Origin and kinematics of a basin-scale, non-polygonal, layer-bound normal fault system in the Levant Basin, eastern Mediterranean

Abstract

Polygonal, layer-bound normal faults can extend over very large areas (>2,000,000 km2) of sedimentary basins. Best developed in very fine-grained rocks, these faults are thought to form during early burial in response to a range of diagenetic processes, including compaction and water expulsion. Local deviations from this idealised polygonal pattern are common; however, basin-scale, layer-bound faults with non-polygonal map-view are not well-documented and accordingly, their genesis is not well-understood. In this study we use 3D seismic reflection data, biostratigraphy, and well-logs from the Southern Levant Basin, offshore Israel, to develop an age-constrained seismic-stratigraphic framework and determine the geometry and kinematics of such basin-scale fault system. The faults tip-out downwards along an Eocene Unconformity, but unlike layer-bound faults in the Northern Levant Basin, they do not reach the base of the Messinian evaporites, instead tipping-out upwards at the top Langhian. On average, the faults in the Southern Levant Basin are 6.3 km long, have an average throw of 120 m, and consistently strike NW-SE. Throw-depth plots, accompanied by thickness changes, indicate the faults nucleated as syn-depositional faults in a mudstone-dominated unit, and are spatially and kinematically associated with a WSW-ESE-striking strike-slip fault. Unlike true polygonal faults, these faults propagated through ~2 km-thick sandstone-dominated Oligocene-Miocene strata. Whereas previous studies from the Northern Levant Basin associate fault nucleation and growth with burial-related diagenesis, the sandstone-dominated character of the Oligocene-Miocene suggests that this process cannot be readily applied to the Southern Levant Basin. Instead, we highlight potential tectonic events that occurred during and may have triggered thin-skinned extension at times of fault growth. Layer-bound normal faults therefore should be considered in the geodynamic and structural context of the basin in which they formed.