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

The Messinian salinity crisis was an extraordinary event that resulted in the deposition of kilometre-thick evaporite sequences in the Mediterranean Sea after the latter became disconnected from the world's oceans. The return to fully and stable marine conditions at the end of the crisis is still subject to debate. Three main hypotheses, based on geophysical and borehole data, onshore outcrops and climate simulations, have been put forward. These include a single-stage catastrophic flood, a two-step reflooding scenario, and an overspill of Paratethyan water followed by Atlantic inflow. In this study, two research questions are addressed: (i) Which event marked the termination of the Messinian salinity crisis? (ii) What was the sea level in the eastern Mediterranean Sea during this event? Geophysical data from the western Ionian Basin are integrated with numerical simulations to infer that the termination of the crisis consisted of a single-stage megaflood following a sea level drawdown of 1900 m. This megaflood deposited an extensive sedimentary body with a chaotic to transparent seismic signature at the base of the Malta Escarpment. Fine, well-sorted sediments are predicted to have been deposited within the thicker sections of the flood deposit, whereas a more variable distribution of coarser sediments is expected elsewhere. The north-western Ionian Basin hosts evidence of episodic post-Messinian salinity crisis slope instability events in the last ~1.8 Ma. The largest of these emplaced a >200 km3 deposit and is associated with failure of the head of Noto Canyon (offshore SE Sicily). Apart from unravelling the final phase of the Messinian salinity crisis and the ensuing stratigraphic evolution of the western Ionian Basin, our results are also relevant to better understand megafloods, which are some of the most catastrophic geological processes on Earth and Mars. © 2020 Elsevier B.V.
The article is based upon work from COST Action CA15103 “Uncovering the Mediterranean salt giant” (MEDSALT) supported by ( COST European Cooperation in Science and Technology ). We are indebted to the CUMECS-2, CUMECS-3 and CIRCEE-HR shipboard parties, captains, crew and technicians for their assistance during data collection. The oceanographic surveys were possible following permits issued by the Italian and Maltese authorities. SPECTRUM (now TGS) are kindly acknowledged for providing access to their seismic reflection data. The use of CROP seismic profiles has been licensed to OGS by CNR, Banca Dati CROP ( www.crop.cnr.it ). The authors would also like to thank Emerson Paradigm for the use of the OGS academic licenses of the ECHOS and Geodepth processing software, and IHS Markit for the OGS license of the Kingdom software. DS is funded by EMODnet Bathymetry, which is financed by the European Union under Regulation 508/2014 of the European Parliament and of the Council of 15 May 2014 on the European Maritime and Fisheries Fund . This work was also supported by the Spanish Ministry of Science, Innovation and Universities (MICINN/FEDER, EU) under Grant SEDRETO CGL2015–70736-R . J.D.d.M.E. was supported by the PhD scholarship BES-2016-079117 (MINECO/FSE, EU) from the Spanish National Programme for the Promotion of Talent and its Employability (call 2016). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 765256 (SaltGiant ITN).