The Levant Basin: A Natural Laboratory for Early Stage Salt Tectonics

Cartwright, Joseph A.¹
(1)Earth sciences, cardiff University, Cardiff, United Kingdom.

The Levant Basin is ideal for the study of early-stage salt tectonics in that the basin contains a modestly strained, thick salt layer has only been subject to regional subsidence and sediment loading with a minor contribution from active basement tectonics since its deposition in the late Miocene. The salt layer was deposited during the Messinian Salinity Crisis (MSC), with over 1.5km of multilayered evaporites accumulating in the basin, thinning to a depositional pinch-out along the present day shelf margin. The likely drawdown of sea level was of the order of 1000m. Slope progradation during the Plio-Pleistocene was modified by two gravity-driven deformation systems: (1) Local thin-skinned slope failure as slides and slumps; (2) Regional thin-skinned tectonics involving the entire Plio-Pleistocene shelf-slope system detaching in the Messinian evaporites. Both gravity-driven systems remain active at present.

The style of the salt tectonics is dominated by upslope extension, salt roller development and rarely, reactive diapirism, and by downslope contraction. Typical values of extensional heave around the basin margin range from 1-15km. Shortening appears to be significantly less, but is harder to quantify because of poor data coverage in the most distal areas. Because the evaporite deposition was highly cyclic, multiple detachments for the salt structures occur, and these localise within opaque seismic facies, presumed to equate to halite rich intervals. Up to four separate levels of detachment have been identified, and the strain distribution is suggestive of a hybrid couette-poiseulle flow regime. The timing of deformation around the margin is diachronous, and the strain distribution is non-uniform, possibly reflecting different degrees of clastic pollution within the gross evaporite succession. Complex re-entrants over former canyons led to localised thicker and salt deposition and thence led to uneven development of principal salt tectonic loci. Hydrocarbon migration through the massive seal sequence occurs sporadically assisted by through going strike-slip faults, by mud volcanoes and by localised areas of almost complete salt dissolution. Similar windows for migration may occur in many other salt basins.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.