A Mediterranean composite sedimentary record was analyzed for Ba/Ca ratios on carbonate shells ofOrbulina universa planktonic foraminifer (Ba/Ca)carb providing the opportunity to study and assess the extent offreshwater inputs on the basin and possible impacts on its dynamics during the Tortonian to Recent period. Anumber of scanning electron microscope analyses and auxiliary trace element measurements (Mn, Sr, and Mg),obtained from the same samples, exclude important diagenetic effects on the studied biogenic carbonates andcorroborate the reliability of (Ba/Ca)carb ratios in foraminifera calcite as indicators of seawater sourcecomponents during the studied interval. A long-term trend with (Ba/Ca)carb values shifting from 7 to 3 mmolmol 1 from the base of the Tortonian to the top of the Messinian is observed. The interval of the late Messiniansalinity crisis, where biogenic carbonates are missing or strongly diagenized, represents a crucial passage notmonitored in our record. At the base of the Pliocene, up to about 4.7 Ma, the (Ba/Ca)carb record shows adecreasing trend from 4 mmol mol 1 stabilizing itself to an about constant value of 0.9 ± 0.3 mmol mol 1 forthe whole Plio-Pleistocene interval. These results suggest a dramatic change in the continental runoff values, upto 3–16 times higher during part of the late Neogene (Tortonian–early Pliocene), with a possible profoundmodification in the physical dynamics of the Mediterranean basin. First-order mass balance equations used toestimate barium and salinity budgets in the Mediterranean Sea during the late Miocene–early Pliocene intervalsupport the hypothesis of an active connection of the basin with the Paratethys region and of a definitiverestriction at the base of the Pliocene after about 0.7 Ma from the well-known Messinian Lagomare phase. Theyalso open intriguing scenarios on possible circulation shifts during the Neogene.
|Numero di pagine||17|
|Stato di pubblicazione||Published - 2008|
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