Isotope stratigraphy (87Sr/86Sr, δ18O, δ13C) of the Sorbas basin (Betic Cordillera, Spain): Paleoceanographic evolution across the onset of the Messinian salinity crisis
Résumé
The Sorbas basin is a reference sector of the Mediterranean basin for the definition of the onset of the Messinian salinity crisis straddling the transition from the open marine deposits (Abad marls) to the Primary Lower Gypsum (Yesares Formation) during the first stage of the crisis, between 5.97 and 5.60 Ma. Because of its proximity to the Atlantic gateway, the Sorbas basin is pivotal for the study of the oceanographic evolution that led to the most dramatic environmental event in the Mediterranean Sea. We measured the carbon (δ13C), oxygen (δ18O) and strontium (87Sr/86Sr) isotope ratio of 50 samples of planktonic foraminifera, mollusk shells, gypsum and carbonate sediments from the Abad and Yesares Members (Turre and Caños Formation) in the Perales, Hueli, Los Yesos and Rio de Aguas sections. Our results show a long-term trend with most of the values plotting within the range of the global ocean strontium isotope curve and distinct short-term fluctuations on precessional time scale. The investigated geochemical proxies suggest that these oscillations reflect significant input of continental waters into the basin during the humid phase of a single precessional cycle. This implies that the Western Mediterranean did not experience a main disconnection from the global ocean water before and during the first stage of the Messinian salinity crisis and that different Milankovitch forcings played a significant role in determining the seawater geochemistry.
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