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

tel-00790852, version 1 - 21 Feb 2013
much higher rate of subidence than that calculated by Ryan (1976). Seranne, 1999 estimates
the average total subsidence as 500 m/Ma.
Bessis (1986), Burrus (1989), and Burrus & Audebert (1990) note an enhanced total
subsidence rate during the Pliocene-Quaternary (5 Ma) in the very deep basin of the Gulf of
Lion that remains largely unexplained and that has also been observed in the Ligurian Sea
(Réhault et al., 1984). Burrus & Audebert, 1990 interpret this increase as related to Alpine
compression.
Bache, 2008 also applied 1D backstripping in the deep Gulf of Lion at the position of ESP
206 (Expanded Spread Profile, see position in fig. 1) (allowing access to thicknesses of the
main units), using the empirical age-depth equation of Parsons & Sclater, 1977. Bache, found
a general post-messinian subsidence (after the refill of the Mediterranean Sea) of around
1100 m for the last 5.3 Ma ; i.e. 210 m/Ma. The same subsidence including the messinian
event, i.e. between 5.96 to present gives a total subsidence of 3,2 km, i.e. : 535 m/Ma
(because of the loading effect of the enormous amount of messinian deposits) (Bache et al.,
2009).
For the Pliocene-Quaternary time-period, Lefebre (1980) realised a cartographic synthesis and
an isopach map of Pliocene-Quaternary deposits at the scale of the Gulf of Lion based on
seismic profiles. He noted the general tectonic stability of the shelf since the messinian.
A conclusion also reached by Lofi et al., 2003 and Mauffret et al. 2001, when studying the
westernmost part of the Gulf of Lion. Most of the faults occur and play in post-aquitanian
sediments and are sealed by the messinian unconformity (Gorini et al., 2005). A late
Miocene-early Pliocene extensional tectonics has been shown in the westernmost part of the
Gulf of Lion, but these faults are active only until the early Pliocene (Mauffret et al. 2001).
We willl come back to this phase in the discussion.
Lefebre, 1980, Genesseaux & Lefebvre (1980) and Guennoc et al. (2000) mapped the
messinian erosional surface on the shelf and showed the effect of the deep cutting of the
messinian Rhône river on the shelf. Guennoc et al. also produced a reconstructed
paleomessinian surface by correcting the present day messinian surface from water and
Pliocene-Quaternary sediment loading. The depth of this reconstructed surface on the slope is
around 1500 m in the vivinity of the GLP2 drillhole, which is also thought to be the position
of the messinian shoreline. Present day depth of the same point (GLP2 is now at 3437 m). On
the Aude-Hérault intefluve a point located at present day at 1800 m has been reconstructed at
600 m). On the inner shelf a point at 1500 m is corrected to 500 m. Note that this surface is
not exactly the surface at time of deposition because thermal cooling (inducing further