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Pervasive Seafloor Gas Flow along the Periphery of the Southeastern Mediterranean

Yizhaq Makovsky, Gideon Tibor, Barak Herut, Nicolas D. Waldmann, Baruch Spiro, Gilad Antler, Orit Sivan, Robert D. Ballard, Dwight Coleman, Christian Huebscher, and Zvi Ben Avraham

Mounting evidence unravel the wealth of active seafloor gas flow along the periphery of the Levantine Basin, significantly to the north of the explicit Nile Delta. High resolution seismic profiling along the continental shelf of Israel (at water depths <100 m) reveals an abundance of gas related acoustic reflectivity truncating the Holocene layered, predominantly clay, sedimentary cover. These corroborate variable patchy to semi-continuous bands of reflectivity sub-parallel to the seafloor, 5 to 30 m below it, suggested here to represent an over-pressured gas front originating at deeper levels and migrating upwards primarily by fracturing the mechanically weak sediments. Seismic profiles suggest an association with deeper gas flow, at least from Mid-Pleistocene channels. A variety of seepage related features were recently discovered along the base of the Israeli continental slope and on Eratosthenes sea mount by E/V Nautilus 2010 to 2012 ROV surveys. These collected sonar and video data and hand and short core samples. Several active gas seepage sites are found at water depths of 1100 to 1300 m, and are associated with carbonate buildups and seafloor pockmarks. These correlate with an abundance of presumably gas related reflectivity within the post-Messinian sediments observed on seismic 3D data. Sediments cores, collected in two sites offshore Israel, portray high concentrations of biogenic methane. Low lying hard rocks, settled with rich fauna and particularly deep water corals, are mapped at water depths of 600 to 800 m along the northern slope of Palmahim Disturbance, offshore central Israel. Preliminary examination of one sample revealed a chimney-like morphology, dolomite composition and δC13 values of -40‰. These, together with a variety of additional enigmatic seafloor features in the region, suggest greater past methane seepage. Observed seafloor gas flow may be associated with deeper leakage through the salt layer, are suggestive of the presence of gas hydrates and is important in geohazard estimations. Moreover, the current seafloor gas system may serve as a model for the deeper Nilotic system, feeding most recentlydiscovered reservoirs.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013