Seismic markers of the Messinian salinity crisis in the deep Ionian Basin

Abstract

We conduct the seismic signal analysis on vintage and recently collected multichannel seismic reflection profiles from the Ionian Basin to characterize the deep basin Messinian evaporites. These evaporites were deposited in deep and marginal Mediterranean sedimentary basins as a consequence of the “salinity crisis” between 5.97 and 5.33 Ma, a basin‐wide oceanographic and ecological crisis whose origin remains poorly understood. The seismic markers of the Messinian evaporites in the deep Mediterranean basins can be divided in two end‐members, one of which is the typical “trilogy” of gypsum and clastics (Lower Unit – LU), halite (Mobile Unit – 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 seven sub‐units by clastic interlayers located in the Levant Basin. The causes of these different seismic expressions of the Messinian salinity crisis (MSC) appear to be related to a morphological separation between the two basins by the structural regional sill of the Sicily Channel. With the aid of velocity analyses and seismic imaging via prestack migration in time and depth domains, we define for the first time the seismic signature of the Messinian evaporites in the deep Ionian Basin, which differs from the known end‐members. In addition, we identify different evaporitic depositional settings suggesting a laterally discontinuous deposition. With the information gathered we quantify the volume of evaporitic deposits in the deep Ionian Basin as 500,000 km3 ± 10%. This figure allows us to speculate that the total volume of salts in the Mediterranean basin is larger than commonly assumed. Different depositional 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 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.

Deformation and Fault Propagation at the Lateral Termination of a Subduction Zone: The Alfeo Fault System in the Calabrian Arc, Southern Italy

“…The northernmost seismic profile ( Figure 5A) also shows the relationship between the AFS and the paleo-margin of the Malta Escarpment. The western part of the section shows a chaotic body, possibly related to one or two major mega-flood events (Micallef et al, 2018;Camerlenghi et al, 2019), which drapes the western lateral toe of the accretionary wedge. Note that, except for minor deformation related to salt tectonics at the toe of the accretionary wedge, there is no evidence of active tectonics recorded by the Pliocene-Holocene unit at the base of the Malta Escarpment, whose activity terminates in the Lower Cretaceous as documented by Tugend et al (2019).…”

A single-stage megaflood at the termination of the Messinian salinity crisis: Geophysical and modelling evidence from the eastern Mediterranean Basin

“…The lithosphere is overlain by 5-7 km of sediments ranging between Jurassic to Recent in age (Cernobori et al, 1996;Speranza et al, 2012). From the Tortonian, the western Ionian Basin has been characterised by abundant accumulation of Messinian evaporites as well as Plio-Pleistocene hemipelagic sediments (Camerlenghi et al, 2019;Gallais et al, 2013;Gutscher et al, 2017).…”

Integrated isotopic and organic geochemical constraints on the depositional controls and source rock quality of the Neogene Kalamaki sedimentary successions (Zakynthos Island, Ionian Sea)

“…The maturity results suggest that the studied sediments have not reached deep enough to be within the oilgeneration zone, which could be possible offshore, where the sediments are thicker (> 3 km; IGRS-IFP 1966;BP 1971). The organic-rich evaporitic horizons could potentially have reached the maturation level in the offshore Ionian areas, where they are covered by thicker sedimentary pile, as evident by the seismic profiles south of Zakynthos proximal offshore (Nikolaou 1986;Kokkalas et al 2013;Kokkinou et al 2015) and deep Ionian region (Lofi 2018;Camerlenghi et al 2019). As the main Neogene gas-related source rocks are considered the Tortonian deposits (TOC = 1-5 wt%; Rigakis et al 2004).…”