Estimating drawdown magnitudes of the Mediterranean Sea in the Levant basin during the Lago Mare stage of the Messinian Salinity Crisis

By: Ben Moshe L., Ben-Avraham Z., Enzel Y., Schattner U.
Published in: Marine Geology
SDGs : SDG 14  |  Units: Marine Sciences  | Time: 2020 |  Link
Description: The Messinian Salinity Crisis (5.97–5.33 Ma) is one of the most dramatic sea level change events in the global geologica l record. During this event, marine connection between the Atlantic Ocean and the Mediterranean Sea was restricted, and episodically blocked. While division of the Messinian Salinity Crisis to three major stages is well established and accepted, the scale of sea level change at each stage is still debated. The magnitudes of the Mediterranean fluctuations throughout the Messinian Salinity Crisis have implications for contemporary connectivity between the eastern and western Mediterranean basins. During the third stage of the Messinian Salinity Crisis, commonly known as the Lago Mare, Mediterranean Sea level fluctuated repeatedly. Lago Mare drawdowns in the eastern Mediterranean were estimated earlier to vary between <200 m and all the way down to the abyssal basin. Here we assemble morphological, lithological and stratigraphic evidence for Lago Mare levels across the Israeli margin. We differentiate between low-stands of various scales and durations to constrain the magnitude of discrete Lago Mare drawdowns. Since the rates of syn-Messinian isostatic rebounds in response to water column removal are ambiguous, drawdown magnitudes are estimated here as a range and not as an absolute value. We propose that during the Lago Mare, ravinement along a continuously regressing-transgressing coastline abraded the upper continental margin offshore Israel. The Mediterranean regressed to a depth of 380–550 m below present-day mean sea level, and the eroded strata were evacuated downslope and deposited basinward of this depth as wedge-shape clastic complexes. During relatively short intervals, sea level receded to altitudes ~100 m below the erosional surface. These sea level recessions exposed a pronounced inflection in the slope gradient to sub-aerial processes, generating knickpoints and headward migration of incising gullies. These gullies developed later into channels, conduits for sediment bypass. Fan-deltas were deposited off these channels outlets. A major sea level fall towards the end of the Messinian Salinity Crisis reached 630–900 m below present-day mean sea level. Streams incised into the exposed tops of the clastic wedges and fan-deltas. Additionally, meteoric water dissolved evaporites within the clastic complexes and formed sinkholes and dolines. During this interval the Mediterranean Sea level fell to below the depth of the Sicily Sill, which separated the eastern and western Mediterranean basins. This finding reinforces previously proposed paradigms, which suggested that the Messinian Salinity Crisis was terminated by spillover events from the Atlantic Ocean to the western Mediterranean basin, and consequently from the western to the eastern basin. © 2020 Elsevier B.V.