PhD studentships 2019

PhD studentships contracts for this year. You can apply for to scientific persons in charge.

1) Submarine landslides in the St. Lawrence Estuary, Québec, Canada

Supervisor:  Nabil Sultan (Nabil.sultan@ifremer.fr) et Guillaume St-Onge (guillaume_st-onge@uqar.ca)
Co-supervisor: Sébastien Garziglia (Sebastien.Garziglia@ifremer.fr)

There are several known seismic zones in Canada including one of considerable size in the east of the country, known as Charlevoix-Kamouraska/Bas-Saint-Laurent – CKBSL. To reduce the risks associated with seismic hazard (loss of human life, deterioration of infrastructure, submarine landslides, tsunamis), we face the major challenge of furthering our comprehension of their behaviour. Current knowledge on the hazard in the area lacks precision as it is based on a restricted number of earthquakes, mainly only those recorded since 1663. This thesis aims at identifying and dating submarine landslides already recorded for the estuary of Saint-Laurent and characterizing the geotechnical properties of intact sediments in order to determine the origin, cause and recurrence of observed landslides. Based on the considerable seismic activity in the area and the great number of submarine landslides and their geographical scope, we put forward the possibility that they are caused by earthquakes. If we are able to verify this hypothesis, the implications would be far-reaching as it is essential we have a clear understanding of the earthquakes in this region and their impact to determine hazard events and their return period. To assess the seismic hazard in accordance with the new requirements of the building codes of Canada, we are required to consider a return period of 2500 years. However, this data is quite simply non-existent.

Keywords: Submarine landslides, earthquakes, hazards, sediment cores, geophysics, geotechnical analysis, Holocene, Québec, Canada.

2) Physical-chemistry investigation of hydrate-bearing sediments: Impacts of the sediment on the formation mechanism and the storage capacity

Supervisor: Arnaud Desmedt (Arnaud.desmedt@u-bordeaux.fr)
Co-supervisor: Livio Ruffine (Livio.Ruffine@ifremer.fr)

Gas hydrates are crystalline materials in which water molecules form networks trapping gaseous molecules. These hydrates have a very large gas storage capacity. In Nature, hydrates consist mainly of methane. They are found within the permafrost in polar regions and in the marine sediments of continental margins. They are by far the largest reservoir of methane on the planet, and sediment hydrates account for about 98-99%. However, the assessment of the amount of gas stored in sedimentary hydrates is based on macroscopic considerations, assuming a constant filling rate of the cages by gas molecules. Recent findings show that this rate is variable and that several cages may remain empty.
This thesis proposes to investigate the factors that can affect the filling rate of cages, and therefore the ability of hydrates to store methane. The planned work aims to (2) synthesize gas hydrates in the laboratory by mimicking their natural environment, and (2) characterize the resulting samples at the microscopic scale by Raman spectroscopy, diffraction (neutrons and X-ray) and very high resolution X-ray tomography techniques to determine the structures formed, the cage-occupancy rates, the nature of the host molecule as well as the impact of the sediment / hydrate interface on these properties. These results will provide information on the storage capacities and heterogeneities encountered. All these data will provide improved insights into the estimate of the quantities of gas stored. From a multi-scale approach, these laboratory experiments will be compared to the measurements from natural samples taken at selected geological settings (Sea of Marmara, Black Sea or Lake Baikal).

Keywords: Methane hydrates, clays, sand, formation mechanism, cage occupancy and gas storage capacity, high-pressure experiments, spectroscopy, diffraction, chemical analysis.

3) In situ characterization of gas plumes by coupling acoustic and chemical measurements: a methodological development

Supervisor: Emmanuel Rinnert (Emmanuel.Rinnert@ifremer.fr)
Co-supervisor: Carla Scalabrin (Carla.Scalabrin@ifremer.fr)

The European project ETN-ITN ASSURE includes 14 Ph.D. thesis topics aimed at studying the impact of the extractive industry (hydrocarbons, metals, sands, etc.) on the physical and biological ecosystems associated with deposits. The objective is to propose complementary subjects, combining scientific issues and technological developments, the whole of which makes it possible to characterize, quantify emissions and propose solutions to reduce or even stem them. This Ph.D. thesis subject is coordinated by Ifremer in collaboration with IOLR and Kongsberg Maritime Contros. It aims to carry out experimental studies to allow a quantitative characterization of the methane emissions in the water column. It puts in place a methodological approach to provide (1) results on the evaluation of the effectiveness of detection tools and (2) protocols to define an optimized strategy for the measurement and characterization of underwater emissions of methane. The originality and the innovative character reside mainly in an in-depth evaluation of the sensors in the laboratory under conditions similar to those encountered in-situ in order to study the influence of 'key' parameters on the sensor response, supplemented by seawater tank experiments, always under controlled conditions, for the acoustic and chemical characterization of an artificial emission of gaseous methane. The expected results will allow a better appreciation of the robustness and accuracy of the measurements and a quantitative characterization of the behavior of gas emissions in the water column. The fields of application are the estimation of the methane budget, which is useful for both the scientific community and the hydrocarbon industry.

Keywords: Methane sensors, in situ mass spectrometer, acoustics, laboratory experiments, sea-water tank experiments, marine seeps.

4) Mesozoic-Cenozoic evolution of the southeastern margin of South Africa: A history of transtentional rifting, uplift and subsidence, and sea-level changes

Supervisors: Marina Rabineau (Marina.Rabineau@univ-brest.fr) et Philippe Schnurle (Philippe.Schnurle@ifremer.fr)
Co-supervisors: Daniel Aslanian (Daniel.Aslanian@ifremer.fr) et Moctar Doucouré (Moctar.Doucoure@mandela.ac.za)

At the boundary between the South Atlantic and the Indian Oceans, the austral African margin is composed of four hemi-grabben-style rifts connected by the deeper Unteniqua Basin, fringed to the south by the Agulhas Fracture zone. This South Africa rift system (SARS) is part of Jurassic-Cretaceous Rift basins, which presents a serie of structural faults, inhereted from the East-West elongated Cape Fold Belt, and bended towards the South in their eastern extremities. The SARS seems to be connected with the Kimmeridgian phase, which produced the first oceanic crust in the Indian Ocean with the southward movement of the East Gondwana blocks. The rifts system seems to end at Valanginian time with a westwards jump, whilst the South Atlantic Ocean started to open. The SARS is therefore a buffer zone between two geodynamic settings of two kinematic phases. It is also a failed pull-apart margin between a strike-slip margin to the east and a volcanic margin to the west, in the Orange Basin. It represents a good, non-deformed example of the first phase of the passive Margin genesis, just before the exhumation phase. Last, the entire Rift system is present onshore and offshore, until the deeper Outeniqua Basin: this study will focus on the differences in subsidence, depositional environment, lateral facies variations, and on the role of deep processes and geodynamic in the Passive Margin genesis.

Keywords: Passive margin genesis - aborted rift; geodynamic, kinematic phases and deep processes, subsidence and uplift, connexion onshore-offshore, kinematic buffer zone.