi extensional rift in a cratonic area. We repeated these numerical tests by increasing the size of the weak zone and varying its lithospheric thickness. The results of these first numerical experiments show the formation of a circular basin in the central part of the cratonic lithosphere, in response to extensional stress, inducing the uplift of the asthenosphere. [1] Kadima, et al. (2011), Structure and geological history of the Congo Basin: an integrated interpretation of gravity, magnetic and reflection seismic data, doi:10.1111/j.1365-2117.2011.00500.x. [2] De Wit, et al. (2008), Restoring Pan-African-Brasiliano connections: more Gondwana control, less Trans-Atlantic corruption, doi:10.1144/SP294.20 [3] F\uf6rste et al. (2014) EIGEN-6C4 The latest combined global gravity field model including GOCE data up to degree and order 2190 of GFZ Potsdam and GRGS Toulouse; doi: 10.5880/ICGEM.2015.1, 2014 [4] Gerya (2009), Introduction to numerical geodynamic modelling, Cambridge University Pres

Seishaz assessment of the K rift segment based on a new sismo-tectonic zonation model

In the frame of the Belgian GeoRisCA multi-risk assessment project focused on the Kivu and Northern Tanganyika Region, a seismic hazard map has been produced for this area. It is based on a on a recently re-compiled catalogue using various local and global earthquake catalogues. The use of macroseismic epicenters determined from felt earthquakes allowed to extend the time-range back to the beginning of the 20th century, thus spanning about 100 years. The magnitudes have been homogenized to Mw and the coherence of the catalogue has been checked and validated. The seismo-tectonic zonation includes 10 seismic source areas that have been defined on the basis of the regional geological structure, neotectonic fault systems, basin architecture and distribution of earthquake epicenters..

Tectonic stress inversion of large multi-phase fracture data sets: application of Win-Tensor to reveal the brittle history of the Lufilian Arc, DRC

status: publishe

The Upper Jurassic Stanleyville Group of the eastern Congo Basin: An example of perennial lacustrine system

International audienceThe intracratonic Congo Basin, located in the Democratic Republic of Congo (DRC), is the largest sedimentary basin of Africa. The Jurassic strata outcrop along its eastern margin, south of Kisangani (formerly Stanleyville). In the last century, the Upper Jurassic Stanleyville Group was described as a lacustrine series containing a thin basal marine limestone designed as the ;Lime Fine; beds. Since the proposal of this early model, the depositional environment of the Stanleyville Group, and especially the possible marine incursion, has been debated, but without re-examining the existing cores, outcrop samples and historical fossils from the type location near Kisangani that are available at the Royal Museum for Central Africa (MRAC/KMMA, Tervuren, Belgium). In order to refine the former sedimentology, a series of nine exploration cores drilled in the Kisangani sub-basin have been described. This study aims at integrating sedimentary facies in existing sedimentary models and to discuss the hypothesis of the presence of Kimmeridgian marine deposits along the Congo River near Kisangani, a region which lies in the middle of the African continent. Eight facies have been identified, which permit a reinterpretation of the depositional environment and paleogeography of the Stanleyville Group. The base of the Stanleyville Group is interpreted to represent a conglomeratic fluvial succession, which filled an inherited Triassic paleotopography. Above these conglomerates, a transition to a typically lacustrine system is interpreted, which includes: (1) a basal profundal, sublittoral (brown to dark fine-grained siltstones with microbial carbonates, i.e., the ;Lime Fine; beds) and littoral lacustrine series; covered by (2) a sublittoral to profundal interval (brown to dark organic-rich, fine-grained siltstones), which corresponds to the maximum extent of the paleo-lake; and, finally (3) a shallow lacustrine series (greenish calcareous siltstones and sandstones with red siltstones). Unlike what has been proposed, the ;Lime Fine; beds are interpreted herein to be of lacustrine origin, rather than representing a Kimmeridgian marine transgression. We conclude that a Jurassic marine transgression did not, in fact, occur in the eastern region of the Congo Basin

Plant silicon isotopic signature might reflect soil weathering degree

Plants fractionate Si isotopes which provides a useful Si tracer in the Si soil-plant cycle. This study reports plant Si content and Si-isotopic signatures in mature banana plants grown on soils with different weathering degree, but all developed from basaltic pyroclasts in the Mungo area, Cameroon. The delta Si-30 compositions were determined in various plant parts and soil surface horizons by MC-ICP-MS in dry plasma mode with external Mg doping to a precision of +/- 0.15aEuro degrees (+/- A 2 sigma(SD)). The Si-isotopic compositions in banana plants grown on weathered clayey soils (+0.54 +/- A 0.15aEuro degrees) are heavier than on weakly developed soils rich in fresh ash and pumice (+0.02 +/- A 0.15aEuro degrees). The corresponding bulk soils display lower delta Si-30 value in weathered soil (-1.41aEuro degrees) than in poorly developed soil (-0.41aEuro degrees). We suggest that the dissolved Si source for the plant, governed firstly by dissolution of easily weatherable minerals, was isotopically enriched in heavy isotopes through clay formation over long periods. At seasonal to annual time scale, this source is influenced by a combination of following processes: Si adsorption of light isotopes onto Fe oxides, plant Si uptake and recycling in surface horizons. This would provide an isotopically heavier Si source in the more weathered soil since the Fe oxides content increases with weathering. Plant Si-isotopic signature might thus reflect the soil weathering degree. This study further suggests that in addition to weathering processes, rivers isotopic signatures likely depend on the fate of phytoliths in the soil-plant-river system