Sedimentary systems, environments and dynamics
Team leader: Emmanuelle Vennin
The SEDS team includes twelve faculty members, working on four research axes with many overlapping areas.
Transfer of matter in past and present systems;
Origin and diagenesis of carbonate reservoirs;
Interaction between the stratigraphic record and continental lithosphere deformation.
Matter transfer in past and present systems
The objectives of this research axis are to characterise and quantify transfer processes, as well as their kinetics. The goal is to determine the response of such phenomena to tectonic, climate and anthropogenic forcings, on both long and short timescales. This entails the study of systems actively producing sediment today and receptor systems which record past processes. Sediment budget and transfer timescales are defined as follows:
- Short timescales: from an instantaneous event to tens of thousands of years.
- Long timescales: from hundreds of thousands to tens of millions of years.
The methodology includes data acquisition, treatment and analysis. Types of data :
- measurement in situ (biophysicochemical analyses, sediment traps, continuous measurements, geophysical imagery)
- experimental (vertical transfer in soil columns);
- field study (mapping; sedimentological logs);
- digital cartography (aerial and satellite photography, DEM) combined with GIS analysis
- Numerical modelling of transfers.
The notion of hot, homogeneous climates on a global scale during the Mesozoic was generally accepted in the early 1980s. However, over the last decade, high-resolution sedimentological and geochemical studies carried out on deposits from high palaeolatitudes have challenged this notion.
The inventory of markers of the presence of ice in high palaeolatitudes (tillites; dropstones) or of cold-water masses (glendonite) has revealed the existence of colder periods within a greenhouse-type context.
The aim is to understand the reasons for changes in the climate system and the carbon cycle during these periods. What were the mechanisms involved? What retro-actions came into play? How long did these cold periods last? Were they systematically marked by the development of aridity? Did they reply to a single mechanism or do they present specificities? How do these cold periods fit within the global geodynamic framework?
This study focuses on the following Jurassic and Cretaceous periods:
- the Pliensbachian/Toarcian
- the Berriasian-Valanginian
- the Late Barremian and Early Aptian
- the Middle/Upper Turonian boundary
There are three aspects to the research:
- Highlighting palaeoclimatic crises during the Jurassic and the Cretaceous
- Confronting results with climate models
- Exploring the causes of these climate crises and their consequences on biodiversity
The team also explores the influence of explosive aerial/subaerial volcanism on the biogeosphere: climate impact, disruption of geochemical and biogeochemical cycles, biological crises, internal and external geodynamic relationships
Origin and diagenesis of carbonate reservoirs
The aim is to understand the installation (sedimentogenesis) and post-sedimentary evolution (diagenesis) of sedimentary bodies likely to contain water, oil or gas. This is an important issue with implications not only for the current and future management of energetic or hydrological resources, but also for the management of potential greenhouse gas sinks. In these domains, over many years, the Biogeosciences Joint Research Unit has acquired considerable experience in the study of porous sedimentary bodies composed of neritic marine carbonates. This experience is borne out by many joint ventures with private or public organisms (TOTAL, Gaz de France, IFP, ANDRA, and BEICIP) and by the number of doctoral candidates who find employment rapidly on completion of their PhD studies in this field.
The main research questions focus on the following areas:
- the production and redistribution of calcarenites on platform/basin and ramp/basin transects;
- an understanding of the laws of chemical and/or biochemical precipitation of neritic carbonates through the use of software modelling basin infilling (Dyonisos), and software modelling the petrophysical characteristics of reservoirs (Heresim)
- the influence of the original facies and early diagenesis on diagenetic evolution during burial (the example of the influence of low clay concentrations on processes of pressure dissolution and cementation).
Interaction between the stratigraphic record and deformation of the continental lithosphere
The stratigraphic record of a sedimentary basin reveals the evolution of the Earth's relief in response to lithospheric deformation and/or climate variation. Reading the stratigraphic archive of a sedimentary basin (palaeoenvironment and time) is of fundamental importance for the analysis of ancient lithospheric deformations. The current scientific objectives of many teams are the method of deformation of the continental lithosphere, in the context of continental collision and rifting. Few studies are interested in the long-term behaviour of continental lithosphere in a reputedly stable cratonic domain.
The African continent has been marked by remarkable tectonic stability for the past 600 My, with the exception of the Atlasian collision zone in the north and the East African rift zone in the east (Figure 1). The African lithosphere does not have a homogeneous composition. It associates Archaean cratons with terranes which accreted at the time of the Pan-African event. Because of its characteristics (stability and heterogeneity), the African lithosphere is an excellent example to comprehend and document the mechanical behaviour of a stable lithosphere.
The research axis focuses on three main projects/sites. It concerns the mechanical behaviour of the African lithosphere in response to the following forcings:
- tectonic forcing (push at oceanic ridges);
- climate forcing (volume forces linked to the installation and melting of an ice-cap);
- tectonic and climate forcings on a vast timescale (300 Ma).
The basic methodological approach, from the study of deformation markers and stratigraphic archives (2D-3D geometry, accommodation, sedimentary provision, and time), aims to analyse the interactions between the stratigraphic record and lithospheric deformation as well as the response time of sedimentary systems to the three types of forcing.
last update: november 2007