Bulletin de la société géologique de France

En somme la république Démocratique du Congo ; reste jusqu’à la preuve du contraire un des pays d’Afrique qui a à son sein une grande potentialité minière et qui ces dernières lui vaut l’appellation de « scandale géologique », ces ressources étant éparpillées partout sur son étendue du territoire national d’une superficie de 2.345.410 Km²  et dont la partie Est du Nord-Sud compte un nombre impressionnant de ces ressources minières entre autre ; or, diamant, colombo-tantalite, tourmaline, wolframite, etc. parmi ces ressources une qui est la plus incontournable dans les nouvelles technologie de pointe, utiliser pour la réalisation de soudures, brasures, étamage, crucial même dans le secteur de composants électronique, ce métal est étain qui, dans cette partie du pays est retrouvé dans plusieurs gisements en exploitation et non exploités et le plus grand d ces gisements en exploitation se trouve dans la province du Nord-Kivu territoire de Walikale, plus précisément dans la mine de Bisie où ce minéral est exploité par la société minière Alphamin AMB, qui, repose sur la ceinture orogénique Kibarienne dans une zone de collusion intercratonique  de différentes périodes d’extension et de compression. Suivant les différents facteurs de classification de gisement d’étain celui de Bisie possède tous les atouts nécessaires d’être un bon gisement et selon les conditions de formation dont ; les gisements d’étain en association avec les structures tectoniques du type géosynclinal et ceux en association avec les fractures profondes et aux zones de faibles de plateforme continentale, le gisement d’étain de Bisie est de type géosynclinal et est exploité par cette société minière Canadienne par la méthode mixte à chambre remblayé, à l’aide de dragues à chaine de godets qui remontent les minerais alluvionnaires vers une installation de pré-concentration.
L’exploitation artisanale de cette ressource a débuté en 2002 après sa découverte par les indigènes, qui, au fils des temps, elle a pris une grande ampleur et alimenta plusieurs comptoirs œuvrant dans la province du Nord-Kivu à la qualité et teneur élevée et une quantité suffisante, pendant ces temps les creuseurs artisanaux étaient regroupés dans les différentes organisations et coopératives minières telles que l’association locale de Bungandula qui, en 2005 devint un groupe minier de Bungandula société de personnes à responsabilité limitée ainsi la coopérative minière MPC.
L’industrialisation de Bisie par la société minière Alphamin a permis en 2015 non seulement le développement industriel mais aussi l’intégration socio-économique des différents groupes des indigènes et la construction des infrastructures routières, écoles, ponts etc. la canalisation de différentes recettes, taxes perçu par le gouvernement provincial venant de cette partie de sa province est non seulement le point de l’économie nationale.

The age of the cementation of the Fontainebleau sandstones, located in the upper part of the Rupelian Fontainebleau Sand Formation and largely outcropping in the south of the center of the Paris Basin, remains a matter of debate: did the silicification occurred at early times during Miocene, following sedimentation, or did it occurred during Quaternary cold climate episodes? In this work, we determined an orthogonal fracture network (main directions N115° ±5° and N025° ±5°) over an area of ∼6000 km2. The fractures are oblique to the adjacent valley orientation and to the quarry working face orientation, discarding a gravitational origin. This tectonic fracturing is superimposed on regional scale antiforms and synforms that may be at least partly controlled by inherited basement faults reactivation during Alpine episodes. The whole Fontainebleau Sand Formation seems to be folded, including the Fontainebleau sandstones. We establish a relative chronology of the various phenomena and p...

The stratigraphic revision of the southern coastal Ecuadorian series makes possible the reconstruction of the pre-collision history of the Caribbean plateau accreted to the Ecuadorian margin. The Coniacian age of the oceanic basement (Piñón Fm) indicates that ...

Introduction. – In the Anti-Atlas, south of Morocco (fig. 1), the Precambrian terrains are usually divided into several “series” (fig. 2) : the Paleoproterozoic (PI) is an old crystalline basement, at least Eburnean ; the Neoproterozoic (PII) is constituted by metasedimentary rocks, quartzites and limestones, indicative of a shelf, in which volcano-sedimentary and volcanic flows are intercalated, laterally grading to an ophiolitic complex along the Sirwa-Bou Azzer axis. These PII rocks have been deformed in the course of the Panafrican orogeny ; above the underlying upper Proterozoic terrains and in major unconformity on the Panafrican structures, the Saghro group (PII3) and Ouarzazate group (PIII) series are volcanic and volcano-clastic sequences, often considered as late-Panafrican molasses. Above them, the Tata group (Adoudounian), constituted by marine carbonates and siltstones, represents the earliest Cambrian. Recent structural and sedimentological observations Recent observat...

A new Cenomanian amber-and plant-bearing deposit has been discovered at Neau, in the Mayenne department (France). The Cenomanian fossiliferous lignites are located in karst filling in a substratum of Cambrian limestones. The amber corresponds mainly to tiny millimetric grains, devoid of arthropod inclusions, but rich in microorganisms, especially the sheated bacteria Leptotrichites resinatus, and containing pollen grains (Classopollis) and wood fibers (Araucariacae or Cheirolepidiaceae). The lignites provide abundant conifer and ginkgoale cuticle fragments (Frenelopsis, Eretmophyllum) and a lot of palynomorphs (e.g. Gleicheniidites senonicus, Cyathidites, Deltoidospora, Appendicisporites and Cicatricosisporites). The chemical signature of the amber suggests it was produced by conifers of the extinct family Cheirolepidiaceae. According to the palynological assemblage, the age of the lignites is upper lower Cenomanian or lower mid Cenomanian. The deposit environment corresponded to th...

The Rhodope Metamorphic Complex (RMC) is a high-grade crystalline massif located at the northern margin of the Aegean region. Numerous scenarios have been proposed for the evolution of the RMC during Alpine times. A debated issue is whether there has been a single protracted orogenic cycle since around the mid-Mesozoic or whether Alpine orogeny involved distinct episodes of subduction and crustal accretion. We describe a key outcrop located on the Nestos Shear Zone (NSZ), a major NNE-dipping top-to-SW shear zone characterized by an inverted metamorphic sequence. Structural and petrological data document the existence of two anatectic events. The first event, best preserved in decametric structural lenses, is pre-kinematic with respect to top-to-SW shearing and involved high-temperature “dry” melting. Zircon and monazite LA-ICPMS U-Th-Pb data indicate that this event occurred at ∼140 Ma. The second event is syn-kinematic with respect to top-to-SW shearing and involved lower-temperatu...

With an output of 1700 metric tons between 1916 and 1959, the Leucamp ore deposit supplied about half the tungsten produced from the (( la Châtaigneraie district D (Cantal, France). Recent exploration by the French BRGM indicates a potential resource of 7000 metric tons WO,. Typical of the economic tungsten deposits of this district, Leucamp ore deposit is composed of quartz-wolframite veins that crosscut epimetamorphic schists of unknown age and are spatially associated with a Carboniferous granite, the Veynazes granite in this case. The control of the vein system is both lithological and structural : a pelitic wall-rock seems to be more favorable than a psammitic one; the complex outcrop pattern may be due to fluid pressure and the simultaneous reopening and filling of planar structures (cleavages, axial planes, ...) created by the polyphase folding that preceded the emplacement of the Veynazes granite. Subsequently, the veins are cut by numerous normal faults, which are sealed by...

The sedimentary architecture of basins and passive margins is determined by a complex interaction of parameters, including subsidence, eustasy, and sediment supply. A quantification of the post-rift (20 Ma-0 Ma) vertical movements of the Gulf of Lion (West Mediterranean) is proposed here based on the stratigraphic study of sedimentary paleomarkers using a large 3D grid of reflection seismic data, correlations with existing drillings, and refraction data. Post-rift subsidence was measured by the direct use of sedimentary geometries analysed in 3D and validated by numerical stratigraphic modelling. Three domains of subsidence were found: on the continental shelf and slope, subsidence corresponds to a seaward tilting with different amplitudes, whereas the deep basin subsides purely vertically. We show that these domains fit with the deeper crustal domains highlighted by previous geophysical data, and that post-break-up subsidence follows the initial hinge lines of the rifting phase. Su...

Intracratonic basins tend to subside much longer than the timescale predicted by thermal relaxation of the lithosphere. Many hypotheses have been suggested to explain their longevity, yet few have been tested using quantitative thermo-mechanical numerical models, which capture the dynamic of the lithosphere. Lithospheric scale geodynamic modelling preserving the tectono-stratigraphic architecture of these basins is challenging because they display only few kilometres of subsidence over 1000 of km during time periods exceeding 250 Myr. Here we present simulations that are designed to examine the relative role of thermal anomaly, tectonics and heterogeneity of the lithosphere on the dynamics of intracratonic basins. Our results demonstrate that initial heterogeneity of accretionary continental lithosphere explains long-term subsidence and the arches-basins architecture of Saharan type intracratonic basins at first order. The simulations show that initially warm and heterogeneous litho...

Organic matter studies find an echo within different topics such as biogeochemical cycles, processes occurring in continental surfaces, anthropogenic activities, climate science, earth and planetary sciences, etc. Today’s challenges include finding and developing the most appropriate method(s) supporting the differentiation and characterisation of various types of recalcitrant organic matter in modern environments. In this study, we focus on combustion residues and coals as these two types of organic matter contain a significant amount of so-called recalcitrant organic carbon (black carbon and fossil organic carbon). Both these materials are ubiquitous, broadly stem from the same living organisms and have similar polyaromatic structures. In this respect, we tested a spectrophotometry method, classically used for sedimentology, as a very fast method for preliminary investigations. Analyses were performed with a wide range of standards and referenced samples. The results discriminate ...

La synthèse de 240 analyses isotopiques du plomb, mesurées sur les gisements miniers marocains d’âges édiacarien à néogène appartenant à tous les domaines géotectoniques du Maroc autorise une réflexion globale sur la métallogénie du Maroc. Les compositions isotopiques varient grandement, de 17,738 (Bou Skour) à 18,905 (Draa Sfar) pour le rapport 206Pb/204Pb, et de 15,521 à 15,706 pour le rapport 207Pb/204Pb. La source du plomb des gisements étudiés se situe dans la croûte continentale supérieure, excepté pour ceux de l’Anti-Atlas (Bou Skour, Imiter…) et certains du Haut-Atlas (Azegour) à nette contribution du manteau. Les variations isotopiques relevées à l’échelle d’un district résultent soit de la présence de plusieurs événements hydrothermaux superposés sollicitant différentes sources locales comme à Tighza, soit d’un seul événement perturbé par la segmentation d’un bassin volcanosédimentaire, comme pour les amas sulfurés des Jebilet et Guemassa. À l’échelle du gisement (Draa Sfa...

The P–T evolution of a mafic eclogite sample from the Haut-Allier was studied in order to constrain the dynamic of the Variscan subduction in the eastern French Massif Central. Three successive metamorphic stages M1, M2 and M3, are characterized by assemblages comprising garnet1-omphacite-kyanite, garnet2-plagioclase, and amphibole-plagioclase, respectively, and define a clockwise P–T path. These events occurred at the conditions of eclogite (M1; ∼ 20 kbar, 650 °C to ∼ 22.5 kbar, 850 °C), high-pressure granulite (M2; 19.5 kbar and 875 °C) and high-temperature amphibolite facies (M3; 

The Institute for Nuclear Safety and Protection (IPSN) launched the « Tournemire » program, in 1988. One of its aims is to understand and characterize the fluid transfer processes in argillaceous rocks. They are interesting rocks for the long-term storage of nuclear waste. To this purpose, the IPSN installed an experimental site in a tunnel, which gives access to a 250 m-thick Toarcian and Domerian shale unit near Tournemire (Aveyron, France) (fig. 1). The fluids, in this type of rock with very low intrinsic permeability, 10−14 m/s [Boisson et al., 1998], used to flow (calcite crystallizations in fractures), and still flow, principally in the fractures [Barbreau et Boisson, 1993 ; Boisson, 1995] formed during the tectonic history of the formation. In order to constrain the history of fluid flow in the formation, it was necessary to characterize the tectonic fracturing and to identify the tectonic events responsible, on the one hand, for the apparition of the fractures and, on the ot...

The identification of mineral supply sources and trade routes are at the heart of the archaeological issues. The tracing of sources of metal production via lead isotopy has been used since the 1980s to identify the deposits from which the metal constituting the archaeological objects came. Such studies are based on mineral signature repositories and archaeologists have thus built up databases containing thousands of ore deposit analyses. The databases, however, only very rarely include geological information and are limited to geographic information. But considering only geographical data leads to many limitations of studies, including the overlapping of signatures between remote regions. This problem could nevertheless be circumvented by taking into account precise ore deposit data that enables to think in terms of restricted mineralized subsets. We illustrate this through the example of data collected in the Alps by Marcoux (1986) and Nimis et al. (2012). Taking into account geolo...

A new Cenomanian amber-and plant-bearing deposit has been discovered at Neau, in the Mayenne department (France). The Cenomanian fossiliferous lignites are located in karst filling in a substratum of Cambrian limestones. The amber corresponds mainly to tiny millimetric grains, devoid of arthropod inclusions, but rich in microorganisms, especially the sheated bacteria Leptotrichites resinatus, and containing pollen grains (Classopollis) and wood fibers (Araucariacae or Cheirolepidiaceae). The lignites provide abundant conifer and ginkgoale cuticle fragments (Frenelopsis, Eretmophyllum) and a lot of palynomorphs (e.g. Gleicheniidites senonicus, Cyathidites, Deltoidospora, Appendicisporites and Cicatricosisporites). The chemical signature of the amber suggests it was produced by conifers of the extinct family Cheirolepidiaceae. According to the palynological assemblage, the age of the lignites is upper lower Cenomanian or lower mid Cenomanian. The deposit environment corresponded to th...

Located in the Internal domain of the Rif belt, the Beni Bousera massif is characterized by a stack of peridotites and crustal metamorphic units. The massif is intruded by granitic dykes and affected by several normal ductile shear zones. Structural, petrological and 40Ar–39Ar dating analyses performed on these two elements highlight that (1) the granitic dykes are emplaced within major N70° to N140° trending normal faults and shear zones, resulted from an NNE-SSW extension (2) the Aaraben fault in its NE part is characterized by N70° to N150° trending ductile normal shear zones, resulted from a nearly N-S extension and (3) the age of this extensional event is comprised between 22 and 20 Ma. Available paleomagnetic data allow a restoration of the initial orientation of extension, which was nearly E-W contemporary with the Alboran Basin opening in back-arc context, during the Early Miocene. At the onset of the extension, the peridotites were somehow lying upon a partially melted cont...

This article describes anomalous changes in the diurnal behavior of the temperature measured in the near-surface soil at the Tlamacas monitoring site, Popocatépetl. Results of the statistical analysis show two essential changes for the temperature characteristics observed during the 2007–2009 (quiet volcano) and 2013–2014 (active volcano) monitoring periods. Under normal conditions, the absolute minimum daily temperature is observed at about 7:40 Local Time (LT) during sunrise for the atmosphere and, with a time delay, at about 8:30 LT, for soil measurements. The absolute temperature maximum is observed about 15:30 LT for the atmosphere and 16:30 LT for in-soil measurements. The dispersion of the residual temperature (24-h running trend of the temperature substituted) is 5.6 times lower for the 2013–2014 period in comparison with the 2007–2009 period. In other words, in 2013–2014, the temperature variability became 5.6 times lower that it was in 2007–2009.

Le sous-sol des villes est structuré par plusieurs millénaires d’interactions société-environnement, qui ont créé les strates et sols urbains dont la puissance sédimentaire peut aujourd’hui dépasser une dizaine de mètres. Depuis une trentaine d’années, le développement de la géoarchéologie des environnements artificialisés, et l’application des géosciences à ces formations anthropogènes, a permis de caractériser les processus pédo-sédimentaires et les systèmes d’activités qui en sont à l’origine. Ainsi, il est possible de constater que les strates des Ve–XIe siècles sont majoritairement caractérisées par des couches de terre sombre, d’apparence homogène, épaisses de plusieurs dizaines de centimètres, voire de plusieurs mètres, qui se rencontrent dans tous les espaces urbains anciens d’Europe, depuis Moscou jusqu’à Séville. Cet article présente une synthèse des résultats obtenus par l’étude systématique de ces terres noires, à l’échelle de l’Europe. Les résultats ont été acquis en as...

This paper summarizes a six-year study of the Nsimi Small Experimental Watershed (SEW), considered as a model for the South Cameroon humid tropical ecosystem. When this small watershed was set up, no similar survey of input/output hydrobiogeochemical fluxes in granitoid rocks in stable cratonic environment was available, to our knowledge, on any site close to the Equator. Moreover, this is the first attempt, world-wide, to combine different approaches in hydrology, (bio)geochemistry, mineralogy, crystallography, microbiology, geophysics and pedology. Research is based on (1) regular hydrobiogeochemical surveys in various water reservoirs of the SEW ecosystem (atmospheric deposits, groundwater and stream), (2) surveys related either to the organisation and composition of different reservoirs in the superficial layers (basement rocks, saprolite, soils) or to various hydrological, biological and geochemical processes. These surveys aim at (1) finding the main parameters involved in the...

At the northern end of the Cap Corse peninsula, several klippes of ultramafic rocks (peridotite and serpentinite), among which the Monte Maggiore klippe is the least serpentinized one, rest upon continental-crust derived rocks (Centuri gneisses) and basic or metasedimentary schists (Schistes Lustrés). The Monte Maggiore ophiolitic klippe shares several characteristics with the Cima di Gratera klippe located 30 km further south. First, the two units are composed of a lherzolitic peridotite. Second, they record the same succession of metamorphic events. Third, in the Cap Corse tectonic pile, the two units occupy the highest structural position. Several differences are also observed. First, mafic rocks are significantly less abundant in the Monte Maggiore unit, where they are restricted to dykes cross-cutting the peridotite, than in the Cima di Gratera unit, where they constitute an entire sub-unit. Second, pyroxenite layers are more common at Monte Maggiore than at Cima di Gratera. De...

The recent development of unconventional resources has triggered a regain of interest for source-rocks. The presence of hydrocarbons in these unconventional systems is generally associated with organic-rich sediments. This study aims at better understanding the factors controlling the accumulation of marine organic matter at basin scale, using a process-based approach. This work focuses on the Montney, Doig and Halfway Formations (Lower and Middle Triassic, Alberta and British Columbia, Canada). Recent studies show that the Triassic strata of the Western Canada sedimentary basin can be considered as a transitional period between the Paleozoic passive margin and the Jurassic foreland basin. Based on a 3D regional stratigraphic architecture and on a description of the organic rich interval distribution, a process-based numerical model (DionisosFlow and DORS) has been used to simulate the stratigraphic evolution of the Montney, Doig and Halfway Formations and reproduce the organic dist...

Since the early 70’s the majority of tectonic reconstructions of the western Mediterranean employ the Alboran domain notion as a migrating microcontinent or landmass mainly composed of Paleozoic-Triassic rocks affected by ‘Alpine’ HP-LT metamorphism. For nearly three decades, since the mid-80’s, the Alboran domain was considered as a fragment of the Alpine chain that moved westward, colliding into Iberia and North Africa to produce the Gibraltar arc and Betic-Rif chain. In 2012, a new hypothesis for the evolution of the western Mediterranean was presented in which the Betic-Rif orogenic chain originates from rollback of an initially SE-dipping subduction of the westernmost segments of the Ligurian-Tethys under the Africa margin. This interpretation considers the metamorphic ‘Alboran domain’ rocks as crustal successions of the hyper-extended African and Iberian continental margins, which have undergone a complete subduction-exhumation cycle above a NW- to W-retreating subduction. A k...

In this paper, we provide the first structural map of Les Saintes archipelago (Guadeloupe, Lesser Antilles). The finite strain pattern displays four families of fault systems characterized by their statistical structural orientations: N000-N020, N050-N070, N090-N110 and N130-N140 trending fault systems. Our onshore results thus underline a fault network much more complex than the one depicted by the previous offshore geophysical investigations around Les Saintes archipelago, which show only N120-N150 trending system. According to the available K-Ar dating of the volcanic rocks and the relative chronology of the faults defined in the field, we determine the deformation history in Les Saintes islands since the last 3 Ma. The four highlighted trending fault systems are already active since the Pliocene and are consistent with the present-day extensional tectonics in the Guadeloupe archipelago compatible with the reactivation of inherited structures at the active arc scale. We interpret...

Thylacocephalans (Euarthropoda, Thylacocephala) are characterized by their “bivalved” carapace and three anterior prehensile appendages. It is still not clear how they used to live, or what their evolutionary history is. This study focuses on new thylacocephalans from the Late Cretaceous Konservat-Lagerstätten of Lebanon, which yielded the youngest representatives of the group. Three new genera and species are described in the Cenomanian sublithographic limestones of Hakel and Hadjoula, and two new genera and one new species are described in the Santonian chalky limestones of Sahel Alma. Among the specimens from Hakel and Hadjoula, Paradollocaris vannieri, Thylacocaris schrami and Globulacaris garassinoi are the first reports of thylacocephalans in the Cenomanian of Lebanon. Paradollocaris and Thylacocaris are assigned to Dollocarididae based upon their large optic notches limited by rostral and antero-ventral processes, their hypertrophied eyes, and their posterior notches with dor...