Setting and tectonic evolution of some Eastern Mediterranean deep-sea basins

Abstract

Nine discrete deep-sea basins (seven from the Calabrian and Mediterranean ridges and two from the Strabo Trench) were explored geologically during several cruises carried out from 1978 to 1984 in the Eastern Mediterranean. The seven basins, displaying similar geological features (Calabrian and Mediterranean ridges), may be divided into three groups on the basis of their size: (1) very small basins (Botticelli and Raffaello basins) whose area ranges from 1.1 to 4.3 km 2; (2) small basins (Ares, Aphrodite and Katia basins), from 7 to 13 km 2; and (3) large basins (Bannock and Cleft basins), from 22 to 74 km 2. The two basins from the Strabo Trench (Tyro and Kretheus basins), whose areas range from 16 to 20 km 2, are considered separately. Tectonics is the most important element affecting basin formation processes: progressive folding and faulting of Messinian, Pliocene and Quaternary sediments in the Calabrian and Mediterranean ridges allows the infiltration of water into the subbottom and dissolution of Messinian evaporites, so that collapse of the overlying unconsolidated Plio-Quaternary cover creates local distensive tectonics superimposed on the regional compressive tectonic setting. The size of the basins reflects different steps in this process. Very small basins are related to the fracturing occurring at the top of anticlines; small basins originate when anticlines are faulted and large amounts of water are able to reach the evaporites and increase the intensity of leaching. Finally, large basins are related to regional tectonic lineaments both compressive (large reverse faults, overthrusts) and strike-slip. Salt diapirism may be associated with some of these situations. The process responsible for the Tyro and Kretheus basins formation is the “pull-apart” mechanism connected with the strike-slip motion occurring in that area. The geometric position of subaqueously dissolved evaporites seems to influence the environment on the basin floor: brines originating from the dissolution of buried evaporites are thought to disperse in the subbottom, whereas brines originating from dissolution of evaporites cropping out on the basin walls can flow to the floor and cause stagnation only if the shape of the basin prevents the action of bottom currents.