Seismic Interpretation of the Messinian Salinity Crisis in the Levant Basin, Eastern Mediterranean Sea
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Kilometer-thick sequences of evaporites were deposited in the Mediterranean Sea during the Late Miocene (5.96-5.33 Ma). The event is known as the Messinian Salinity Crisis and was a result of progressive restriction of the marine gateways between the Mediterranean Sea and the Atlantic Ocean. The event lasted for approximately 600,000 years until normal marine conditions were re-established.Three-dimensional, depth converted seismic data from the northeastern Levant Basin (offshore Lebanon, eastern Mediterranean Sea) has been interpreted. A regional interpretation study was conducted, which shows that the Levant Basin is a rift-basin with a passive margin to the east. The first part of the deep basin is filled with sediments of Late Cretaceous to Late Miocene age that have been accumulated by massive subsidence of the basin. The second part of the sedimentary infill consists of sediments from Late Miocene-present time. This is marked by the deposition of a thick sequence of Messinian evaporites, underlying deep-marine sediments of Pliocene-Pleistocene age. Interpretation of the seismic data has revealed the occurrence of a well-imaged, relatively high-amplitude sedimentary layer deposited between the Messinian evaporites and the deep-marine deposits. The unknown layer, referred to as the Transition layer, has different characteristics than the evaporites deposited below and the deep-marine sediments deposited above. A detailed seismic interpretation study of the Messinian and younger sediments has been conducted in order to investigate evidence for the origin of the Transition layer. The results show that the thick sequence of evaporites in the northern Levant Basin is bounded by two erosional surfaces. The base erosion surface marks an important sea-level fall at the beginning of the Messinian Salinity Crisis. The top is an erosional surface of subaerial origin that marks a period of desiccation at the end of the salinity crisis. Two major phases of deformation related to salt tectonics can be observed in the seismic data. The first phase took place in the Late Messinian between deposition of the evaporites and the erosion event that marks the top of the evaporites. The second phase has affected the entire Pliocene-Pleistocene succession, including the top of the evaporites and the seabed. This phase is linked to gravity-driven, thin-skinned deformation. The seismic characteristics of the Transition layer and the analogy with other coeval deposits in the Mediterranean area favor two possible deposition scenarios for the Transition layer. The layer could have been deposited subaerially by fluvial channels, in similar settings as what can be observed in the Death Valley, USA, today. The other scenario suggests that the sedimentary layer can be fresh to brackish water deposits, known as the "Lago Mare", which can be observed other places in the eastern Mediterranean. Due to the lack of well data from the northeastern Levant Basin, an exact conclusion for the origin of the layer cannot be drawn. The Levant Basin is an under-explored area, and the evaporite deposition in the eastern Mediterranean is different from that of the more explored western Mediterranean. With available well data, a correlation between the different parts of the Mediterranean Sea would be possible to make. The origin and depositional history of the Transition layer could then be determined with more accuracy. Having correct knowledge about the geological history of the Levant Basin is very important for the understanding of the petroleum systems in the area.