EVENT STRATIGRAPHY AND PALEOCEANOGRAPHY IN THE FORTUNA BASIN (SOUTHEAST SPAIN): A SCENARIO FOR THE MESSINIAN SALINITY CRISIS

The timing and duration of evaporitic deposition during the Messinian in the Mediterranean is poorly known. To assist with this problem, we have correlated sedimentological events at widely separated locations in the Mediterranean and dated paleoceanographic events in the world ocean (event stratigraphy). Our working hypothesis is as follows: The Messinian Salinity Crisis caused the formation of evaporites in a deep desiccated basin which implies that (1) the evaporites were deposite during a steady marine influx, (2) multiple intervals of isolation led to drastic changes in the sediments and in the fauna of the Mediterranean, (3) the sea level of the Mediterranean Sea was mostly several hundreds of meters below that of the Atlantic Ocean, and (4) the seaways (Betic and Rif Strait) connecting the Mediterranean with the Atlantic during the late Miocene were affected by eustatic sea level changes caused by Antarctic glaciation. We found supporting evidence in the sedimentological and paleoceanographic records in the Betic Strait (Fortuna and Sorbas basins) which was one of the sites of major inflow into the late Miocene Mediterranean Sea. Drastic sealevel changes and fluctuations during the late Tortonian and Messinian caused chronologically: (1) the deposition of brackish sediments overlying marine deposits, (2) the progradation of deltas, (3) reef growth at lower levels and their destruction by erosion and coverage by conglomerates, (4) evaporite deposition alternating with marine marls containing Atlantic diatom assemblages, and (5) five marine/terrestrial cycles associated with coral reefs. Based on event stratigraphy the following scenario for the Messinian "Salinity Crisis" is proposed: The Tripoli Formation (Chron 6R1/5N2: 5.93- 5.7 Ma), the Lower Evaporites (Chron 5N2, 5R: 5.7- 5.5 Ma), and the Upper Evaporites (lowermost Gilbert c:5.25-5.15 Ma) were deposited during influx of Atlantic water into the Mediterranean. During this time, a unidirectional circulation dominated from the Atlantic through the Betic Strait. Only during the intra-Messinian inundation (Chron 5N1 into lowermost Gilbert c:5.4-5.25 Ma) that occurred after a short intra-Messinian erosional event (Chron 5N1: 5.5-5.4 Ma) was a normal bidirectional circulation pattern established. This is reflected in the diatomites of the Chicamo Formation and the Mediterranean (site 124) as well as most likely in a reef on Cyprus. The marine record of the Pliocene filling of the Mediterranean is missing in these basins. Overall, marine water inflow into the Mediterranean through the Betic Strait dominated during the Messinian. The threefold marine/terrestrial cyclicity with severe paleoceanographic changes in the Fortuna and Sorbas basins favor the "deep, desiccated basin" model.