Seismic Characterization and Depositional Significance of the Nahr Menashe deposits: Implications for the terminal phases of the Messinian Salinity Crisis  in the Northeast Levant Basin, Offshore Lebanon.

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SM Mainul Kabir, DaVID Iacopini, Adrian Hartley, Vittorio Maselli, Davide Oppo 


Over the last decade, there has been a resurgence of interest in the climatic and tectonic mechanisms that drove the Messinian salinity crisis (MSC) and the associated deposition of thick evaporites. The MSC represents an unprecedented palaeoceanographic change that led to a very short (c. 660 kyr) ecological and environmental crisis. However, across the Levantine offshore basin, the sedimentological nature of the top evaporitic units and the mechanisms that controlled the transition from a hypersaline evaporitic unit to brackish deposits (final
MSC stage 3) are still disputed. Here, we re-evaluate the deposits associated with the
terminal phase of the MSC, named in offshore Lebanon as the Nahr Menashe Unit (NMU). We describe the NMU seismic facies, characterize and map its internal seismic stratigraphy, and provide a new interpretation of its depositional environment, which persisted during the late Messinian and then evolved through a regional reflooding event. The base of the NMU overlies semi-circular depressions, randomly distributed linear marks and surface collapse features, which are indicative of a period of intense evaporite dissolution. The NMU seismic facies observed from the slope to the deep part of the basin support the interpretation of a layered salt-evaporite-sand depositional system subject to complex reworking, dissolution, deposition, and final erosion. A drainage network of valleys and complex tributary channels incising into the top NMU shows marked erosional characteristics, which indicate a dominant southwards sediment transfer following deposition of the NMU. This erosional drainage network formed due to the base-level fall associated with the last phase of the MSC. The base
of the channel/valley network does not cut below the bottom of the Narh Menashe dissolution surfaces. The channel and valley network was subsequently infilled by layered sediments interpreted here to represent the post-MSC marine sediments deposited during reflooding. Our analysis challenges the previously proposed fluvial nature of the NMU and instead suggest that it is a mixed evaporite-siliciclastic unit deposited in a shallow marine or lacustrine environment during the tilting of the offshore Lebanese basoin . Only subsequently did the NMU experience a rapid erosional event followed by swift burial of transgressive/high-stand sediments.



Earth Sciences


Marine Geology, eismic facies, dissolution, inscise , passive infill, Messinian, Levant, Messinian salinity crisi, Seismic interpretation;, evaporites;


Published: 2021-04-02 19:56

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