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Ba/Ca evolution in water masses of the Mediterranean late Neogene

机译：地中海晚期新近纪水体中Ba / Ca的演变

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摘要

A Mediterranean composite sedimentary record was analyzed for Ba/Ca ratios on carbonate shells of Orbulina universa planktonic foraminifer (Ba/Ca) carb providing the opportunity to study and assess the extent of freshwater inputs on the basin and possible impacts on its dynamics during the Tortonian to Recent period. A number 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 and corroborate the reliability of (Ba/Ca) carb ratios in foraminifera calcite as indicators of seawater source components during the studied interval. A long-term trend with (Ba/Ca) carb values shifting from similar to 7 to 3 mu mol mol(-1) from the base of the Tortonian to the top of the Messinian is observed. The interval of the late Messinian salinity crisis, where biogenic carbonates are missing or strongly diagenized, represents a crucial passage not monitored in our record. At the base of the Pliocene, up to about 4.7 Ma, the (Ba/Ca) carb record shows a decreasing trend from similar to 4 mu mol mol(-1) stabilizing itself to an about constant value of 0.9 +/- 0.3 mu mol mol(-1) for the whole Plio-Pleistocene interval. These results suggest a dramatic change in the continental runoff values, up to similar to 3-16 times higher during part of the late Neogene (Tortonian-early Pliocene), with a possible profound modification in the physical dynamics of the Mediterranean basin. First-order mass balance equations used to estimate barium and salinity budgets in the Mediterranean Sea during the late Miocene-early Pliocene interval support the hypothesis of an active connection of the basin with the Paratethys region and of a definitive restriction at the base of the Pliocene after about 0.7 Ma from the well-known Messinian Lagomare phase. They also open intriguing scenarios on possible circulation shifts during the Neogene.
机译：分析了地中海复合沉积记录中的Orbulina universa浮游有孔虫（Ba / Ca）碳酸盐碳酸盐壳中的Ba / Ca比值，这为研究和评估盆地中淡水输入的范围以及在Tortonian期间对其动力学的可能影响提供了机会到最近时期。从相同样品中获得的许多扫描电子显微镜分析和辅助微量元素测量值（Mn，Sr和Mg），排除了对研究的生物碳酸盐的重要成岩作用，并证实了有孔虫中（Ba / Ca）碳比的可靠性。方解石作为研究期间海水源成分的指标。从Tortonian的底部到Messinian的顶部观察到（Ba / Ca）carb值从类似的变化到7到3μmol mol（-1）的长期趋势。墨西拿晚期盐度危机的间隔，即缺少生物成因碳酸盐或强烈成岩作用，代表了我们记录中未监测到的关键时期。在上新世的基部，直到大约4.7 Ma，（Ba / Ca）碳记录显示出下降的趋势，从类似的稳定至4μmol mol（-1）稳定到约0.9 +/- 0.3μ的恒定值整个上新世间隔的mol mol（-1）。这些结果表明，大陆径流值发生了巨大变化，在新近纪晚期（Tortonian-早期上新世）的一部分期间，最高升高了3-16倍，可能对地中海盆地的物理动力学产生了深远的影响。一阶质量平衡方程用于估算中新世-上新世晚期晚期地中海地区的钡和盐度预算，支持以下假说：盆地与Paratethys区域有活跃的联系，并且在上新世底部有明确的限制距著名的墨西拿Lagomare相约0.7 Ma。他们还提出了有关新基因时期可能发生的循环变化的有趣方案。

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