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

tel-00790852, version 1 - 21 Feb 2013
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
(Barber, 1981; Barr and Walker, 1973; Chumakov, 1973; Clauzon, 1973, 1978, 1982;
Denizot, 1952; Ryan and Cita, 1978; Savoye and Piper, 1991). This event was the paroxysm
of the Messinian Salinity Crisis (MSC). The well-accepted “desiccated, deep basin” model
(Cita, 1973; Hsü, 1972; Hsü et al., 1973; Ryan, 1973) is based on a demonstrated deep
Mediterranean Sea (over 1500 m) at the onset of its desiccation phase. In the 1990s, the
peripheral Mediterranean basins, easily accessible to field studies, were used to constrain the
timing of the MSC (Gautier et al., 1994; Hilgen and Langereis, 1993; Krijgsman et al., 1999;
Lourens et al., 2004; Van Couvering et al., 2000). These advances have resulted in several
new conceptual scenarios, mostly derived from the initial “desiccated, deep basin” model.
Two groups of conceptual scenarios are usually referred to (Fig. 1): one that favours a
synchronous deposition (at 5.96 Ma) of the first evaporites in all the Mediterranean basins
before the huge sea-level fall (Krijgsman et al., 1999; Rouchy and Caruso, 2006), and the
second that favours a diachronous deposition of the evaporites through two phases of
desiccation (Butler et al., 1995; Butler et al., 1999; Clauzon et al., 1996; Riding et al., 1998).
According to the second scenario, peripheral basins experienced deposition of evaporites (at
5.96 Ma) before the onset of a major sea-level fall and erosion and central basins experienced
deposition of evaporites only after the onset of the sea-level fall. The peak of the MSC is the
phase that begins with the huge sea-level fall and that ends with the catastrophic marine
reflooding (phase 2 on figures). There is a large agreement on the age of the beginning of this
paroxysm phase (5.60 Ma; CIESM, 2008), but its duration is still debated (70 kyrs: Krijgsman
et al., 1999; ca. 140 kyrs: Bache et al., 2012; Butler et al., 1995; ca. 270 kyrs: CIESM, 2008)
as also the age of its end (5.46: Bache et al., 2012; 5.332: CIESM, 2008; Krijgsman et al.,
1999). Anyway, its brevity, together with the magnitude of the associated sea-level variation
(Clauzon, 1982; Savoye and Piper, 1991), make this event quite unique in terms of
depositional processes.
3