Discovery of vast fluvial deposits provides evidence for drawdown during the late Miocene Messinian salinity crisis

Abstract

The late Miocene Messinian salinity crisis (MSC) was a significant oceanographic event that caused widespread evaporitic accumulation throughout the Mediterranean Basin. Although multiple hypotheses exist regarding the origin of evaporitic and post-evaporitic deposits, researchers remain divided on the magnitude of base-level fall, and on whether these accumulations record deep-water or non-marine conditions. Here, we introduce a previously unknown, upper Messinian fluvial deposit comparable in size to the late Miocene Nile River fluvial valley fill and show that near-complete desiccation of the eastern Mediterranean was responsible for its development. The basin-wide accumulation, which is located offshore Cyprus, Syria, Lebanon, and Israel, lies directly atop deep-basin evaporites and related erosional surfaces, and is one of the largest known riverine deposits associated with the terminal MSC. From marked onshore incision and basinward thinning trends, the source of the accumulation is presumed to be a formerly unidentified drainage basin in southern Turkey and western Syria; the deposit extends >500 km into the western Levant Basin, where its depositional sink is marked by six well-developed backstepping lobes. Based on the deposit's seismic stratigraphy and morphology, which provide clear evidence of subaerial exposure, we question current hypotheses proposing a deepwater origin for late Messinian accumulations. We also draw specific attention to the development of extensive circum-Mediterranean nonmarine conditions prior to Zanclean marine transgression, and to the previously overlooked role of fluvial systems in diluting hypersaline lakes in evaporitic basins.

Evidence of sea level drawdown at the end of the Messinian salinity crisis and seismic investigation of the Nahr Menashe unit in the northern Levant Basin, offshore Lebanon

“…The sediment package overlying the IMTS is interpreted as the Nahr Menashe deposit, consisting of redeposited evaporites and clastic sediments deposited in a fluvial system along the Levant Margin in the early phase of stage 3 of the MSC. This is in agreement with Madof et al (). In the study area, the system was sourced predominantly from a large fan system in the northeastern part of the seismic dataset feeding reworked evaporites and siliciclastics from the margin into the basin, and probably also from similar systems along the Latakia Ridge and Syria in the north.…”

“…Our seismic investigations correlates well with the results of Madof et al () in terms of geomorphologic observations (Figure ). Several channels in the basin are easily recognized and the thickness trends are identical in both studies, forming an axial system along the eastern basin margin.…”

“…They also recognized siliciclastic turbidites sourced from the Nile Delta to the south and east of the ESM. Detailed interpretations of the post‐IMTS unit in our study area, offshore Lebanon, are scarce, but of recent studies Madof and Connell () and Madof et al () stands out and should be mentioned: These studies place the Nahr Menashe unit, interpreted as clastic Lago Mare deposits by Madof and Connell (), above the IMTS. The authors hypothesize that the unit originates from western Syria or the Anatolian Plateau, which stands in great contrast to interpretations elsewhere in the basin.…”

“…This discrepancy in the interpreted regional stratigraphy is poorly understood, and is either due to a more complex depositional environment than previously believed or, alternatively, erroneous interpretation of the local stratigraphy in parts of the basin. Madof et al (2019) assign the post-IMTS sediment package in our study area to the Nahr Menashe unit, and interpret it as a fluvial system extending from southern Turkey and western Syria to the Eratosthenes Seamount. An accurate interpretation of the post-IMTS strata in the Levant Basin is essential in order to understand both the termination of the MSC as well as the re-establishment of marine conditions and associated depositional processes in the Pliocene.…”

“…Based on gamma-ray and resistivity logs, Gvirtzman et al (2017) suggest that the unit consist of interbedded halite, anhydrite and clay of latest Messinian age. Other studies have suggested that the strata immediately overlying the intra-Messinian truncation surface (IMTS) consists of nonmarine clastic sediments time equivalent to the Lago Mare phase deposited in fluvio-deltaic systems along the basin margin and/or Nile-derived sediments (Ben-Gai, Ben-Avraham, Buchbinder, & Kendall, 2005;Madof, Bertoni, & Lofi, 2019;Madof & Connell, 2017;Safadi, Meilijson, & Makovsky, 2017;Tibor, Ben-Avraham, Steckler, & Fligelman, 1992). This discrepancy in the interpreted regional stratigraphy is poorly understood, and is either due to a more complex depositional environment than previously believed or, alternatively, erroneous interpretation of the local stratigraphy in parts of the basin.…”