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INTERPRETATION OF SEISMIC PROFILES IN wESTERN-MEDITERRANEAN SEA M. Bellucci1, A. Del Ben1, R. Geletti2, E. Forlin2, M. Rabineau3, E. Leroux3,4,5, D. Aslanian4, R. Pellen2,3

1 Dip. Matematica e Geoscienze, University of Trieste, Italy 2 OGS, Borgo Grotta Gigante-Sgonico, Trieste, Italy3 CNRS, Domaines Océaniques, IUEM, Plouzané, France4 IFREMER, Centre de Brest, GM, Plouzané, France5 UPMC, Univ. Paris 06, ISTEP, Paris, France

Introduction. �he conjugate margins s�stems of the �ulf of Lion and west �ardinia is natural la�oratories to address fundamental questions a�out rifting. In particular, the detailed anal�sis of Messinian evaporites could �e useful to understand man� dou�tful aspects of this event and to provide several evidence on the shallow and deep crustal nature of the �ardo-Provençal Basin.

In this work, an integrated seismic dataset (Fig. 1) has �een interpreted within a colla�oration of Institution located in Ital� and French within a Erasmus �raineeship 2016/2017 of the first author. �he Italian group is composed �� Dipartimento di Matematica e �eoscienze dell’Università di �rieste (DM�) and the Istituto Nazionale di �ceanografia e �eofisica �perimentale (���)� the French group includes l’Institut Universitaire Européen de la Mer (IUEM) and l’Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER).

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Fig. 1 - Position map of the multichannel seismic reflection datasets used in this stud�.

�he Messinian �alinit� Crisis (M�C) is a short-term event at the geological scale (5.96-5.32 Ma, �autier et al., 1994), that take place after closure of connection �etween the Atlantic �cean and the Mediterranean �ea. �he evaporites were deposited in isolated and deep �asins, reaching more than 1000 m thickness a�ove the deep a��ssal plains (Hsu et al., 1973). �he evolution,

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the origin and the characterization of the event is still de�ated. �he stud� of evaporitic series and the relation �etween the post and pre-event sediments are the ke� to tr� to explain this unresolved question.

Previous stud� of reflection/refraction seismic, com�ined to gravimetric and magnetic data, allowed to divided the two associated margins and the �asin in five distinct domains (Moulin et al., 2015� Afhilado et al., 2015). �he domains I and V, on the �ulf of Lion and eest �ardinia margins, respectivel�, correspond to the continental slope domain. �he nature crust of domain III is assumed oceanic. In the center of �asin, the magnetic anomal� pattern is different from the adjacent domains, showing a concomitant low gravit� anomal�. �he domains II and IV are the transitional area, called �C� (�cean-Continent �ransition). �he crust velocities are high and this is still matter of de�ate. �everal h�pothesis have �een proposed, as the exhumation of lower crust material (Bache et al., 2010) or mantle material, serpentinized �� water (Le Douaran et al., 1984).

�he aim of this stud� is the anal�sis of several seismic profiles in order to correlate the different seismic evidences of the M�C markers across the margins and the �ardo-Provençal �asin. Furthermore, the work tries to explain if a correlation �etween the deformation of salt domes and the crustal domains reall� exists.

Geological setting. �he central-western Mediterranean consists of a su�-�asins series, developed from �ligocene time onward in the context of �ack-arc extension contemporaneous to the eastward to southward roll-�ack of the originall� W-directed Apennine-Maghre�ide su�duction zone (Carminati et al., 2010� Rehault et al., 1984). During �ack-arc spreading, �locks moved radiall�, from NE-ward to southward, and rotated �oth clockwise (southern arm, African Atlas) and counter-clockwise (northern arm). A�out 60° counter-clockwise rotation affected the �ardinia-Corsica continental �lock (�peranza et al., 2002).

�he Corso-�ardinian shelf is steeper and was affected �� a minor extension than the slope of the �ulf of Lion, where the Rhone River provides an important contri�ution to the large deep-sea fan of the French margin.

�he rift and post-rift �ligo-Miocene sediments are the �asal oldest units of the sedimentar� sequence of the north-western Mediterranean �asin. �he Upper �ligocene (?)- Lower Miocene continental s�n-rift sediments are covered �� Neogenic pelagic deposition (�eletti et al., 2014).

In the western Mediterranean, during the M�C event, a�out 1600-2100 m of evaporites series are deposited (�eletti et al., 2014). �nl� the uppermost part has �een sampled �� �oreholes. �his scarcit� of cali�ration makes difficult the exact identification of the different facies interpreted along the seismic profiles.

Lofi et al. (2011) proposed a new terminolog� for evaporites units, which were alread� identified �� Rehault et al. (1984), and include Lower Unit (LU), Mo�ile Unit (MU) and Upper Unit (UU). �n the continental slope, in the lower part, a thinning salt la�er overlaid �� the Upper Unit, turns into the Messinian Erosional �urface, which is generall� a strong reflector that truncated the pre-Messinian reflectors (�eletti et al., 2014).

�he a�rupt restoration of marine conditions at the �eginning of the Pliocene is another point not completel� defined. In a recent stud�, Bache et al. (2012) suppose a two-step reflooding of the western Mediterranean Basin at the end of the M�C. �he first step is characterized �� a relativel� moderate sea-level rise (500 m), resulted from the �eginning of erosion of the �i�raltar �arrier. �he second step (5.46 Ma) was dramatic, due to the collapse of the �i�raltar channel and the following sea level rise of 600-900 m.

�he Lower Pliocene unit has a t�pical semi-transparent seismic facies. A�ove it, Upper Pliocene and Quaternar� tur�iditic la�ers of sediments, transported �� the Rhone (Aslanian et al., 2012), present a more reflective facies (Rehault et al., 1984). �n the �ardinian slope the PQ units are thinner than the �ulf of Lion or on the deep �asin.

Seismic dataset. �he profiles that we interpreted �elong to different datasets: West

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�ardinia10 project (W�10) acquired and processed in 2010 �� the R/V ��� Explora in the western �ardinian offshore� one profile of M� surve�, sponsored �� National Council of Research (CNR) and acquired and processed �� ��� in 1972� �ARDINIA experiment project� Campagne �céanographique LI�A, IFREMER� Campagne �céanographique �E�AME, CNR�.

�he re-processing of the profile W�10_02 has �een carried out at ��� in �rieste, using Echos software (Paradigm Inc.).

Discussion. �he Messinian �rilog� can �e recognised in the deep �asin� LU unit is present onl� in the �asin, until the foot of the slope. �n the lower continental slope are present graduall� thinning MU and UU units. �he MU disappears more quickl�, due to its detachment and sliding toward the deep �asin, often producing rollover tectonics. In the central part of the slope has �een interpreted the onl� presence of Upper Unit, which turns into the Messinian Erosional �urface.

Halokinesis is characterized �� several differences in the shape of dome: from the deep �asin to the coast are o�serva�le frequent and narrow salt domes, “terraced” salt and ta�ular salt with isolated domes. From the �ardinian coast toward the �asin, the MU deforms in a “terraced salt”� in this case, the domes are ver� close and deform the Pliocene reflectors. �ometimes, the salt can �e recognized a�ove the UU, where it intruded producing some little dome. �he �ase of MU is interpreted at 4.5/4.8 �W� seconds. Further, the area of “terraced salt”, toward the �asin, the domes are narrow and frequent and the� often deform the sea level. In this case the MU �ase is at 5.2/5.4 s �W�. In Fig. 2 are highlighted the differences �etween the �ulf of Lion and the �ardinian margins. �he main differences are due to the different size of the salt domes, which are �igger and more isolated in the �ulf of Lion, where also the sea �ottom deformation testifies to �e often still active. �he total volume of salt seems to �e similar on the two opposite margins. Furthermore, the PQ sequence is thicker on the French side, due to the rivers entr�.

�he gravimetric map presents a low gravit� anomal� in the �asin and a high anomal� close to the margin. At the same time, the magnetic anomal� presents ver� similar pattern to that one of the gravit� anomalies.

Conclusion. �he work anal�sed the Messinian to recent geological evolution of the eastern sector of the �ardo-Provençal �asin. �he main feature involving the sedimentar� sequences of the studied area is the presence of the evaporite units deposited during the Messinian event. �he salt tectonic forms domes, diapirs and sliding on deepening �asement. �his deformation

Fig. 2 - Lines �ARDINIA 102-101 (on the left) and line W�10_05 recorded �� ��� (on the right) in the �ardo-Provençal �asin. �he Messinian �rilog� is clearl� imaged: LU (Lower Unit), MU (Mo�ile Unit), UU (Upper Unit). Halokinesis of MU deform the over�urden composed of UU and Plio-Quaternar� sequence. �n the E-W line is highlighted the pull-up event, a�ove the �ligo-Miocene deposits. �eismic images have the same horizontal and vertical scales.

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developed mainl� during the Lower Pliocene, �ut continues until Present, as testified �� some structures that deform the sea level. Integration of different seismic datasets allowed identification of the pro�a�le presence of a halite la�er within the UU.

�he �oundaries �etween the different domains descri�ed in literature �� Moulin et al. (2016) and Afhilado et al. (2016) correspond to those �etween the t�polog� of salt domes. �he morpholog� of the salt structures could �e related to the nature of the crust, pro�a�l� also due to different thermal conditions of the �asement.

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