Quantification des flux sédimentaires et de la subsidence du bassin ...

tel-00790852, version 1 - 21 Feb 2013
the slope, would go through 6,2 km of sediments deposited during the last 23 Millions years, down
to the substratum. This drilling imposes the use of a drill ship equipped with a BOP (Blow Out
Preventer) in order to go through the 1 km thick Messinian salt layer that has never been reached.
The project gathers a large range of Marine Science disciplines (geology, microbiology, geochemistry,
geophysics, biology) as well as Engineering Sciences (instrumentation, signal processing)
• Major challenges and innovative aspects
The major challenges of this drilling project are focused around 6 major scientific, social and
economic themes
1) Greenhouse gases storage: the drilling would enable to estimate potential greenhouse gases Storage
in sandy reservoirs located below the Messinian salt layer, in the deep offshore of the Gulf of Lion
in an area near major north Mediterranean industrial centres (Marseille-Fos, Barcelone).
2) Energy Ressources: the drilling below the salt would enable to evaluate potential hydrocarbon
resources in the Mediterranean Sea. The only well know source rock is Messinian in age and are
generally immature in most of the Algero-Provencal basin. We need to explore deeper and older
series (Aquitanien, Burdigalien, Langhien et Tortonien). On another hand, the drill site also offers
strong potential for geothermal energy. The concentration of Lithium in the thick evaporites layer
(3000 m) should also be evaluated.
3) Climate and Sea-level changes: the Gulf of Lion is a unique place to study exceptionnally wellpreserved
sedimentary archives. The quantity of sediments deposited is directly dependant on the
existence of the northern hemisphere Ice sheet, and its variations in size and thickness. These
variations are related to climate changes, so that we can read glacioeustatic cyclicities in teh
sediments. This has been demonstrated using a dense grid of seismic lines for the last 500 000 years
and validated by the shallow Promess drill site on the shelf. The new very deep drilling would
extend this type of results to the last 23 Ma.
4) Geodynamic, thermicity and margin formation: The formation of the sedimentary basins and
continental passive margins have long been explained by numerous physical models, usually built on
only one passive margin considered as the reference. However, The recent ante-salt discoveries,the
presence of carbonate at the end of the passive margin building… demonstrate that these models fail
usually to fit the observations. Passive continental margins are so diverse that the existence of a
unique thinning process must be re-considered and discussed. However, the recurrence of some
general features (abrupt thinning, large transitional domain, whatever the nature of the crust
oceanic, continental or mixed) pleads in favour of general rules. No margin presents all the features
needed to support a general model, but each margin supplies pieces of the jigsaw. Drilling the
substratum of a deep margin, studying the paleo-envirronement of the first deposits in order to
reconstruct the geodynamic history of this margin, is not common. Few places have already been
drilled in that purpose. None of them occurs in a young Basin, built in a back-arc context. We need
this information to understand the thinning of the continental crust, the building of the passive
margins and the continental basins. What is the nature of the crust in the intermediate domain? In
what kind of environment are the first sediments deposited? The drilling will offer the ground-truth
necessary to constrain models of margin formation and subsidence and their consequences on
potential hydrocarbon resources.
5) Deep Biosphere and the limits of Life: What is the maximum depth where life exists? What form does
it take ? Today’s maximum depth where signals of life have been proven is 1626 m below sea-floor,
but this is only the maximum depth where life has been searched for. The deep drilling (7.7 km) is a
unique opportunity to constrain the physicochemical limits of life in extreme conditions in terms of