MIGHT KARST EVIDENCE FURTHER CONSTRAIN MESSINIAN SEA LEVEL DRAWDOWN?

Mediterranean base level lowering models were proposed to account for thick evaporates revealed in seismic profiles and confirmed by drilling.

Discovery of deep diagnostic karstic features near Messinian evaporites could refine magnitude of desiccation now ranging from 100s to >1000 m. Scientific and proprietary drilling are encouraged to address this problem.

Leg 13 attempted a Mediterranean borehole to identify the prominent M-Reflector on seismic profiles. Gravel jammed the drill pipe and evaporates 3 km below the ocean where impenetrable with equipment on board. Hsü et al concluded the basin dried several times (shallow water desiccated deep basin model) when >1x10⁶ km³ of evaporates were deposited during the Messinian. Others favored a basin largely filled with saturated brine with moderate base level lowering. Basin marginal erosional features were attributed to density currents not sub aerial erosion.

A minimum 800-1200m drawdown was proposed in 2018 for continental terrestrial fauna and flora to colonize Balearic Islands via a submerged land bridge. New evidence was provided in 2019 by discovery of back stepping Mahr Menashe deposits up to 300 m thick believed to be of riverine origin and extending >500 km into the Western Lavant Basin. Other basin margin sediments interpreted as non-marine were noted.

Former siphons, flowstone, caves and conduits with terrestrial sediment, tufa, fresh water v marine fossils in spring deposits, breccia pipes and deep canyon fill might be revealed by drilling.

Cave divers have explored Karst siphons 70 m – 100 m within Dinaric karst influenced by sea level drawdown during the last glacial advance. Submarine springs like Ombla emerge along the Mediterranean coastline at >160m below sea level and serve as analogues for possible existence of deeper Messinian karst drainage networks. Sea level was about 100 m deeper when this siphon may have formed. Then Neretva River extended kms beyond the Adriatic coast where the sea is about 1200 – 1250 m deep. French researchers showed evolution of Estrama karst systems during the Messinian when the Mediterranean was assumed dry. Their work encourages further karst model testing. Drilling should target suspected deep structures, likely presence of thick basin marginal carbonates near evaporate contacts opposite large elevated catchments.