Is the Messinian Salinity Crisis Responsible for the Outstanding Biogenic Gas Expulsion in the Levantine Basin

The Levantine basin offshore Cyprus and Israel contain huge reserves of biogenic gas. This gas was generated by microbial activity at low temperature. Part of the generated amount of the gas is a) adsorbed onto kerogen internal surface, b) dissolved in water and c) retained in kerogen microporosity. These three retention processes depend on pressure, temperature, porosity and TOC. The excess of gas that is not retained is expelled. It can migrate directly to the surface and get lost or it can be trapped if the conditions are favourable. At the beginning of the Messinian Salinity Crisis (5.971 Ma, Manzi et al. 2013), the precursor of the Strait of Gibraltar closed and due to dry climate conditions the Mediterranean Sea nearly entirely desiccated. One of the consequences was a hydrostatic pressure drop of the already deposited sediments. At this occasion, part of gas dissolved into the water was released since the dissolution capability of the water is directly related to pressure. This reduction created a second biogenic gas expulsion pulse. At that time the rock was more deeply buried and the likeliness of trapping this gas is higher. This could explain the huge quantities of biogenic gas present in Levantine basin.