Sedimentary systems, environments and dynamics

Team leader: Emmanuelle Vennin

Assistants: Olivier Mathieu et Pierre Pellenard

 

The SEDS team includes twelve faculty members, working on four research axes with many overlapping areas.

Transfer of matter in past and present systems;

Jurassic/Cretaceous palaeoclimates;

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.

 

Jurassic/Cretaceous Palaeoclimates

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:

1. Highlighting palaeoclimatic crises during the Jurassic and the Cretaceous
2. Confronting results with climate models
3. 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