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Messinian Evaporite Facies in the Eastern Mediterranean and the Impact on Depth Conversion and Imaging of the Pre-Messinian

Hayley Allen, Dana Tolessin, Matthew Plummer, Alastair J. Fraser, and Chris Jackson

The offshore Eastern Mediterranean region covers c. 230,000 km2 and is located on the northern margin of the subducting African plate. It is an area of numerous tectonic domains that have resulted in a complex, high-relief crustal structure, which is characterised by a series sub-basins and highs such as the Levantine Basin and Eratosthenes Seamount; it is these two areas that are the focus of the present study. Superimposed on the underlying structural framework and the Mesozoic-Cenozoic sedimentary basin-fill are the vast evaporite-dominated successions that were deposited during the Messinian Salinity Crisis (MSC) between 5.96-5.33ma. Recent discoveries in the pre- Messinian of the Levant and offshore Cyprus areas have heightened industry interest and brought the variable seismic facies and structural styles of the basinal Messinian into sharp focus, particularly with regards to their impact on depth conversion and seismic imaging.

This study aims to improve our understanding of the stratigraphic development of the MSC in the deep basin by utilizing regional 2D, time-migrated seismic surveys and well data to perform a comprehensive seismic facies analysis of evaporites in the offshore Levant. The data has allowed the identification of seven distinct, laterally persistent seismic sequences, which exhibit a high degree of both lateral and vertical variability of facies and structural styles. A series of structural domains have also been identified that are related to ongoing, thick-skinned, collisional tectonics in the region and thin-skinned, gravity processes associated with the Nile Delta and Levant margin. This has led us to propose a new model for the tectono-stratigraphic development of the Messinian, and poses new questions regarding the implications that these facies variations have on the construction of velocity models for the Messinian evaporite. Previous attempts at depth conversion have adopted a somewhat simplistic approach, characterising the Messinian as a continuous, homogeneous, halite-dominated layer. The detailed subdivision of the Messinian into its constituent depositional sequences provides a hitherto unachieved level of detail from which to build the velocity model. The velocities associated with the observed seismic facies have been calibrated by correlation with the offset Hannah-1 well and by reference to similar lithologies in analogous depositional settings.

This multi-layered depth conversion approach predicts that the base Messinian surface is c. 400 metres deeper than the one generated using a single velocity value. Therefore, our more detailed facies sub-division and associated depth conversion method has helped us understand the possible variations of interpreted depth, amplitude and wavelength of sub Messinian prospects and reinforced the importance of applying a multi-layered approach.

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