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

tel-00790852, version 1 - 21 Feb 2013
This study also demonstrated an abrupt change of the subsidence around Km 200 (on ECORS
profile). From 30 Km onshore to this point, the subsidence corresponds to a strong tilt of the
margin (1.44° of tilt since the beginning of salt deposition at 5.6 Ma). This area of strong tilt
on the slope is located in the domain II of highly thinned continental crust just above the Treflector
described by De Vogt et al., 1991. From Km200 seaward, the subsidence of the
margin is nearly vertical allowing the preservation of the tabular salt. The value of total
subsidence may have reach up to 1070 m/Ma in the center of the Basin. The point at Km 200
falls in the Domain III above the “undetermined crust” between the strongly thinned
continental crust domain II and the oceanic crust domain IV (Bache et al., 2010). Further
studies and modelling will need to investigate the detailed relation between these
observations.
Such high and vertical subsidence rates in the center of the basin allows the deposition of
thick amount of sediments that do not fit classical conservational extensional models as has
been also observed in much older open ocean, like the South Atlantic (Moulin et al., 2005;
Aslanian et al., 2009) leading to new models for the evolution of margins (Aslanian et al.,
2009 ; Bache et al., 2010).
8. Conclusions
The seismic shows that our studied area subsided regularly without substantial local
deformation nor variations in rates; this enables us to propose a model for the
subsidence with a linear and constant tilt during Plioquateranry. The rate increases with
the distance from the Coast, the rotation point is located 13 Km landward of the coast, it
reaches a rate of 250 m/Ma at 70 km from the coast, for the last 5,3 Ma, i.e. with an
angle of rotation of 0.88° for the last 5 Ma. The same measurement on a larger scale
(Ecors profile) also show an inclined base of salt surface up to Km 200 with an angle of
1.41° for the last 5,6 Ma. From 200 Km seaward there is a break in slope, subsidence is
nearly constant and vertical from this point to the central part of the Provence basin
where it may reach 1070 m/Ma for the last 5.6 Ma. The total subsidence rates are very
high in the Gulf of Lion and allow an extremely detailed record of climate history and
consequences on the sedimentary system (erosion/deposition). This work needs to be
further extended in space and time to provide full 3D description of subsidence history
of the margin. Ideally, IODP drillings on the shelf and in the deep Gulf of Lion would
enable to better constrain this scenario of subsidence quantification.