The Sdom evaporite formation in Israel and its relationship with the Messinian Salinity Crisis

Abstract

The Sdom Formation (Fm.) comprises an approximately 2 km thick sequence of evaporite sediments that Zak (The geology of Mount Sdom, Ph.D. Thesis, Hebrew University, Jerusalem, p. 208, 1967) postulated as being of early Pliocene age and marine origin. A major core drilling program of Mt. Sdom was undertaken that investigated the upper 1000 m. Integration of the data has thrown into question many of the concepts regarding the Sdom Fm. and Mt. Sdom in particular. The Sdom Fm. is now considered to represent a major non-marine evaporite sequence equivalent in time to the Upper Evaporite Messinian Fm. of the Mediterranean, (5.60–5.50 Ma), which was deposited from the Sea of Galilee to the Dead Sea basin. Mt. Sdom comprises approximately 44 cycles, ranging from sapropelic shales to carnallitites. The beds are subvertical and gave a consistent younging direction to the west, contrary to previous models. The sediments from the upper section of Mt. Sdom represent a shoreline facies; probably the eastern margin of the basin with the center of the basin at depth. Only minor deformation of the sediments was observed along the margins of the salt wall of Mt. Sdom. It is now suggested that the sediments crept with overburden pressure, down the Sdom intergraben fault from a horizontal to vertical position with increased tectonic subsidence. In more recent years, with tensional movement of the Dead Sea Transform, the salt wall became diapiric. The Sdom formation has been correlated throughout Israel and an attempt has been made to correlate the formation with the Messinian evaporites in the Eastern Mediterranean. It is considered here that the Levant Basin and the separate Dead Sea Basin were both tectonically active over the same time period when the climate was predominantly arid. The evidence of multiple evaporite cycles suggests rapid changes in climate from pluviatile to arid, with syndepositional sedimentation and not a deep basin filled with brine. It is postulated that the Messinian Salinity Crisis was an event that extended from the Mediterranean Sea and Dead Sea basins to the Gulf’s of Eilat and Suez, the Red Sea, Gulf of Aden and Danakil Basin in separate tectonically active basins, with shallow brines for the deposition of potassium minerals and even bischofite. This would imply a period of intense aridity for the region. If it is possible to relate all these Middle to Upper Miocene deposits, then this would be one of the largest salinas in the world.