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 (ca. 640 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 semicircular 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. The drainage network was subsequently infilled by layered sediments interpreted here to represent the post-MSC marine sediments. Our analysis adds important details regarding previous interpretations of the NMU as fluvial in origin. Specifically, the presence of subcircular, linear dissolution features coupled with mound-like features indicates that the NMU is composed dominantly of evaporites that were subject to dissolution prior to erosion associated with the drainage network. The NMU is interpreted to represent the deposition/redeposition of a mixed evaporite-siliciclastic succession in a shallow marine or lacustrine environment during the tilting of the offshore Lebanese basin.
We gratefully acknowledge Ramadan Ghalayini, Wissam Chbat and the Lebanese Petroleum Administration (LPA) for the provision of data without which this project would not have been possible. Schlumberger for granting Petrel© academic licences. SM Kabir is expressing his sincere thanks to the Bangabandhu Fellowship Trust, Bangladesh for sponsoring his PhD grant. We thank C. Gorini for the fruitful discussion during wring of this paper. We also thank the editor of the journal and reviewers Madof, Camerlenghi, Patruno and Amadori, who have spent their valuable time enhancing and improving the scientific con-tent of this paper.
Data Availability StatementThe data that support the findings of this study are available from the corresponding author upon reasonable request.
- passive infill
- seismic facies