Mud volcanoes, gas chimneys, pockmarks and mounds in the Nile deep-sea fan (Eastern Mediterranean): geophysical evidences

Abstract

The Nile deep turbiditic system displays many fluid-releasing structures on the seabed: mud volcanoes reassembling small cones (100–900 m in diameter), mud pies (5 km in diameter), and pockmarks. The cones are restricted to the western province. Mud ‘pies’ delineate a belt of apparently very active gas chimneys along the upper continental slope. Pockmarks are associated either with strongly destabilized sedimentary masses or with gas chimneys. We distinguish five main controlling parameters interacting in fluid release locations: (1) the presence, at depth, of potential source rocks and reservoirs; (2) the distribution of Messinian evaporites preventing upward fluid migration; (3) the distribution of sedimentary overloading inducing localized overpressures on under-compacted and fluid-rich sediments; (4) the presence of syn-sedimentary faults acting as potential conduits for fluid migration; and finally (5) chiefly for pockmarks and mounds, the occurrence of large-scale sedimentary instabilities.