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

tel-00790852, version 1 - 21 Feb 2013
F. Bache et al.
Deposition of the central evaporites (Lower, Mobile
and Upper units: Lofi et al., 2011; total thickness: up to
2800 m) requires a continuous input of marine water at
the beginning of Step I of reflooding, before the brine
concentration reached a critical threshold (Fig. 22). However,
it is not excluded that some halite was deposited earlier,
i.e. during the sea-level drawdown, and was mixed
with detrital deposits. In fact, it can be assumed that two
phases are distinguishable and in close succession (Bache
et al., 2009): (i) the main erosion phase coeval with the
sea-level drop and deposition of detrital material in the
almost desiccated basin and (ii) deposition of the major
part of evaporites during the beginning of Step I of reflooding,
a phase during which fluvial erosion continued on
lands and margins. Using modelling, Govers (2009) suggested
that most of the evaporites were deposited before
sea-level drop. Our data contradict this conclusion
because the MES and related detrital products underlie
the central basin evaporites (Bache et al., 2009; Montadert
et al., 2011), which thus formed after sea-level lowering.
Also using modelling, Meijer & Krijgsman (2005)
concluded that there were repeated desiccations and
re-fillings of the Mediterranean, based on the supposed
correspondence of the exposed Sicilian Upper Evaporites
and the Upper Unit in the central basins. We
oppose this hypothesis too on the basis of the observed
relationships between seismic units in the central basins
(Bache et al., 2009; Montadert et al., 2011). Duration
of evaporite deposition in the central basins, especially
the thick halite, was probably brief (