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Oceanic anoxic events (OAEs) are periods in Earth's history when oceans were depleted in dissolved oxygen and characterized by deposition of organic-rich sediments. The Oceanic Drilling Program (ODP) has drilled through OAEs in a number of areas worldwide, collecting core and borehole log data. This project attempts to identify a characteristic signature from known ODP OAE sections using these data and to apply the signature to identify OAE intervals in Gulf of Mexico wells where cores are lacking. Additionally, pseudo density curves were generated from ODP logs and compared to bulk density logs to determine if the deviation between the two would aid identification of OAE intervals. A general, though not fool proof, signature of high gamma ray, uranium, neutron porosity and low density was seen in nearly all of the ODP holes. Using this signature 20 potential OAE intervals were identified in the Gulf of Mexico.

Small fragments of artificial polymers (microplastics, MPs) has been reported for multiple environmental matrices from our planet. The omnipresent existence of these microplastics even in remote polar areas have raised concern about their potential environmental impacts and created a need for effective and standardized analytical methods targeting their detection in environmental samples. So far, no methods have been developed for detecting microplastics in organic-rich soils. In this master thesis, I evaluate two analytical methods (both based on canola oil extractions) targeting microplastics in two contrasting soil matrices; one mineral rich (sandy mineral soil from a Podzol) and the other by organic matter (sample from a Histosol). I hypothesize that the detection of microplastic has a bias that depends on specific plastic particle properties (size, polymer type and morphology) as well as on the organic content of soil samples. My results show that the recovery of added plastics is strongly dependent on particle size and diminishes with decreasing microplastics length. This result was repeated by both extraction approaches.  Polymer shape and soil characteristics (organic matter content) affect MPs recovery if oil extractions are conducted without pre-treatment (oxidation) step. Here, fibers proved most difficult to detect and low recoveries suggested that the method was not applicable to organic rich samples. The addition of a pretreatment step including oxidation with sodium hypochlorite improved recoveries for organic rich samples and removed the effect of soil type and polymer shape. Hence, the use of a pretreatment is essential to extract MPs from organic-rich soils, but it also decreases the overall recovery for all type of studied polymers and mostly fibers. My study suggests that there is a substantial bias when detecting MPs in soils that is causing a general underestimation, especially for small, fibrous particles in organic rich soils.

Les hétérogénéités de répartition de la matière organique (MO) du Crétacé de l'océan Atlantique central sont souvent liées à des facteurs d'ordre géodynamique et paléocéanographique. Or, la forte proportion de MO terrestre questionne l'hégémonie de ces mécanismes et appelle à mieux contraindre la dynamique sédimentaire des dépôts associés à cette MO. Par une approche source to sink couplant une étude géochimique de provenance à une étude de bassin à partir de données de subsurface, nous montrons une réorganisation du drainage sur les cratons ouest-africain et guyanais, caractérisée par une extension progressive des bassins versants vers les domaines internes pendant le Crétacé supérieur. En Afrique, ce processus s'accompagne d'un arrêt de la dynamique turbiditique dès le Turonien, et d'une diminution de celle-ci au Guyana Suriname. Dans les deux cas, ces changements ont été défavorables à l'accumulation de matière organique en domaine océanique profond. / The distribution heterogeneities of Cretaceous organic matter (OM) in the Central Atlantic Ocean are often related to geodynamic and paleoceanographic factors. However, the high proportion of terrestrial OM questions the hegemony of these mechanisms and shows the need to better constrain the sedimentary dynamics of organic-rich sediments. Using a source-to-sink approach coupling a geochemical provenance study with a basin study from subsurface data, we show a reorganization of drainage on the West African Craton and the Guyana Shield, characterized by a gradual extension of watersheds to the inner areas during the Upper Cretaceous. In the African deep basin, this process is coeval to a break of the turbiditic sedimentation from the Turonian and to its decrease in the Guyana-Suriname deep basin. In both cases, these changes were unfavorable to the enrichment of OM in the deep oceanic domain of the Central Atlantic.

L'éventail sous-marin profond du Congo, situé sur la marge continentale Congo-Angolaise (côte Ouest Africaine, Océan Atlantique Equatorial Sud) représente un écosystème sédimentaire marin profond unique.Celui-ci est caractérisé par de forts apports en matière organique provenant du fleuve Congo, qui se déversent le long du canyon et au travers de systèmes chenal Jevées actuels jusque dans les zones les plus profondes (5 000 m) où se développe le système des lobes.L'objectif de cette thèse est d'étudier la distribution spatiale et la diversité phylogénétique et fonctionnelle des communautés archéennes et bactériennes en relation avec les caractéristiques et les contraintes de I'environnement.Cette étude a permis de mettre en évidence une distribution géographique régionale et locale des communautés microbiennes contraintes par la distance des différents lobes par rapport à l'embouchure du chenal. La distribution des communautés microbiennes est liée à la disponibilité en accepteurs et donneurs d'électrons issus de la diagénèse précoce de la matière organique. La composition et l'identité taxonomique de ces communautés microbiennes sont comparables aux communautés rencontrées dans des sédiments marins et des zones d'émission de fluides froids riches en méthane.Cette étude révèle également des densités cellulaires relativement élevées de bactéries méthanotrophes aérobies associées à différents habitats sédimentaires particuliers, colonisés par des bivalves Vesicomyidae, des tapis microbiens et des sédiments réduits caractéristiques des environnements d'émissions de fluides froids riches en méthane et hydrogène sulfuré. Ces communautés sont non seulement apparentées à celles rencontrées dans des habitats d'émissions de fluides froids, mais également à celles des habitats terrestres, malgré la distance ~ 1000 km des côtes Africaines.Les travaux menés au cours de cette thèse montrent l'intérêt des études pluridisciplinaires pour comprendre la diversité et le fonctionnement des écosystèmes dans les lobes terminaux du système turbiditique du Congo et apportent de nouvelles informations sur la diversité des microorganismes peu explorée dans les éventails sous-marins profonds. / The Congo deep sea fan, located in the Congo-Angola continental margin (West African coast, Equatorial South Atlantic Ocean) represents a unique deep-sea sedimentary ecosystem. It is characterized by high organic matter inputs from the Congo River, that flow along a canyon and through presently active channel system-lifted into the deeper areas (5 000 m) where the lobes system develops.The aim of this thesis is to study the spatial distribution as well as the phylogenetic and functional diversity of archaeal and bacterial communities in relation with environmental characteristics and constraints of the terminal lobes of the Congo deep see fan, one of the largest submarine fan systems in the world.This study highlights geographical distribution of microbial communities constrained by the distal and proximal distance of the different lobes from the Congo river's channel mouth as well as linked to the electron donor and acceptor availability from organic matter diagenesis. This study revealed quite high abundance of aerobic methane oxidizing bacteria cells at peculiar sedimentary habitats dominated by Vesicomyid bivalves, microbial mats and reduced sediments typical of cold-seep environments. These communities are not only related to the ones encountered in cold seeps, but also to the ones in terrestrial habitats despite an approximately distance of 1000 km offshore the African coast.This thesis underlines the interest of pluridisciplinary studies to understand the ecosystem diversity and functioning in the terminal lobes of the Congo turbiditic system and provides further insights into the underexplored microbial diversity from deep-sea fans.