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Seismic Markers of the Messinian Salinity Crisis in the Deep Ionian Basin

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Seismic Markers of the Messinian Salinity Crisis in the Deep Ionian Basin Received: 11 April 2019 | Revised: 26 July 2019 | Accepted: 29 July 2019 DOI: 10.1111/bre.12392 EAGE ORIGINAL ARTICLE Seismic markers of the Messinian salinity crisis in the deep Ionian Basin Angelo Camerlenghi1 | Anna Del Ben2 | Christian Hübscher3 | Edy Forlin1 | Riccardo Geletti1 | Giuseppe Brancatelli1 | Aaron Micallef4,5 | Marco Saule1,2 | Lorenzo Facchin1 1National Institute of Oceanography and Applied Geophysics OGS, Trieste, Italy Abstract 2Department of Mathematics and We conduct the seismic signal analysis on vintage and recently collected multi- Geosciences, University of Trieste, Trieste, channel seismic reflection profiles from the Ionian Basin to characterize the deep Italy basin Messinian evaporites. These evaporites were deposited in deep and marginal 3CEN ‐ Center for Earth System Research Mediterranean sedimentary basins as a consequence of the “salinity crisis” between and Sustainability, Institute of Geophysics, University of Hamburg, Hamburg, Germany 5.97 and 5.33 Ma, a basin‐wide oceanographic and ecological crisis whose origin 4Marine Geology and Seafloor Surveying, remains poorly understood. The seismic markers of the Messinian evaporites in the Department of Geosciences, University of deep Mediterranean basins can be divided in two end‐members, one of which is the Malta, Msida, Malta typical “trilogy” of gypsum and clastics (Lower Unit – LU), halite (Mobile Unit – 5GEOMAR – Helmholtz Centre for Ocean Research Kiel, Kiel, Germany MU) and upper anhydrite and marl layers (Upper Unit – UU) traced in the Western Mediterranean Basins. The other end‐member is a single MU unit subdivided in Correspondence seven sub‐units by clastic interlayers located in the Levant Basin. The causes of Angelo Camerlenghi, National Institute of Oceanography and Applied Geophysics these different seismic expressions of the Messinian salinity crisis (MSC) appear to OGS, Trieste, Italy. be related to a morphological separation between the two basins by the structural re- Email: [email protected] gional sill of the Sicily Channel. With the aid of velocity analyses and seismic imag- Funding information ing via prestack migration in time and depth domains, we define for the first time the Directorate‐General for Research and seismic signature of the Messinian evaporites in the deep Ionian Basin, which differs Innovation, Grant/Award Number: ERC Starting Grant n°677898 (MARCAN) from the known end‐members. In addition, we identify different evaporitic deposi- and Marie Curie Career Integration Grant tional settings suggesting a laterally discontinuous deposition. With the information PCIG13‐GA‐201; Universität Hamburg, gathered we quantify the volume of evaporitic deposits in the deep Ionian Basin as Grant/Award Number: RV Meteor 3 Expedition M142/2; European Cooperation 500,000 km ± 10%. This figure allows us to speculate that the total volume of salts in Science and Technology, Grant/Award in the Mediterranean basin is larger than commonly assumed. Different depositional Number: COST Action CA15103 units in the Ionian Basin suggest that during the MSC it was separated from the Western Mediterranean by physical thresholds, from the Po Plain/Northern Adriatic Basin, and the Levant Basin, likely reflecting different hydrological and climatic conditions. Finally, the evidence of erosional surfaces and V‐shaped valleys at the top of the MSC unit, together with sharp evaporites pinch out on evaporite‐free pre‐ Messinian structural highs, suggest an extreme Messinian Stage 3 base level draw This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2019 The Authors. Basin Research published by International Association of Sedimentologists and European Association of Geoscientists and Engineers and John Wiley & Sons Ltd. 716 | wileyonlinelibrary.com/journal/bre Basin Research. 2020;32:716–738. CAMERLENGHI ET AL. 717 EAGE | down in the Ionian Basin. Such evidence should be carefully evaluated in the light of Messinian and post‐Messinian vertical crustal movements in the area. The results of this study demonstrates the importance of extracting from seismic data the Messinian paleotopography, the paleomorphology and the detailed stratal architecture in the in order to advance in the understanding of the deep basins Messinian depositional environments. KEYWORDS evaporites, Ionian Basin, Mediterranean, Messinian salinity crisis, salt giant 1 | MOTIVATION OF THE STUDY Highlights The understanding of the Messinian salinity crisis (MSC; e.g. • First description of a new type of deepwater Ryan 2009; Roveri, Flecker, et al., 2014) as a Mediterranean Messinian salt giant in the Ionian Sea. basin‐wide event requires an improved knowledge of the • First quantification of the Messinian salt volume stratigraphy in the deep basins and continental margins, in the Ionian Sea. where the vast majority of the evaporitic deposits lay below • New seismic evidence of erosional surfces and today's seafloor. Lago Mare deposits in the deep Ionian Basin. The seismic markers of the deposition of Messinian evap- • Further evidence of sea level lowering during the orites in the deep Mediterranean basins (sensu Lofi, 2011, Messinian Salinity Crisis. 2018) are (Supplementary Figure S1): • Evidence for a different, physically separated deep- water Messinian salt basins in the Mediterranean. • the Lower Unit (LU), generally poorly known due to the high absorption of seismic energy by the upper evaporitic layers, inferred to be composed of gypsum and clastics; • the reflector‐less Mobile Unit (MU), corresponding to salt thick, can be correlated across thousands of kilometres in the filling the basins and onlapping the Late Miocene conti- Algero‐Balearic and Provençal basins with a fairly constant nental margins; distribution (e.g. Dal Cin et al., 2016). • the Upper Unit (UU), consisting of a package of parallel Conversely, in the Levant Basin the MSC is primarily rep- and continuous reflectors, interpreted as an alternation of resented by a single, different type of MU, up to 2 km thick, anhydrite and marl layers; composed of up to six alternations of a transparent and lay- • the Complex Unit (CU), corresponding to a chaotic, dis- ered seismic units (Bertoni & Cartwright, 2006; Gvirtzman, continuous and variably transparent unit thought to be Reshef, Buch‐Leviatan, & Ben‐Avraham, 2013; Netzeband, made of deposits of material eroded from upper to lower Hübscher, & Gajewski, 2006). According to Feng, Yankelzon, Mediterranean continental slopes during lower sea level Steinberg, and Reshef (2016), and Meilijson et al., 2019 this phases of the MSC. transparent layers consists of halite, and the internal reflec- tions are caused by intercalated clastics. At the top of MU In addition, the following main observed seismic surfaces are: there is an additional thin (a few tens of metres) uppermost the Margin Erosion Surface (MES), identified on the upper unit interpreted as a clastic‐rich anhydrite unit overlain by an margins and interpreted as a subaerial erosion related to the ab- even thinner “Lago‐Mare” facies (Afiq Formation; Gvirtzman sence of the Messinian layers; the Bottom Surface (BS), which et al., 2017; Meilijson et al., 2019). The presence of UU and marks the base of the evaporitic deposits in the deep basins; LU has never been demonstrated in the Levant Basin, although the Top Surface (TS), which separates the MSC deposits from analogous seismic facies have been recognized in the Antalia the overlying Plio‐Quaternary units; the Intermediate Erosion and Cilicia Basins (Cipollari et al., 2013; Geletti, Del Ben, Surface (IES), corresponding to local intermediate erosional Mocnik, & Camerlenghi, 2018; Madof & Connell, 2018) and truncation developed during the last MSC. in the Florence Rise (Loncke, Sellier, & Mascle, 2011). Two depositional end‐members are identified in the The causes of the differences in the seismic expressions Mediterranean Basins (Supplementary Figure S1). In the of the MSC between the Western Mediterranean and the Western Mediterranean, a laterally continuous succession of Levant Basin are not understood. They appear to be related to the three seismo‐stratigraphic units LU–MU–UU, ~2.5 km a morphological separation between the Western and Eastern 718 CAMERLENGHI ET AL. | EAGE Mediterranean basins by the structural regional sill of the position between the Western Mediterranean and the Levant Pelagian Sea/Sicily Channel (e.g. Roveri, Lugli, Manzi, Basin, right to the east of the Pelagian Sea/Sicily Channel Gennari, & Schreiber, 2014). regional sill. Shallow penetrating Deep Sea Drilling Project The Ionian Sea (Figure 1a) is the deepest sedimen- (DSDP) and Ocean Drilling Program (ODP) wells demon- tary basin in the Mediterranean, located in an intermediate strate the existence of evaporitic deposits below a Pliocene (b) (c) (a) FIGURE 1 (a) Study area, in the central Mediterranean Sea (GeoMapApp) with location of figures. A‐BB, Algero‐Balearic Basin; C‐SB, Corsica–Sardinia Block; PB, Provençal Basin; TB, Tyrrhenian Basin; VT, Valencia Trough. (b) Bathymetry, main structural elements (Arsenikos et al., 2013; Del Ben et al., 2008, 2015; Finetti & Del Ben, 1986; Kokinou et al., 2005; Mocnik et al., 2018; Reston, Fruehn, et al., 2002) and seismic line location. Red lines on seismic profiles indicate the portion of the profile illustrated in the figure. IAP is the Ionian Abyssal Plain. The thin brown dashed lines
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