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Mega-Scale Swells and Diapirs in the Deep Levant Basin, Eastern Mediterranean, and their Association with Recent World-Class Gas Discoveries

Yuval Ben-Gai and Yehezkel Druckman

The recent gas discoveries in Oligo-Miocene sand layers in the deep Levant basin are trapped in Miocene age fold structures. Most of these structures are cored by swells and diapirs of unknown lithologies. None of these diapirs were penetrated so far in any of the wells.

Three possible lithologies can be inferred comprising these intrusions: Magmatic (or volcanic) intrusions, salt upwelling or mud diapirism, all must have been elevated from the deep-lying Early Mesozoic strata or below.

Magmatic intrusions can be rejected on the basis of the magnetic data; only one, the Jonah structure, is associated with positive magnetic anomaly. Salt might have been deposited during the rifting stage (Triassic and Early Jurassic). Salt deposits of these ages are known from the distal Arabian Craton, though sulphate deposits are known onshore Israel. Mud diapirism is suggested to be the most likely cause. Fine grained clastics dominate the Late Jurassic and Early Cretaceous sections penetrated in boreholes in the studied area.

The history of the Levant margin and basin can be summarized by the following four major phases: 1.Early Mesozoic rifting; 2. Middle Jurassic to Late Cretaceous passive margin; 3. Late Cretaceous to Early Cenozoic contraction. This phase is associated with the Syrian Arc inverted structures, mapped onshore and throughout the shelf and slope of the basin. 4. Tertiary to present sagging and filling of the Levant Basin with some 6,000m of sediment. The Miocene structures in the deep basin differ from the Syrian arc structures not only by their age of folding but by several other parameters as well. Some of the deep-water structures are associated with severe disruption of the strata at their cores, sometimes piercing their way up through the Tertiary section; In most cases, they are not associated with older, Late Cretaceous or Early Cenozoic inverted structures; They are symmetrically folded unlike the Syrian Arc structures which are asymmetric; No reverse faults are observed at any level in the vicinity of these structures; they are dissected by normal faults of pre-Messinian age; Their amplitude is lower and their wave length is longer than the Syrian Arc structures.

It is thus suggested that the diapirism is caused by the gravitational instability of unconsolidated sediments during the fast subsidence of the basin since Early Tertiary. As the folding ceased prior to the Messinian, it is assumed that the intrusive material reached a state of equilibrium during the Late Miocene. Mud diapirs are known in other basins that experience plate’s collision and fast subsidence, such as the South Caspian Sea and the Caribbean forearc basin. The possible role of the diapirism in the hydrocarbon charging of the sandstone reservoirs trapped in the Miocene structures is not yet clear.

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