Unravelling one of Earth Science’s most fascinating mysteries
Formed about 6 million years ago, the Mediterranean Salt Giant (MSG) is one of Earth’s largest giant salt deposits located in the Mediterranean basin. It lies below the Mediterranean seafloor, buried under a few hundred metres of ‘normal’ marine sediments. The EU-funded SALTGIANT project, with the support of the Marie Skłodowska-Curie Actions programme, set out to investigate the formation of the MSG and its implications for fundamental science, industry and society. “To do this, the project brought together 30 academic organisations from 12 countries in a network with 15 PhD students,” outlines Giovanni Aloisi, scientific project coordinator.
MSG formation and deep life findings
The work of the project uncovered many key insights. One is the radical change in oceanic circulation patterns between the Atlantic Ocean and the Mediterranean Sea preceding the formation of the MSG. “We also showed that a major sea level fall occurred at least once during the formation of the MSG. During these episodes, the water level in the Mediterranean Sea was several hundred metres – and possibly up to 2 km – lower than that of the global ocean,” highlights Aloisi. Furthermore, the high salinity of the Mediterranean water mass during the formation of the MSG resulted in an environment free of higher living organisms. Extensive ecosystems of microorganisms thrived in the absence of dissolved oxygen in the water column by using hydrogen sulfide as a source of energy. “These organisms may be involved in the formation of extensive mineral gypsum deposits outcropping in the Apennines of Italy because they produce sulfate,” adds Aloisi. Project results from laboratory experiments with haloarchaea microorganisms brought to light how they adapt to survive while being entombed in halite (sodium chloride salt). Aloisi adds: “We demonstrated that halite protects against different forms of radiation, which has relevance for survival on Mars.”
Mitigating the risks of drilling
SALTGIANT quantified the overpressure generated by salt deposition on normal, marine pre-salt sediments. Salt has the characteristics of being deposited very rapidly and having very low permeability. “When significant overpressures form in salt bearing successions, this can represent an important hazard for hydrocarbon exploration drilling operations both in the form of hydrocarbon well ‘blowouts’ and because overpressured formations provide a mechanically weak surface below the salt, favouring salt deformation and gliding – subsea landslides,” reports Aloisi. The project proved that the overpressure estimated for the Mediterranean sub-salt deposits might induce sedimentary gliding. Moreover, the pressure is so strong that it might induce the rupture in the salt sequence allowing pre-salt fluids to escape across the salts into the post-salt Plio-Quaternary sequence.
Integrated history of the discovery of the MSG
“We further explored the history of seafloor exploration from the aftermath of World War II in Europe, addressing how ambitions to exploit marine resources led to the seafloor’s scientific understanding and to its perception as a new deep territory,” outlines Aloisi. This led to a thesis suggesting geological knowledge from the seafloor increasingly became a crucial asset for the French government, which could mobilise it to negotiate international relations and foster national prestige. “In addition to the scientific results, the project has helped enhance the career perspectives and employability of researchers with many moving onto postdocs, or jobs in academia and the private sector,” concludes Aloisi.
Keywords
SALTGIANT, MSG, salt deposit, Mediterranean Salt Giant, Mediterranean basin, MSG formation, haloarchaea, subsea landslides
