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Origin of Mound-Like Structures on the Outer Continental Shelf Off-Central Israel


Seepage activity on continental margins is a relatively widespread phenomenon, emphasized in particular by the increase in available high-resolution 3D subsurface datasets and technological advances of the last decade. Over 160 mounded features were identified on industrial 3D seismic data at the distal part of the continental shelf off central Israel. While most of the pinnacle-shaped features are buried under Holocene overburden and occur at depths of ~120 m water depth, some are exposed at the seafloor. A sediment core obtained on top of one of these mounded structures reveal that they are mainly composed of carbonate with high amount of bioherms. Moreover, high resolution study of the deep subsurface reveals that these features are concentrated on a specific area overlying an anticlinal structure of the top of the Messinian unconformity. We hence propose that these morphologies may represent paleo-seepage structures cemented by methane-derived authigenic carbonates. We further suggest a flowing mechanism of the gas that originated from sources beneath the top Messinian unconformity. We argue that one of the main driving mechanisms responsible for their formation is the variation in hydrostatic pressure driven by relative sea level changes. However the effect of oceanographic conditions in shaping the mounded features cannot be neglected.