Sr isotope constraints on the Mediterranean environment at the end of the Messinian salinity crisis

Abstract

PROBABLY the most profound event that has affected the Mediter-ranean is the desiccation which occurred at the end of the Miocene^1–8. During this period, there was a very rapid change from deep, open-marine conditions to environments of shallow-water carbonate and massive evaporite deposition^1–10. Here we show that ostracod valves found in Messinian Lago Mare (Lake Sea) sediments, have a uniform but generally lower Sr isotopic composition than contemporary sea water thus providing evidence that some of the major Mediterranean basins (for example, Balearic and Levantine basins) formed large lacustrine systems that were probably interconnected towards the end of the Messinian salinity crisis^1–3 after the major evaporites were deposited. The most likely source of fresh water is from continental rivers flowing from the eastern European inland Paratethys sea or perhaps the Nile River. In the lower part of the Lago Mare, some ostracods have Sr isotopic compositions identical to contemporary sea water indicating a transient influence of marine-derived water. Sr compo-sitions greater than that in contemporary sea water are only found in ostracods from onshore sediments in the Sorbas Basin^4,5 of southeastern Spain suggesting that this small basin, adjacent to the Straits of Gibraltar, became isolated after the deposition of the major evaporite sequences.