Quantification des flux sédimentaires et de la subsidence du bassin ...
Quantification des flux sédimentaires et de la subsidence du bassin ...
Quantification des flux sédimentaires et de la subsidence du bassin ...
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tel-00790852, version 1 - 21 Feb 2013<br />
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formed in a very short time at the beginning of the Messinian drawdown, when the shelf was<br />
already exposed to subaerial erosion but before the almost compl<strong>et</strong>e <strong><strong>de</strong>s</strong>iccation of the basin.<br />
Further observations support a <strong>de</strong>position of Messinian evaporites in the Provence Basin after<br />
the main Messinian sea-level drawdown. The MES is commonly <strong><strong>de</strong>s</strong>cribed as extending<br />
below the salt (MU) in the Gulf of Lions (C<strong>la</strong>uzon <strong>et</strong> al., 1996; Lofi <strong>et</strong> al., 2005). Lofi <strong>et</strong> al.<br />
(2005) suggested that the MES could also be traced at the base of the Lower Evaporites (LU1)<br />
based on the on<strong>la</strong>p termination of their seismic reflectors. Our observations highlight that the<br />
most significant erosion in the basin is located at the base of Dm prisms (Fig. 3). Erosional<br />
surfaces have been observed within the evaporitic units (LU1-MU-UU) but of lesser<br />
significance, suggesting that a huge sea-level drawdown after a first stage of evaporite<br />
<strong>de</strong>position un<strong>de</strong>r a significant water column is unlikely.<br />
An Upper Miocene tectonic phase has also been highlighted in the western part of the Gulf of<br />
Lions (Mauffr<strong>et</strong> <strong>et</strong> al., 2001). Lofi <strong>et</strong> al. (2008) suggested that this episo<strong>de</strong>, probably<br />
accompanied by an increase of c<strong>la</strong>stic sediment supply, is a possible origin for the formation<br />
and subsequent filling of the submarine canyons observed within Dm prisms. In or<strong>de</strong>r to<br />
<strong>de</strong>cipher the tectonic and eustatic origin of theses canyons, the same authors suggested<br />
looking for the existence of submarine canyons on the eastern Gulf of Lions which was not<br />
affected by Upper Miocene tectonics. The i<strong>de</strong>ntification of Dm prisms and of their basal<br />
incision in the eastern part of the Gulf of Lions (Fig. 3; see also Bache <strong>et</strong> al, 2009) allows to<br />
discard such a tectonic hypothesis.<br />
Observation of c<strong>la</strong>stic <strong>de</strong>posits beneath the central evaporites in the Gulf of Lions provi<strong><strong>de</strong>s</strong><br />
new perspectives for the interpr<strong>et</strong>ation of pre-evaporites <strong>de</strong>posits elsewhere in the<br />
Mediterranean. Dives have been performed offshore the region of Nice where a Messinian<br />
low sea-level d<strong>et</strong>ritic cone has been <strong><strong>de</strong>s</strong>cribed by Savoye and Piper (1991) who did not<br />
provi<strong>de</strong> clear re<strong>la</strong>tionships b<strong>et</strong>ween d<strong>et</strong>ritals and the central evaporites. The c<strong>la</strong>stics are<br />
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