Seismic indicators of focused fluid flow and cross-evaporitic seepage in the Eastern Mediterranean

Abstract

We present for the first time a synthesis of the evidence of focused fluid flow in the Eastern Mediterranean, providing an updated record that includes recent and past occurrences through the last ca. 6 My of evolution of the basin. We do this by adding the interpretation of a previously unpublished regional 2D seismic dataset to the existing occurrences of focused fluid flow reported in the literature. Our interpretation shows a high number (141) of focused fluid flow features, which span the stratigraphic interval from late Miocene to Recent. Of these features, (82) are at the seabed, and (59) are buried. The previous published record is more difficult to quantify, but in comparison shows an overwhelming majority of seabed features, with only rare examples of buried features.The spectrum of the buried and seabed features covers pockmarks, pipes, mud volcanoes, clastic intrusions and collapse structures. Clustering of the fluid flow features is observed at different times in specific areas, including the Nile Cone, and the Levant, Herodotus, Cyprus and Latakia basins. With the buried record, we are able to highlight the evolution of the leakage points through time. Focused fluid flow venting has been occurring since the onset of the Messinian Salinity Crisis and the start of basinwide deposition of evaporites. We focus in particular on seismic indicators of leakage through evaporites, and of sub-evaporitic source for fluids and remobilised sediments. We also discuss the role of the evaporites as a seal to ascending fluids, and in which circumstances they can be breached.Fluids (and associated remobilised sediments) are sourced from different intervals, from the sub- and supra-evaporitic section, and possibly within the evaporites. Only a minor proportion of the fluid flow features are certainly sourced from below the Messinian evaporites, and most of them are located in the Nile-Levant-Eratosthenes areas. The few examples of pathways that are able to cross thick, undeformed and well preserved evaporites are typically correlated to overpressure release and hydrofracturing. This confirms that the evaporites do act regionally as a very good seal as expected, while fluids are able to cross the evaporites only in their most extreme expression, i.e. in near-lithostathic overpressure conditions. This is confirmed by our observations made in the Eastern Mediterranean, where in the presence of relatively undisturbed evaporites, cross-evaporite vertical fluid pathways are only observed at the high end of the flux-pressure range, and involve sediment remobilisation. Maps combining these different elements can be used to detect areas potentially more prone to breaching.