Le bassin paléoprotérozoïque (2,1 à 2,0 Ga) de Franceville, situé au Sud-est du Gabon, est étudié depuis des décennies pour son fort potentiel métallifère (uranium et manganèse), depuis 2010, pour avoir livré les plus anciens macro-organismes multicellulaires connus à ce jour, repoussant la limite de l'apparition de la vie multicellulaire complexe à 2,1 Ga. Cette période, est synchrone de grands bouleversements ayant affectés à l'échelle du Globe la chimie de l'atmosphère et des océans et correspond à la mise en place de la formation FB de la série sédimentaire du Francevillien. C'est dans la région de Mvengué, au centre du bassin, que le stratotype de la formation FB a été initialement défini. L'objectif de cette étude est de pouvoir apporter de nouvelles informations sur les conditions de sédimentation et de diagenèse précoce de ces sédiments, et de mieux comprendre la mise en place de la sédimentation carbonatée essentiellement au sein de niveaux de black shales et d'intercalations silto-gréseuses.<br/>Dans la zone de Mvengué, les dépôts de la formation FB sont composés d'unités déposées dans un environnement marin avec des profondeurs variables en dessous de la limite d'action des vagues de tempête. On distingue les unités (1) FB1b comprenant des pélites noires, des grès intercalaires et des pélites rubanées ou dolomites litées, (2) FB1c formée par l'alternance de black shales et de grès noirs et enfin (3) FB2a caractérisée par les grès massifs ou grès de Poubara. La variabilité verticale est identique dans les différents sondages. Les analyses pétrographiques, minéralogiques et chimiques montrent que ces sédiments ont subi une diagenèse modérée. Toutefois, les effets de cette diagenèse est variable selon les faciès.<br/>Les carbonates sont associés aux black shales, de manière souvent diffuse, ils peuvent s'exprimer en lits et bancs individualisés à Mvengué, mais également en concrétions sur le site de Moanda, où elles apparaissent sur une épaisseur de 12 m intercalées dans les niveaux de black shale de l'unité FB1c. Ces concrétions, ovoïdes à lenticulaires, de taille centimétrique à décamétrique, forment des alignements au sein de 8 niveaux successifs. Quelle que soit leurs formes, leurs relations géométriques avec les lamines de l'encaissant black shale argue en faveur d'une mise en place dans un sédiment encore meuble, bien avant le début de la compaction. En se développant les concrétions ont incorporé une fraction argileuse semblable à celle de l'encaissant et dont la composition est relativement homogène depuis leur bordure externe jusqu'à leur centre. Les analyses isotopiques du carbone et de l'oxygène de la phase carbonatée et du carbone de la phase organique ainsi que les relations morphologiques et texturales indiquent que la dolomitisation ayant générée ces concrétions s'est effectuée durant les premiers stades de la diagenèse et a été favorisée par l'oxydation bactérienne de la matière organique conduisant à l'augmentation de l'alcalinité des eaux interstitielles des sédiments. / The Paleoproterozoic (2.1 to 2.0 Ga) Franceville Basin, South-east of Gabon, has been studied for decades for its high metalliferous (primarily uranium and manganese) potential. The discovery of the oldest known macro-multicellular organisms in the FB Formation in the basin in 2010 caused a repositioning of the appearance of complex multicellular life to 2.1 Ga in Earth history. This period is synchronous with great upheavals that affected the global chemistry of the atmosphere and oceans, and corresponds to the deposition of the FB Formation in the Franceville Basin. Core samples from the FB Formation were sampled from the centre of the basin (MVengué syncline) and the western flank of the basin (Moanda) for comparative analyses. The objective of this study is to provide new information on precipitation conditions of the early diagenetic carbonate cements and concretions associated with the organic-rich black shales and siltstones in the FB Formation using facies analyses, petrographic, and geochemical techniques.<br/>At the basin centre, the FB Formation is composed of sedimentary units that reflect deposition in a deep marine environment with variable depths below the limit of storm wave actions. Three units can be distinguished: (1) FB1b consisting of black shales, fine grained sandstones, and laminated mudstones or layered dolomites; (2) FB1c consisting of alternating black shales and sandstones; and (3) FB2a that is characterized by massive sandstone (namely the Poubara sandstone). Detailed analytical studies showed that these sediments have undergone moderate diagenetic modifications. However, the degree of diagenesis varies between different lithofacies.<br/>The carbonates are commonly diffused within the associated black shales throughout the FB Formation. In addition, at the Mvengué, the carbonates are present as individual beds, and as ovoid to lenticular centimeters to tens of centimeters thick concretions at Moanda, where they occur interlayering the FB1c black shales at eight levels. Irrespective of their form of occurrence, their relationships with the laminated black shale argues in favour of their formation before significant compaction. As a result, the incorporated clay minerals in the concretions are similar to the host rocks (black shales) and their composition is relatively homogenous from the edge to the centre. Isotope analyses of carbon and oxygen in the carbonates and of carbon in the organic matter, as well as the morphological and textural relationships suggest that the dolomitiation processes at the origin of the concretions, occurred during the early diagenetic stage, were favoured by bacterial oxidation of organic matter resulting in increasing pore water alkalinity in the sediments.

Iron (oxyhydr)oxide concretions in the Navajo Sandstone of southern Utah have been extensively researched as Martian analogues. However, the discovery of calcium carbonate concretions in areas such as Coyote Gulch, Utah, has encouraged recent studies to understand the relationship between calcium carbonate spheroidal concretions as possible precursors to iron (oxyhydr)oxide concretions, and to determine the fluid chemistries involved in diagenesis. This is important because nucleation and precipitation mechanisms of these spheroidal calcium carbonate and iron (oxyhydr)oxide concretions and fluid mechanisms in iron rich environments could affect the preservation of possible biosignatures in other subsurface features on Mars. The elemental and mineralogical compositions of the concretions were examined in order to determine physical and chemical features shared by the two types of concretions and did show that they share similar morphologies; however, the Coyote Gulch concretions are calcite cemented (~30 wt.%), with secondary iron (oxyhydr)oxide precipitation and decreases in calcite in transects away from the calcium carbonate concretions. Several chemical and mineralogical differences exist between the two separate populations of concretions, possibly due to regional variability of reacting phases in fluid systems. Spring fluids emanating from the Navajo Sandstone in Coyote Gulch were tested to determine the fluids responsible for the development of any of the concretion mineralogies in the study area which could form in distinctive geochemical systems. Geochemical modeling performed in this research explored the question of fluid chemistry involved in concretion formation in the Navajo Sandstone and findings suggest that the calcite concretions formed prior to the precipitation of secondary iron (oxyhydr)oxides and may have provided a localized buffering environment for the precipitation of iron (oxyhydr)oxides. Paleofluid circulation, redox processes, and elemental mobility are examined using the geochemistry of Navajo Sandstone concretions and host rock. Various simulations applicable to diagenetic fluids in the studied concretions show the importance of salinity and pH in paleoaquifers in order to precipitate mineral assemblages similar to those found in the Navajo Sandstone. Widespread dissolution features, major and trace element distributions, and geochemical modeling identified feasible fluid-rock interactions in paleofluids, including the importance of limited H2S gas and the limited feasibility of hydrocarbon rich fluids in concretion formation using current data. A universal mechanism for calcium carbonate to iron (oxyhydr)oxide concretion formation could be applied on other planets and provide exciting implications in the search for carbon rich redox gradients which could support life in the subsurface of otherwise inhospitable planets.

This thesis is focused on the methodes of crushing kidney’s concrements with continual wave for the frequency 27 kHz and the intensity of ultrasound 10 W/cm2. The main aim is design of the ultrasound head with layer converter and design circuitry. First part of this work describes physical principle of ultrasound, ultrasound waves and methods by which could be remove kidney’s concretions. Practical part of this work is focused on compreshive design of ultrasound crushing system. In the introdiction is analyzed the proposal of applicator and the next step decscribing proposal excitation generator. The work contains results of simulation which was done on proposal curcuit, drawings of scheme, list of components and drawing of PCB.