MES
Time (sec TWTT)
PQ 1
MIOCENE
2
PRE-RIFT BASEMENT Figure 3.6. Dip profile LRM96-08 (Total) illustrating the presence of the Messinian Margin Erosion Surface (MES) beneath the shelf.This discordance corresponds to a prominent unconformity with a strong erosional character. It is downlapped by Plio-Quaternary reflections. A high angular discordance between tilted and faulted Miocene deposits and Plio-Quaternary deposits is commonly observed. The MES is extremely rugged, displaying high relief beneath the inner and middle shelf (see also fig. 3.8) and becoming smoother basinward (fig. 3.8 & Z3.2).
0
SW
MSC valley
Time (sec TWTT)
0
MSC interfluve
MES
5 km MSC valley
NE
PQ
1
MIOCENE
PRE-RIFT BASEMENT
Figure 3.7. Strike profile LRM96-15 (Total) illustrating the morphology of the MES at the bottom of the Plio-Quaternary sequence, with 2 paleo-MSC valleys now buried beneath the inner shelf [modified from Lofi et al., 2011].
Time (sec TWTT)
3
extensional structures
5 km
BES
TS
UU
SE contractional structures BS/BES LU
Salt tectonics
MU
ork etw 4
. Fig
6
Fig
MIOCENE
0
1 km
NE
2.4
NW
0
1 km
SE
0
SW
1 km
Inner shelf: the MES is highly erosional at the bottom of the Plio-Quaternary sequence. Here, a sub-horizontal plateau incised by a V-shaped fluvial valley.
Z3.2 Middle slope: the MES is smooth and gently dips seaward. Erosion is evidenced by angular discordance and truncated underlying reflections.
3.4
Z3.2
8
Fig
.3
NE
3.4
NW
0
1 km
SE
4.4
NW
0
1 km SE
INTERFLUVE 3.0
Z3.3
+100 0 -200 -400 -600 -800 -1000 -1200 -1400 -1600 -1800 -2000 -2500 -3000 -3500 -4000
.6
0.5
0.8 Z3.1
t-day preeslfenbreak MES sh Depth (m)
3.7
.8
E4°
E5°
Z3.5
Volcanism?
2.8
2
.3
Figure 3.8. Calmar74-75 profile (migrated, IFREMER). The MES extends out downslope to a depth of ~4.0 sec twtt at which UU pinches out. The MES divides into the TS extending at the top of UU and into the BES, extending basinward beneath the UU & MU, and possibly beneath the LU, in onlap. Above, the Plio-Quaternary sequence is faulted due to salt retreat. The onlap point of UU (before salt tectonics) reflects the position of the paleo-shoreline at the end of UU deposition. The most landward fault marks the initial pinch-out of MU, before salt retreat [modified from Lofi et al., 2005]. SW
.1
Z3
5
7
1
3
TS (TOP SURFACE) Seismic facies: high amplitude relatively continuous reflection at the top of UU or CU. Most of the time concordant. Labelled TES when shows evidences of erosion (truncated reflections below, Z3.4). Geometry/spatial organization: at the top of the MSC units (CU, beneath the slope (Z3.3) & UU more basin distally (Z3.5)). Disturbed, faulted, non-flat surface in the basin because of Plio-Quaternary salt tectonics (Z3.6).
Z3.7
Paleo-shoreline before Mediterranean décollement residual MU basin refilling
en ag
E3° MES (MARGIN EROSION SURFACE) Seismic facies: prominent erosion unconformity (see underlying truncated reflections Z3.1 & Z3.2) characterized by a high amplitude, mostly continuous reflection or by an angular unconformity. The MES displays high relief beneath the shelf (figs. 3.4 to 3.7, Z3.1) and becomes smoother basinward (Z3.2), gently diping toward the evaporitic basin (fig. 3.4). Geometry/spatial organization: above the pre-MSC units and below the Plio-Quaternary. It has a widespread extension and displays a fluvial drainage network morphology (fig. 3.4) [see also detailed isobath map in Guennoc et al., 2000]. The MES extends out downslope to ~4.3 sec twtt. Where top of UU pinches out against paleo Miocene slope, the MES divides into the TS/TES and the BS/BES.
PQ
4
5
0
NW MES
Figure 3.5: present-day depth map of the Messinian Margin Erosion Surface (MES) [modified from Clauzon, 1973; Duvail et al., 2005 and Guennoc et al., 2000]. The MES is a widespread erosion surface observed at the bottom of the Plio-Quaternary sequence. The volume of sediment eroded from the western shelf N43° has been estimated to 3.103 km3 which is equivalent to a column of sediment with a mean thickness of 500 m [Lofi et al., 2005]. The morphology of the MES consists of two paleo fluvial networks: the Languedoc-Roussillon system to the West (4: Orb-Hérault, 5: Proto Aude, 6: Berre, 7: Têt-Tech & 8: Rascasse valleys) and the Rhône system to the East (1: Rhône, 2: Durance & 3: Vidourle valleys). Onshore the MES forms deep canyons, transformed into Pliocene rias at the achievement of the crisis [Clauzon, 1973]. Other mapped MSC markers are the N42° complex unit (CU, in grey) and the mobile unit (MU, in yellow).
.3
SE
drainage netwo rk ône h R
Z3
5 km
uedoc-Roussi Lang llon
0
0
NW
dra in
MSC SURFACES
Authors: Lofi J., Berné S. & Gorini C.
VALLEY
Middle slope: the MES is visible in the interfluve. Laterally, the MSC paleo-valley is infilled with clastics (CU). The BES extends below CU and the TES at the top.
4
Z3.4 Lower slope: the TES extends at the top of UU. Erosion is evidenced by some underlying truncated reflections. The BS (locally erosional ?) extends beneath UU.
5.0
Z3.5 Lower slope/basin: BS/BES? extends beneath LU. More basinward, it is clearly conformable with deposits below (Z3.9). TS is at the top of UU.
BS/BES (BOTTOM (EROSION) SURFACE): Seismic facies: angular discordance (Z3.4) or conformable surface (see Z3.9 in "MSC UNITS"). Labelled BES when clearly erosional (truncated reflections, Z3.3). The BS/BES is hardly imaged beneath CU. Geometry: at the base of the MSC units. It has a gullied-type morphology beneath the slope, at the base of CU (Z3.10). Downslope, when CU is absent (fig. 3.8, Z3.5), the BS, locally erosional (BES), extends at the base of LU (in onlap) and progressively becomes conformable.
3.B- GULF OF LIONS
3. GULF OF LIONS
