3.3.5. Opening and closing of marine gateways

Tectonically controlled opening and closing of marine gateways, combined with climatic and glacio-eustatic sea-level changes, have played an important role in the Neogene and Quaternary history of the Mediterranean and Black Sea area, with the most dramatic event being the Messinian salinity crisis that spanned approximately 5.96-5.33 Ma. Isolation of the Mediterranean Basin from the world oceans, commencing in the late Tortonian under a relatively low humidity climate resulted during the Messinian in an evaporation-induced rapid drawdown of its sea level by as much as 2 km (Buttler et al., 1999; Flecker and Ellam, 1999; Andersen et al., 2001; Krijgsman et al., 2002; Mart et al., 2004). Mechanisms contributing to the isolation of the Mediterranean Basin include a glacio-eustatic sea level fall but mainly the gradual closure of marine gateways connecting it with the Atlantic Ocean via the Betic and Rif foreland basins and with the Indian Ocean via the Taurus (Bitlis)-Zagros foreland basin (Ziegler, 1988).

As the mechanisms by which, and the exact time when, these marine gateways were closed are still poorly constrained, this is a research objective of TOPO-EUROPE (e.g. Middle-Late Miocene permanent silting up of Taurus-Zagros foreland basin combined with its compressional deformation prior to early Pliocene activation of the Kara Su rift (Bahroudi and Koyi, 2004; Mart et al., 2005)). The Messinian sea level drawdown (7.24-5.33 Ma) and ensuing erosion in exposed areas had a major unloading effect, whereas the accumulation of up to 2 km thick salts and clastics in remnant deep-water basins had a counteracting loading effect on the Mediterranean lithosphere. The isostatic response of the lithosphere to Messinian loading and unloading needs to be quantified in order to assess its contribution to the amplitude of the Messinian unconformity. Similarly, the end-Messinian water-loading effects ought to be taken into consideration. In this context, it is of interest to note that during the (Late?) Messinian a marine connection was opened between the Black Sea and the Aegean via the Marmara Trough (Mart et al., 2004). However, this connection was interrupted during the early Pliocene (Görür et al., 2000) when open marine communications between the Mediterranean Basin and the Atlantic were re-opened, owing to breakdown of the Gibraltar arc (Ziegler, 1988).

The objectives of the proposed TOPO-EUROPE studies are to improve the understanding of the cause-and-effects and the relative contribution of geodynamic processes and climatic changes to the Messinian salinity crisis, as well as to changes in the interconnection of the Mediterranean and Black Sea, which in the latter caused around 5600 BC flooding of large stretches of inhabited lands, triggering major migrations (Ryan and Pitman, 1999).