Crustal structure and post-rift evolution of the Levant Basin

Petroleum exploration activity in the deep basins of the Eastern Mediterranean has been rejuvenated over the last decade with the discoveries of the giant Tamar and Leviathan gas fields made by Noble Energy and its partners, and more recently with the discovery of the Zohr field by Eni. With exploration efforts pursuing deeper and older leads, a first-principles quantitative study of the region seems timely. While it is generally agreed that the Levant Basin formed along the northern passive margin of Gondwanaland during the Early Mesozoic, its complex post-rift evolution has not been documented in detail. Located in a unique junction of three active tectonic plates and at the distal end of the Nile, one of the largest rivers on Earth, the Levant Basin is characterized by a thick sedimentary section, more than half of which has accumulated since the Oligocene, in the last similar to 15% of its existence. This study implements a quantitative basin-modelling workflow that assesses the three-dimensional crustal geometry of the Levant Basin and its post-rift evolution, by integrating 3D-gravityinversion and 3D-flexural-backstripping techniques. The focus of the gravity inversion, which includes corrections for the lithosphere thermal gravity anomaly resulting from lithosphere thinning and for the magmatic addition from decompression melting, has been to predict both the 3D crustal-structure and the magnitude of total lithospheric stretching for the Levant Basin. The 3D-flexural-backstripping workflow, using the outputs of the gravity inversion, invokes three major processes in its calculations, accompanying the layer-by-layer removal of the stratigraphy: (i) 3D flexural-isostatic unloading, (ii) decompaction in response to the removal of overburden and (iii) reverse thermal-subsidence modelling, controlled by the stretching factor derived from the gravity inversion. Backstripping has produced a series of maps and cross sections depicting the evolution of post-rift palaeobathymetry in the Levant Basin. The integration of these techniques allows us to assess the evolution of the basin and the various sedimentary and tectonic events that have occurred since basin initiation. Although the calculated stretching factors indicate that while the lithosphere underlying the Levant Basin has been very highly stretched and thinned, the stretching did not progress to the formation of new oceanic crust. Predicted palaeobathymetry portrays a thermally-subsiding basin reaching maximum water-depths at the onset of the Cenozoic. This deep basin provided ample amount of accommodation space for the large volumes of terrigenous clastics, sourced from the contemporaneous uplift and exhumation of the basin margins and delivered in large part, at least since the Oligocene, by the continental drainage of the Nile. These sediments have been filling and shallowing the basin ever since. The basin evolution described here is consistent with available geophysical and geological data and has important implications for petroleum-systems modelling within the basin.